662
ACUS01 KWNS 081246
SWODY1
SPC AC 081244
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0744 AM CDT WED APR 08 2020
VALID 081300Z - 091200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON INTO TONIGHT FROM THE MID MS VALLEY INTO PARTS OF THE OH
AND TN VALLEYS...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING ACROSS PARTS OF CENTRAL AND SOUTH CENTRAL TX...
..SUMMARY
SCATTERED TO NUMEROUS SEVERE THUNDERSTORMS CAPABLE OF PRODUCING
LARGE HAIL AND DAMAGING WINDS, SOME SIGNIFICANT, ARE EXPECTED FROM
LATE THIS AFTERNOON ACROSS THE MIDDLE MISSISSIPPI VALLEY EASTWARD
INTO THE OHIO AND TENNESSEE VALLEYS OVERNIGHT.
..MS/OH/TN VALLEY REGIONS THIS AFTERNOON THROUGH TONIGHT
AN AMPLIFYING NORTHERN STREAM SHORTWAVE TROUGH WILL DIG
SOUTHEASTWARD FROM MT/ND THIS MORNING TO THE MIDDLE AND UPPER MS
VALLEY REGION BY EARLY THURSDAY. THE MIDLEVEL TROUGH WILL BE
PRECEDED BY A DEEPENING SURFACE CYCLONE FROM THE OH VALLEY TO THE
LOWER GREAT LAKES THIS EVENING INTO TONIGHT, AS A TRAILING COLD
FRONT SURGES SOUTHEASTWARD ACROSS THE MIDDLE MS/TN/LOWER OH VALLEY
REGIONS. RICH LOW-LEVEL MOISTURE (BOUNDARY-LAYER DEWPOINTS IN THE
UPPER 60S TO LOWER 70S) WILL CONTINUE TO SPREAD NORTHEASTWARD FROM
THE NORTHWEST GULF COAST TO THE LOWER OH VALLEY TODAY, BENEATH AN
ELEVATED MIXED LAYER PLUME. THE OVERALL SCENARIO APPEARS SUPPORTIVE
OF INCREASINGLY WIDESPREAD CONVECTION FROM LATE AFTERNOON ACROSS
MO/IL TO THE LOWER OH AND TN VALLEYS OVERNIGHT, IN AN ENVIRONMENT
SUPPORTIVE OF FAIRLY WIDESPREAD LARGE HAIL AND DAMAGING WINDS.
THUNDERSTORM DEVELOPMENT IS ANTICIPATED BY EARLY-MID AFTERNOON
ACROSS EAST CENTRAL/SOUTHEAST IA AS HEIGHT FALLS WITH THE NORTHERN
STREAM TROUGH (AND A LEAD SPEED MAX) BEGIN TO INTERACT WITH THE MORE
MARGINAL MOISTURE ON THE NORTHWEST EDGE OF THE UNSTABLE WARM SECTOR.
THE INITIAL STORMS WILL LIKELY EVOLVE SUPERCELLS CAPABLE OF
PRODUCING VERY LARGE HAIL INTO IL. CONVECTION WILL SUBSEQUENTLY
SPREAD EAST-SOUTHEASTWARD THROUGH THE EVENING ALONG THE INSTABILITY
GRADIENT ACROSS CENTRAL IL/IN, AND LIKELY GROW UPSCALE INTO A LARGER
CLUSTER WITH INCREASING DAMAGING WIND POTENTIAL.
