SPC AC 291633

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1133 AM CDT Sat Apr 29 2017

   Valid 291630Z - 301200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM
   CENTRAL/EASTERN TEXAS ACROSS THE ARKLATEX INTO SOUTHERN MISSOURI...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   ENHANCED RISK FROM SOUTHERN TEXAS INTO THE OHIO VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   SOUTHERN PLAINS ACROSS THE OHIO VALLEY INTO THE MID-ATLANTIC
   STATES...

   ...SUMMARY...
   Severe thunderstorms are expected from parts of south central Texas
   northeastward to portions of the Ohio Valley and northern Middle
   Atlantic region, especially this afternoon and evening. The most
   likely region for severe weather will from eastern Texas across
   western and central Arkansas into southern Missouri.  Storms will be
   capable of large hail, damaging winds, and a few tornadoes.

   ...Central/Eastern Texas into southern Missouri...
   An upper low near the Four-Corners regions is expected to move
   eastward through the period reaching the Texas Panhandle and western
   Oklahoma late tonight.  Strong mid-upper level winds associated with
   the low will translate across west Texas and over the southern
   Plains tonight, accompanied by 150-180 m height falls at 500 mb.  At
   lower levels in advance of the upper low, a broad low-level jet is
   in place from eastern parts of Texas and Oklahoma into Louisiana and
   Arkansas with 50-60 kt winds in the 1-2 km agl level.  These factors
   will provide strong low-level shear throughout the period, with
   strengthening deep-layer shear progressing eastward across the
   southern plains toward the lower Mississippi Valley tonight.

   At the surface, the primary low over eastern Oklahoma is forecast to
   move mainly northward into southeast Kansas/southwest Missouri
   tonight.  A cold front currently extending southwestward from the
   low toward the Big Bend region will advance into central/south
   central Texas by this evening, and arc across central Arkansas into
   southwest Louisiana by the end of the period.  A quasi-stationary
   front extending east-northeast from the low into southern Illinois
   will move little, and an outflow boundary persists south of the
   front across the Missouri/Arkansas border eastward into Kentucky may
   serve as the effective focus for storms.

   Ample low-level moisture is present over the warm sector with
   surface dew points of generally in the low 70s.  Extensive cloud
   cover over the region will tend to inhibit stronger diabatic heating
   to occur, although breaks in overcast will promote local areas of
   more focused heating/destabilization this afternoon.  A capping
   inversion evident in 12Z soundings at FWD, SHV and LZK is likely to
   limit convective development in advance of forced bands of storms,
   although storms currently near the Sabine River may persist as they
   move northeast this afternoon in association with a weaker
   perturbation evident in water vapor imagery.

   Otherwise, storms from southwest Missouri into extreme eastern
   Oklahoma are expected to spread eastward with time with
   intensification expected this afternoon.  Some southward development
   along the cold front is also expected by mid-late afternoon as
   stronger heating appears likely over central into northeast Texas. 
   NWP guidance including CAM forecasts suggests potential for several
   bands/lines of storms to progress eastward with some bowing segments
   developing.  Large hail and damaging wind gusts will be possible
   with more intense cells.  A few tornadoes will also be possible,
   especially with any discrete storms that can develop ahead of the
   cold front, as well as within QLCS mesovortices that may develop. 
   The activity is likely to progress eastward during the overnight
   hours with a continued severe threat.

   ...Ohio Valley into the Mid-Atlantic States...
   Corridors of eastward-moving precipitation including heavy rainfall
   and a few strong storms will continue to reinforce a generally
   west/east-oriented frontal zone from the Ohio
   Valley to the coastal Northeast States. A gradually weakening
   low-level jet and moist conveyor, along with prevalent rising upper
   heights, may allow for some northward shift of the effective
   boundary and increasingly moist warm sector this afternoon.
   Regardless, one or more storm clusters ongoing across the
   upper Ohio Valley at this time may persist or reinvigorate
   in vicinity of the effective frontal zone toward PA/Delmarva
   vicinity with mainly a damaging wind risk. Other storms are expected
   to develop near the effective warm front from MO into IL
   and spread eastward with damaging winds and severe hail as the
   primary severe risks.

   ..Weiss/Mosier.. 04/29/2017

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