SPC AC 050640

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1240 AM CST Sun Dec 05 2021

   Valid 061200Z - 071200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   COASTAL/EAST TEXAS INTO THE LOWER MISSISSIPPI VALLEY AND
   SOUTHEAST...

   ...SUMMARY...
   Isolated strong to severe thunderstorms may occur Monday from parts
   of coastal/east Texas into the lower Mississippi Valley and
   Southeast. Damaging winds should be the main threat.

   ...Synopsis...
   A highly amplified upper trough will move eastward from the Upper
   Midwest/Great Lakes across the OH Valley, Mid-Atlantic, and
   Northeast on Monday. A weak upper low in the southern stream should
   shift eastward across northern Mexico while devolving into an open
   wave, eventually reaching south TX late in the period. A surface low
   initially over the Upper Great Lakes should develop northeastward
   into Ontario/Quebec through the day, while a trailing cold front
   sweeps east-southeastward across much of the southern Plains,
   Southeast, and eastern states.

   ...Coastal/East Texas into the Lower Mississippi Valley and
   Southeast...
   Numerous to widespread thunderstorms will likely be ongoing at the
   start of the period Monday morning from parts of east TX to the TN
   Valley along/just ahead of the cold front. The more pronounced
   large-scale ascent associated with the upper trough will likely
   remain displaced to the north of this region. Regardless, the
   low-level forcing from the front should be sufficient to support
   continued robust convection from Monday morning through at least the
   early afternoon. Generally upper 50s to mid 60s surface dewpoints
   are forecast to be present ahead of the front. Even though mid-level
   lapse rates are expected to remain poor, modest diurnal heating of
   this airmass should support weak boundary-layer instability and
   surface-based storms.

   The low/mid-level winds should be fairly strong at the beginning of
   the period Monday morning, but they will tend to veer to a more
   westerly component and gradually weaken through the day as the upper
   trough shifts farther to the northeast. Still, around 30-40 kt of
   effective bulk shear will likely prove favorable for continued
   updraft organization. Given the mainly linear mode expected with
   convection along the front, isolated strong to damaging winds will
   likely be the primary threat as thunderstorms develop
   east-southeastward through the day. A brief embedded QLCS tornado
   also appears possible, mainly Monday morning, while the low-level
   west-southwesterly winds remain modestly enhanced. With time,
   convection along the front will encounter either a much more
   unfavorable thermodynamic environment with eastward extent across
   TN/GA/AL, or become displaced to the south of the stronger
   deep-layer shear in TX/LA/MS. Net result should be for gradual
   weakening of the line of thunderstorms by late Monday afternoon.

   ...Northeast...
   Very strong low/mid-level flow is expected to overspread much of the
   Northeast on Monday as the upper trough progresses over this region.
   Guidance continues to suggest that low-level moisture return ahead
   of the front will remain meager, with only low to perhaps mid 50s
   surface dewpoints possible across parts of southern New England.
   Even with MUCAPE expected to remain quite weak, there may still be
   enough instability to support isolated lighting flashes with
   elevated convection. The potential for surface-based thunderstorms
   with any appreciable strong/gusty wind threat appears low due to the
   limited low-level moisture and related lack of boundary-layer
   instability.

   ..Gleason.. 12/05/2021

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