SPC AC 031713

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1213 PM CDT Wed Nov 03 2021

   Valid 041200Z - 051200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   The risk for severe thunderstorms appears negligible across the
   U.S., Thursday through Thursday night.

   ...Synopsis...
   Large-scale mid-level ridging now inland of the Pacific coast
   appears likely to broaden and lose amplitude while shifting eastward
   during this period, a bit slower than an upstream short wave trough,
   which is forecast to accelerate across the Pacific Northwest coast
   through the northern Rockies, ahead of amplified larger-scale
   troughing approaching the Pacific coast.  As this occurs, models
   indicate that one downstream short wave impulse, initially digging
   to the lee of the southern Rockies, will gradually turn eastward,
   across the Texas Gulf coast and into the Gulf Basin by 12Z Friday. 
   To the northeast, another consolidating impulse is forecast to turn
   east-northeast of the upper Great Lakes and lower Ohio Valley, into
   the northern Atlantic Seaboard.

   In lower levels, a confluent regime between the two lead
   perturbations will maintain cold surface ridging, but the center of
   this ridging may consolidate over the Ohio Valley while surface
   troughing develops and deepens across higher portions of the
   northern and central Great Plains.  The surface cold front may
   gradually progress offshore of the northwestern/northern Gulf coast,
   and a bit faster off the south Atlantic coast by late Thursday
   night, in the wake of a developing frontal wave over the western
   Atlantic.  Another cold front may continue inland across the
   northern intermountain region and northern Rockies, while stalling
   across northern portions of the Great Basin and California, ahead of
   another cold front forecast to approach the Pacific Northwest toward
   12Z Friday.

   It appears that an initial narrow plume of moist return flow
   emanating from the subtropical Pacific will become increasingly cut
   off by the frontal progression, somewhere across the southern Sierra
   Nevada through the coastal areas south of San Francisco Bay, but
   another will gradually develop across the eastern Pacific into the
   Pacific Northwest.  East of the Rockies, higher moisture content
   will be confined to areas along/south of the cold front, but
   moisture emanating from the southeastern Gulf of Mexico and
   Caribbean may stream northward toward the Florida Peninsula by late
   Thursday night.

   ...South Texas...
   Thunderstorm probabilities are generally expected to have diminished
   or be in the process of diminishing by 12Z Thursday.  However, low
   thunderstorm probabilities may persist into the day, associated with
   weak lingering instability above/to the northwest of the surface
   front and forcing for ascent associated with the digging mid-level
   short wave impulse.

   ...Florida...
   Higher probabilities for scattered thunderstorm development probably
   will not develop until Thursday night, associated with the
   low/mid-level moistening and increasing large-scale ascent in
   advance of the mid-level troughing developing over the Gulf Basin. 
   Even this may be largely confined to areas southwest of the southern
   Florida Gulf coast, and areas east of the Atlantic coast,
   particularly along the front north-northeast of the Melbourne
   vicinity.  

   Latest NAM forecast soundings suggest an environment characterized
   by moderate CAPE (on the order of 1000 J/kg) and shear (40-50+ kt)
   is possible along coastal areas near/north of Melbourne by late
   Thursday night.  If this becomes the case, it could be accompanied
   by at least some risk for isolated severe storm development. 
   However, based on consideration of other model output, severe
   probabilities still appear less than 5 percent at this time.

   ...Northwest...
   Initial modest mid-level cooling is forecast to shift east of the
   Cascades by late Thursday morning, and into the northern Rockies by
   Thursday evening.  In the wake of preceding precipitation aided by
   warm advection, various model forecast soundings suggest that weak
   destabilization conducive to at least scattered weak thunderstorm
   development is possible across parts of the northern intermountain
   region.  Thereafter, it appears that mid-level cooling supportive of
   an appreciable risk for low-topped thunderstorm development may not
   reach Pacific Northwest coastal areas until after 12Z Friday.

   ..Kerr.. 11/03/2021

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