SPC AC 171251

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0751 AM CDT Mon Apr 17 2017

   Valid 171300Z - 181200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE HIGH
   PLAINS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS DEEP
   SOUTH TEXAS...

   ...SUMMARY...
   Very isolated severe thunderstorms with hail and strong wind gusts
   are expected across parts of the High Plains and south Texas mainly
   this afternoon and evening.

   ...High Plains...
   A shortwave trough over OR/ID early this morning will continue
   eastward and reach the Dakotas late tonight. A related belt of
   strengthening mid-level westerly winds will overspread a sharpening
   lee trough across the north-central High Plains and Black Hills
   vicinity. While the boundary layer will not be moist (40s to near
   50F surface dewpoints) near and east of the north-central High
   Plains lee trough, relatively cool temperatures aloft and steep
   mid-level lapse rates may support as much as 750 J/kg MLCAPE by peak
   heating. Current thinking is that a couple of sub-regional corridors
   of isolated thunderstorm development will occur from the Black Hills
   vicinity southward into northeast Colorado by late afternoon.
   Adequate moisture/buoyancy and 40+ kt of shear could support a few
   supercells capable of large hail and strong downdrafts. 

   Farther south, other isolated severe thunderstorms will be possible
   this afternoon across southeast CO/northeast NM and the Raton Mesa
   vicinity with aid of a lee-side trough and low-level upslope
   trajectories. Steep lapse rates, moderate buoyancy, and around 30-35
   kt of effective shear would conditionally support some
   east/southeastward-moving marginal supercell structures and
   multicell clusters capable of severe hail.

   ...South TX including the lower/middle TX coast...
   A decaying MCS continues to progress toward the lower TX coast and
   lower valley early this morning. While forecast confidence is low
   regarding details later today given the influence of the early-day
   MCS and related outflow, there appears to be some potential for MCV
   and/or outflow-related redevelopment later this afternoon. Given the
   possibility for deep convective redevelopment within a
   recovering/destabilizing air mass, will continue a severe risk
   across Deep South TX, mainly near and south of the early-day MCS and
   outflow.

   ...Mid-south/lower MS River Valley...
   A weak mostly heavy-rain-producing MCS continues to move slowly
   southeastward across the Ozarks and Ark-La-Tex vicinity early this
   morning. With possible aid of an MCV across the Ozarks, pockets of
   somewhat stronger downstream heating could allow for a
   reinvigoration of storms across the Mid-South vicinity this
   afternoon along composite outflow. A few stronger storms capable of
   locally damaging winds cannot be entirely discounted in areas
   spanning far southern/eastern AR into western TN and northern MS,
   although cloud cover and outflow-related uncertainties temper any
   confidence in a semi-organized severe risk.

   ...Southern VA/northeast NC...
   Ample heating will occur across the region this afternoon within a
   modestly moist air mass (surface dewpoints in the 50s F) ahead of a
   southeastward-moving cold front. While overall buoyancy will likely
   remain limited, steepening low-level lapse rates and a modestly
   strengthening belt of mid-level westerlies could allow for a few
   stronger storms near the front this afternoon. Some risk for locally
   damaging winds may exist, although organized severe thunderstorms
   are not currently expected.

   ..Guyer/Jewell.. 04/17/2017

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