SPC AC 310714

   Day 2 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   0114 AM CST Fri Dec 31 2021

   Valid 011200Z - 021200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF THE DEEP SOUTH AND TENNESSEE VALLEY....

   CORRECTED FOR SIGNIFICANT TORNADO LINE TYPE

   ...SUMMARY...
   Widespread thunderstorms are expected from the ArkLaTex to the
   Western Appalachians on New Year's Day. All severe-weather hazards
   are possible including large hail, damaging winds, and tornadoes, a
   couple of which may be strong.

   ...Synopsis...
   A positively tilted upper-level trough will be centered near the
   Great Basin to start the period. This trough will maintain its
   positive tilt as it shifts eastward across the Plains and into the
   Midwest by 12Z Sunday. An embedded mid-level shortwave trough will
   move quickly from the southern High Plains across the Midwest and
   Ohio Valley Saturday to the Northeast by Sunday morning. A surface
   reflection of this mid-level shortwave trough is expected to travel
   along the front from the Ozarks to the Ohio Valley and into the
   Mid-Atlantic.

   ...Ohio Valley into the central Appalachians...
   There is still considerable uncertainty regarding the northward
   extent of the destabilization and severe-weather threat based on the
   position of the position of the surface front and the strength of
   the surface low. The NAM is stronger with the surface low with a
   much farther north warm front bringing low 60s dewpoints north of
   the Ohio River into southern Illinois, southern Indiana, and
   Southwest Ohio. However, the operational GFS is much weaker and
   southeast with the surface low and only brings low 60s dewpoints
   into south-central Kentucky. The ECMWF solution is between these two
   locations with the frontal position, which also closely resembles
   the GEFS mean. Therefore, the northern extent of the marginal and
   slight risk threat areas match the ECMWF and GEFS mean. 

   A line of storms is expected to move through this region during the
   afternoon and early evening hours. Forecast soundings show more than
   50 knots of flow only a few hundred meters above the surface.
   Therefore, mixing this strong flow to the surface should not be that
   difficult, even in a weak buoyancy environment. Low 60s dewpoints
   should yield MLCAPE around 250 to 500 J/kg across southern Kentucky,
   which increases the confidence for severe winds as the squall line
   moves through. In addition, a QLCS tornado threat will exist given
   the strong low-level speed shear present ahead of this line of
   storms. However, the limited instability and veered surface flow
   will be limiting factors to a greater tornado threat along this
   portion of the line. 

   ...Portions of the Deep South into the Tennessee Valley...
   A large area of thunderstorms, some of which may be severe, is
   expected to be ongoing from western Kentucky to northern Texas
   Saturday morning. As the surface low moves from the Plains into the
   Ozarks Saturday morning, this convection is expected to become
   better organized, likely into a squall line, and start to advance
   eastward. Dewpoints are forecast in the mid to upper 60s ahead of
   these storms, which should yield MLCAPE around 500 to 1500 J/kg from
   north to south. This should be more than sufficient to maintain a
   strong squall line through the afternoon and into the overnight
   hours across eastern Arkansas, most of Tennessee, and northern
   Mississippi and Alabama. A 50 to 60 knot low-level jet will result
   in strong low-level speed shear across the entire warm sector.
   Forecast soundings show mostly unidirectional flow in the lowest 1
   km due to the veered surface flow across most of the warm sector as
   a result of the elongated nature of the surface pressure pattern.
   This should temper the tornado threat somewhat, but with the strong
   speed shear and the expectation of a well balanced squall line, the
   environment will still be supportive for QLCS tornadoes. 

   Most guidance hints at the potential for some warm sector supercell
   development across portions of Mississippi, Alabama, and Tennessee
   Saturday afternoon/evening. The ECMWF has been especially bullish
   with pre-frontal convection for the last several days, which
   continues through the latest 00Z run. Any strong supercells which
   can develop in the open warm sector will likely have the greatest
   threat for significant to potentially intense tornadoes. The most
   likely region for pre-frontal supercell development will be from
   eastern Arkansas to northern Alabama and possibly southern Tennessee
   where greater instability is forecast. Veered low-level flow will
   keep low-level directional shear limited during the first half of
   the day. However, at least slightly greater low-level turning is
   shown by forecast soundings during the late afternoon into the
   evening hours as surface flow remains south-southwest, while the
   low-level jet starts to veer more westerly as the main wave shifts
   east. This may result in a slightly higher tornado threat into the
   overnight hours from far eastern Mississippi into northern/central
   Alabama and northwest Georgia.

   ..Bentley.. 12/31/2021

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