SPC 0700Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1250 AM CST Sat Nov 28 2020

Valid 291200Z - 301200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER MISSISSIPPI VALLEY...SOUTHEAST...AND CAROLINAS...

...SUMMARY...
Isolated strong to severe thunderstorms may occur Sunday into Sunday
night across parts of the lower Mississippi Valley, Southeast, and
Carolinas. Damaging winds and perhaps a couple of tornadoes should
be the main threats.

...Lower Mississippi Valley into the Southeast and Carolinas...
A closed upper low centered over the southern Plains Sunday morning
will move eastward through the day. This upper low should begin to
merge with a positively tilted, northern-stream upper trough over
the eastern states Sunday evening into early Monday morning. A weak
surface low initially near the coast of southwestern LA is forecast
to develop northeastward across parts of LA/MS/AL through the day
while gradually deepening. Additional deepening of this surface low
should occur from Sunday night through the end of the period as it
continues developing northeastward along/near the spine of the
southern/central Appalachians. A warm front attendant to the surface
low will lift northward across parts of the Southeast and Carolinas,
while a trailing cold front sweeps eastward across these regions
through the period.

Most guidance indicates that storms will be ongoing Sunday morning
over the northern Gulf of Mexico near the LA Coast. Low-level warm
advection should be the primary forcing mechanism for this activity,
with the low-level jet forecast to shift northward across MS/AL
through the day. Some concern remains regarding how much low-level
moisture will be able to return inland given the potential for
numerous to widespread storms over the northern Gulf of Mexico
Sunday morning. If mid to upper 60s surface dewpoints can develop
inland across parts of southern LA/MS/AL and the FL Panhandle in
tandem with the deepening surface low and northward-advancing warm
front, then only modest diurnal heating would be needed to support
weak instability and surface-based storms. Strong effective bulk
shear of 45-60 kt will easily support organized convection, with
supercells possible along/ahead of the cold front. Isolated strong
to damaging winds should be a concern given the strength of the
low/mid-level flow and potential for storms to grow upscale into a
low-topped line along the cold front by Sunday evening. Low-level
shear also appears strong enough for updraft rotation, with a couple
tornadoes possible across the warm sector with any semi-discrete
storms.

This isolated severe threat will probably continue across parts of
GA into the Carolinas Sunday night and early Monday morning (end of
the Day 2 period), as low-level moisture return occurs from the
western Atlantic, and as a south-southwesterly jet rapidly
strengthens over these areas. However, even though the low-level
flow will likely be quite strong, instability is forecast to remain
rather weak (generally less than 500 J/kg of MLCAPE). The northern
extent of any meaningful damaging wind/tornado threat across the
Southeast remains unclear, as there is uncertainty in how far north
the mid 60s to upper surface dewpoints will advance. If confidence
increases in a narrow corridor of greater instability developing
across the warm sector on Sunday, then a Slight Risk for damaging
winds and/or tornadoes may be included across some portion of these
regions in a later outlook.

..Gleason.. 11/28/2020

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