SPC AC 270535

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1135 PM CST Sun Jan 26 2020

   Valid 271200Z - 281200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   While scattered thunderstorm activity may impact a few areas of the
   U.S., mainly this evening into tonight, and perhaps most notably
   across portions of the southern Plains, the risk for severe storms
   appears negligible.

   ...Synopsis...
   Much of the nation remains under the general influence of split
   branches of westerlies emanating from the mid-latitude Pacific. 
   However, stable conditions generally prevail, largely due to a cool
   and/or dry low-level environment in the wake of broad troughing now
   present across the Mississippi Valley through western Atlantic.  

   Models indicate that the troughing will begin to shift east of the
   Mississippi Valley, and the mean trough axis offshore of the
   Atlantic Seaboard, today through tonight.  But, beneath a lingering 
   confluent mid-level regime, westerly to northwesterly (offshore)
   low-level flow will prevail across much of the Atlantic and eastern
   Gulf coasts.  There appears likely to be little further development
   of a frontal wave migrating across the north central and
   northeastern Gulf of Mexico, and it may actually weaken as it
   approaches the southern Florida Peninsula and Keys.

   Upstream, it does appear that mid-level troughing which has crossed
   the Sierra Nevada into the Great Basin may dig southeastward and
   undergo considerable amplification east of the southern Rockies. 
   This may support weak to modest lower/mid-tropospheric cyclogenesis
   across the southern high Plains by late tonight.

   At the same time, another significant short wave trough emerging
   from a strong mid-latitude Pacific jet is forecast to accelerate
   toward the Pacific Northwest coast, within the crest of amplifying
   larger-scale ridging across the eastern Pacific into the Rockies by
   12Z Tuesday.

   ...Florida...
   Any appreciable boundary layer destabilization ahead of the frontal
   wave appears likely to remain largely confined to the southeastern
   Gulf of Mexico and Florida Straits.  In the presence of strong deep
   layer shear, it is possible that scattered vigorous thunderstorm
   development could impact at least the lower Keys vicinity around or
   shortly after 28/00Z.  This could be accompanied by some risk for a
   potentially damaging wind gust or two around Key West.  However,
   given somewhat modest low-level hodographs and thermodynamic
   profiles characterized by weak lapse rates, among other
   uncertainties, severe probabilities still appear less than 5
   percent.

   ...Southern Plains...
   Although generally weak, it appears that a narrow corridor of
   low-level moisture return, in the presence of steepening lapse
   rates, will become at least marginally sufficient to support
   scattered thunderstorm activity by tonight.  North of the Rio Grande
   Valley, this is expected to be rooted above the boundary layer,
   aided by large-scale ascent associated with lower/mid tropospheric
   warm advection, particularly during the 28/03-09Z time frame across
   southwestern and south central Oklahoma into central Texas.

   ...Pacific Northwest...
   A frontal band with embedded convection may spread into coastal
   areas between 28/00-04Z.  However, thermodynamic profiles more
   conducive to convection capable of producing lightning appear likely
   to be confined to beneath the mid-level cold pool (-28 to -30C at
   500 mb) of the approaching troughing, which might not begin
   impacting Washington and Oregon coastal areas until after 28/08-09Z.

   ..Kerr/Squitieri.. 01/27/2020

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