Day 1 Severe Weather Outlook

Valid 142000Z – 151200Z


Isolated to scattered severe wind gusts are possible this afternoon
and evening across southern and central Arizona. Isolated severe
storms with large hail and damaging wind gusts are possible from the
Upper Midwest to the central Great Plains through tonight.


Only minor adjustments have been made to the previous forecast.

..Dial.. 09/14/2019

.PREV DISCUSSION… /ISSUED 1130 AM CDT Sat Sep 14 2019/

…Southern/central AZ…
An MCV over western Chihuahua will drift north-northwestward across
southeast AZ through tonight. 50s surface dew points are common
across southern AZ amid easterly flow north of this MCV. In
conjunction with ample heating northwest of the thicker cloud cover
near the MCV, a modestly buoyant air mass with MLCAPE approaching
1000 J/kg should develop by peak heating. 15-25 kt east-northeast
700-500 mb winds around the north side of the MCV will be favorable
for cells and semi-organized clusters to spread off the Mogollon Rim
into the lower deserts with a threat for severe gusts. Whether more
organized clustering can evolve is uncertain compared to the
significant severe wind event two weeks ago, but there is at least
sufficient damaging wind potential to warrant a Slight Risk across
parts of the Gila Valley.

…Upper Midwest to the central Great Plains…
Elevated thunderstorms are ongoing in western IA on the leading edge
of a low-level warm theta-e advection plume. This plume and
attendant zone of ascent will spread east-northeast across the Upper
MS Valley into tonight in advance of a low-amplitude shortwave
trough near the ND/MB border that will move east-southeast into Lake
Superior. This elevated convection will pose a threat for isolated
large hail, mainly this evening into tonight with a probable decay
cycle this afternoon. A risk for locally damaging winds may also
develop tonight towards the IA/IL/WI border region if a cluster can
become semi-organized.

In the wake of the warm advection regime, storm initiation will
depend on weak low-level ascent along a surface trough that extends
southwestward across NE/KS. Stronger surface heating and deeper
mixing is expected along the trough in KS, with lesser mixing depths
and a greater probability of maintaining MLCIN through the afternoon
in the warm sector farther northeast. Thus, surface-based
thunderstorm development should be sparse and may struggle to be
sustained during the late afternoon/early evening. If surface-based
storms can form as far northeast as southern MN this afternoon,
vertical shear profiles will be sufficient for supercells. Weaker
vertical shear is expected with southwestward extent into southwest
KS, where high-based storms would pose a threat for isolated severe
wind and hail.

…Central Appalachians…
A narrow corridor of weak to modest buoyancy is expected with
scattered storms along a cold front and over the higher terrain
through early evening. Isolated strong downburst winds are possible
on the periphery of weak to moderate mid-level southwesterlies.


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