SPC AC 161625

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1125 AM CDT Wed May 16 2018

   Valid 161630Z - 171200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   WEST AND CENTRAL TEXAS...FROM EASTERN OKLAHOMA INTO WESTERN
   ARKANSAS...AND FROM NORTHEAST CALIFORNIA INTO NORTHWEST NEVADA...

   ...SUMMARY...
   A few strong to severe thunderstorms, accompanied by a risk for
   damaging winds and large hail, are possible over parts of the
   southern Plains this afternoon and evening.  Other strong to
   marginally severe storms will be possible over eastern Oklahoma,
   western Arkansas and northeast Texas, and over parts of northeast
   California into northwest Nevada.

   ...Eastern OK into western AR and northeast TX...
   A weakening MCS over Oklahoma has generated two MCVs that are
   expected to progress eastward into Arkansas this afternoon and
   evening.  Visible imagery shows limited clouds to the east and
   southeast of the system, which will promote strong diabatic heating
   and further air mass destabilization within a moist low-level
   environment.  Stronger west-northwesterly mid-level winds are
   observed on the southwest flank of the MCVs, and these are expected
   to move eastward toward the Arklatex region this afternoon and
   enhance vertical shear, mainly to the immediate south of the MCVs.

   Model guidance including morning CAM/HREF simulated reflectivity
   forecasts indicate a few strong storms will increase in coverage
   this afternoon and evening from eastern Oklahoma into western
   Arkansas.  Favorable instability with MLCAPE of 1500-2000 J/kg
   suggests potential for a few strong to severe storms, with primary
   threats for wet microbursts and hail.  See Mesoscale Discussion 435
   for additional details.

   ...Northeast CA into northwest NV...
   A compact cold upper low is moving northeastward into central
   California this morning.  Dynamic forcing within the left exit
   region of a mid-upper level jet coupled with steep mid-level lapse
   rates has resulted in thunderstorm development from parts of the
   central valley into the Sierra foothills, with other more isolated
   storms extending into western Nevada.  Convection is likely to
   increase this afternoon as the upper low moves slowly to the
   northeast and diurnal destabilization occurs on the periphery of
   existing cloudy regions.  Steep lapse rates will favor hail
   potential in stronger storm cores, while development of a
   surface-based well-mixed layer in the lower levels suggests
   potential for a few strong wind gusts.

   ...Western into parts of central TX...
   No changes have been to this area.  Persistent overnight and morning
   convection over the eastern Panhandle and south Plains generated an
   outflow boundary that moved westward/southwestward this morning to
   near the Texas/New Mexico state line.  This has resulted in
   temporary convective stabilization over parts of the region. 
   Visible imagery shows decreasing clouds and the onset of strong
   diabatic heating, especially over the south Plains, and
   destabilization is likely this afternoon as steeper mid-level lapse
   rates persist over the area.  Dynamic forcing aloft for large scale
   ascent is expected to remain very weak as an upper ridge migrates
   eastward over the area, and this is expected to limit coverage of
   thunderstorms.  However, a few storms are expected to form as the
   dry line mixes eastward this afternoon, and favorable lapse rates
   coupled with veering winds with height suggest potential for
   isolated severe storms to develop.  Large hail and strong wind gusts
   will be the primary threats.

   ..Weiss/Coniglio.. 05/16/2018

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