SPC AC 161731

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1231 PM CDT Tue Mar 16 2021

   Valid 171200Z - 181200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
   ARKANSAS...NORTHEAST LOUISIANA...SOUTHWEST TENNESSEE AND MUCH OF
   MISSISSIPPI AND ALABAMA...

   ...SUMMARY...
   A regional outbreak of severe storms is expected Wednesday into
   Wednesday night across portions of the lower Mississippi Valley into
   Alabama. Widespread severe storms capable of producing tornadoes
   (several of which may be intense), very large hail and intense
   damaging wind gusts are expected. More than one round of severe
   storms are possible across parts of Mississippi into Alabama during
   the afternoon into the overnight hours.

   ...Synopsis...

   A compact and intense upper low over the southern Plains will eject
   eastward to the Ozark Plateau/lower MS Valley on Wednesday. A
   surface low centered over northeast OK will develop east/northeast
   in tandem with the upper system. At the beginning of the period, a
   cold front will extend southward from the low across eastern OK into
   eastern TX before arcing southwest into south TX. A warm front
   draped northwest to southeast from near the MO/AR border into
   northern AL will gradually lift northward through the period. There
   is some uncertainty in how far north this boundary will lift across
   northern GA/eastern TN given strong cold air damming across the
   Carolinas until very late in the period. The cold front should push
   eastward to Middle TN/central AL and the western FL Panhandle.
   Across the broad warm sector, dewpoints in the mid/upper 60s are
   expected beneath steepening lapse rates and intense vertical shear,
   resulting in an environment capable of supporting a widespread
   severe weather outbreak. 

   ...Southern Plains to the Mid-MS Valley...

   Convection will be ongoing Wednesday morning near the surface low,
   southward along the cold front, and eastward along the northward
   retreating warm front from central AR into northern MS/AL. Any
   convection north of the warm front will be elevated and pose a
   threat mainly for large hail. However, shear profiles will improve
   through the morning and surface-based storms near the triple point
   and along the warm front are possible and will increase the risk for
   damaging gusts and a few tornadoes. Further south along the cold
   front across eastern OK into eastern TX, convection will move into
   an increasing unstable and moist environment. A line of supercells
   and line segments is expected to develop as convection moves into AR
   and approaches the Sabine Valley. All severe hazards are expected
   with this activity from Wednesday morning into the afternoon. 

   ...Lower MS Valley into AL/GA...

   Multiple rounds of intense, severe convection will be possible,
   mainly across MS/AL on Wednesday afternoon into the overnight hours.
   Convection will intensify along the eastward progressing cold front
   across central and eastern AR/LA during the late morning/afternoon
   as it encounters effective shear greater than 60 kt, MLCAPE around
   1500-2500 J/kg and midlevel lapse rates around 7-8 C/km. Fast storm
   motion, with 925-700 mb flow greater than 40 kt will support
   widespread damaging gusts with some gusts greater than 65 kt
   expected. Large hail (some greater than 2 inch in diameter,
   especially from the AR/MO border into northern LA, southwest TN and
   northern/central MS) is also expected with this activity.

   Further east across northeast LA into MS and AL a more concerning
   scenario appears possible. Most forecast guidance agrees that a
   round of afternoon thunderstorms are expected. This activity is
   expected to develop in weaker ascent, driven by heating and low
   level warm advection. Strong 0-3 km shear near 30-40 kt will already
   be in place with enlarged low level hodographs evident. Given weaker
   forcing, this activity will have an opportunity to remain more
   discrete and any cell will quickly become a supercell capable of
   producing strong tornadoes. As a 40-50 kt low level jet increases
   around 00-03z, intense supercells are expected to advance eastward
   along with the cold front across MS and into AL overnight. This will
   bring a second round of significant severe storms capable of intense
   tornadoes, large hail and intense damaging winds across much of
   MS/AL. If these trends are maintained, an upgrade to a High risk
   could be necessary with the initial Day 1 Convective Outlook at 06z
   tonight.

   ..Leitman.. 03/16/2021

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