SPC AC 180515
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1215 AM CDT Wed Sep 18 2019
Valid 181200Z - 191200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
A few strong thunderstorms are possible across parts of the Upper
Midwest this afternoon and evening, but the risk for organized
severe weather appears low.
...Upper Midwest Vicinity...
An amplified upper ridge will stretch from the southern Plains to
the Great Lakes today. A compact shortwave trough over eastern
ND/northwest MN early this morning will quickly shift northeast
across the international border. Thunderstorms associated with this
wave will diminish through the morning hours. South/southwesterly
flow will maintain mid 60s to low 70s dewpoints across the mid-MO
Valley into the upper MS Valley ahead of a southeastward-advancing
cold front. Thunderstorms will likely redevelop along the front
during the late afternoon and into the evening/overnight hours as a
southwesterly low level jet increases. Moderate to strong
instability is expected to develop as temperatures warm into the
80s, but upper forcing will be modest at best as the upper shortwave
trough continues to lift northeast into Ontario after 18z.
Furthermore, effective shear will likewise remain modest, around
20-25 kt, limiting organized thunderstorm activity. A couple of
strong storms could produce gusty winds, but overall severe threat
appears too limited to include probabilities.
Tropical Depression Imelda would continue to drift north and east in
the vicinity of east Texas and the Sabine Valley. Heavy rain will
continue to be the main concern with this system. Low level shear
may be sufficient for occasional, weakly rotating cells across far
southeast TX into far southwest LA. However, conditions are expected
to remain too marginal for inclusion of tornado probabilities.
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