Moderate Risk Area Expanded to Include Most of Alabama

The updated SPC severe weather outlook tells us what we have already been telling you. The entire area has a significant risk of severe weather today.

..SUMMARY

AN OUTBREAK OF SEVERE THUNDERSTORMS IS LIKELY THROUGH TONIGHT, WITH
THE GREATEST THREAT EXPECTED FROM NORTHEAST LOUISIANA, MISSISSIPPI,
ALABAMA, SOUTHERN MIDDLE TENNESSEE AND WESTERN GEORGIA. STRONG
TORNADOES, WIDESPREAD DAMAGING WINDS, AND LARGE HAIL ARE ALL
POSSIBLE.

..SYNOPSIS

A COMPLEX FORECAST WITH MULTIPLE SCENARIOS POSSIBLE ACROSS A
BROAD AREA FROM THE LOWER MS VALLEY INTO THE TN/OH VALLEYS AND THE
SOUTHEAST. A COMPACT SHORTWAVE TROUGH OVER THE EDWARDS PLATEAU OF TX
WILL ACCELERATE EAST-NORTHEAST INTO THE ARK-LA-MISS BY THIS EVENING
AND TOWARDS EASTERN KY/TN BY THE END OF THE PERIOD, IN RESPONSE TO
CONTINUED AMPLIFICATION OF A LARGE-SCALE TROUGH OVER THE
NORTH-CENTRAL STATES.

..NORTHWEST LA TO NORTHERN AL/MIDDLE TN

AN ONGOING MCS WITH A HISTORY OF SEVERAL CONFIRMED BUT BRIEF TDSS
EARLIER THIS MORNING WILL CONTINUE TO MOVE EAST-NORTHEAST ALONG AN
INTENSIFYING BAROCLINIC ZONE ACROSS PARTS OF NORTHERN/CENTRAL MS
INTO NORTHERN AL/MIDDLE TN. TORNADOES AND DAMAGING WINDS WILL BE
LIKELY WITH THIS MCS WHICH WILL INCLUDE A MIXED CONVECTIVE MODE OF
BOWING SEGMENTS AND POTENTIAL SUPERCELLS DEVELOPING JUST AHEAD OF
THE CLUSTER ON ITS SOUTHERN FLANK.

THE PRESENCE OF UPPER 60S TO LOW 70S SURFACE DEW POINTS IN MUCH OF
LA AND SOUTHERN MS WILL SPREAD NORTH AND LIKELY REACH NORTHERN MS TO
WESTERN AL BETWEEN 21-00Z. THIS SHOULD OVERLAP STRONG LOW-LEVEL
SHEAR (0-1 KM SRH OF 400+ M2/S2) AS THE LOW-LEVEL JET STRENGTHENS
AND SHIFTS NORTHEAST. THE ENVIRONMENT WILL FAVOR EMBEDDED SUPERCELLS
CAPABLE OF PRODUCING STRONG TORNADOES AND DAMAGING WINDS, THE MOST
SUBSTANTIAL OF WHICH MAY OCCUR FROM NORTHEAST LA THROUGH
NORTH-CENTRAL MS INTO NORTHERN AL AND SOUTHERN MIDDLE TN. THERE IS
STILL ENOUGH UNCERTAINTY WITH REGARD TO CONVECTION OUTPACING
STRONGER SURFACE-BASED INSTABILITY (ESPECIALLY WITH NORTHEAST
EXTENT), AS WELL AS THE OVERALL CONVECTIVE MODE, TO PRECLUDE AN
UPGRADE TO HIGH RISK.

..SOUTHERN MS TO GA/CAROLINAS

TO THE SOUTH OF THE INITIAL MCS CROSSING NORTHERN MS/AL INTO TN, A
SEPARATE PRE-FRONTAL BAND OF CONVECTION IS EXPECTED TO BECOME
SUSTAINED BY EARLY EVENING FROM SOUTHERN MS INTO CENTRAL AL. THIS
CONVECTION WILL BE WELL EAST OF THE SYNOPTIC COLD FRONT, IN AN
ENVIRONMENT WITH MODERATE SURFACE-BASED BUOYANCY AND VERY STRONG
VERTICAL SHEAR. A BROKEN BAND OF EMBEDDED SUPERCELLS APPEARS LIKELY
TO DEVELOP THROUGH THE EVENING AND OVERNIGHT, WITH AN ASSOCIATED
THREAT FOR STRONG TORNADOES AND DAMAGING WINDS. THE PRE-FRONTAL
CONVECTION SHOULD REACH THE WESTERN CAROLINAS BY 09-12Z.

..LOWER RED RIVER VALLEY TO THE OH VALLEY

AN ARC OF CONVECTION WILL LIKELY FORM LATER THIS AFTERNOON JUST
AHEAD OF THE COMPACT SHORTWAVE TROUGH AND ASSOCIATED SURFACE CYCLONE
IN EASTERN OK TO NORTHEAST TX, WITHIN THE LEFT-EXIT REGION OF THE
MID-UPPER JET. THIS CONVECTION WILL SUBSEQUENTLY SPREAD EAST THEN
NORTHEAST ACROSS THE MID-SOUTH DURING THE LATE AFTERNOON/EVENING.
THE NORTHWARD EXTENT OF DESTABILIZATION IN AR/WESTERN TN THIS
AFTERNOON/EVENING WILL DEPEND LARGELY ON THE INTENSITY AND EXTENT OF
THE EARLY-DAY MCS MOVING FROM LA INTO NORTHERN MS.

STILL, STEEP MIDLEVEL LAPSE RATES WITH THE EJECTING MID-LEVEL WAVE
AND STRONG DEEP-LAYER VERTICAL SHEAR WILL FAVOR FAST-MOVING
SUPERCELLS AND LINE SEGMENTS CAPABLE OF PRODUCING LARGE HAIL AND
DAMAGING WINDS. THE NORTHEAST EXTENT OF THE DAMAGING WIND AND
TORNADO THREAT INTO TONIGHT WILL DEPEND LARGELY ON HOW
WIDESPREAD/ORGANIZED THE CONVECTION IS ACROSS NORTHERN MS/AL THIS
AFTERNOON/EVENING, AND THE DEGREE OF LOW-LEVEL RECOVERY IN THE WAKE
OF THAT CONVECTION.

..GRAMS/BENTLEY.. 04/12/2020

Category: Alabama's Weather, ALL POSTS, Severe Weather