Day 1 Severe Weather Outlook

Valid 291300Z – 301200Z


Scattered severe thunderstorms are probable this afternoon into
tonight from the central Great Plains to southern Wisconsin. Large
hail, damaging winds, and a tornado or two will be possible.

…Mid-MO Valley to central Great Lakes…
A vigorous shortwave trough near the MN/ON border will rapidly
progress into western QC by early Friday. Mid-level height falls
with this feature will generally be confined to northern portions of
WI/MI. A surface cold front will sweep east and push south,
extending from eastern WI/Upper MI southwest towards the KS/NE
border at 21Z.

Low-level warm advection-driven convection is ongoing across
central/southern IA along the leading edge of moisture return from
the central and southern Great Plains. This activity should persist
through the day as simulated by recent NCEP/ESRL-HRRR runs, while
additional elevated convection has recently formed in northwest WI
closer to the shortwave trough. The low-level moisture plume will be
rather confined with northeast extent but should support increasing
surface dew points from the southwest as mixing ensues. Confidence
is not particularly high with the degree of surface-based buoyancy
indicated by guidance given the persistence of early-day elevated
storms and the need for substantial moist advection/mixing. Even
with more muted buoyancy, deep-layer shear will be pronounced
(effective values of 35-50 kt) and favorable for organized
updrafts/clusters with any pockets of convection that can be
sustained near the front during the late afternoon to early evening.
Thus, will refrain from making any substantial changes to the
Marginal and Slight Risks with this outlook.

…Central Great Plains…
Most guidance is fairly consistent in sustaining late afternoon
storm development near the intersection of the southward-moving cold
front and dryline along the southwest NE/northwest KS border. A
minor mid-level impulse is expected to approach this region from
southwest WY, yielding some enhancement to west-northwesterlies
aloft. With hot surface temperatures across western KS, increasingly
rich low-level moisture near the front, and a plume of rather steep
mid-level lapse rates, a few supercells may form prior to growing
upscale into a large MCS tonight towards the Lower MO Valley. Large
hail and a tornado will be possible early, with severe wind gusts
likely becoming the primary threat into the overnight as a 30-35 kt
low-level jet develops from the southern High Plains to central KS.

..Grams/Mosier.. 08/29/2019


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