Chase Log: August 17th, 2005


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.


MAP
(ZOOMED)

Total Distance: 570 miles
Target Area: Pratt, KS
Chase Area: Northwest to east of Pratt, KS
Maximum SPC Risk category: Slight
Watches:
Mesoscale Discussions (MCDs):

I wasn't really expecting to chase this day, but a look at "morning of" data and model output gave me a little confidence that there would at least be a good chance of supercells across parts of western Kansas northward into Nebraska. A modest mid-upper level wave coming out of the western US would spread some enhanced westerlies acorss western Kansas and areas northward. With dewpoints in the low-mid 70s, temperatures in the upper-80s, and a good veering wind profile, Gabe and I decided it was worth the drive to head into Kansas.

After looking at data when we were approaching Wichita, we decided that the environment to the north wasn't much better than to the west. Since we were expecting relatively slow storm motion, and we knew initiation could be well west of us, we opted to head west out of Wichita. We stopped in Pratt for some food and opted to stay there after looking at data again. Strong instability and a veering (yet relatively weak) wind profile continued to suggest at threat of supercells. A few turkey towers developed to our west and northwest, so we decided to make a little progress that way since it was evident that there was some enhanced localized convergence there.

A storm developed ahead of us, making us happy that we hadn't clear-sky busted. Over the next few hours, the storm exhibited intermittent supercell structures, with numerous wallclouds and RFD surges. Throughout this time, it was evident that low-level shear was just a tad too weak, as precip from the front-flank downdraft continually undercut the updraft. In addition, all but one of the RFD surges was accompanied by large amounts of precip. Interestingly enough, the one RFD surge that was relatively dry was also the one that produced a weak tornado. Gabe and I debated about whether to label it a tornado or a gustnado. After a minute of discussion, we opted to call it in as a tornado, since it developed under the mesocyclone along the inner edge of the RFD surge. Either way, it was weak and only lasted about 10 seconds.

In the end, this chase was very enjoyable, despite the disappointment in the supercell not producing much. However, the storm did exhibit classic supercell structures and was visually appealing. In addition, the storm only moved about 10 mph, so we stopped and set up our tripods for 20-25 minutes at a time. Add in the fact that we nailed our target, and it made for an enjoyable chase.

08-17-2005 Chase Pictures

Click on any photo to see a larger version

This picture was taken shortly after we first stopped to watch the storm. As can be seen, precipitation from the downdraft was undercutting the updraft. The base looked disorganized for a while, but slowly began to develop supercell structures. Another view of the updraft base immediately beside the downdraft. Note again that the precip/downdraft is undercutting the updraft base. It did appear that there were severe-caliber winds on the left side of that rain-foot. The right-to-left motion on that precipitation was awesome. Soon after the last picture was taken, we had to move as precipitation approached our location. After driving east a couple of miles, we noticed the first clear RFD occlussion. This picture was taken a few miles east of the previous pictures. A nice wallcloud developed to our west associated with the RFD advancement. Another view of a nice lowering associated with the first RFD advancement. We moved southeast of the previous position, and this was a good pull-off. Unfortunately, there were a bunch of cattle to our immediate southeast, which made this stop very smelly. Again, another attempt at an organized wall-cloud, and I thought that we might just get a tornado out of this. That was not to be, however. Another RFD occlussion looked to be getting underway at this time. Yet again, as had been the case for all but one RFD advancement previously, note the abundant precipitation in the RFD region and to the west and southwest of the low-level mesocyclone. Ah ha! Finally, a clear / non-precipitation-filled RFD push! This wall-cloud looked rather ragged at this time, but I was very confident that the rotation would tighten up rapidly given the awesome vertical motion of the wall-cloud and the advancing dry RFD. Contrast-enhanced view of a spin-up underneath a wall-cloud. There were several gustnadoes seen on the periphery of the RFD (or on the RFD gust front), but this one was more intense than any of the gustnadoes, and was located immediately beneath the wall-cloud. Tough call, but given its location and brief intensity, we were at 75%/25% tornado/gustnado probability. Regardless, F0 in the middle of a field that lasted only for about 5seconds is insignificant. A lot of dust was kicked up by the RFD at this time (note the clear-slot visible on the right). By this time, the storm had some very nice structure. I actually wish that I was able to move farther away from the storm to get a "whole-updraft" picture. The tail-cloud of the wall-cloud is on the left side of the image, with the beaver tail feature the main structure in this picture. By this time, the storm was starting to dissipate. There was only slight rotation evident at cloud-base (not seen -- to the left). I thought this was a pretty neat feature -- there were "swirly" tube-like features hanging down from this mid-level inflow band on the edge of the downdraft and precipitation. This was the south part of the updraft base, which looked like a horseshoe. The main precip core is to the right of this picture, and there really wasn't much in the way of rotation at cloudbase by this time. We got absolutely bombarded by very intense rainfall from the north about 5 minutes after this picture was taken.