Chase Log: February 28th, 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.

MAP

Total Distance: 250 miles
Target Area: Stillwater and east (OK)
Chase Area: Stillwater to east of Pawnee
Maximum SPC Risk category: Moderate
Watches: Tornado Watches 36, 38, and 41, Severe Watch 37
Mesoscale Discussions (MCDs): 218-222 and 224

Another early-season chase setup presented itself as another very strong cyclone was forecast to develop and deepen as a 150+kt 250mb jet streak moved out of the western U.S. Moisture looked to be less of an issue as the previous event, as we had more than a day for moisture return. Despite model projections of 58-62F dewpoints east of the dryline across eastern Oklahoma, afternoon surface obs indicated 53-57F dewpoints widespread in the warm sector. There was also concern about veered 850mb winds produced by a wave that passed through during the morning hours, which some feared would result in a very strong cap and drying surface conditions. A special 20z OUN sounding showed that the veered 850mb flow had little effect on moisture depth, with 100mb of substantial moisture in the low-levels. With strong shear profiles, supercells and tornadoes seemed quite possible, though marginal CAPE (750-1250 j/kg sbCAPE) was expected to be a limiting factor.

Dan Dawson, myself, and a couple others decided to try our luck with any convection that developed off the dryline in central and northern Oklahoma. We left OUN around 3:45pm and headed NNEward where satellite was showing enhanced Cu north and northeast of OKC. It didn't take very long for that field to dissipate, and, by the time we made it to Stillwater, the sky was clear. Oy. Of course, by that time, we noted two cells developing in southern Kansas, but quickly realized they were too far away. After eating at Eskimo Joes in Stillwater, we figured we'd check out the situation once more before heading home. Much to our surprise, the 01z SWODY1 upgraded most of eastern Oklahoma east of the dryline to MDT risk. We weren't much more confident in initiation after reading the SWODY than we were before reading it, but we decided to wait it out in Stillwater just a little longer. The 00z OUN sounding was nearly uncapped (though showed a little bit of drying above the surface), but there wasn't a whole lot of convergence along the dryline. Regardless, we were resilient and had fun drooling over the southeastern KS supercell that seemed to be a prime example of a tornadic supercell (with reported wedges and strong/violent tornadoes) in low CAPE (mesoanalysis was indicating <250 j/kg for a while, with high CINH). By 10pm, convergence was quite strong along the cold front that was overtaking the dryline, so we waited. And waited. By about 11pm, a blip we noted just WNW of Stillwater actually developed into a storm, and we were off. Not entirely surprising given the degree of forcing/convergence and the apparent CINH, this convection quickly "lined out", and we gave up chase east of Pawnee since we didn't want to chase a highly-forced, narrow squall line after dark in northeastern Oklahoma (with deep-layer shear vectors 45degrees off the cold front and 80-90 degrees off the dryline, we had been holding out a little bit of hope that we'd see discrete activity).

All in all, it wasn't a terrible chase, though we're 0-for-2 in terms of potentially significant events in Oklahoma. I'm still amazed at the supercell(s) that developed in eastern KS and nw MO last night... I remember laughing with my advisor when looking at the 20-40F dewpoints along the OK/KS border in the early afternoon yesterday. Given the time of year and questions about moisture and initiation, we didn't want to make a drive to southeastern Kansas when areas of Oklahoma looked nearly as favorable, a decision supported by the RUC (which initiated precip along I44 by late afternoon) and the NAM (which showed precip north of Stillwater and into southern KS). The 20z OUN sounding pleasantly surprised me by indicating much deeper moisture than I was expecting given the veered flow that existed near 850mb, and I thought it was more likely that moisture depth farther north to the OK/KS border was considerably lower, a 'guess' that I used, in part, to justify not driving to KS. It sure would have been nice to have the 57-62F dewpoints widespread east of the dryline as the NAM had forecast. Ooops.