SPC AC 081730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Wed Apr 08 2020

   Valid 091200Z - 101200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
   OF THE TX COASTAL PLAIN...

   ...SUMMARY...
   Severe thunderstorms are possible across portions of central and
   south Texas on Thursday, mainly during the afternoon and evening.
   Very large hail and strong wind gusts are the primary threats.

   ...Synopsis...
   Upper pattern will have two prominent features on Thursday, a large
   upper low over southern CA and the southern Great Basin and a
   deepening/mature mid-latitude cyclone over the Northeast States. The
   southern CA upper low will be displaced southwest of the stronger
   flow aloft, with little progression of this system anticipated
   throughout the day. Maturing of the cyclone over the Northeast will
   be supported by a pair of shortwave troughs, one moving through the
   region during the first half of the period and the other moving
   through early Friday morning. Very strong mid-level flow (i.e. 110+
   kt at 500mb) will accompany these shortwaves, spreading
   eastward/northeastward over the northern Mid-Atlantic states and
   southern New England by Thursday afternoon. 

   Despite these more prominent features, the primary severe weather
   threat will likely be tied to a more subtle shortwave trough
   ejecting out of northern Mexico and across TX. Ample low-level
   moisture will be in place ahead of this shortwave, leading to
   strong/severe thunderstorm development Thursday afternoon.

   ...Central/South TX...
   A cold front will likely extend from northern LA southwestward into
   the Edwards Plateau early Thursday morning. This front is expected
   to slowly push southward throughout the day as temperatures and
   low-level moisture gradually increase ahead of it. By the early
   afternoon, temperatures will like be in the upper 80s and dewpoints
   in the upper 60s/low 70s south of the front. Ascent along the front
   will be augmented by the subtle shortwave trough mentioned in the
   synopsis, leading to thunderstorm initiation by the early afternoon.

   The warm and moist low-levels coupled with steep mid-level lapse
   rates (generally steepest between 800 to 600 mb) will support strong
   buoyancy and the potential for very strong updrafts. Winds up
   through about 700 mb will be modest but strong westerly flow will
   exist about 700 mb, supporting ample deep-layer shear for updraft
   organization. Large to very large hail appears to be the main severe
   threat, although the potential exists for upscale growth into an
   organized convective line. As such, threat for strong wind gusts
   exists from both water-loaded downdrafts within more cellular
   activity and more organized updrafts/downdrafts within a convective
   line. The tornado threat is non-zero, but weak low-level flow
   suggest very low probability.  

   ...Mid-Atlantic...
   Remnants of the overnight convective line are expected along the
   front across the region early in the period. Much of the stronger
   forcing for ascent will be displaced north but strong vertical shear
   will be in place over the region and a few stronger storms are still
   possible.

   ...Southern New England...
   Secondary surface cyclogenesis will likely be ongoing early Thursday
   morning across portions of southern New England, with the resulting
   low continuing to deepen as it moves into Downeast Maine Thursday
   evening. In addition to the mesoscale forcing provided by this
   cyclogenesis, the first of the pair of shortwaves mentioned in the
   synopsis will move into the region during the early afternoon. The
   better low-level moisture and buoyancy will be displaced farther
   south, but there is expected to be enough low-level moisture to
   support modest elevated instability as mid-level temperatures cool
   and lapse rates steepen. As such, thunderstorms are expected within
   the warm conveyor as well as along the front. The strong flow aloft
   will support fast storm motions as well as the potential for a few
   more organized/stronger storms capable of hail and/or downdrafts
   strong enough to penetrate the low-level stability to produce
   damaging wind gusts at the surface.

   ..Mosier.. 04/08/2020

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