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Today’s NWS Discussions
With seasonally cool temperatures aloft, very steep lapse rates will develop ahead of the front over western OK as temperatures soar through the 80s into the lower 90s. This will allow surface parcels to reach their convective temperatures by 21-22z. With frontal convergence, thunderstorms are expected to initiate a bit earlier across south-central/southeast KS then grow upscale within a very unstable air mass (MLCAPE in excess of 4000 J/kg). There is increasing concern that a potentially damaging squall line.
A majority of the high resolution models initially moisten 850MB via lift on front until the front reaches southeast KS, where moisture will have time to return. The 0000 UTC GFS relies on moisture advection and breaks out convection near OK border prior to frontal passage. All portend sufficient instability for severe storms given shear. Will have hail threat early with more discrete cells, but should transition to wind event fairly quickly as storms cluster and/or line out.
Expect CI (Convective Initiation) around 21Z (4pm CDT) initially near Ponca City, and then rapid development along the front from 21-00Z from near Stillwater to Shawnee. Storms may initially remain semi-discrete and have a low chance of producing quick tornadoes there. As the front progresses southward, storms should merge into a squall line with an increasing threat of damaging winds across south central and southeastern OK around 00-03Z. A highly unstable environment and steep mid level lapse rates will also support very large hail.
This will be an early and fast-moving system. There are still some differences in model forecasts, but the convective-allowing models seems to be converging on the threat for southeast Kansas being primarily wind and hail, with which one causes the most impact being determined by how quickly the storms line out into a squall line. In the initial couple of hours, if a storm can stay discrete and stay near weak triple-point that looks to be in the Wellington area, there could be a few brief tornadoes.
The system moves out of Kansas pretty rapidly, clearing the Turnpike corridor before 5pm and clearing the southeast corner counties by around sunset. I don’t plan to chase it into Oklahoma unless it remains tornadic longer than expected. One thing that hasn’t gotten a lot of mention because it does not look like a severe event: the chance for thunderstorms in central Kansas this evening on the cold side of the system.
The speed of the system until it is almost clear of Kansas will limit flooding potential. But the WPC has posted an area of excessive rainfal in the southeast corner, so some flash flooding may be possible.