SPC AC 151215

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0715 AM CDT Sat Mar 15 2025

   Valid 151300Z - 161200Z

   ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ALONG A CORRIDOR
   FROM CENTRAL MISSISSIPPI INTO NORTHERN/CENTRAL ALABAMA...

   ...SUMMARY...
   A tornado outbreak is expected across the central Gulf Coast States
   and Deep South into the Tennessee Valley. Numerous significant
   tornadoes, some of which should be long-track and potentially
   violent, are expected this afternoon and evening. The most dangerous
   tornado threat should begin across eastern Louisiana and Mississippi
   during the late morning to afternoon, spread across Alabama late
   today into the evening, and reach western parts of the Florida
   Panhandle and Georgia tonight.

   ...Synopsis...
   Water-vapor imagery this morning shows an intense mid-level
   low/trough moving northeast into the Upper Midwest with an upstream
   trough over the southern Great Plains.  A 100+ kt mid-level speed
   max will move through the base of the trough and into the lower MS
   and TN Valleys through tonight.  A dryline draped from east TX into
   the lower OH Valley will serve as a western/northwestern delimiter
   of a moist/unstable warm sector across portions of the South today. 
   An occluded low will migrate northward from the Upper Midwest into
   Ontario as a secondary low evolves and quickly moves northeast from
   the Arklatex into the southern Great Lakes through late evening.  A
   seasonably high moisture-rich and unstable airmass will expand
   across parts of the Deep South and contribute to a dangerous tornado
   outbreak featuring long-track intense to potentially violent
   tornadoes (EF3-EF4+).

   ...Central Gulf States/Tennessee Valley Region...
   Early morning surface analysis indicates a expanding warm sector
   across the central Gulf Coast states with upper 60s to 70 deg F
   dewpoints becoming established over much of LA through the southern
   2/3 of MS and into southwest AL.  Developing thunderstorms on the
   northern rim of the richer moisture extend from western/northern MS
   northeast through northern MS this morning.  The 12 UTC raobs from
   Lake Charles and Slidell, LA and Jackson, MS showed 700-500 mb lapse
   rates (7-8 deg C) and lowest 100-mb mean mixing ratios 13-15
   g/kg---indicative of a potent warm sector.  The northeast movement
   of a 125-kt cyclonically curved 250-mb jet into the lower MS Valley
   through midday will act to further strengthen wind profiles as a
   60-kt southerly LLJ slowly shifts east across the central Gulf Coast
   during the period.  The stronger storms this morning developing
   within the warm conveyor from LA into northern MS/TN will pose a
   risk for all hazards, including the possibility for strong
   tornadoes.  

   To the south and east of this morning thunderstorm activity, strong
   heating with temperatures warming into the upper 70s will lead to
   favorable warm sector convective initiation in a few confluence
   bands beginning in the 17-19z period over MS and adjacent portions
   of LA.  This preferred storm initiation process in conjunction with
   moderate buoyancy (1500-2500 J/kg MLCAPE) and very large and
   elongated hodographs, will favor the rapid development of intense
   supercells.  Forecast hodographs show 400-500 0-1km SRH within the
   Moderate-High Risk area across LA/MS/AL.  Numerous tornadoes are
   forecast with an attendant large-hail risk during afternoon/evening
   as this activity gradually shifts east.  Upper-end parameter space
   of composite indices (i.e., Significant Tornado Parameter values
   ranging from 5-10) will support long-track intense to potentially
   violent tornadoes this afternoon and into evening.  Eventually storm
   consolidation --especially with north extent across northern MS into
   northern AL/southern Middle TN) will serve as a north delimiter to
   the forecast stronger tornadoes.  Upscale growth with embedded
   supercells and bowing structures appear increasingly likely this
   evening over the northern portion of the warm sector.  Have made a
   small northeastward expansion of the Moderate Risk into portions of
   Middle and southeast TN for a significant wind risk.  The risk for
   strong tornadoes will likely continue tonight as sufficient
   destabilization occurs immediately ahead of established supercells
   as one or more clusters of storms track east late this evening into
   the overnight.  

   ...Southern Appalachians tonight...
   As the upper trough pivots east into the region late tonight, strong
   low-level warm/moist-air advection will contribute to a
   destabilizing airmass.  Despite weaker buoyancy with eastward extent
   over northeast GA into the western Carolinas, very intense low to
   mid-level flow will aid in maintaining a risk for a few supercells
   and line segments to survive into a more limited thermodynamic
   environment and potentially yield a risk for damaging gusts and a
   tornado threat through early Sunday morning.

   ...Upper OH Valley/southern Great Lakes...
   A band of ongoing thunderstorms this morning will continue to move
   east into weaker instability as drier low-level trajectories from
   the central/southern Appalachians act to pinch off the northern
   portion of the warm sector.  A hail/wind risk may linger through the
   morning before weak mid-level shortwave ridging ensues between the
   departing Upper Great Lakes negatively tilted trough and the
   amplifying trough over the lower MS Valley.  Models maintain a belt
   of strong 850-mb flow through midday before an intensification (70
   kt) of the northern periphery of a LLJ --extending from the central
   Gulf Coast into the Mid South-- overspreads the region.  Primary
   uncertainty is the magnitude of destabilization and its resultant
   effects on severe potential.  The latest model guidance generally
   only depicts weak buoyancy (at or below 250-500 MUCAPE) but some
   airmass recovery in wake of early day storms may occur over Indiana
   into southern Lower MI.  If this scenario occurs, higher severe
   probabilities may be warranted in subsequent outlooks.

   ..Smith/Squitieri.. 03/15/2025

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