SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0740 AM CDT Sun Oct 25 2020

Valid 251300Z - 261200Z


Organized severe thunderstorms are not expected through tonight.

In mid/upper levels, heights will fall across much of the central/
southern Rocky Mountains, Great Basin and Southwest through the
period, as substantial troughing now over the interior Northwest
digs southeastward and intensifies further.  This will result in a
broad fetch of southwest flow aloft from AZ across the southern/
central High Plains to the upper Great Lakes.  Strong cooling aloft
ahead of the western CONUS trough will steepen low/middle-level
lapse rates across the Four Corners region today into this evening,
combining with weak but sufficient low-level moisture to yield
MLCAPE in the 100-400 J/kg range.  Well-mixed afternoon boundary
layers beneath strengthening midlevel currents may promote strong
gusts in a few cells, but organized severe potential appears too
minimal for an outlook.

At 11Z, the surface chart showed a wavy frontal zone, moving slowly
toward the south as a cold front across NC and quasistationary
elsewhere across northern GA, eastern AL, and the LA shelf waters of
the Gulf.  Frontolysis is underway and will continue on the  western
segment of this boundary over TX coastal waters and deep south TX,
while frontogenesis already drawn over the South Plains and Red
River regions also continue.  The latter front will sharpen and sag
southward across the southern Plains through the period.  By 12Z, a
frontal-wave low may develop near ACT, with the cold front arching
southwestward to westward across the southern Hill Country, Edwards
Plateau and Trans-Pecos regions.  A stationary to very slow warm
front will extend from the wave over the Arklatex region.  Late
overnight and northwest of the surface front, increasing elevated
moisture and isentropic lift within a strengthening warm-advection
plume will combine with frontal forcing, to increase chances for
thunderstorms embedded within an earlier-developing precip plume.

Meanwhile, a weak southern-stream perturbation now over the
Carolinas will continue to move east-northeastward and offshore from
the Tidewater area by this evening.  General-thunder potential will
diminish quickly behind this trough, in a region of strong mid/upper
drying shown on moisture-channel imagery.  Farther south, isolated,
disorganized thunderstorms will be possible in a very moist and
weakly capped air mass, but with marginally supportive midlevel
lapse rates, across parts of southern/central FL.

..Edwards/Mosier.. 10/25/2020

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