Tornado Central

Friday, I went out with Robin, Dan, and JR, targeting an area near and south of CDS. We arrived in CDS and hoped that the convection that fired around 1pm west of ABI and south of Quanah wouldn't become a problem. By mid-late afternoon, new convection was developing along the cold front - dryline intersection to the west of CDS. We followed this intersection southward for a bit, but it was becoming quite obvious that the cold front was undercutting the convection. It's never a good thing when you have a southward moving cold front with storms that are moving NE slowly... So would develop sw of CDS, but then quickly get undercut... We did see several dust devil / gustnado vortices right along this cold front, which was kind of neat. Between CDS and Matador, we decided to head back north to see if we could catch up with the cell that was entering Harmon Co OK. We moved through Hollis, and stopped in Duke after seeing that this sw OK storm was weakening. New storms had developed back to the SW near Matador, but we were fearing that they would see the same fate as a handful of other hopefulls saw earlier in the day... We made it to Quanah, but the cells were lining out, so we opted to call it a day.

I think there were several failure modes with the convection in the northern part of the risk area... First off, the convection that fired around noon in western north TX moved eastward only very slowly, so that by mid-afternoon, there was only a 2 county wide area between the dryline and the cool outflow from those storms. In addition, this cooler air was advected towards the CDS area on the southeasterly sfc flow. Secondly, the cold front continued to move southward faster than I was anticipating, so the half dozen or more storms that did try to develop at the cold front / dryline intersection were quickly undercut and left in cooler, more stable air. Third, the storms seemed to initiate in a SW-NE fashion. We a northeasterly shear vector and southwesterly flow aloft, there was a tendency for upscale growth to line segments (anvil seeding, etc). Related to these previous two points is the flow in the mid-levels, with a slight backing vertical wind profile in the ~700mb area per local VWPs and RUC analyses immediately ahead of the dryline.

I can say that the hodograph on the Friday evening (00z) FWD sounding is one of the most impressive I have seen in a long time. >500 0-1km SRH and 75kt 0-6km shear? That 0-3km layer on the hodograph is incredible! The low-level hodograph on the DRT and OUN soundings were nearly as impressive... Man, I would have liked to have seen what would have happened if we had more significant destabilization Friday given the shear that was in place...

As far as chasing is concerned... My attention is currently on Tuesday, but I won't get into any specifics given (a) generally bad model performance in this pattern, and (b) the fact that I'm just busy (the next two weeks will be busy). There will be chances for severe storms across much of the KS/OK areas the next few days, but the supercell and tornado potential is more uncertain. Tomorrow may see a couple of supercells from OKC-TUL and southeastward, but any tornadic supercell risk appears limited. While the progged instability and hodographs look decent on Tuesday, convective initiation is less certain, given that the bulk of any mid-level "energy" will stay to the north. I have few issues actually chasing Tuesday, but I don't think I can be as risky as usual (in terms of how marginal a day I will chase on) given my busy schedule.

Well, there is pretty good potential for supercell develop from far southwestern OK, southwestward into western/central Texas, as a strong upper-level low moves out of the southern NM / northwestern Mexico area. A strong low-level jet (~50-60kts on area VWPs) is currently in place across much of central Texas, which is helping to advect Gulf moisture northwestward. Convection has developed and persisted across the panhandles and eastern NM this evening.

As the low moves east-northeastward tomorrow, strong flow aloft will overspread the expanding warm sector. Widespread, isentropically-developed precipitation will likely be ongoing across much of northern TX and OK by mid-morning. Tonights 0z NAM run does indicate that there will be a break in the precipitation through 21z, after which time the model breaks out convection along the dryline. As it stands, my primary concern regarding the chase prospect tomorrow is the potential for persisten cloud-cover and precipitation across the target area, limiting destabilization and leading to poor CAPE. If this occurs, I will probably stay home, but I'll have to anticipate in the morning whether such things will persist through the afternoon. The 0z NAM does show some significant CAPE developing from near CDS southward at 21z (with SBCAPE to 3000 j/kg), but said CAPE diminishes by 0z as the model turns on convective parameterization. RH progs at 250mb and 500mb indicate that the CDS-SPS area may see some sun by afternoon, but 850mb RH remains high across much of the warm sector, indicating potential cloud-cover.

With 40+kt flow at 850mb and 700mb, 50-70kt flow at 500mb, and 110-120kt flow at 250mb, deep-layer shear profiles will be quite favorable for long-lived supercells. The 0z NAM indicated a surface low near CDS by 0z, with favorably-backed surface flow across much of the warm sector. This creates strong low-level shear, increasing to the east as one moves away from the dryline. There does appear to be a little gap between the dryline and the western edge of the strong low-level shear (0-1km SRH ~150+ m2/s2), but we'll see if that actually verifies. The backed low-level flow also helps keep storm motion in the 'favorable' range, with 25-35kt forecast motions for right-moving supercells per the Bunkers method.

I will assess the situation tomorrow morning, obviously. Right now, I'd put my chase probability at 60%. The main reason why I would not chase tomorrow would involve the anticipation of cloud-cover and precip hanging around much of the day. If this does not occur, I'll likely head southwest towards western north Texas. The NAM progs one rather significant vort max to be approaching the western north Texas area by 21z, with the leading edge of the vort max near I35 by 0z. This adds a little more complexity, since DPVA and associated upward motion would be over western north Texas in the 18-21z period, before shifting more towards I35 in the 21-23z timeframe.

I'm awaiting some 0z WRF output... All graphics are from wxcaster.com, but I moved some onto my server so I don't waste his bandwidth. Oh yeah, I do think the potential increases southward, and the area between I20 and I10 looks the hottest. However, that is likely out of range tomorrow, so I'm limiting most of my attention to the area north of I20.

Just a quick note to notify that I have posted my chase log and pictures HERE. My camcorder is still drying out in front of a fan that's been on all day... I tested it this afternoon, and it played tapes and recorded just fine. However, it does not turn off! When I try to turn it off, it tries, but then turns back on. After 1-2 second, it tries to turn off again, but comes right back on. As of now, the only way to actually power down the camcorder is to remove the battery. I really hope this is just due to some switch being damp, and not because something is fried inside the camcorder.

