SPC AC 251956

   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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