Day 1 Severe Weather Outlook

Valid 151200Z – 161200Z


Organized severe thunderstorms are not expected across the U.S.


The upper level pattern over the U.S. will become more amplified
today. A deepening upper trough will move southeast to the Pacific
Northwest coast. In response, an upper ridge will build over the
Plains today, while shifting eastward toward the Mississippi Valley
by Monday morning. Further east, a shortwave trough over the upper
Great Lakes will progress east, overspreading the northeastern
states by the end of the period.

Thunderstorms should be ongoing along a cold front attendant to the
Great Lakes upper shortwave trough from northern IL/IN into lower
MI. This activity will be elevated and is expected to remain
sub-severe through the afternoon as the downstream environment will
not be conducive to intense convection. While moisture will stream
northward across the Plains today beneath the amplifying upper
ridge, limited forcing and capping will preclude thunderstorm
activity. Further west, a weak mid/upper level low over southern
AZ/NM will drift northward while weakening. Still, this feature will
provide support for diurnally driven thunderstorms across the Four
Corners region. Weak deep layer shear and modest instability will
preclude organized/long-lived convection, though a dry boundary
layer could result in some gusty outflow winds with the strongest
cells. Additional thunderstorms are possible in the vicinity of the
central and western Gulf coasts as a weak low migrates westward
across the Gulf of Mexico. Further east, the National Hurricane
Center forecast keeps Tropical Storm Humberto well offshore from FL,
though isolated thunderstorms are possible in areas of convergent
low level flow from FL through the eastern Carolinas.

..Leitman/Dean.. 09/15/2019


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