SPC Mar 15, 2025 1300 UTC Day 1 Convective Outlook

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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