SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0730 AM CDT Wed Oct 21 2020

Valid 211300Z - 221200Z


No severe thunderstorms are expected through tonight.

An upper-air pattern initially characterized by broadly cyclonic
flow across the entire northern CONUS, from coast to coast, will
flatten east of the Mississippi River and amplify over the West. 
This will occur as a northern-stream shortwave trough -- evident in
moisture-channel imagery over southwestern coastal BC -- moves
southeastward and amplifies through the period.  By 12Z, the trough
should reach central/eastern MT and northwestern WY, with height
falls as far south as the Four Corners and southern Rockies.  

The approach of that trough will foster low-level cyclogenesis in
the immediate lee of the central Rockies, shifting from WY toward
northeastern CO near the end of the period.  As that occurs, a broad
low-level warm-advection and moisture-transport regime -- already in
place and supporting sporadic thunder from the lower Missouri Valley
to the Northeast near a low-level frontal zone -- will strengthen in
its western portions.  A 45-60-kt LLJ should develop overnight from
the south-central High Plains northeastward to IA.  Lift of
increasingly moist parcels to LFC will support thunderstorm
potential from parts of the Lower Missouri Valley region over the
Corn Belt, spreading/shifting northeastward toward the southern
Upper Great lakes by the end of the period.  

Meanwhile, widely scattered thunderstorms will remain possible in a
deep, extensive regime of easterly flow, rich moisture and minimal
CINH, from FL across much of the Gulf, spreading into portions of
south Texas.  Isolated to widely scattered thunderstorms also will
be possible from southern GA northeastward, near an old frontal zone
analyzed at 11Z near the Carolinas coast.

..Edwards/Leitman.. 10/21/2020

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