SPC AC 140553

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1253 AM CDT Sat Apr 14 2018

   Valid 141200Z - 151200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE
   CENTRAL GULF COAST TO THE TENNESSEE VALLEY...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE
   GULF COAST TO MIDDLE TENNESSEE...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
   THE GULF COAST TO THE MIDWEST...

   ...SUMMARY...
   Scattered severe storms are expected from the central Gulf Coast to
   the Tennessee Valley today into tonight. The primary threats will be
   damaging winds and tornadoes, some of which could be strong.

   ...Synopsis...
   An expansive/amplified mid-level trough and embedded closed low will
   slowly shift east from the Plains towards the Mississippi Valley
   today. As it does so, it will gradually acquire a more negative
   tilt, owing to a secondary jet maximum advancing around the southern
   periphery of the trough and reaching the central Gulf by tonight. In
   response, a surface cold front will accelerate eastward from the
   lower Mississippi Valley, reaching the approximate Alabama/Georgia
   border near the end of the period Sunday morning.

   ...Central Gulf Coast to the Tennessee Valley...
   A pair of convective systems (one across east/southeast Texas and
   the other near the Mid-South) are making steady eastward progress
   and their evolution through the early morning hours will likely
   influence severe potential for the upcoming D1/Saturday period. Each
   of these systems are forecast to weaken some by 12Z this morning, as
   they push farther into eastern Louisiana and Mississippi. Although
   one low-level jet max will be lifting away towards the Ohio Valley
   at this time, a secondary enhancement is likely to occur from the
   Louisiana coast northward into Mississippi. Focused ascent
   associated with this 50-60kt 850mb jet corridor is forecast to
   re-intensify a line of storms from Louisiana northward into
   Mississippi during the morning hours. 

   Combined with surface dew points in the upper 60s/lower 70s and
   MLCAPE values around 1000-2000 J/kg, strengthening low-level shear
   should foster a maturing squall line, composed of embedded bowing
   segments and perhaps supercell structures, that pushes east across
   parts of Louisiana, Mississippi, and Alabama through the
   afternoon/evening. Damaging winds and a few embedded tornadoes will
   be the primary threats, and some of these tornadoes could be strong,
   considering continued moistening of the boundary layer and 0-1km
   shear upwards of 40-45 kt. Some severe threat should then persist
   into the overnight hours, as the line reaches eastern Alabama and
   the Florida Panhandle. 

   ...Mid Mississippi and lower Ohio Valleys...
   Cooling temperatures aloft and amplifying large-scale ascent will
   yield pockets of convection ahead of the primary surface low and
   cold front over southern Illinois this afternoon. While some
   destabilization may occur here, overnight convection to the south
   and little recovery time ahead of the cold front cast considerable
   doubt on the coverage of robust convection. Indeed, 00Z CAMs are
   unanimous in showing little in the way of vigorous thunderstorm
   activity today. Therefore, slight risk probabilities have been
   removed. A few stronger storms, capable of gusty winds and perhaps
   isolated large hail, may still develop later today, though.

   ..Picca/Cook.. 04/14/2018

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