Day 1 Severe Weather Outlook

Valid 220100Z – 221200Z


Large hail, damaging winds, and perhaps a couple of tornadoes remain
possible this evening from Kansas to Iowa. A marginal severe threat
is also possible across parts of north-central Minnesota into
northwest Wisconsin.

…Central Plains/Lower to Mid Missouri Valley…
The latest water vapor imagery shows southwest mid-level flow over
the central U.S. At the surface, a cold front is analyzed from
western Kansas northeastward into southeast Nebraska. A line of
strong to severe thunderstorms is ongoing along the front. Other
more isolated cells are located eastward across the warm sector.
Model forecasts gradually increase convective coverage this evening
as an MCS develops and move northeastward across northeast Kansas,
northwest Missouri and southern Iowa. The airmass along this
corridor is moderately unstable with the Topeka observed 00Z
sounding showing about 1500 J/kg of MLCAPE. The wind profile has
strong directional shear in the lowest 2 km AGL with 40 kt of 0-6 km
shear. This should support supercell development with isolated large
hail with the stronger cells in the line. As the line grows upscale
this evening, the wind damage threat will likely increase. The
greatest chance for wind damage will be associated with bowing line
segments. A tornado or two can not be ruled out with rotating cells
embedded in the line or with discrete cells ahead of the line…see
MCD 1998 and 1999.

…Upper Mississippi Valley…
The latest water vapor imagery shows an upper-level trough over the
northern High Plains extending southwestward into the Intermountain
West. Southwest mid-level flow is in place in the northern Plains
and upper Mississippi Valley. At the surface, a cold front is
analyzed across central and northern Minnesota. Thunderstorms are
ongoing along the front in north-central Minnesota and ahead of the
front in northwest Wisconsin. Model forecasts gradually move this
activity eastward and slowly decrease convective coverage. An axis
of instability is located from northwest Iowa into northern
Wisconsin where MLCAPE is estimated in the 2000 to 2500 J/kg. This
is evident on the Minneapolis 00Z sounding. In addition, the
sounding has a wind profile with 45 kt of 0-6 km shear. Steep lapse
rates are also evident from the surface to mid-levels. This could be
favorable for rotating storms with cells that remain discrete. This
cells would have a wind damage and hail threat. As instability
weakens over the next few hours, the severe threat is expected to
further diminish.

..Broyles.. 09/22/2019


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