844
ACUS01 KWNS 122002
SWODY1
SPC AC 122000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT WED AUG 12 2026
VALID 122000Z - 131200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE NORTHERN AND CENTRAL PLAINS AND LOWER OHIO VALLEY...
..SUMMARY
SCATTERED SEVERE THUNDERSTORMS WITH OCCASIONAL WIND DAMAGE REMAIN
LIKELY THIS AFTERNOON/EVENING FROM ILLINOIS/INDIANA INTO KENTUCKY.
INITIAL SUPERCELLS WITH VERY LARGE HAIL ACROSS THE CENTRAL/NORTHERN
HIGH PLAINS ARE EXPECTED TO EVOLVE INTO A CLUSTER OR TWO OVERNIGHT
WHILE SPREADING EASTWARD ACROSS NEBRASKA/SOUTH DAKOTA WITH THE
POTENTIAL FOR SEVERE GUSTS.
..20Z UPDATE OH VALLEY
SEVERAL CLUSTERS OF STRONG TO SEVERE STORMS REMAIN ONGOING IN
PROXIMITY TO THE OUTFLOW FROM THE PRIOR COMPLEX THIS MORNING.
EXPECTATIONS ARE FOR ADDITIONAL STORM DEVELOPMENT TO OCCUR ALONG THE
SOUTHERN PORTIONS OF THE OUTFLOW ACROSS SOUTHERN IN/IL AND
WESTERN/NORTHERN KY WHERE THE AIR MASS REMAINS QUITE WARM AND
UNSTABLE (MLCAPE 300-4000 J/KG). DEEP-LAYER SHEAR OF 25-35 KT WOULD
SUPPORT A MIXED MODE OF CLUSTERS AND SHORT LINE SEGMENTS, WITH
SEVERE GUSTS (SOME 70-75 MPH), ISOLATED HAIL AND A TORNADO OR TWO
POSSIBLE INTO THIS EVENING. HAVE TRIMMED PROBABILITIES BEHIND THE
CURRENT STORMS/OUTFLOW AND ADJUSTED CIG1 WIND PROBABILITIES FARTHER
SOUTHWEST.
..WY/SD/NE
INITIAL SUPERCELLS HAVE DEVELOPED AND ARE MATURING WITHIN A BROAD
POST-FRONTAL UPSLOPE FLOW REGIME ACROSS EASTERN WY/MT, WESTERN SD
AND NORTHWEST NE. THESE STORMS ARE EXPECTED TO REMAIN MOSTLY
SUPERCELLULAR AND SHOULD CONTINUE TO POSE A THREAT FOR LARGE TO VERY
LARGE HAIL (2-3 INCH), SEVERE WIND GUSTS AND POTENTIALLY A TORNADO
OR TWO INTO THIS EVENING AS THEY TRACK EASTWARD ALONG A DIFFUSE
FRONTAL BOUNDARY. ADDITIONAL, LIKELY HIGHER-BASED STORMS SHOULD
DEVELOP ACROSS NORTHEAST CO AND WESTERN NE BEFORE SPREADING
NORTHEASTWARD WITH A RISK FOR SEVERE GUSTS AND SOME HAIL.
EVENTUALLY, UPSCALE GROWTH INTO ONE OR MORE CLUSTERS/BOWING SEGMENTS
APPEARS LIKELY AS A 40-50 KT LOW-LEVEL JET AND STRONG LOW-LEVEL WARM
ADVECTION IS FORECAST TO DEVELOP ACROSS THE CENTRAL/NORTHERN PLAINS.
THIS WOULD SUPPORT A RISK FOR SEVERE GUSTS OF 65-80 MPH ACROSS PARTS
OF CENTRAL AND EASTERN NE/SD, LIKELY REACHING WESTERN IA BY EARLY
THURSDAY MORNING. 2% TORNADO PROBABILITIES HAVE BEEN ADDED TO
WESTERN SD AND EASTERN WY WHERE THE SUPERCELLULAR MODE COULD SUPPORT
SOME TORNADO RISK.
..LYONS.. 08/12/2026
PREV DISCUSSION
/ISSUED 1130 AM CDT WED AUG 12 2026/
..OH VALLEY AREA THROUGH THIS EVENING
AN MCS IS ONGOING ACROSS NORTHERN IL WITH THE PRIMARY COLD POOL
SURGE AND BOWING SEGMENT PROGRESSING FROM NORTHEAST IL INTO
NORTHWEST IN. ELEVATED CONVECTION IS ONGOING IN THE ZONE OF WARM
ADVECTION ATOP THE COLD POOL IN IN. THIS ELEVATED CONVECTION WILL
POSE A THREAT FOR ISOLATED LARGE HAIL INTO THIS AFTERNOON, WHILE A
FEED OF STEEPER MIDLEVEL LAPSE RATES AND LOW-LEVEL MOISTURE FROM THE
WEST WILL HELP MAINTAIN THE IL/IN MCS INTO THIS AFTERNOON WITH A
CONTINUED THREAT FOR OCCASIONAL WIND DAMAGE WITH GUSTS OF 60-75 MPH.
