SPC AC 181956

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0256 PM CDT Wed Mar 18 2020

   Valid 182000Z - 191200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM
   WEST-CENTRAL TEXAS INTO SOUTH-CENTRAL OKLAHOMA...

   ...SUMMARY...
   Scattered severe thunderstorms are expected this afternoon through
   tonight across parts of the southern and central Plains.  Severe
   wind gusts, large to very large hail, and tornadoes are possible.

   ...20z Update...

   The outlook remains unchanged across the Plains with this update
   cycle. The ongoing forecast remains on track and in-line with latest
   guidance and surface observations. Reference MCD 193 for further
   details on the short-term risk across parts of Texas.

   The only change to probabilities has been the removal of the 2%
   tornado area across southern AZ, where convection will likely remain
   higher-based and low level shear only marginally favorable. The main
   threat will continue to be isolated, marginally severe hail and
   gusty winds.

   ..Leitman.. 03/18/2020

   .PREV DISCUSSION... /ISSUED 1207 PM CDT Wed Mar 18 2020/

   ...Southern Plains region...

   Primary change to previous outlook has been to increase tornado
   probabilities across west central into northwest through north
   central TX area. An old outflow boundary will persist in this
   region, but should become more diffuse with time. Several CAM runs
   and especially the HRRR continue to initiate storms in warm sector
   by late afternoon initially along the dryline across west central
   TX. This initiation would be in advance of primary zone of forcing
   associated with the shortwave trough currently moving through
   northern Mexico. While 0-1 km shear will initially be weak/modest,
   an increase in the low-level jet during the early evening within an
   otherwise favorable deep-layer shear environment will support
   potential for supercells with low-level mesocyclones, tornadoes and
   very large hail as storms move northeast toward central through
   northwest and north central TX this evening. Otherwise additional
   storms will likely develop across west TX along retreating dryline
   during the evening and spread east through TX and OK during the
   overnight. The shear/instability parameter space will support
   organized storms with potential for linear/bowing segments as well
   as supercells capable of all severe hazards. 

   ...Arizona...

   A strong shortwave trough will rotate northeast through AZ this
   afternoon accompanied by steep lapse rates and strong vertical
   shear. Though weak instability will remain a limiting factor, a few
   storms could pose a threat for mainly locally strong wind gusts and
   marginally severe hail.

   ...Tennessee through Ohio Valley region...

   Strong vertical shear accompanying a shortwave trough has spread
   across TN and KY, but widespread showers/rain continue to limit
   overall destabilization potential. Will maintain a marginal risk for
   this region for now, but threat appears very conditional.

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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z