SPC AC 131930

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0230 PM CDT Thu Mar 13 2025

   Valid 151200Z - 161200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS IN EASTERN
   LA...MS...AND AL...

   ...SUMMARY...
   A severe weather outbreak is expected on Saturday across the central
   Gulf Coast States and Deep South into the Tennessee Valley. Numerous
   significant tornadoes are possible on Saturday afternoon and
   evening, centered on eastern Louisiana, Mississippi, and Alabama.
   Widespread damaging wind swaths and scattered large hail are likely.

   ...Central Gulf Coast/Deep South/TN Valley...
   Primary change is to expand level 4-MDT north in AL and all
   categories west in the tight gradient of severe potential from the
   Sabine to Lower MS Valleys. A particularly volatile scenario for
   destructive severe remains evident during the afternoon to evening
   on Saturday centered on the level 4-MDT risk region.

   In the wake of the vigorous shortwave trough and very deep surface
   cyclone crossing the North-Central States on D2, a broad upper
   trough will linger across the southern Great Plains. An intense
   mid-level jetlet, in excess of 100 kts at 500-mb, should eject
   through the basal portion of this trough in south TX on Saturday
   afternoon. This will induce secondary cyclogenesis along the
   slow-moving baroclinic zone from the Ark-La-Tex to the central Great
   Lakes. Another day of air mass modification ahead of this wave will
   yield a pronounced plume of rich northwest Gulf moisture that should
   be pristine across southeast LA into central MS through late
   morning. As mid-level height falls overspread the diurnally warming
   air mass, increasing convective development is expected along the
   deepening baroclinic zone, as well as residual outflows to its
   northeast in the TN Valley from prior late D2 convection.

   Steep mid-level lapse rates atop the richly moist boundary layer
   should yield at least moderate MLCAPE across the Lower MS Valley.
   Vertically veering wind profiles with strong anvil-level divergence
   amid the favorable instability should support robust updrafts and
   intense supercells. Low-level shear will strengthen during the
   afternoon and evening, setting the stage for a severe-weather
   outbreak including significant tornadoes, damaging gusts, and large
   hail. A pronounced dropoff in severe may be realized with northward
   extent across the TN Valley as an emerging band and/or highly
   organized line outpaces the rich Gulf air. Despite weaker
   instability with eastern extent into GA/SC, the intense wind fields
   may sustain damaging wind and embedded tornado potential well into
   the overnight.

   ...OH Valley to Lower Great Lakes...
   Forecast confidence is low with regard to severe potential north of
   the TN Valley. Weakening late D2 convection should be in a decaying
   process at 12Z Saturday. Much of the region will then be in between
   waves until late afternoon. Guidance differs on the degree of
   diurnal destabilization ahead of the deepening surface cyclone that
   should track north-northeast from the Ark-La-Tex. It is plausible
   that widespread Mid/Deep South to TN Valley convection during the
   day Saturday will temper the northward extent of instability by
   Saturday evening/night within a predominately meridional deep-layer
   wind profile. As such, the overall severe risk appears conditional,
   but given the fast flow regime, potential for damaging winds and
   perhaps a few tornadoes may be realized.

   ..Grams.. 03/13/2025

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