SPC 0700Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1255 AM CST Tue Nov 24 2020

Valid 251200Z - 261200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER/MID MISSISSIPPI VALLEY INTO THE OHIO/TENNESSEE VALLEYS AND
SOUTHEAST...

...SUMMARY...
Isolated strong to severe thunderstorms may occur Wednesday across
parts of the lower/mid Mississippi Valley into the Ohio/Tennessee
Valleys and Southeast. Locally damaging winds should be the main
threat, although a tornado or two also appears possible.

...Lower/Mid Mississippi Valley into the Ohio/Tennessee Valleys and
Southeast...
A closed upper low with associated mid-level southwesterly jet
should be centered over the lower/mid MS Valley at the start of the
period Wednesday morning. These features are forecast to track
eastward across the OH/TN Valleys and Southeast through the day. At
the surface, a low initially over northern MO should develop
east-northeastward towards the lower Great Lakes by Wednesday
evening while gradually weakening. A trailing cold front is expected
to move generally eastward across the lower/mid MS Valley, OH/TN
Valleys, and parts of the Southeast through the day.

A line of showers and thunderstorms should be ongoing along or just
ahead of the cold front Wednesday morning across parts of the lower
MS Valley into the Mid-South. Only weak destabilization is forecast
ahead of this line as low-level moisture gradually increases across
these areas. Still, the presence of around 40-50 kt of effective
bulk shear and enhanced low-level southwesterly flow suggests a
continued threat for isolated damaging winds with the line as it
moves eastward through the morning. A tornado or two also cannot be
ruled out. The more pronounced large-scale forcing for ascent
associated with the upper low is forecast to gradually shift away
from the Southeast and TN Valley regions through the day. Additional
robust storm development Wednesday afternoon/evening appears
uncertain, with low-level convergence along the front providing the
main source of lift. If additional storms can form Wednesday
afternoon across parts of MS/AL and perhaps middle TN, they could be
strong to severe given at least weak instability and sufficient
deep-layer shear. Strong/gusty winds would remain the primary threat
with this activity through early Wednesday evening.

Farther north across parts of the mid MS Valley into the OH Valley,
low-level moisture should remain more limited, with mainly mid to
upper 50s surface dewpoints possible. These regions will be in close
proximity to both the surface and upper low, with somewhat stronger
low/mid-level wind fields compared to locations farther south. Cool
mid-level temperatures (around -18 to -20 C at 500 mb) associated
with the upper low combined with modest diurnal heating ahead of the
cold front may support weak surface-based instability by early
Wednesday afternoon. A broken, low-topped line of storms may develop
across parts of the Midwest into the OH Valley in this high
shear/low instability environment. Given the strength of the
low-level flow, isolated damaging winds would be the main threat if
adequate destabilization occurs.

..Gleason.. 11/24/2020

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