SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1239 AM CDT Wed Oct 21 2020

Valid 211200Z - 221200Z


No severe thunderstorms are expected across the continental United
States on Wednesday.

Shortwave trough currently progressing through the Upper Midwest is
expected to continue northeastward through eastern Ontario and
western Quebec today, moving within the strong, broadly cyclonic
upper flow extending from the Pacific Northwest through Quebec. An
associated surface low will take a similar path, moving just ahead
of the parent shortwave, while an attendant cold front extends from
this low southwestward into the southern Plains. Isolated lightning
strikes are possible near this weakening front early in the period.
Limited instability will temper the overall severe potential.

Another shortwave trough is forecast to drop from British Columbia
into the northern Rockies. Progression of this shortwave will
encourage a deepening lee trough, with the resultant increase in the
surface pressure gradient contributing to a northward surge of
low-level moisture across the southern/central Plains and mid MS
Valley.  A dynamically enhanced low-level jet will also develop
ahead of the approaching shortwave, stretching from the southern
High Plains through the mid MS Valley. Warm-air advection associated
with this low-level jet will result in elevated thunderstorms across
the mid MS Valley Wednesday night through early Thursday morning.
Instability will be limited but vertical shear may be strong enough
to support a few stronger, more persistent updrafts capable of hail.
Likely low coverage coupled with low overall potential preclude
introducing any hail probabilities in this outlook. Cold mid-level
temperatures accompanying this shortwave may also result in enough
instability for a few lightning strikes over the northern Rockies. 

Farther south, a weakening tropical wave will support isolated
thunderstorms across FL and portions of the GA and the Carolinas.
Moist easterly flow across the Gulf and into the middle/lower TX
Gulf Coast could also support isolated afternoon thunderstorms.

..Mosier/Lyons.. 10/21/2020

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