SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0652 AM CST Fri Feb 12 2021

Valid 121300Z - 131200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated thunderstorms are possible across parts of the Southeast,
for another few hours in deep south Texas, and late overnight near
parts of the northern California and southern Oregon coastline.

...Synopsis/Discussion...
A high-latitude blocking pattern will continue over Canada, in
mid/upper levels, anchored by a high over northern Yukon and a
persistent cyclone centered over southern MB.  The "undercutting"
belt of westerlies to its south will persist with zonal to subtly
cyclonic flow across the northeastern Pacific and northern CONUS.  A
shortwave trough was evident in that flow belt near 150W, around
40N.  This perturbation will penetrate the mean ridge offshore from
the Pacific Coast and move ashore in northern CA and OR between
09-12Z.  Associated strong DCVA/cooling aloft is expected, under the
left-exit region of a cyclonically curved upper jet max. 
Accordingly steepened low/middle-level lapse rates the last few
hours of the period will lead to around 100-300 J/kg MUCAPE atop the
marine layer, some of which will could deep enough to support
isolated lightning. 

Meanwhile, a southern-stream trough now over central/northern MX and
west TX will pivot northeastward and weaken, reaching the western
Gulf by the end of the period.  Countless minor vorticity lobes --
some convectively induced/enhanced -- will eject northeastward over
the Gulf and Southeast in the foregoing, gently confluent
southwesterlies.  Beneath those, a slow-moving surface frontal zone
was analyzed from a low near MCN southeastward across the GA
coastline, and southwestward over the FL Panhandle to the
northwestern Gulf.  The bulk of thunder will remain over the open
Gulf, where air/sea fluxes will optimize low-level theta-e. 
However, a broad sheet of low-level warm advection and moisture
transport will persist in extending inland, largely elevated
poleward of the front.  Isolated, diurnal, surface-based, but
disorganized thunderstorms also may form in an environment of modest
deep-layer lapse rates and weak buoyancy south of the front in parts
of GA and central/northern FL.

..Edwards.. 02/12/2021

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