NWS Storm Prediction Center - Day 1 Convective Outlook

Oct 17, 2021 1300 UTC Day 1 Convective Outlook
Updated: Sun Oct 17 12:15:20 UTC 2021
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Overview Overview

 Forecast Discussion - Day 1 Convective Outlook

   SPC AC 171215

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0715 AM CDT Sun Oct 17 2021

   Valid 171300Z - 181200Z


   Isolated thunderstorms are possible over south Florida, and some
   areas southeast of Lakes Erie and Ontario.

   In mid/upper levels, a progressive/high-amplitude pattern will
   continue over the CONUS, south of a splitting flow regime related to
   the evolution of both eastern and western troughs to closed
   cyclones.  The eastern trough is initially positioned from Hudson
   Bay over Lake ON to the Carolinas and northern FL.  This feature
   will shift eastward across western/southern QC, NY to New England,
   and offshore from the Mid-Atlantic and southern Atlantic Coast
   through the period, while forming an elongated cyclone centered over
   southeastern Canada.  Cold air aloft -- reinforced by northwest-flow
   shortwave perturbations behind the synoptic trough - will combine
   with relatively warm/moist boundary layers advecting off parts of
   Lakes Erie and Ontario, steepening lapse rates enough to yield
   buoyancy into layers colder than -20C. As such, isolated thunder is
   possible in some of the convection downwind from those lakes. 

   The surface cold front related to the eastern upper trough was 
   drawn at 11Z across eastern ME to south-central FL.  This boundary
   should exit both ME and south FL by this evening, leaving behind a
   vast, continental/polar anticyclone covering most of the CONUS east
   of the Rockies.  Despite modest frontal lift and a stable layer
   between 600-700 mb, rich low-level moisture and diurnal heating may
   foster a few thunderstorms along and south of the front today over
   south FL.

   In the West, height falls aloft are expected as synoptic ridging
   moves from the Rockies eastward across the Plains States, and a
   strong synoptic trough now over the Pacific moves ashore between
   00-06Z.  A closed 500-mb low is progged over the CA/NV line north of
   RNO by 12Z tomorrow, with difluent mid/upper flow across most of the
   Rockies, Intermountain region and Great Basin.  Sporadic, mainly
   midlevel convection is possible, and a rogue lightning strike cannot
   be ruled out.  However, the low-level air mass across the region
   should remain too cool and/or dry to support a general thunderstorm

   ..Edwards/Leitman.. 10/17/2021



Data courtesy the Storm Prediction Center
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