It looks like Friday may be a chase day down in Texas. I'm a little worried that the warm front will get locked down in central/southern Texas thanks to widespread, isentropically-generated precipitation north of the front, similar to what happened several days ago. Otherwise, strong deep-layer shear and model progs of moderate CAPE would tend to favor strong supercells. Of course, whether we actually see the moisture necessary to develop any CAPE is a question mark, since a lot depends upon how far into the Gulf the current cold front goes before stalled and heading back northward. I'm not sure I want to chase much south of I20, so I'm hoping things start looking better from northern Texas!

I chased with Gabe and others today... We sat in Kingfisher from about of hours this afternoon, watching storms develop near the OFB and cross into the cold outlfow near and east of I35. We were hoping somethign would develop west of Kingfisher and move eastward into the back flow near the OFB. Well, a few tried to go up after the initial round near 3pm, but these only acted to reinforce the cold pool. With only a very narrow axis of instability between the cold front / dryline and the cold outflow near I35 and the relative lack of sustained convection, we opted to drop southward towards a right-propagating supercell that was west of Anadarko. When we approached El Reno, radar was showing that the convection to the south was congealing into a quasi-linear mess, while another storm was exploding just southwest of El Reno. We sat just south of I40 for a while, watching the storm go from a flat cloud base to wallcloud to impressive RFD cut to tornado #1 to tornado #2... The position was nearly perfect, though we did have to shift south about half a mile in order to get some buildings out of the way. We followed this very slow-moving storm eastward after the first two tornadoes dissipated, but never really saw much else.

Overall, I am very pleased to have avenged the Oklahoma curse. I've really had very bad luck chasing in OK, so it was nice to get two very photogenic tornadoes. I haven't looked at my video, and I confused myself as to whether tornado #2 was anticyclonic or cyclonic... Since I accidentally left my camcorder on someone else's car as we got heavy wrap-around precip west of Yukon, I'm currently airing it out and crossing my fingers that it works. I'll have some pics up either later tonight or tomorrow. Yay to tornadoes within an hour of my apartment. The complete absense of precipitation in or near the RFD and tornadoes made the supercell look more LP than anything for a while.

The 0z OUN sounding isn't all that impressive, with 40kts 0-6km shear, and only about 110m2/s2 0-3km SRH for a storm motion that is just north of due east at 26kts. The El Reno storm was moving at like 15kts during the time it produced the tornado I believe, to the SRH may be a tad higher (given the shape of the hodograph). In addition, slowing the storm speed would have creating much more streamwise vorticity in the 1-3km layer (the motion shown on the sounding would yield mainly crosswise vorticity from 500m-2km above ground). Regardless, the CAPE was likely in the 3500 j/kg range, with a bit of 0-3km CAPE. In the end, I think storm mode and strong instability helped the storm produce a couple of tornadoes, since 0-3km SRH wasn't too impressive, and the LCL was on the high end of what we usually like to see (~1500m AGL). The moist layer is a very impressive >200mb in depth, however.

Not a whole lot of time to discuss my forecast for tomorrow. Unfortunately, I'm giving a presentation in my Convective Storms class tomorrow, so the earliest I will be able to leave is 12:45pm. This should be just fine, since it appears that the target is about 2 hrs drive, which'll put me in the area by 2000Z.

The 18z NAM-ETA run continues to slow the cold front a bit, with a surface low forecast to be between Enid and Clinton by 0z and the cold front not far into northwestern OK. The 8km NCEP WRF run is also indicating that the cold front will be near a line from Canadian, TX, to Alva, OK, to Anthony, KS, by 0z. We should actually be able to get real Gulf juice into the warm sector by afternoon afternoon, since the >65F tds are sitting in southern Texas, waiting to be pulled northward. So far today, despite the southerly flow, that 65F isodrosotherm really hasn't budged much, and the 70F isodrosotherm hasn't moved either. Today, I think part of issue lies in large-scale subsidence given that we're in the middle of a ridge aloft. As the upper-level low / shortwave trough move east tonight and tomorrow, ridging should push eastward, and that contributor to poor surface moisture should diminish. I'm not entirely sure about moisture depth, since the 12z soundings from DRT, BRO, and CRP weren't overly impressive. However, the 12z OUN sounding was quite nice, indicating a moist layer nearly 200 mb deep.

Assuming we can get at least 63-64F dewpoints into the area, strong CAPE will develop by afternoon east of the surface low and the dryline that extends south of that surface low. With strong low-level flow (18z NAM indicating 30-35kts at 850mb) and moderate mid-level flow (35-45kt in OK, 55-60kt KS), shear profiles (both low-level and deep-layer) should be adequate for supercells and tornadoes. The tornado threat appears to be maximized east and northeast of the surface low across north-central OK and south-central KS, extending eastward through the evening.

Aside from moisture questions (have have plagued us all year so far), I'm also rather concerned about upper-level / anvil-level flow. The 18z NAM indicates that 250mb flow will be rather anemic over the target area (largely <30kts), which may favor HP bombs over more-climatologically-favored-to-produce-tornadoes classic supercells. The 12z GFS indicated that 250mb would be more in the 45-60kt range, which would help a lot. The 12km NAM-WRF (from NCEP) is showing ~50kts, so I'm hoping the NAM-ETA is underforecasting the 250mb flow. FWIW, the 8km WRF NCEP run for 0z tomorrow indicates areas of CAPEs >3500 j/kg across OK tomorrow, with favorable low-level shear east of Enid across northern OK and far southern KS.

As it stands now, I'll leave OUN ASAP tomorrow, probably aiming for the area between Anthony, KS, and Medford, OK. I may post more info tonight after I look at the 00z runs.

The 12z NAM is in, and it's indicating a potential chaseday Sunday across northcentral and northeasern Kansas. As it stands now, a weak surface low is progged to move to near Hays KS by afternoon, as a warm front lifts northhward into northern Kansas, east of the surface low. Strong instability is forecast to develop in the warm sector, south of the warm front and east of the dryline. Speaking of the dryline, the NAM is indicating that we may see a dryline bulge somewhere west of Salina. With forecast temps in the 85F area and dewpoints in the 63-68F range, the cap may be removed by afternoon, and the NAM inidicating convective initiation west of the surface low and along the dryline bulge. Despite this solution, I see potential problems. Firstly, the NAM has been notorious for overforecasting surface moisture this year. Despite having southerly flow behind the warm front, much of the moisture is progged to mix and dry across central portions of KS and OK. Veering 850mb flow in the morning may help to mix dry air down from the top, and the upper-level ridge may result in large-scale subsidence that acts to dry out the entire column. In addition, flow aloft will be relatively weak until strong flow associated with the wave to the west approaches late in the period. As it stands now, it looks like I may be making a trip to Salina or Columbia on Sunday.

