Apr 13, 2019 0600 UTC Day 1 Convective Outlook

Day 1 Convective Outlook  

   NWS Storm Prediction Center Norman OK
   1248 AM CDT Sat Apr 13 2019

   Valid 131200Z - 141200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   FAR EAST TEXAS...LOUISIANA...FAR SOUTHEAST ARKANSAS AND WEST-CENTRAL
   MISSISSIPPI...

   ...SUMMARY...
   Numerous severe thunderstorms capable of producing tornadoes, wind
   damage and large hail, are expected across parts of east Texas,
   Louisiana, southern Arkansas, Mississippi, western Alabama and
   surrounding areas today and tonight.

   ...East Texas/Louisiana/Southern Arkansas/Mississippi/Western
   Alabama...
   A vigorous upper-level trough will move across the southern Plains
   today as a mid-level jet rounds the base of the system. At the
   surface, a low will move into the Arklatex with a moist airmass in
   place to the southeast of the low across east Texas, Louisiana and
   western Mississippi. Surface dewpoints in the moist sector should be
   in the upper 60s and lower 70s F by late morning. Thunderstorms
   should be ongoing across north-central into northeast Texas at the
   start of the period. This convection with a hail threat, is likely
   to move into the Arklatex by midday. Further south across southeast
   Texas into Louisiana, the airmass should become moderately unstable
   and remain primarily undisturbed. In response to the approach of the
   upper-level trough, a low-level jet is forecast to move into far
   eastern Texas and western Louisiana during the early afternoon.
   Thunderstorms should initiate to the northwest of the low-level jet
   on the northern edge of the stronger instability. Strong deep-layer
   shear profiles will favor supercell development. Supercells will
   have a potential for large hail in the early afternoon. The more
   dominant storms could produce 2-inch diameter hailstones. As the
   upper-level trough approaches and the exit region of a progressive
   mid-level jet moves into southeast Texas during the early afternoon,
   surface-based thunderstorms should rapidly initiate and move
   eastward into western Louisiana.

   RAP forecast soundings across the moist sector at 21Z from Monroe,
   LA southward to Alexandria, LA show MLCAPE values in the 2000 to
   2500 J/kg range. Deep-layer shear is forecast to steadily increase
   due the approach of the mid-level jet with forecast soundings
   showing 0-6 km shear of 50 to 60 kt by late afternoon. This combined
   with strong low-level shear will be favorable for supercells and
   tornadoes across the moderate risk area. 0-3 km storm-relative
   helicities are forecast to be in the 350 to 450 m2/s2 range
   supporting strong tornadoes with the more dominant supercells near
   the axis of the low-level jet. A potential for long-track tornadoes
   will be possible and a regional outbreak of tornadoes could occur
   across parts of the moderate risk area. By early evening, the
   cluster of severe storms is forecast to move into southwestern and
   central Mississippi where a potential for strong tornadoes will
   continue. However, the wind-damage threat may become the more
   dominant hazard as the convection moves further to the east where
   instability is forecast to be weaker.

   ...Northern South Carolina/Central and Eastern North Carolina/Far
   Southeast Virginia...
   Southwest mid-level flow will be in place across the East Coast
   today. At the surface, a moist airmass will exist across the
   Atlantic Coastal plains where dewpoints should be in the upper 60s
   and lower 70s F.  As surface temperatures warm across the moist
   airmass, pockets of moderate instability may develop from northern
   South Carolina northeastward into eastern North Carolina.
   Thunderstorms are forecast to initiate in the foothills of the
   Appalachians and move eastward into the stronger instability during
   the afternoon. SBCAPE values around 1000 J/kg evident on RAP
   forecast soundings, along with 30 to 40 kt of 0-6 km shear should be
   enough for a marginal severe threat. Strong wind gusts and hail will
   the primary threats.

   ..Broyles/Bentley.. 04/13/2019