ADDITIONAL STORM DEVELOPMENT IS ALSO LIKELY ALONG AND AHEAD OF THE
COLD FRONT FARTHER SOUTH, STARTING LATE THIS AFTERNOON IN THE
VICINITY OF SOUTHEAST MO. LARGE BUOYANCY (MLCAPE OF 3000 J/KG OR
LARGER) IS LIKELY FROM SOUTHEAST MO EASTWARD AS BOUNDARY-LAYER
DEWPOINTS NEAR 70 F SPREAD NORTHEASTWARD BENEATH 8-9 C/KM MIDLEVEL
LAPSE RATES. DEEP-LAYER VERTICAL SHEAR WILL INITIALLY BE A LITTLE
WEAKER IN THIS CORRIDOR BETWEEN THE AMPLIFYING NORTHERN STREAM AND A
SOUTHERN STREAM FROM TX TO THE SOUTHEAST, BUT THE LARGE
BUOYANCY/STEEP LAPSE RATES AND INCREASING DEEP-LAYER FLOW/SHEAR BY
THIS EVENING WILL FAVOR A MIX OF SUPERCELLS AND GROWING CLUSTERS
CAPABLE OF PRODUCING VERY LARGE HAIL AND DAMAGING WINDS. LIKE THE
INITIAL CONVECTION FARTHER NORTH IN IL, UPSCALE GROWTH INTO AN
EXTENSIVE QLCS APPEARS LIKELY THIS EVENING INTO TONIGHT ACROSS THE
TN AND LOWER OH VALLEY REGIONS, WITH AN INCREASING THREAT FOR FAIRLY
WIDESPREAD DAMAGING WINDS. A COUPLE OF TORNADOES MAY ALSO OCCUR
WITH THE INITIAL DISCRETE CELLS, THOUGH LOW-LEVEL SHEAR WILL BE
RELATIVELY WEAK, OR WITH EMBEDDED CIRCULATIONS IN THE LATER QLCS AS
LOW-LEVEL SHEAR INCREASES OVERNIGHT AND MODERATE-STRONG BUOYANCY IS
MAINTAINED WELL INTO THE OVERNIGHT HOURS.
CONFIDENCE IN THE CORRIDOR OF GREATEST HAIL/WIND THREAT IS STILL A
BIT UNCERTAIN THIS MORNING, BUT AN UPGRADE TO HIGHER
PROBABILITIES/MODERATE RISK IS POSSIBLE IN LATER UPDATES.
..SOUTHERN WV TO THE VA/NC BORDER THIS AFTERNOON/EVENING
WEAKENING OUTFLOW AND A DIFFERENTIAL HEATING ZONE NEAR THE SOUTH
EDGE OF THE MORNING CONVECTION FROM WV INTO VA SHOULD PROVIDE A
FOCUS FOR WIDELY SCATTERED THUNDERSTORM DEVELOPMENT THIS AFTERNOON.
WARM AFTERNOON TEMPERATURES IN THE 80S AND BOUNDARY-LAYER DEWPOINTS
IN THE 56-60 F RANGE WILL SUPPORT MLCAPE OF 1000-1500 J/KG, AND
EFFECTIVE BULK SHEAR OF 35-40 KT WITH STRAIGHT HODOGRAPHS WILL FAVOR
SPLITTING CELLS CAPABLE OF PRODUCING DAMAGING GUSTS AND ISOLATED
LARGE HAIL.
..CENTRAL MS/AL INTO SOUTHERN GA THIS AFTERNOON/EVENING
A FEW CLUSTERS OF THUNDERSTORMS WILL BE POSSIBLE TODAY FROM CENTRAL
MS/AL INTO SOUTHERN GA, A PRECURSOR OF WHICH COULD BE THE ISOLATED
THUNDERSTORM NOW FORMING ACROSS SOUTHERN AR. THE PRIMARY STORM
DEVELOPMENT IS EXPECTED ALONG THE EASTERN EDGE OF THE RICHER
MOISTURE (DEWPOINTS NEAR 70 F) AND IN CONCERT WITH DAYTIME HEATING
AND WEAKENING OF CONVECTIVE INHIBITION, WITHIN THE RIGHT ENTRANCE
REGION OF THE UPPER JET. MLCAPE NEAR 1500 J/KG AND STRAIGHT
HODOGRAPHS WITH EFFECTIVE BULK SHEAR OF 40-50 KT WITHIN THE SOUTHERN
STREAM WILL FAVOR SPLITTING SUPERCELLS CAPABLE OF PRODUCING A FEW
DAMAGING GUSTS AND ISOLATED LARGE HAIL.
..CENTRAL/SOUTH CENTRAL TX THIS AFTERNOON/EVENING
A WEAKLY CONVERGENT DRYLINE AND EMBEDDED SPEED MAXIMA WITHIN A
SOUTHERN STREAM COULD PROVIDE THE FOCUS FOR THUNDERSTORM DEVELOPMENT
THIS AFTERNOON AS CONVECTIVE INHIBITION WEAKENS AND BUOYANCY BECOMES
VERY LARGE. DESPITE WEAK LOW-LEVEL FLOW/SHEAR, EFFECTIVE BULK SHEAR
NEAR 50 KT AND MLCAPE NEAR 4000 J/KG COULD SUPPORT SUPERCELLS
CAPABLE OF PRODUCING ISOLATED VERY LARGE HAIL AND DAMAGING WINDS
THIS AFTERNOON/EVENING.
..THOMPSON/GLEASON.. 04/08/2020
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