THE EASTERN EXTENT OF THE SEVERE THREAT INTO OH IS UNCERTAIN GIVEN
THE ONGOING/ELEVATED CONVECTION AND LIMITED RECOVERY TIME. THUS,
THE EASTWARD EXTENT OF ANY WIND THREAT ASSOCIATED WITH THE ONGOING
IL/IN MCS IS LIKEWISE UNCERTAIN. ADDITIONAL THUNDERSTORM
DEVELOPMENT IS POSSIBLE THIS AFTERNOON ALONG THE TRAILING OUTFLOW
FROM CENTRAL IL INTO SOUTHERN IN AND KY, WHERE OCCASIONAL WIND
DAMAGE WILL BE POSSIBLE INTO THIS EVENING.
..NORTHERN PLAINS THIS AFTERNOON THROUGH TONIGHT
A SUBTLE MIDLEVEL SPEED MAX OVER SOUTHWEST WY WILL PROGRESS EASTWARD
AROUND THE NORTHWEST PERIPHERY OF THE SOUTHERN PLAINS RIDGE. WEAK
ASCENT PRECEDING THIS WAVE, IN COMBINATION WITH SURFACE HEATING IN
CLOUD BREAKS AND LOW-LEVEL UPSLOPE FLOW WITH BOUNDARY-LAYER
DEWPOINTS IN THE 60S, WILL SUPPORT SCATTERED AFTERNOON/EVENING
THUNDERSTORM DEVELOPMENT FROM NORTHEAST CO INTO WESTERN SD.
LINGERING STEEP MIDLEVEL LAPSE RATES ON THE FRINGE OF THE MONSOONAL
MOISTURE PLUME IN WY AND EFFECTIVE BULK SHEAR NEAR OR ABOVE 40 KT
(WITH LONG HODOGRAPHS ALOFT) WILL FAVOR SUPERCELLS INITIALLY WITH
THE POTENTIAL FOR VERY LARGE HAIL (2-3 INCHES IN DIAMETER). THERE
WILL LIKELY BE SOME UPSCALE GROWTH INTO A CLUSTER OR TWO THIS
EVENING INTO TONIGHT ON THE NOSE OF A 30-40 KT LOW-LEVEL JET ACROSS
NE/SD, WITH A TRANSITION TO SEVERE OUTFLOW GUSTS OF 65-80 MPH AS THE
MAIN THREAT. THE STORM CLUSTER(S) WILL LIKELY REACH WESTERN IA
EARLY THURSDAY MORNING.
..LOWER MI INTO WESTERN NY/PA THROUGH LATE EVENING
SUBTLE SPEED MAXIMA WILL MOVE EAST-SOUTHEASTWARD FROM LOWER MI TO
NY/PA THROUGH THIS EVENING. MIDLEVEL LAPSE RATES OF 6-7 C/KM AND
BOUNDARY-LAYER DEWPOINTS IN THE MID 60S WILL SUPPORT MLCAPE NEAR OR
ABOVE 1000 J/KG, IN AN ENVIRONMENT WITH SUFFICIENT DEEP-LAYER
SHEAR/HODOGRAPH LENGTH FOR STORMS WITH SUPERCELL STRUCTURES.
ISOLATED LARGE HAIL AND WIND DAMAGE WILL BE THE MAIN THREATS, THOUGH
A MORE DISCRETE MODE WOULD BE LESS FAVORABLE FOR WIND DAMAGE, AND
STORM COVERAGE COULD REMAIN SOMEWHAT ISOLATED. THUS, WILL MAINTAIN
A MRGL RISK, THOUGH THERE WAS SOME CONSIDERATION FOR AN UPGRADE TO
SLGT ACROSS WESTERN NY AND VICINITY.
..SOUTH GA/NORTH FL THIS AFTERNOON
SCATTERED THUNDERSTORM DEVELOPMENT APPEARS PROBABLE FROM SOUTH GA
INTO NORTH FL THIS AFTERNOON ALONG A SUBTLE CONFLUENCE ZONE WITH
LARGE BUOYANCY IMMEDIATELY SOUTHWEST OF A REMNANT MCV OVER SOUTHEAST
GA. A FEW MULTICELL CLUSTERS WILL BE CAPABLE OF PRODUCING ISOLATED
STRONG OUTFLOW GUSTS/WIND DAMAGE WITH DOWNBURSTS.
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