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Aug 18, 2017 0730 UTC Day 3 Severe Thunderstorm Outlook
Updated: Fri Aug 18 07:15:33 UTC 2017 (Print Version | 20170818 0730Z Day 3 shapefile | 20170818 0730Z Day 3 KML)
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 Forecast Discussion
   SPC AC 180715

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0215 AM CDT Fri Aug 18 2017

   Valid 201200Z - 211200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE SUNDAY
   AFTERNOON INTO SUNDAY NIGHT ACROSS PARTS OF CENTRAL AND EASTERN
   SOUTH DAKOTA...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS
   SURROUNDING AREAS OF THE NORTHERN PLAINS INTO UPPER MISSISSIPPI
   VALLEY...

   ...SUMMARY...
   A few severe thunderstorms are possible across parts of central and
   eastern South Dakota late Sunday afternoon into Sunday night.  This
   may include the eventual formation of a large thunderstorm cluster
   by late Sunday evening, accompanied by a risk for potentially
   damaging wind gusts.

   ...Synopsis...
   Models suggest that the stronger mid-latitude westerlies may
   continue a northward retreat into areas mostly north of the
   Canadian/U.S. border during this period.  At lower latitudes,
   western Atlantic subtropical ridging is forecast to continue
   building westward, and expanding northward, across the Southeast,
   into the southern Plains, middle Mississippi and Ohio Valleys. 
   Farther west, broad weak troughing with numerous embedded
   perturbations may continue to evolve west of the California coast
   into the southern Great Basin and Rockies.

   On the southern fringe of the mid-latitude westerlies, a plume of
   warm elevated mixed layer air may nose east of the Wyoming/Colorado
   Rockies into the mid Missouri Valley.  At the same time, modest
   southerly low-level flow will contribute to northward moisture
   transport across the Plains, into the vicinity of a cold front
   advancing southward into the northern Plains and Upper Midwest,
   before stalling.  This latter feature is expected to accompany a
   short wave trough crossing the Canadian prairies, before turning
   northeastward across northwestern Ontario by early Sunday.  Another
   significant short wave impulse may dig east southeast of the
   Canadian Rockies through the Canadian prairies by late Sunday night.

   ...Parts of northern Plains into upper Mississippi Valley...
   There remains considerable spread among the various models
   concerning pertinent features which could impact convective
   development Sunday afternoon and evening.  This includes the
   positioning of the zone of potentially strong differential surface
   heating and plume of elevated mixed layer air, and possible subtle
   perturbations near the southern-most fringe of the mid-latitude
   westerlies.

   In general, though, the development of large CAPE, with continued
   moistening beneath steepening mid-level lapse rates, in the presence
   of favorable shear for organized storm development (largely due to
   pronounced veering with height), appears likely to contribute to an
   environment potentially supportive of severe storm development.  At
   the present time, this seems most probable across parts of
   central/eastern South Dakota Sunday evening, where/when forcing for
   ascent may become enhanced near the nose of a modest strengthening
   southerly 850 mb jet.  A transition from isolated supercell
   development to a consolidating/upscale growing mesoscale convective
   system appears possible.

   ..Kerr.. 08/18/2017

   CLICK TO GET WUUS03 PTSDY3 PRODUCT

   NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z

        
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Page last modified: August 18, 2017
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