2011-6-19 FCST: NE/KS/CO

[jshields]

Tomorrow(well today now) looks to be a very good day before the main show. it looks like a classic warm front set up as low pressure sets up along the colorado and kansas border with the warm front retreating to the ks/ne border by late afternoon. easterly/southeasterly surface winds veering to westerly mid level winds of 50 kts at 500 mb will lead to very good shear. very steep low and mid level lapse rate greater than 8.0 c/km and tons of low level cape(NAM has near 300 J/kg) will lead to storms with very large hail and tornadoes. the NAM has tons of precip breaking out early, but the WRF is peculiar with its lack of storms and nothing really popping til out in the nebraska panhandle in the evening. a moderate risk has been issued, as i type this, and i see there is now a moderate risk for day 2 as well!! i'll be out both days hopefully finally getting my first tornado of the season.

 

[Jeff Duda]

...but the WRF is peculiar with its lack of storms and nothing really popping til out in the nebraska panhandle in the evening...

That would probably be due to the quite warm 700 mb temps (and cap, in general) meandering around the KS-NE border for much of the day. I think that is the biggest issue with this setup east of CO - whether the cap will break. Some models say it will, just about as many say it won't. Obviously you'd want to stay right on the edge of the cap for preferential storm development (again, for being east of CO).

 

[Jeff Snyder]

Nick Bierman, Jana Houser, and I are en route to the north-central / northeastern KS (and adjacent portions of NE) target. We have to be back later tonight, so we cannot take the bait in northeastern Colorado. This, it turns out, is just fine with me, since it makes targeting much easier. My primary concerns for the NE KS / SE NE target are two-fold: the depth of the easterly flow N of the front and whether we'll see daytime CI.

Regarding the former -- I'm not sure I've chased too many setups with >1 km easterly (or ESErly) flow near the surface. I did check out the SPC Severe Events database, and the best analog I can find that featured something similar was 5/22/04. However, the big Hallam storm, IIRC, developed right along the front and moved, essentially, along it. At any rate, one good thing about the deep easterly flow is that it'll help keep the very hot 850 m air to the south. Now, what happens nearer 800-750 mb isn't certain, since southerly flow there may advect in the extremely well-mixed air from the >100 F temps south of the front. 12z soundings revealed extremely steep mid-level lapse rates (>9 C/km) as a result of the very deep mixing that's been occurring in much of the central and southern Plains for the past few weeks. At any rate, forecast wind profiles show nearly unidirectional, generally weak shear in the 0-1 or 0-1.5km AGL layer. This can be seen in comparing 0-1 km SRH vs. 0-3 km SRH forecasts.

Regarding the latter -- well, I don't really need to rehash this concern much, it's relatively obvious. I also don't have good luck with extreme CAPE days (CAPE >6000 j/kg) -- I don't know if it's an issue of extreme dry-air entrainment along the periphery if the updrafts or what, but I haven't had much success with such days. I know the RUC is overforecasting CAPE, as usually, since I don't think we'll see 100/77 along the front today...

Our plan is to head to the CNK area and keep our eyes on visible satellite (and the planned 21z TOP sounding?).