SPC AC 220730
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 AM CDT Sun Sep 22 2019
Valid 241200Z - 251200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
IOWA...WESTERN WISCONSIN...AND SOUTHERN MINNESOTA...
Severe storms are possible Tuesday across much of Iowa, Wisconsin,
and southern Minnesota, with isolated storms from parts of the
central Plains to the Upper Great Lakes.
An elongated upper jet will dive southeastward across the northern
Plains and into the upper MS Valley on Tuesday, with significant
cooling aloft and increasing shear. The strongest lift will focus
over MN, IA and WI as a cold front collides with returning low-level
moisture with at least mid 60s F dewpoints. The cold front will
progress eastward toward northern IL by Wed morning, while western
parts of the front stall from KS into the TX Panhandle.
To the west, an upper low will continue southward across western AZ
and into the northern Baja, maintaining a favorable environment for
scattered storms over southern AZ and NM.
...Upper MS Valley to the central Plains...
Most of the area will remain free of thunderstorms for much of the
day as the moist plume becomes established and temperatures aloft
cool. By around 00Z, storms are expected to form along the front
from southern MN into IA and perhaps eastern NE, and will expand in
coverage through the evening into WI. Strong deep-layer shear
perpendicular to the front will favor supercells, with steep lapse
rates aloft and around 200 m2/s2 ESRH favoring very large hail and
perhaps a tornado or two.
Farther south into KS, strong heating of a 65-70 F dewpoint air mass
will lead to over 3000 J/kg MUCAPE, with isolated severe storms
expected across central and eastern KS. Hail will be possible, with
localized wind damage. Parts of this area may require a categorical
upgrade in later outlooks once placement of potential storm clusters
is more precise.
...Southern AZ and southwest NM...
Scattered to numerous storms may be ongoing Tuesday morning over
southern AZ and NM in association with the upper low. Pockets of
destabilization may occur once again during the day, with isolated
strong to severe storms possible capable of hail or localized wind
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NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z