Then comes Monday. A 'winter-like' cold front is progged to dive down the lee of the Rockies Monday, with quite cold surface temps across Nebraska, Colorado, and northwestern Kansas. In fact, the 12z NAM indicates temperatures in the upper-20s by Monday evening in southeastern Wyoming! The NAM is forecasting significant (~4000 CAPE) instability to develop ahead of the cold front as it dives southward. My main concern for Monday, however, lies in the fact that there will be deep lift above the relatively shallow cold air as it spreads southward. With southerly 850mb flow and a southward-moving cold front, it may be difficult to develop and mature storms before they move into the colder air. Forecast storms motions are to the east, which may be fine given that the cold front should be oriented SW-NE by afternoon across far northwestern TX, western OK, and central/eastern KS. I suppose we may see a south or southeastward moving squall line develop, as the deep-layer shear vector is progged to be to the northeast along the front. Still way too early to know for sure, but I still wonder why the heck we are seeing this winter-like, 'gravity current'-type cold front in late April... This is the type of surface system that brings very cold temperatures western KS, the OK and TX panhandles, and western Texas. We can also see significant warm-air advection / isentropic-lifting snow and ice events with this type of system in the winter (moreso when the front stalls and we get deep southwesterly flow aloft lifting over the relatively shallow cold air). Oh well, I should never expect April to be "normal".

I will say that I will be very frustrated if we only end up with 60-63F dewpoints Sunday and Monday. Ridging aloft won't help a whole lot, but I'm sick and tired of chases all but ruined by crappy moisture.

Yesterday, I said that the main issue would be exactly where the warm front sets up by afternoon. Overnight and morning convection obviously impacted the location of said front. When I awoke this morning, I cringed! Relatively widespread convection north of the front would not (and isn't really) allowing the warm front to spread northwestward. You can see either the warm front itself or a strong outflow boundary on the Austin radar right now, extending ENE out of San Antonio. Shear profiles aren't too bad, but the widespread cloud cover and precipitation is not allowing for the development of much instability. RUC forecast soundings showed almost zero cap over the area, which is likely contributing to allow the widespread convection to continue. I can't imagine that the near-surface layer is mixed enough to really allow for surface-based convection, but it appears as though development is largely being driven by strong warm-air advection atop the rain-cooled near-surface layer. Wind profilers and VWPs in the area indicate intense veering vertical wind profiles (indicating strong warm-air advection).

It looked like there was going to be a small area along and just south of i20 (from DFW to Austin to Abilene) that was going to destabilize given some morning insolation / sun. However, that area has filled in, both with cloudcover and stratiform precipitation (with embedded convection). As it stands now, easterly flow on the cool side of the warm front is yielding frontolysis, which may allow the front to apparently "jump" northwestward later today. However, with persistent convection across central and northern TX, this will be difficult to do. As it stands now, the best area for supercells appears to be west and southwest of San Antonio. There may be severe elevated activity farther north, but I can't imagine there will be any significant instability given the ongoing cloudcover and convection.

The upper-air forecasts from the GFS indicates a very chaotic pattern continuing, with a splatter of cut-off lows across North America; the GFS indicates three seperate cut-off lows by early next week -- one over Nevada, one west of Winnipeg, and another north of New York. This is creating all sorts of "messiness" in the low-levels. Right now, it appears that the next chase day may be sometime in the Monday - Tuesday timeframe. Moisture will spread northward across the southern plains on Sunday, but strong ridging aloft should preclude any warm-sector convection. As another shortwave approaches Sunday night and morning, a surface low may develop in the TX panhandle, yielding a potential chase day on Monday. The GFS indicates that a cold front will slam southward on Tuesday, but we may see enough support for a chase day in southern OK or northern TX. I do hope that the upper-level pattern will deamplify a bit. I'd be happy with zonal flow for a few days, in comparison to this current split-flow business (not to mention the slow-moving cut-offs here and there). I'm still a little worried that the cold front progged to approach the southern plains early next week may wipe out the Gulf of Mexico, but that is still quite a ways in the future. I start to get anxious whenever we see forecasts of cold fronts in the Gulf as we head into late April... Still plenty of time for that forecast to change, fortunately.

Not much to talk about in way of chasing prospects through the next week or 10 days. A cut-off low will develop from a strong shortwave moving into Nebraska tomorrow, while some better Gulf moisture is established in the warm sector ahead of a moderately-strong cold front. Right now, it looks like the main threat will be to western and possibly central Missouri, as mid-60 dewpoints yield CAPE >2500 for one of the first times this year. Flow aloft is pretty weak, so I'm not sure about the significant supercell prospects. I'll be in my office doing work, but I guess I'll keep an eye on it.

The models slowly meander the upper-level low from the northern plains into the Great Lakes region by late in the week. I'm taking this with a grain of salt, however, since it seems that models can have tough times with cut-off lows. While the operational models indicate that tropical moisture will return to the Gulf coast region this week (67-70F dewpoints are already into Texas and Louisiana), I fear the Gulf may get wiped again next weekend. At this time, the GFS and ECMWF indicate a high-amplitude trough (and perhaps cut-off low) along the east coast and in the southeastern US by the end of next weekend. A winter-like surface cyclone is progged to develop along the New England coast, with a cold front plunging southward into the Gulf. Of course, this is a long ways off, but it doesn't look like I'll be chasing much through the rest of April, that's for sure. This doesn't necessarily upset me too much, since the semester is coming to a close, and I have a lot of stuff to get done before early May. I would thoroughly enjoy seeing a >2500 j/kg CAPE setup in northern TX / OK / KS sometime... I don't expect to see a big-time risk day in the next 10 days, or at least as long as we remain in a split-flow pattern. Then again, with my experiences so far this year, I'd probably rather enjoy a decent slight risk than one of these mega-systems...

