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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab SPC Page Main Text Page