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    Day 2 Outlook >
May 21, 2018 1300 UTC Day 1 Convective Outlook
Updated: Mon May 21 12:51:41 UTC 2018 (Print Version | 20180521 1300Z Day 1 shapefile | 20180521 1300Z Day 1 KML)
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 Forecast Discussion
   SPC AC 211251

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0751 AM CDT Mon May 21 2018

   Valid 211300Z - 221200Z


   Isolated to widely scattered strong to severe thunderstorms are
   possible across the Ohio Valley as well as portions of New Mexico
   and the central and southern High Plains. Damaging wind and large
   hail will likely be the main severe threats.

   ...Ohio Valley...
   Scattered showers and thunderstorms remain prevalent early this
   morning from near the confluence of the Mississippi and Ohio Rivers
   northward across Illinois toward the southern Lake Michigan
   vicinity. Part of this convection continues to muddle a warm sector
   to the east of a weak northeastward-transitioning surface wave and
   near/south of an eastward-extending warm front that will continue to
   develop slowly northward across Illinois, Indiana, and Ohio.

   The ongoing precipitation and related cloud cover casts some
   uncertainty on the exact degree/locations of more appreciable
   destabilization later today, although cloud breaks are noted in
   early-morning visible satellite imagery from Kentucky into southern
   portions of Indiana and Ohio. While the overall magnitude/extent of
   the severe risk remains uncertain, at least some severe
   thunderstorms can be expected this afternoon into evening. The most
   supercell-favorable deep-layer and low-level shear later today will
   exist just ahead of the aforementioned weak surface wave and the
   eastward extending warm front, mostly across central portions of
   Indiana into Ohio in areas along/north of I-70. Severe hail and
   possibly a tornado could occur within this general corridor, while
   isolated bouts of damaging winds will be the main hazard across a
   broader part of the region.

   ...New Mexico and west/southwest Texas...
   Moist post-frontal low-level upslope flow will continue to yield an
   increase in moisture with west-northwestward extent across New
   Mexico during the day. The region will not be overtly influenced by
   the slow-moving/digging closed low over the southwest states, but
   relatively plentiful moisture and orographic ascent will lead to
   scattered thunderstorms this afternoon. Initial thunderstorm
   development is expected this afternoon across interior New Mexico
   and by late afternoon/early evening farther east across eastern New
   Mexico and far west Texas. 30-35 kt of effective shear, steep lapse
   rates, and ample moisture for the region will support multicells and
   possibly a few supercells capable of severe-caliber hail, along with
   gusty winds. Areas such as far west Texas and southeast/
   south-central New Mexico will continue to be reevaluated for a
   possible categorical Slight Risk upgrade given a somewhat more
   severe-favorable environment.

   ...Central High Plains...
   Gradual lee-side cyclogenesis will influence weak upslope
   trajectories with a modest influx of low-level moisture through the
   day. While upper heights will generally rise, weak low-level upslope
   flow and differential heating along the mountains/higher terrain
   should yield isolated east/southeastward-drifting thunderstorms this
   afternoon. Sufficient low-level moisture and effective shear (30-40
   kt) coincident with very steep lapse rates could support some strong
   multicells/brief supercells capable of severe hail/gusty winds on a
   very isolated basis.

   ..Guyer/Goss.. 05/21/2018



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