As my last post indicated, we/I opted to refrain from chasing today based on (a) moisture concerns and (b) dryline placement concerns. As it stands, it appears as though evapotranspiration helped raise the Tds 1-3 degrees in the morning, as the 60F isodrosotherm made it to Bartlesville by about 10am. The 12z NAM showed 0 QPF (no precipitation) south of the KS/NE border before 0z... Well, by mid-afternoon, convection was developing from north of Salina into Nebraska. The dryline, which the GFS had forecast to be near Kansas City to Tulsa line by 0z, moved very slowly through most of the afternoon, and only cleared Wichita near 4-5pm. TCu went up along much of the dryline, but the cap proved too strong. I was surprised to see convection west of TOP just 3-4 hours after the 18z sounding was taken up there (Topeka), which showed a monstrous, thermonuclear cap (~750 CINH with a rapid 10C temperature rise between like 880mb and 870mb). I would have been able to jump on any storms that developed near Enid (since they would have worked into a catchable range), but none did. Thanks to Gabe for some afternoon collaboration regarding this situation.

The 00z soundings (head to http://www.spc.noaa.gov/exper/soundings/06041600_OBS/ )showed some of the most intense low-level shear you'll really ever see in a dryline setup. I think the 0z OUN sounding indicated nearly 400m2/s2 0-1km SRH, and the 0z TOP sounding showed nearly 440m2/s2 0-1km SRH. Yes, that's just 0-1km SRH! This is pretty much the top of the range in terms of low-level shear in the warm sector (and not assocatiated with landfalling tropical systems). The hodographs also show a distinctive "kink" in the near-surface layer... A similar feature was noted by the Norman NWSFO on the 18z OUN sounding from 5-8-03, which featured several strong-violent tornadoes. Back to today... It seems that all operational models underforecast the low-level wind profiles, as the TOP sounding shows 50kts at 1000m above the ground, compared to model forecasts (from this morning's runs) of 35-40kts at about 1500m above the ground. Oh yeah, and the 0-6km (deep-layer) shear was in the 75-80kt range along most of the length of the dryline (OUN had 77kts, TOP had 78kts I believe).

In addition to the wind shear, the 00z OUN sounding showed a relatively long, slender CINH profile. Such distributions of CINH are quite sensitive to surface mixing ratios / dewpoints, since a relatively small increase in the low-level moisture yields lower LCL (after which time latent heat results in a parcel rising along the wet adiabat) and much lower CINH. This type of profile is in contrast to a short, fat CINH distribution, where a minor right-ward shift in the parcel trace may not drastically decrease CINH. I'd draw a picture/cartoon to illustrate this, but I don't really have time.

At any rate, the point is that, IMO, we avoided a major tornado outbreak today. The low-level shear (particularly the near-surface / 0-1km shear) was in the ballpark of 5-3-99 and other tornado outbreak days that featured long-track violent tornadoes. If dewpoints had been in the 66-70f range, we would have seen:
+ Breakable CINH (particularly given the very impressive convergence along the dryline)
+ Strong CAPE (with intense low-level vertical acceleration given the very steep lapse rates)
+ Sufficiently-low LCLs (the 30+ degree dewpoint depressions in OK today would not have cut it)
However, as has been the case all year it seems, we just couldn't get >63F Tds at any cost. Despite the fact that the Gulf got FROPA'd more than 5 days ago, surface ridging along the coast and horrible trajectories around a southeastern US ridge resulted in only modified continental air in the warm sector. This afternoon's AFD from OUN contains some good discussion about this as well. To keep this in perspective, we almost always see "good" setups in early spring (before April 20th, let's say) that don't materialize because of insufficient / marginal low-level moisture. Heck, if you read some of my chase logs from last spring (or the spring of 2002), you'll certainly read of my frustration with "wasted setups" that just didn't have enough moisture. The fact that true Gulf moisture can make it up into the central plains during some events around this time of year is remarkable it seems...

So, what's my point? My point is that a low-level hodograph does not get much better than was seen on the 00z TOP or 00z OUN sounding. It is my opinion that if we had seen >66F dewpoints, we may have had an event not much unlike 5-4-03 (except farther west) or even 5-3-99. I'll give a cookie to the next person who shows me a warm-sector sounding that indicates >400 0-1km SRH from any event after today. It happens (and there have been soundings with even strong 0-1km SRH), but it surely doesn't happen very often.

Well, I awoke this morning with every expectation to head up towards Concordia KS (be there ~1pm). However, looking at obs, I can't imagine we'll see any dewpoints within even 5 degrees of the NAM forecast. Current surface obs show the real 60-61F dewpoints entering southcentral OK, with mid-upper 50s in ne OK and se KS. I DO think at least the southern end of the MDT risk could see 55-59F tds by mid-late afternoon, barring sustained SSE 80mph winds in TX and OK. Looking at morning soundings, we should see the dryline mix pretty quickly to the east, as moisture on DDC is ankle-deep, dewpoints >50F on OUN is only ~25mb deep, and SGF's moisture is only ~50mb deep.

The shear profiles in the risk area is pretty nice, but I am concerned about the fact that we'll probably see a low-level veering wind profile beneath mid-level backing wind profile (as cold-air advection destabilizes the risk area from the top). The latest (12z) RUC indicates that the 60F isodrosotherm may make it to the I70 area by 0z... However, by that time, the dryline is progged to be just west of Kansas City.

So, though I had every intention on chasing today, I'm sitting this one out. It's a complete waste of a system/setup, however, given the nice shear profiles and the chaseable storm motions (<= 40 kts). But with my target area 4.5-5 hrs away, and with 25-30F dewpoint depressions, I guess I'll just have to wait for the next one. It's sad that the Gulf can get fropa'd 5 days ago and still not be open enough to give us real moisture. Then again, I'm not sure we've seen real (~>65f) dewpoints this year so far (not that that's uncommon -- it is only mid-April).

Just an update regarding tomorrow's forecast. The GFS and NAM are still greatly at odds with each other; one solution (NAM) says "CHASE!", and the other (GFS) says "Save your money!". The 18z runs of each of those models still don't bridge the gap very much, with the NAM forecast dryline position along or just east of I35/I135 by 0z, and the GFS showing the same feature considerably farther east. Since it is relatively early in the season, and we will not see true, deep Gulf moisture, I don't want to end up in southwestern IA or northwestern MO by late afternoon. However, I think the area along the dryline bulge could support significant tornadoes by afternoon and into the evening. The 18z NAM indicates >500 0-3km SRH and >2000 CAPE east of a Topeka to Concordia line (in KS), and northwest from there into southcentral NE. This would place much of northeastern KS and southeastern NE in a high-end MDT risk area by afternoon and early evening (before shifting eastward into southwestern IA and western MO). While strong convergence should exist along the length of the dryline, significantly-warm 850mb temps may inhibit convective initiation.

