SPC AC 070545

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1145 PM CST Tue Mar 06 2018

   Valid 081200Z - 091200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

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

   ...Discussion...
   To the southwest of a persistent blocking ridge (centered in the
   vicinity of Newfoundland and Labrador), models indicate the
   continued evolution of a broad and deep mid-level closed low to the
   east of the lower Great Lakes region during this period.  As this
   occurs, amplified cyclonic flow will be maintained east of the
   Mississippi Valley through the western Atlantic.  An associated
   surface frontal zone may continue to advance southward through the
   Bahamas and Caribbean, but, after stalling across parts of the
   southwestern Gulf of Mexico, it probably will begin to retreat
   northeastward.

   Upstream, broad mid/upper ridging is expected to prevail across much
   of the West, into the Plains.  However, within one branch of
   mid-latitude westerlies emanating from the Pacific, it does appear
   that the increasingly sheared/deformed remnants of a cyclonic
   circulation will accelerate inland across the Pacific Northwest
   coast through the northern intermountain region.  This is expected
   to precede another impulse progressing inland across British
   Columbia and Pacific Northwest coastal areas by late Thursday night.

   ...Northern intermountain region...
   In association with the initial inland migrating impulse, it appears
   that modest mid-level cooling may contribute to steepening lapse
   rates across parts of the Columbia Valley and Plateau into the
   northern Rockies on Thursday.  Coupled with at least some
   moistening, pockets of weak destabilization may contribute to
   convection capable of producing lightning.  Although this is still
   expected to be fairly isolated and brief in nature, it is possible
   that the higher terrain of northeast Oregon and central Idaho into
   parts of western Montana could provide a focus for coverage
   exceeding 10 percent, mainly late Thursday afternoon into Thursday
   night.

   ..Kerr.. 03/07/2018

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