SPC AC 020540

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1140 PM CST Wed Dec 01 2021

   Valid 031200Z - 041200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   The risk of severe thunderstorms appears negligible across the U.S.
   Friday through Friday night, but a low probability of thunderstorms
   may develop across parts of the southern Great Plains into Mid
   South.

   ...Discussion...
   Models continue to indicate significant amplification within a
   southern branch of split mid-latitude westerlies across the eastern
   Pacific during this period.  This is forecast to include a vigorous
   short wave trough digging into the southern mid- and subtropical
   latitudes, between 140-160 W longitude.  While a significant impulse
   within another branch progresses toward the British Columbia coast,
   it appears that strong downstream flow will remain broadly
   anticyclonic across the western Canadian/U.S. border vicinity into
   the northern U.S. Great Plains.  However, mid/upper flow across the
   Great Lakes region is forecast to trend at least broadly cyclonic,
   in response to a significant perturbation digging southeast of the
   Canadian Prairies.  Models indicate that this will be accompanied by
   much more modest surface cyclogenesis than the preceding short wave
   impulse, but more prominent cold surface ridging may build southeast
   of the northern Rockies, across much of the northern through central
   Great Plains and upper Mississippi Valley by 12Z Saturday.

   Meanwhile, a series of short wave perturbations is forecast to
   continue to develop eastward across parts of the Southwest into the
   Gulf Coast states, within a weak branch of westerlies emanating from
   the subtropical eastern Pacific.  Across parts of the southern Great
   Plains into Mid South, elevated moisture return of subtropical
   Pacific origin likely will be coupled with moistening southerly
   return flow off the western Gulf of Mexico, ahead of the southward
   advancing cold front.

   ...Parts of southern Great Plains into Mid South...
   Models continue to indicate that boundary-layer moisture return from
   the Gulf of Mexico probably will remain confined to a rather shallow
   surface-based layer Friday through Friday night, beneath warm and
   capping layers aloft.  However, forecast soundings still suggest
   that the elevated moisture return, in the presence of modestly
   steepening mid-level lapse rates, will contribute to weak CAPE based
   around the 700 mb layer.  It appears that thermodynamic profiles may
   become conducive to occasional, widely scattered to scattered
   convection capable of producing lightning, aided mostly by weak
   mid/upper forcing for ascent.

   ..Kerr.. 12/02/2021

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