I'm still quite surprised to see such different solutions (850mb low over southwestern NE / NAM / or northcentral NE / GFS) on a 24-30 hour forecast. Given the history with the dryline moving a little more slowly than model forecasts this year, I think there is a better-than-not chance of the NAM verifying. I think one of the keys will be exactly where the mid-level trough cuts off into a closed low. The NAM indicates this will happen by 12z over far northeastern CO, while the GFS doesn't really close it off until near 18z over NE/KS. An earlier cut-off will slow the progression of the system, and likely allow for a more western dryline location.

So, here's to the 18z NAM verifying! This morning's WRF did not indicate any convective precip south of the NE/KS border.

Regarding the forecast for this Saturday... Tough forecast with such poor model-to-model consistency. The 18z NAM continues to slow things down a bit, with a minor westward shift of the dryline, particularly north of ICT. I remain highly skeptical of the dewpoint forecasts as this point (given the model track records this year), but the 18z NAM has actually increased the td forecast, indicating a nice pocked of >65F Tds in central OK, as well as along the I70 corridor in central and northeastern KS. I think it will be vitally important to get this moisture in place by afternoon, as it'll help ease the CINH situation and bring the dewpoint deficits / LCLs into a more respectable range. Correspondingly, the 18z NAM shows <60 j/kg CINH over much of central and northern KS (though no QPF yet), which may allow for initiation given strong convergence along the dryline (check out the 850mb and 700mb UVV plots), as well as deep-ascent ahead of the vort max (i.e. DPVA). The 12z and 18z NAM runs also show cooler 850mb and 700mb temps compared to a couple runs last night and yesterday.

Flow aloft also looks more "doable" than the past few events, with 45-55kt 0-6km shear (instead of 60-75kt deeplayer shear, which may have been too much for the given amount of CAPE) and 40-45kt storm motions. The flow fields look to support tornadic supercells IF we can realize the forecast moisture. Right now, we're still experiencing modified continental air that's being recycled from the southeastern US, which means we may not see real Gulf moisture. A look at the knee-deep moisture at CRP at 12z today makes me cringe. At least we have 2 full days to see some return, because we're going to need all the time we can get. Dewpoints in the Gulf (per buoy obs) have recovered into the upper 60s, but I question how deep that moisture is given the trajectories.

Of course, this entire forecast is as good as gum on a sidewalk if the GFS verifies. I can't imagine that, given the current state of the upperlevel (cut-off off the southern California coast) that the system will come through too quickly. Models have a tendency to be too fast with these types of troughs/lows, so the trend may be w/in the favor of most Plains chasers. Then again, the core of the upper-level low/trough isn't even being sampled yet, so this forecast may change entirely still.

Kim's schedule to pick up her wedding dress in Tulsa on Saturday, and I know she doesn't want to drive up there and back by herself. It still may work out that we can pick the dress up in TUL Saturday morning before heading northward a bit to setup for the case. However, as it looks now, the target area may be west of TUL (*crossing fingers that NAM wins the battle over the GFS*), and it'd be nice to fill the back seat with a couple of fellow chasers for gas $ purposes. I feel a little bad about leaving her alone so much this early in the chase season, but I have a sneaking suspicioun that there may not be much chasing within a 300 mile range come late May or June.

EDIT: Not sure why the NAM is aggressively raising Tds across the central US in the coming days. The real >63F dewpoints won't really be advected northward since they're still down in the Gulf (and looking at Td forecasts from TX/LA/MS don't show this stream of mid-60 dewpoints). That rather "out of nowhere" look to the model progs makes it seem like the NAM is cranking the evapotransiration contribution enough to punt the dewpoints upward 3-6 degrees. I don't know what the current state of the vegetation is in KS/NE/IA/MO and points east, but this seems a little dubious. Perhaps if it was June and the corn and crops were in full swing, but I'm not quite willing to buy >64F dewpoints in mid April w/o much of an advective contribution.

Not much to update, as I've been sick the past couple of days. I used to get sick every January (happened almost 6 years in a row -- the last week of January knocked me out), but that didn't happen this year (not that I'm complaining). Regardless, I'm back on my feet, getting some school work completed.

There's an outside chance of a chase on Saturday, as an strong upper-level trough swings through. The flow fields look pretty good, but, as has been the case this year (and isn't entirely uncommon in the early season) there may be issues with moisture return. The 0z NAM depicts at ~2000 MLCAPE environment east of the dryline, which is progged to be near I35/I135 south of a low in NE. The GFS is faster / farther east with this system, so it'd be a 100% no-go should that verify. As it is now, the surface patten looks pretty much how it is expected to look during a drought year, with massively hot (record-breaking) air behind the dryline. In fact, areas in northern TX and southwestern OK could top 100F on Saturday. Yuck! It was still officially winter 4 weeks ago! The dry conditions that have persisted in western TX and NM means that there will likely be stronger sensible heating (with less latent heating) this spring, which means higher temps. This hot air is also going to create a rather significant capping problem for any warm-sector convection on Saturday. The highest probs will be in NE and IA, but I don't want to drive that far while we're still early in the season. If it was May, I'd think differently, but climo argues against a big tornado day that far north this early in the year. The deep moisture may not make it up there, etc.

At any rate, I'm keeping my eye on it. The 0z NAM shows a nicely-timed vort max overriding the dryline near peak heating, so at least that would maximize the otherwise low probability if initiation south of I70. If we can maintain 62-65F dewpoints, the CAPE and shear combination should have no problem supporting supercells. High LCLs won't help the tornadogenesis issue very much, but maybe we can get a nicely-sculptured supercell out of it. Then again, with gas nearing $2.60/ga, I'm going to need to pack the car for any chase out of the state. After this next setup, however, it may be a while before we see much in the way of chasing here in the southern plains. Apparently, we skipped from February to early June. Unfortunately, the higher Tds that tend to accompany that calendar month are absent. Maybe I should just resign to chasing north of the OK/KS border from here on out. Except for a one or two supercell day (5-8-03, 5-9-03, 5-29-04, etc), OK hasn't seen a good tornado outbreak or significant supercell event since 10-9-2001. Should I even start naming the good Kansas or Nebraska days since that time? But hey, I can't complain too much -- at least I'm not stuck down in 100F Texas. Western TX lit up well last year, but I'm worried about the already-far-north setups we've had this early in the season. New atmospheric mandate: there will be no surface low in OK or TX.

