Chase Log: April 21st, 2007
Click on any of the SPC products below (Convective Outlooks, Watches, or MCDs) to see the SPC's "Severe Thunderstorm Events" page pertaining to this event.
Total Distance: 660 miles
Target Area: Turkey, TX, to Silverton to Plainview
Chase Area: Around Amarillo, Groom
Maximum SPC Risk category: Moderate
Watches:
Mesoscale Discussions (MCDs):
A potential significant tornado event was forecast, as a compact, but intense, upper-level low moved out of the southwestern USA. The Gulf saw a strong cold frontal passage earlier in the week, which scoured most of the significant low-level moisture well southward. Despite this, models were relatively consistent in forecasting mid- to upper-50 dewpoints across western Texas, the Oklahoma panhandle, and western Kansas. The upper-level trough was forecast to become negatively tilted as a strong 100kt 250mb jet impinged on the western Plains. Strong shear and moderate instability were in line for a significant tornado event, but, with surface dewpoints ~5 F lower than the 3-28-07 event, there was some uncertainty regarding convective mode and LCL height.
I went out towards AMA with Brandon, Gabe, and a several others this afternoon. It's almost 3am, so I won't say much other than give anyone a guess as to say that we ended up with a total tornado count of .... zero. The targeted storms SW of AMA, in the Hereford area. With each new cell that went up in this area and moved NNE, a new cell would develop to its SSW and collide with it. We witnessed at least two such collisions. Each time, we waited a little longer for the southernmost cell to come into view, thinking that the tail-end charlie (locally, at least, since there were more cells to the NW and W of LUB ) was the best bet given uninterrupted inflow. We did experience incredible inflow south of Bushland with a developing supercell that, of course, was heavily disrupted by developing convection to its south-southwest.
With radar looking like everything was congealing N of I40 with widespread initiation in a very linear manner, we opted to stay with a LPish cell that crossed N of I40 w of AMA near Bushland. Of course, while this was occurring, the cells that we watched earlier in the afternoon (one that passed very near Vega, and another that passed between AMA and Vega, the one that on which we experienced amazing inflow) discretized from the mess N of I40, and both went on to produce tornadoes (I believe). Meanwhile, it was getting to be 7pm, and we know we couldn't make it south to the Tulia cell before nightfall. So, we stayed with the LP storm in hopes that it too would become tornadic, but that was not to be the case (before nightfall, at least). In utter frustration, we dropped that storm and headed home in a manner that would allow us to experience the Tulia supercell as it crossed I40 near Groom. While in Groom, we noted very intense convergence (with a large area of >71kt inbound velocities on BV1), and a tight circulation soon developed very nearby. We busted east towards 70, and started heading north towards Pampa. At one time, SRV1 indicated a very intense, very tight circulation west of Hwy 70, between Groom and Pampa. Alas, as we approached this circulation, it weakened. Again, admitting the Mother Nature defeated us, we limped home.
Ugh. This day was so bad all I can do is laugh. We were on 3 storms during the afternoon and evening. Each storm had looked decent in it's initial stages, before more convection kept developing to the immediate SSW. EAch time this occurred, we turned our hopes to the new tail-end charlie (local, again, but there was a decent gap between the Oilton / Tulia cell and the cell(s) we were on). And each time, despite mergers and the abundance of nearby convection, the cell we left developed strong rotation and (again, if I've followed the warnings correctly) produced a tornado (or tornadoes) N of I40. Meanwhile, Gabe and I both had original targets in the Silverton to Plainview area that we had for the past couple of days, a target that would have allowed us to observe the tornadic supercell that roamed to the W and N of that area. Instead, we modified our target slightly based on fears of strong capping possibly inhibiting convection S of I40 (as the various RUC runs indicated), as well as fears over high LCLs. In addition, I believe the more recent NAM runs showed the best low-level shear near I40 through afternoon. So, with all that, we opted to stay near AMA. Bad choice. At least I can hang my hopes on the potential for two high-end severe weather days in the offing...
I'm very curious as to why the cell we were on from Bushland to Marsh (and, eventually, east of Dumas) didn't really do much until near sunset as it approached Moore county... This storm was the local tail-end charlie, with it's inflow only interrupted by a dissipating left-split that was thrown of the Tulia cell. Structure was okay from time to time, but it was extremely disappointing to know that we left at least 2 supercells that would later produce substantial tornadoes.
04-21-2007 Chase Pictures
Click on any photo to see a larger version
