SPC AC 181959

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0259 PM CDT Sun Jun 18 2023

   Valid 182000Z - 191200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE LOWER MISSISSIPPI VALLEY/SOUTHEAST...

   ...SUMMARY...
   Damaging winds, large hail, and a few tornadoes are expected this
   afternoon into tonight from the lower Mississippi Valley region to
   the east-central Gulf Coast.

   ...20Z Update...
   Convective evolution in the wake of thunderstorms this morning and
   early afternoon across southern AL and the FL Panhandle remains
   uncertain. A pronounced MCV and related mid-level circulation is
   clearly evident in visible satellite imagery across MO this
   afternoon. An outflow boundary from the morning/early afternoon
   convection is also draped from far east TX across LA into southern
   MS. This boundary may serve as a focus for renewed severe
   thunderstorm development this afternoon/evening, especially where it
   intersects a weak front in far east TX and vicinity. Have expanded
   the 10% significant hail area westward to include this region in the
   event a supercells can form and be sustained, as very large hail
   appears likely with any supercell given the very favorable
   thermodynamic and kinematic environment.

   Of potentially greater concern, multiple supercells may form closer
   to the MCV this evening across far eastern AR into northern/central
   MS. Both low-level and deep-layer shear appear very favorable for
   intense supercells capable of producing a few tornadoes, very large
   hail, and severe/damaging winds. The primary uncertainty remains
   convective coverage, as destabilization in the wake of earlier
   activity is still occurring. Based on recent observational and
   short-term guidance trends (RAP/HRRR, etc..), have adjusted the
   eastern extent of the Enhanced Risk, and expanded the 5% tornado
   area to include more of MS, far southwest TN, and western AL.

   ..Gleason.. 06/18/2023

   .PREV DISCUSSION... /ISSUED 1129 AM CDT Sun Jun 18 2023/

   ...AR/LA/MS/TN/AL...
   Widespread overnight and morning convection has overturned the air
   mass across much of the lower MS valley into AL.  This leads to a
   very low-confidence forecast for later today and tonight.  Morning
   model guidance shows wide diversity in where the corridors of
   highest risk of severe storms will develop, but several solutions
   continue to show potential.

   What appears to be the most likely scenario is shown by the morning
   NAM and recent runs of the RAP/HRRR.  This suggests storms will
   redevelop this afternoon over parts of AR and track eastward into
   portions of TN/MS/AL.  This area will see substantial heating by
   mid-afternoon as clearing arrives from the west. Forecast soundings
   in this area show a strengthening low-level jet by late-afternoon,
   promoting supercell and bowing structures capable of damaging winds,
   large hail, and a few tornadoes.  

   ...Southern AL to FL Panhandle Today...
   Multiple clusters of strong/severe storms are ongoing early this
   afternoon over parts of southern AL and southeast MS.  The air mass
   ahead of these storms is becoming very unstable with dewpoints in
   the 70s and temperatures warming through the 80s.  This is near the
   core of a 40-50 knot mid level jet max, providing sufficient shear
   for organized multicell and supercell storm structures.  There is
   uncertainty how this activity will evolve through the afternoon, but
   they could persist/intensity and track across much of southern AL
   and the FL Panhandle with a risk of damaging wind gusts and large
   hail.

   ...East TX...
   Several morning CAM solutions show at least isolated intense storms
   forming along a surface boundary extending across northeast TX. 
   Given the ample moisture/CAPE in this area, have extended the SLGT
   risk farther west.

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