SPC AC 040815

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0215 AM CST Sat Dec 04 2021

   Valid 061200Z - 071200Z

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

   ...SUMMARY...
   Isolated strong to severe thunderstorms may occur mainly Monday
   morning from parts of coastal/east Texas into the lower Mississippi
   Valley.

   ...Synopsis...
   A highly amplified, large-scale upper trough should move from the
   central to eastern CONUS on Monday. An upper low in the southern
   stream should shift eastward across northern Mexico through the day,
   eventually reaching south TX late Monday into early Tuesday morning.
   At the surface, a low over the Upper Great Lakes is forecast to
   develop northeastward into Ontario/Quebec, with a trailing cold
   front likely to continue sweeping east-southeastward over the East
   Coast, Southeast, and southern Plains through the period.

   ...Coastal/East Texas into the Lower Mississippi Valley...
   Thunderstorms should be ongoing early Monday morning along/ahead of
   the front across parts of coastal/east TX into the lower MS Valley.
   The primary forcing associated with the upper trough will remain
   displaced to the north of this region. Still, the low-level ascent
   associated with the surface cold front should be enough to support
   continued convection through at least Monday morning. Generally low
   to mid 60s surface dewpoints and modest diurnal heating should
   foster weak instability across the warm sector. Even though the
   low/mid-level wind field will likely veer and gradually weaken
   though the day as the upper trough shifts farther east, there should
   be enough enhancement to the mid-level westerlies to support
   sufficient deep-layer shear for modest updraft organization.
   Isolated strong to severe storms posing a threat for mainly damaging
   winds and perhaps marginally severe hail appear possible mainly
   Monday morning. As convection develops east-southeastward in tandem
   with the cold front, the deep-layer shear should slowly diminish
   through the day. There should be a tendency for these thunderstorms
   to gradually weaken with southward and eastward extent by late
   Monday afternoon.

   ...Northeast...
   Very strong low/mid-level flow is forecast to overspread much of the
   Northeast on Monday as the upper trough progresses over the eastern
   states. Latest guidance suggests that, at best, low 50s surface
   dewpoints may attempt to move inland across parts of southern New
   England ahead of the cold front. Weak MUCAPE extending through a
   sufficiently deep layer could support charge separation and
   occasional lightning flashes with elevated convection. At this
   point, the potential for surface-based thunderstorms with any
   strong/gusty wind threat appears limited due to the meager low-level
   moisture and related lack of boundary-layer instability.

   ..Gleason.. 12/04/2021

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