SPC AC 161628

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1128 AM CDT Tue Mar 16 2021

   Valid 161630Z - 171200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS NORTHWEST AND
   NORTH-CENTRAL OK...

   ...SUMMARY...
   Scattered severe storms with large hail (some significant), damaging
   winds, and a few tornadoes are expected tonight across the southern
   Great Plains to the Ark-La-Miss. Isolated severe storms will also be
   possible from southern Mississippi to central Georgia through this
   evening.

   ...Central/southern portions of MS/AL/GA to
   Ark-La-Tex/Ark-La-Miss...
   A cluster of non-severe convection persists across a swath of
   central AL to southern MS. The predominant WSW-ENE orientation and
   attendant anvil shading will limit stronger boundary-layer heating
   to the south of this convection to the Gulf Coast. This activity
   will likely continue through this afternoon into the evening, along
   the northern/northeastern MLCAPE gradient. The orientation of the
   clusters generally oriented parallel to the deep-layer shear vector
   should be a limiting factor despite 40-50 kt effective shear.
   Effective SRH of 100-150 m2/s2 is expected to persist and may
   support a few transient, low-end supercell structures from southern
   MS to the stationary front in central GA.  Isolated damaging
   winds/severe hail and a tornado or two will all be possible.

   Closer to the Ark-La-Tex and Lower MS Valley, a confluence axis
   currently trails from the ongoing clusters and should advance north.
   Strengthening low-level warm advection after sunset should aid in at
   least isolated discrete cells developing near this confluence axis.
   Mid-upper 60s boundary-layer dewpoints and only weak convective
   inhibition suggest that storms will maintain surface-based inflow
   parcels with a threat of all hazards. The cat 2/SLGT risk has been
   expanded to account for this scenario.

   ...Southern Great Plains to the Lower MS Valley...
   A compact, deep mid-level low over central AZ will progress east,
   reaching the TX Panhandle overnight. Lee cyclogenesis is expected
   this afternoon near the NM/TX border, and the surface cyclone will
   move into west-central OK overnight. In advance of the cyclone,
   low-level moisture (boundary-layer dewpoints in the mid-upper 60s)
   will surge northward from south TX and LA to southern portions of
   OK/AR tonight on strengthening southerly low-level flow. This
   moistening will occur beneath a broad plume of steepening mid-level
   lapse rates between 8-9 C/km, yielding MUCAPE of 2000-3000 J/kg
   overnight. 

   The boundary layer will be capped through the day, but continued
   destabilization and the approach of strong height falls/ascent from
   the west will likely support thunderstorm development by late
   evening from the eastern TX Panhandle into western OK and southern
   KS. The storms closer to KS will likely remain elevated north of the
   warm front, though wind profiles will favor several elevated
   supercells capable of mainly producing large hail, with isolated
   severe gusts still possible. Farther south in OK, storms should be
   rooted near the surface, with deep-layer shear and buoyancy
   favorable for supercells with very large hail. Wind profiles will
   also be sufficient for some tornado threat, though uncertainty
   exists regarding storm mode/coverage with southward extent late in
   the period.

   Thunderstorm development will also be possible late tonight in
   west-central TX as a Pacific cold front overtakes the dryline over
   the Edwards Plateau. The frontal storms will move east and may
   develop northeast as well, posing a risk for mainly large hail and
   damaging wind gusts into central and north-central TX during the
   early morning.

   ..Grams/Bentley.. 03/16/2021

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