SPC AC 092003

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0203 PM CST Sat Dec 09 2023

   Valid 092000Z - 101200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER WESTERN
   AND MIDDLE TENNESEE...AND SMALL PARTS OF NORTHERN MISSISSIPPI AND
   FAR SOUTHERN KENTUCKY...

   ...SUMMARY...
   Several tornadoes, scattered large hail and areas of damaging winds
   are expected through the afternoon into the evening from portions of
   the Ohio and Tennessee Valleys southward to the Lower Mississippi
   Valley and middle Gulf Coast.

   ...Lower MS Valley into much of TN and southern KY...
   Tornado probabilities have been increased within an Enhanced Risk
   for the unfolding tornado situation over western into Middle TN and
   far southern KY, and extending into northern MS. 

   Cells have remained discrete and are currently within a developing
   instability plume, adjacent to an area of enhanced low-level shear
   over Middle TN, southern KY and northern MS. The combination of
   favorable storm mode, and fully-effective 0-1 SRH of 150-200 m2/s2
   will pose a damaging tornado risk through the late afternoon. The
   greatest threat area may remain relatively concentrated due to the
   cooler air mass to the east, but an isolated strong tornado or two
   is possible.

   For more information, see mesoscale discussion 2305.

   ..Jewell.. 12/09/2023

   .PREV DISCUSSION... /ISSUED 1036 AM CST Sat Dec 09 2023/

   ...Gulf Coast/Lower Mississippi Valley/Tennessee Valley...
   Region is being increasingly influenced by height falls but
   otherwise resides between larger scale influences of an upper trough
   over the Upper Midwest and a positive-tilt trough over the southern
   High Plains. Increasing warm-sector moisture (generally lower to
   some middle 60s F surface dewpoints) ahead of a southeastward-moving
   cold front, along with considerable deep-layer/low-level shear, will
   be favorable factors for a long-duration severe risk through the
   afternoon into tonight. However, the likelihood of a complex/mixed
   quasi-linear convective mode casts uncertainty regarding the
   magnitude of the severe risk, particularly regarding a
   supercell-related sustained/focused tornado risk. It is also noted
   that some guidance suggests that 1-3km AGL winds may somewhat weaken
   by late afternoon/early evening within the warm sector, while noting
   SRH will still remain favorable for rotating/severe storms.

   Storms should continue to increase in coverage through early
   afternoon, initially near the front across Arkansas northeastward
   into western portions of Tennessee/Kentucky. Sufficiently steep
   mid-level lapse rates will support some hail potential, especially
   the first part of the day, but the tendency for storm clustering
   will otherwise limit this overall potential, as well as limiting
   prospects for more consequential hail magnitudes. As the boundary
   layer warms this afternoon, the potential for initially
   semi-discrete supercells will increase along with related damaging
   wind risk as well as tornado potential, which will persist through
   the afternoon/evening even with a quasi-linear convective mode. 

   As warm-sector inhibition further weakens later this afternoon,
   additional deepening convection may develop within weak pre-frontal
   convergence/confluence regime, mainly across Mississippi into
   Alabama, with this development eventually merging with or taking
   over as the main convective band this evening. Similarly,
   pre-frontal confluence may support isolated supercellular
   development along the Gulf Coast/Florida Panhandle vicinity through
   late night hours/early Sunday, within a somewhat separate regime
   capable of a few severe storms.

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