I chased with several folks today (Gabe, Brandon; then caravaned with JR, Justin, Adam, and Robin) in northeastern OK and extreme southeastern KS. We targeted Bartlesville, and were quite pleased to see that hte storms that developed near I35 north of OKC were taking aim at our location. We meandered north from Bartlesville towards Dewey to get a good view of the storm as it approached. We knew it was tornado-warned, and the south side of the updraft was quite rigid. However, in time, it's radar appearance dropped... We headed north into extreme southern KS (in Carney), to watch this storm further. There was plenty of turbulent motion, but nothing too organized. We then dropped back south into OK, as radar showed addl storms developed that way. There was a nice RFD occlussion with the storm near the OK/KS border, but we thought that a storm to that one's south that was precipitating into the inflow of the that northern storm would squash the chances for a tornado with that one... So, we dropped south further, hearing of a new tornado-warned supercell southwest of Bartlesville. After getting to just east of Nowata, everything looked quite poor. With a nowcast update from Phil H., we dropped south again, hoping to catch a tornado-warned supercell very near the Tulsa 88D / radar site. We punched the core, making it to Pryor before trying to head east. At this time, the supercell was tornado warned again... On our way out of Pryor, we experienced very strong RFD winds, breaking a small tree not too far ahead of us. The storm exhibited a pretty nice RFD clear slot, but it was quite wet at that time. We tried to keep up with it, but we lost it on the most pathetic of roads that is Hwy 20 south of Langley (east of Lake Hudson).

Overall, another rather disappointing chase. The structure wasn't particularly noteworthy, and cloud-base rotation was weak. I noticed that, on radar, many of the cells exhibit some anticyclonic rotational tendencies intermittently. Looking at the RUC/SPC mesoanalysis valid for 0z, it's no wonder why storms struggled, with only ~500 j/kg CAPE near the storms in northeastern OK and southeastern KS. The 0z NAM initialized 750-1250 mlCAPE in the same area.

Similar to what happened on 3/30, I think one of the main failure modes was lack of strong instability in the face of strong shear (the supercell that moved from Paul's Valley to McAlester on 3/30 was also located in marginal CAPE -- 250-500 j/kg CAPE per SPC mesoanalysis by late afternoon and early evening). 0z NAM initialization indicates 0-6km shear of 70kts, with 80-85kt 500mb winds across that area at 0z. Broken strato-cu developed east of Osage county through the afternoon, which kept temps largely in the low-mid 70s. Farther west near and just east of I35, temps rocketed into the 80s. I don't think it's any coincidence that storm updrafts looked quite solid as they first approached Bartlesville, before turning more "mushy" in appearance as they marched northeastward. With relatively cool sfc temps, CINH was relatively significant. I do think that some storms were able to sustain themselves long enough to establish decent vertical perturbation PGF fields, which helped maintain the storms as they moved into the weaker/weak instability in se KS and ne OK. I do think we would have seen an event more like what was forecast if temps had warmed a bit and Tds would have risen a few more degrees. 0-1km SRH wasn't a problem, with RUC mesonanalysis at 0z indicating >400 0-1km SRH in se KS / ne OK. I think the cooler surface temps likely prevented storms from ingesting surface-based parcels (or at least not stretching them much owing to relatively weak CAPE), which is turn made the very strong low-level shear rather irrelevant.

The somewhat saving grace was experiencing the intense RFD in Pryor. In all, however,this chase falls in line with the other high-hype chases of the year (including 3/30 and 4/1), which is disappointment and frustration. I wish I had the will-power to just stay away from these early season setups, since they almost always seem to fail for one reason or another. Congrats to those who were able to bag today... Bring on May.

EDIT: After looking at the radar loop from Tulsa... Our original storm (which developed near I35 and tracked just north of Bartlesville) died as it moved into KS, near which time another storm formed to its southwest. However, a storm down near Tulsa threw off a left-split that slammed into that second storm. It looks like that second storm produced the tornado near Independence not too long after the left-split slammed into it. The cell that gave us some RFD fun in Pryor looked good for a while, but quickly went to garbage not too long after it moved through Pryor (which we noticed, as the updraft was quite mushy and rather unimpressive as it moved away from us at light speed).

My forecast thoughts align quite well with the new SWODY1. With a westward shift in dryline forecast position in this evening's model runs, I'm back into chase mode. I'm not a huge fan of strongly meridional mid and upperlevel flow (southerly / southeasterly), so I''m not too hot on the area north of the OK/KS border. It does appear as though a secondary warm front will set up from near Hebron to Kansas City to Springfield by 0z, with southeasterly surface flow supporting some better low-level shear profiles. Between that warm front and the OK border, however, winds and wind shear will largely be unidirectional (at least through 500mb), courtesy of southerly 500mb flow. These setups with veering low-level , backing mid-level , and veering upper-level profiles tend to make forecasts quite tricky, with the possibility of anticylonic and cyclonic mesos in the absence of stronger low-level helicity.

Farther south into OK, the 500mb flow is progged to be more veered, yielding a better looking deep-layer shear vector orientation relative to the dryline (SW, compared to almost due S in eastern KS). This should help favor discrete activity. Im still concerned about surface dewpoints, since we've seen several times this year that the models have overforecast Tds by 3-7F. Since we're already on the high side of LCLs (with T-td of 20+F degrees possible), I do think we need all the CAPE we can get. Not to mention, in such a strongly sheared environemnt (deep-layer shear of 50+kts), storms can struggle when deprived of strong CAPE. This may have been a reason why storms took a little while to organize into supercells on 3/12. Regardless, my preliminary target is Bartlesville, OK. The cap may be an issue, but this area will be in the left-exit region of a strong upper-level jet streak, yielding upper-level divergence and vertical motion (if any is needed in light of intense DPVA ahead of the vort max). The 0z NAM and WRF (as noted above) initiate precip all along the dryline before 0z. Low-level shear isn't particularly strong south of the warm front, so any backing of the surface flow that we can muster would be quite helpful.

