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SPC Dec 10, 2019 0830 UTC Day 3 Severe Thunderstorm Outlook

SPC 0830Z Day 3 Outlook
Day 3 Outlook Image
Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0111 AM CST Tue Dec 10 2019

Valid 121200Z - 131200Z


Isolated to scattered thunderstorms are expected across portions of
the Deep South and central Gulf Coast eastward to the Florida

Broad, cyclonically curved mid-level flow will encompass much of the
Lower 48 from the central Plains through the East Coast.  A
shortwave trough will migrate through this flow from the central
Plains to the Mid-Mississippi Valley.  The approaching mid-level
trough will induce modest cyclogenesis across the northern Gulf of
Mexico, with increasing low-level flow atop a shallow cool boundary
layer across the Southeast encouraging development of showers and a
few thunderstorms across the Lower Mississippi Valley in the
afternoon - spreading eastward toward the southern Appalachians
through the night.  Isolated thunderstorms will also develop across
the Florida Peninsula during the afternoon as well, and very cold
air aloft may result in a couple lightning flashes across western
Washington State.

...Coastal areas of southeast Louisiana through Alabama...
The combination of surface cyclogenesis across the north-central
Gulf of Mexico and increasing low-level flow across the region will
result in eventual northward evolution of a moist low-level airmass
characterized by near 70s F dewpoints.  The northward progression of
this airmass will likely demarcate the northern limit of any
potential for surface-based convection, and most models suggest that
this risk of surface-based activity should hold off over land areas
until after 12Z Friday.  A faster northward progression of this
airmass may result in a brief window for supercellular development
near coastal areas, however, given vertically veering wind profiles
and modest buoyancy.  Pending evolution of this airmass, low severe
probabilities may be needed in later outlooks.

..Cook.. 12/10/2019

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SPC Dec 10, 2019 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook
Day 4-8 Outlook Image
Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0336 AM CST Tue Dec 10 2019

Valid 131200Z - 181200Z

Early in the extended forecast period, a broad, long-wave trough
will take on a negative tilt while migrating eastward toward the
Ohio Valley and central Appalachians.  Subtle differences in the
evolution of this trough and embedded shortwaves appear to cause
spread in evolution of a surface low that should evolve from the
north-central Gulf of Mexico northeastward along the eastern
seaboard.  At this time, model consensus depicts that northern
Florida should experience some severe risk around the D4/Friday
timeframe as this surface low organizes and results in backed
low-level flow and inland intrusion of modified maritime air/weak
buoyancy.  Beyond this timeframe, any severe risk along coastal
areas of the Carolinas will be heavily modulated by the eventual
track of any surface low traversing the region and resultant inland
destabilization.  These uncertainties are too great to introduce 15%
probabilities, though it appears probable that they will be needed
for portions of the Southeast in subsequent outlooks.

Beyond this timeframe, uncertainty increases due to typical
increases in model errors, though a reservoir of moist, buoyant air
should reside not too far from the Gulf Coast as another upstream
system approaches from the Plains around D7/Monday.  A severe threat
may evolve across the Deep South around that timeframe, though
details remain too unclear for probabilities.

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