RSS Mesoscale Discussions from Storm Prediction Center

SPC MD 1989

MD 1989 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR EASTERN WYOMING...NORTHWEST NEBRASKA AND WESTERN SOUTH DAKOTA
MD 1989 Image


Mesoscale Discussion 1989
NWS Storm Prediction Center Norman OK
0307 PM CDT Fri Sep 20 2019

Areas affected...eastern Wyoming...northwest Nebraska and western
South Dakota

Concerning...Severe potential...Watch possible 

Valid 202007Z - 202200Z

Probability of Watch Issuance...40 percent

SUMMARY...Storms are expected to increase in coverage and intensity
this afternoon into the evening, posing a risk for isolated large
hail, damaging wind and a tornado or two. Depending on convective
trends, a WW might be needed by 22Z.

DISCUSSION...A couple of storms are in the process of developing
over the higher terrain of southeast WY as well as farther north
over the Black Hills of western SD. This regime is mostly
post-frontal with a quasi-stationary or slow moving cold front from
the western Dakotas into southeast WY where surface dewpoints are in
the 50s and temperatures are rising through the 70s. Latest
objective analysis show 500-1000 J/kg MLCAPE in the post-frontal
regime with 1500-2000 j/kg farther east in warm sector. Storms are
expected to increase in coverage from eastern WY into western SD and
northwest NE as deeper forcing for ascent accompanying an upstream
shortwave trough spreads east above the destabilizing boundary
layer. Winds aloft will strengthen with approach of the shortwave
trough, supporting 40-50 kt effective bulk shear and some supercell
structures. Isolated large hail and damaging wind will be the main
threats. A secondary branch of the low-level jet is forecast to
increase this evening from western NE into western SD in response to
the approaching upper trough. A small window might exist by early
evening in this region for a couple of tornadoes, before the surface
layer begins to decouple.

..Dial/Hart.. 09/20/2019

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...LBF...UNR...CYS...

LAT...LON   41720495 43370439 45040367 44840190 43720179 42030322
            41720495 

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