Well, as it stands now, I'll probably sit out tomorrow. An impressively deep cyclone was develop tomorrow morning and afternoon in Nebraska (18z NAM has the low down to 977mb, but the GFS is about 10mb higher). However, only weak ridging in the southeastern US behind the cut-off low currently spinning over the New England area is resulting in a low-level pressure gradient that is yielding 850mb winds that are SW or WSW south of I70 in KS and OK. This is likely allowing the dryline is spread eastward rapidly as very dry air mixes down towards the surface. The NE/IA target looks okay, but I have questions about moisture depth and quality by tomorrow afternoon up there. In addition, 250mb winds are forecast to be between S and ESE (yes, ESE), as the upper-level low cruises across the plains south of the surface low.

I'm disappointed to say the least. This setup does look like it could support long-track, strong tornadoes east of the dryline. However, with forward motions of 50-60mph, and in an area of questionable chase terrain, I'll probably save the money for later use later in the season. Ugh. I REALLY hope models shift the dryline west about 100 miles, but the time for such a change is rapidly running out.

It appears that we will see another high-end MDT risk (or possible High, depending upon mesoscale details) for this Thursday, as an intense low moves out of the western US. The overall synoptic pattern is nearly textbook for a large-scale severe weather outbreak.. Of course, there are plenty of details that will need to be resolved before I get too confident in a high tornado risk (such details include cloud-cover, low-level moisture, etc). I'll try to post more thoughts on this later this evening.

Most of the WFOs are highlighting the risk, though to various degrees. After having just read the afternoon AFD from SGF, you'd think Thursday was shaping up to be the outbreaks of all outbreaks. Now, I don't know as if I'm that anxious about the setup, since we've had a couple of relative flops the past several days (namely, 3/30 and 4/1). I DO think we'd see a high-end severe weather / supercell tornado event if we could get true 63-68F dewpoints and 2500+ j/kg CAPE. The 3/30 and upcoming event both remind me a bit of 5/4/03 and 5/8/03, but those days saw 66-72F dewpoints and 3000-4000 j/kg MLCAPE. When faced with intense shear (0-6km shear progged to be 50-70kts across much of the risk area on Thursday), every bit of instability you can get can make a significant difference between a struggling supercell (such as the supercell in southern OK on 3/30, which was in an environment of 300-600 j/kg CAPE by late afternoon) and one that produces long-lived, strong/violent tornadoes. Note that the RUC analyzed CAPE (and NAM initialized CAPE for that matter) associated with the 4/2 supercells in AR and TN was in the 2500-3200 j/kg CAPE.

EDIT: Just looking at the 12z NAM images, the possibility of a high-end outbreak is encapsulated by looking at the NAM forecast for Significant Tornado Parameter valid Thursday 7p. LOL I know, the STP is a combination parameter that combines things that are difficult for models to forecast to begin with, meaning their combination should be viewed with a very large grain of salt. However, the STP, in this case, does indicate that where there is a combination of very strong low-level shear, CAPE, and low LCLs.

Well, it looks like another big trough is going to slide out of the western US, leading to strong cyclogenesis somewhere near or in Nebraska this Thursday. The overall synoptic setups appears remarkedly similar to this past Thursday's setup (3/30/06). As I had anticipated, the models (particularly the NAM, since I haven't had much time to interrogate the GFS output) have shifted westward (OK, their forecasts have shifted westward) with the surface features by afternoon, with the dryline somewhere in vicinity of eastern KS and OK. Relatively strong flow at all levels should yield decent low-level shear (0-1km SRH of >250 in ne OK per the 0z NAM) and strong deep-layer shear (>55kts over the 0-6km layer east of dryline by afternoon). With dewpoints PROGGED to be in the 61-68F range from eastern KS into OK and northern TX, CAPE may surpass 2000 j/kg. Note that I made sure to emphasize "PROGGED", since the models have had a tendency to overforecast surface dewpoints, which has had a detrimental impact on CAPE. The cap does appear to be stronger this go round, which either means that we may see more isolated, discrete activity (if one assumes that stronger cap would inhibit widespread convection, which may not always be a valid assumption), or that we may see a big 'ole clear-sky cap bust (ala 3/29/06 in OK/TX).

Overall, however, I think I'll probably chase. My head tells me that if the setup looks that similar to 3/30, I should probably save the gas money for a time when we'll have some real moisture and CAPE since we may very well see the same outcome as 3/30 (not much in the way of tornadic supercells, save one or two in eastern KS). However, I have high suspicion that my chasin' nature will kick in, and once I commit, it's hard to stay home.

I'll try to look over the 4/2 synoptic maps to see what I can figure out in terms of differences between that day (which featured a couple of long-track, significant tornado producing supercells ni AR and TN) and the previous setups. Just off-hand, however, I do see that the CAPE was significantly higher (in the 3000-3500 j/kg range) invof the supercell on 4/2, compared to 1000-1500 j/kg CAPE days we've seen several times this year. In fact, IIRC, the only chase day with >1500 CAPE was 4/1 in OK and northwestern TX. Of course, for various reasons hypothesized below and elsewhere, the storm on 4/1 saw a rather rapid transition to HP status, followed by upscale growth into a quasi-linear MCS. There was also a nice-looking supercell (per radar at least) southeast of Dallas, TX, yesterday afternoon. It had a nice flying-eagle shape to it, and contained a hook echo signature from time to time. Speaking of TX, I'm a little surprised that we haven't much in the way of setups for that state this year. Then again, almost every system we've seen so far has been of the type more common in May and June than March and early April. I'm ready for a surface low southern KS, OK, or northern TX! No more of this garbage of strong surface cyclogenesis in Nebraska! Sure, shear profiles in such an environment tend to favor large-scale severe weather events (assuming moisture and CAPE are "sufficient", whatever that means), but I'm not so hot on chasing supercells moving 55kts+ east of I35. What about a 10/9/01 type of setup? Or 5-12-04 setup?

I'll take a less active early season (active in terms of the number of large troughs and cyclones that, climatologically, produce large-scale svr wx events in the plains) if we can have a couple of smaller, more localized events nearer this chaser's residence.

