Day 1 Severe Weather Outlook

Valid 271630Z – 281200Z


Scattered to numerous severe thunderstorms are possible, including a
few tornadoes, mainly during the late afternoon and evening from
northern Illinois to eastern Kansas.

…KS to Lower MI…
Elevated convection is ongoing within a low-level warm advection
regime across the Mid-MO Valley and northern IL. Robust
boundary-layer heating is underway in the wake of this morning
activity beneath an elevated mixed layer that is attempting to
advect northeast from the central Great Plains/Lower MO Valley. In
conjunction with surface dew points increasing into the upper 60s to
lower 70s surface dew points, a strongly unstable air mass with
MLCAPE of 2500-3500 J/kg should develop ahead of a
southwest-northeast cold front from eastern KS to the IA/IL/MO
border area.

Despite near-neutral mid-level height tendency, guidance is fairly
consistent with the presence of a mid-level speed max developing
across northeast KS this afternoon and reaching the IA/IL border
area this evening. While the bulk of initial convective development
may be atop a more stable boundary-layer from central IA to southern
WI, sufficient convergence should exist for storm development along
the front and into the warm sector from its intersection with the
differential heating boundary in northern IL to the dryline
intersection in south-central KS. The greatest convective coverage
should reside near the IA/IL/MO border region with more scattered
coverage back into eastern KS.

Low to deep-layer wind profiles will favor potential for several
supercells during the early evening which will probably consolidate
into multiple organized clusters through late evening. Large hail
will be the most probable hazard with scattered severe wind gusts
expected as well. Given rich boundary-layer moisture and an enlarged
low-level hodograph, certainly a tornado risk will exist with any
supercells just ahead of the front. 12Z HREF guidance and related
CAMs are indicative of higher-end tornado coverage. However, with
cyclolysis expected, the overall synoptic pattern should be a
limiting factor. Still, given the potential for at least a few
tornadoes, will double-upgrade from less than 2 percent to a 5
percent area with this outlook.

…Southeast NM and west TX…
A low-amplitude shortwave trough near the AZ/Sonora border should
approach the TX Panhandle. Scattered storms should develop this
evening into the overnight. Modest buoyancy, the bulk of which
should remain below the strong speed shear from the mid to upper
levels, will probably marginalize the overall severe hail and wind

..Grams/Smith.. 09/27/2019


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