SPC 2000Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0156 PM CST Mon Jan 25 2021

Valid 252000Z - 261200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING
ACROSS PARTS OF NORTHEASTERN MISSISSIPPI AND NORTHWESTERN ALABAMA
INTO MIDDLE TENNESSEE...

...SUMMARY...
A few severe thunderstorms are possible this evening within a
corridor across northeastern Mississippi and northwestern Alabama
into middle Tennessee.  This includes a risk for potentially
damaging wind gusts and perhaps a couple of tornadoes.

...20Z Outlook Update...
Adjustments to the categorical and probabilistic outlook lines were
made to account for the progression of synoptic and sub-synoptic
features, and latest trends concerning ongoing destabilization.

...Mid South vicinity...
Low-level moisture return is ongoing on southerly return flow across
the lower Mississippi into Tennessee Valleys.  This appears to be
contributing to modest boundary-layer destabilization (including
CAPE  up to 500-1000 J/kg), which is expected to continue developing
northeastward as an initial short wave impulse, which has emerged
from the Southwest, progresses east-northeast of the central Great
Plains late this afternoon and evening.  As the associated frontal
wave migrates into the lower Ohio Valley, there appears a window of
opportunity for vigorous convective development focused along/just
ahead of the trailing surface trough across Tennessee into
Mississippi.  This may coincide with a 40-50 kt southerly 850 mb jet
axis, along which enlarged low-level hodographs may become support
of supercells structures accompanied by the risk for damaging wind
gusts and/or a couple of tornadoes.  With the influence of the
mid/upper forcing on the warm sector expected to be
glancing/short-lived, it appears this risk will be maximized this
evening, but at least some severe weather potential may linger as
remnant convection spreads eastward/southeastward overnight.

...Arizona...
A corridor of modest boundary-layer destabilization is ongoing
across the international border into southern Arizona, ahead of the
vigorous short wave impulse now turning inland of the southern
California coast.  Coincident with strengthen of west-southwesterly
flow to 30-40+ kt in the 850-700 mb layer, the environment may
become conducive for isolated thunderstorm development with the
potential to produce strong surface gusts approaching or briefly
exceeding severe limits.

..Kerr.. 01/25/2021

.PREV DISCUSSION... /ISSUED 1025 AM CST Mon Jan 25 2021/

...TN Valley today...
A progressive shortwave trough continues to move across the central
Plains today, with an associated 100kt+ mid level jet extending from
north TX into MO.  The primary surface low for this system is over
northwest AR, with a warm front extending eastward along the KY/TN
border.  Strong low-level wind fields are present across the warm
sector, with sufficient CAPE to pose a marginal risk of a few
fast-moving storms capable of gusty winds.  However, model guidance
continues to suggest that slight veering in the low-level winds will
weaken convergence/forcing and limit coverage of deep convection.

...MS/AL/TN this evening and tonight...
After dark, a few thunderstorms are expected to form over parts of
MS/Al and middle TN along/ahead of the advancing cold front. 
Low-level and deep-layer vertical shear profiles in this area will
be favorable for storm organization/rotation, and will maintain the
marginal probabilities for isolated tornadoes or damaging wind
gusts.  The primary forecast concern in this region will be storm
coverage, and poor thermodynamics in the lowest 3-4 km suggest that
updrafts may struggle to intensify.  This area will continue to be
evaluated in later outlooks.

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