I typed up a chase report from the 4-1-06 chase. You can read it HERE.

I also have a few comments regarding my thoughts on the relative bust yesterday. For the most part, it's from my Stormtrack post...

OK, so I'll largely consider today a bust. At least it wasn't a clear-sky bust, but it certainly was a bust in terms of the number of supercells and the lack of tornadoes. Here are my 2 cents...

All models had forecast Tds in the 63-68 range across southwestern OK by afternoon. When I looked at the 3pm obs, it was obvious that the models were way overdoing surface moisture. It's interesting to note that the same was true of 3/12 for the most part. When I looked at the FWD sounding and saw the 140mb deep moist layer, and noticing that shear wasn't terribly strong, I figured we wouldn't need to worry about mixing out the good juice. However, OK mesonet obs didn't really show any sites >63F dewpoint west or north of I44 by afternoon (and all areas from the 1st-tier of counties in western OK and westward into the TX panhandle were <58F td). So, it was quite obvious that the real nice dewpoints stayed down in southcentral OK (and southeastward from there), where places like Ardmore and Duncan saw 65-69F dewpoints most of the day. So, it appears that (a) the richer moisture couldn't advect far enough westward (into western OK and eastern TX panhandle), and ( the moisture that was there mixed out a bit. This led to much greater dewpoint depressions (and much lower boundary-layer RH) than were (was) forecast. So, in any particular storm's downdraft, there was likely plenty of evaporational cooling (with low RH present), which in turn likely lead to stronger cold pools. With strong cold pools, more convection was forced along its leading edge. Eventually, we saw rather quick upscale growth to a linear mode. With modest upper-level flow, along with plenty of potential for cold downdrafts, I feel the end was result were outflow dominant storms.

Now, I think we may have actually had too much insolation today. As strong diabatic heating occurred, the mixing depth increased (boundary layer deepened), which helped mix out some of the higher across western OK (dewpoints in many southwestern and west-central OK mesonet sites dropped 2-4F in Td between 1pm and 5pm). This likely allowed a very large area to near the convective temperature. With lowered Tds, and more potential for evaporative cooling in the low-levels, strong downdrafts developed. Since there was very little capping left over a relatively large area, the convergence along the leading edge of the downdrafts / cold pools was likely sufficient to initiate more convection. In addition, the RFD was likely strongly negatively buoyant (in fact, an OUN warning decision update even addressed the low theta-e air in the RFD). So, add all of this together, and I think that may explain why we saw a rapid evolution to a linear mode. Perhaps if we had a little less insolation, a little stronger capping may have persisted, and this issue may not have been as dominant.

There is some possibility (perhaps a good possibility) that the storm was being seeded from the anvil associated with upstream convection south and southwest of Childress. Anvil-level precip from this upstream convection may have been falling very near the RFD region of the west-central OK supercell. I'd have to look at some tilt 3 and 4 base reflectivity data from KFDR in order to see how much of an effect this may have had.

It's also worth noting that low-level shear wasn't particularly strong. FWIW, RUC/SPC mesoanalysis didn't show >250m2/s2 0-3km SRH until about 2z. The relatively weak low-level shear in extreme western OK and the eastern TX panhandle, may have allowed the cold pools to spread away from the storm more than desired. The mid-level was actually stronger than the models had forecast (by about 10-15kts in most places of the target area), with 60kts at AMA and 35kts at OUN. I'm going to chalk this up almost entirely to the low-level thermodynamic and kinematic fields (moreso the thermodynamic environment, however).

On a different note, I continue to see some sometimes-large discrepancies in the dewpoints reported at ASOS obs and those reported at OK Mesonet sites. For example, Vernon was reporting a 70F dewpoin the late afternoon. Just a few 10s of miles away, Tipton and Grandfield Mesonet sites were only reporting 61-62F dewpoints. On the whole, it seems as the ASOS obs tend to be 1-5F higher in dewpoint than nearby Mesonet obs. Now, the ASOS sites directly measure dewpoint (with a chilled mirror), while the Mesonet sites calculate dewpoint from temperature and RH. So, I'm not entirely sure which one to believe, but there seems to be better spatial continuity with Mesonet obs compared to ASOS obs.

A note about chase day hype-casting. I typed this for ST in reponse to some folks who seem to be letting their chase wishcasts and excitement get the best of them..

Before we start crying that F5s are going to hit major metro areas, I think we should be a little more cautious. I can't (nor shouldn't) tell anyone what to say, but just think we could be a bit more cautious. Some of us said similar things yesterday (3/29) and that event was largely a nonevent for most of OK. If there's one thing about severe convective forecasting and tornado forecasting, it's that forecasts are extremely difficult, especially for high-end events. There are always failure modes, especially if you take model output exactly as is. Extreme events (such as violent tornadoes) are extremely rare for a reason, and it's not necessarily because models don't forecast environments/setups that appear to favor them. If you look at most chase years, there are usually at least a few setups that look to be favorable for violent tornadoes, and few of those pan out.

I'm still undecided on a specific target for tomorrow. It almost always seems like the area east of the sfc low near the warm front is a good choice, owing to winds that tend to be more backed in that area. However, current model output would lead me to southwestern OK and adjacent areas of TX, where seasonably high Tds will be juxtaposed with strong low-level shear. The NAM is depicting some sort of boundary very near the Red River tomorrow afternoon, as evidenced by a change in the surface winds across the boundary and a rather impressive temperature increase to the south. I'm not entirely sure that I'll believe that solution, but it has been persistent for a couple of model runs. What has also been consistent has been the presence of some weak shortwave (ahead of the main vort max) that the NAM progs to be over western OK by 0z (you can see this in the 500mb height contours as well as the vorticity plots).

I think the main potential failure mode tomorrow involves widespread cirrostratus that would limited insolation and near-surface destabilization. As it stands now, the 0z NAM indicates that mid and upper-level RH >80% will overspread the TX panhandle and begin to affect western OK by late afternoon. In the morning, however, it appears that we should see significant sunshine across the target area. Of course, a visible satellite image tomorrow morning will tell all.

As it stands, this more classic dryline southern plains setup look to offer the potential for a couple of strong tornadoes. While flow aloft is not particularly strong, deep-layer shear should be in the 40-45kt range (certainly favorable for supercells given the CAPE).