USA Weather — Severe Weather Division
This outlook is expired and is no longer valid.
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS EXTENDING ACROSS PORTIONS OF THE EASTERN PLAINS INTO THE MID MISSISSIPPI VALLEY AND PARTS OF THE MIDWEST...
...SUMMARY...
WIDESPREAD SEVERE THUNDERSTORMS ARE EXPECTED FRIDAY AFTERNOON AND EVENING ACROSS THE MISSISSIPPI VALLEY, SOUTHERN AND EASTERN PLAINS, THE MIDWEST, AND GREAT LAKES. SEVERAL INTENSE TORNADOES AND GIANT HAIL ARE EXPECTED WITH SUPERCELL ACTIVITY, WITH WIDESPREAD DAMAGING TO DESTRUCTIVE WINDS AND QLCS TORNADOES EVENTUALLY BECOMING THE PREDOMINANT HAZARD.
...SYNOPSIS...
A LARGE UPPER TROUGH IS NOTED TO SLOWLY BE DIGGING INTO THE PACIFIC NORTHWEST THIS MORNING. THE TROUGH WILL CONTINUE TO DIG INTO THE WESTERN US WHILE AMPLIFYING THROUGH FRIDAY MORNING, SUBSEQUENTLY EJECTING INTO THE PLAINS THROUGHOUT THE D2 PERIOD. ANOTHER TROUGH NEAR SOUTHERN CALIFORNIA WITHIN THE SUBTROPICAL JET EJECTS NORTHEASTWARD DURING THE PERIOD WHILE SLOWLY PHASING WITH THE NORTHERN TROUGH. AHEAD OF THESE TWO FEATURES, A BROAD EXPANSE OF STRONG SOUTHWESTERLY FLOW ALOFT OVERSPREADS MUCH OF THE CENTRAL CONUS, WITH 500MB JET MAXIMA IN EXCESS OF 70-80KT EXPECTED ACROSS THE PLAINS AND THE MISSISSIPPI VALLEY BY LATE FRIDAY AFTERNOON, THEN EXCEEDING 80KT BY FRIDAY EVENING OVER PORTIONS OF THE NORTHERN MS VALLEY AND MIDWEST. A LARGE SURFACE CYCLONE ALREADY EXISTING 12Z FRIDAY OVER THE NORTHERN PLAINS/UPPER MIDWEST WILL TRANSLATE EASTWARD ACROSS THE GREAT LAKES REGION WHILE GRADUALLY DEEPENING. A TRAILING COLD FRONT EXTENDS SOUTHWESTWARD INTO THE SOUTHERN PLAINS, WHERE SECONDARY LEE CYCLOGENESIS IS FORECAST TO OCCUR FRIDAY INTO FRIDAY AFTERNOON, WITH A DRYLINE EXTENDING SOUTH THROUGH WEST TEXAS. THE COLD FRONT WILL GRADUALLY SWEEP EASTWARD AND SURGE SOUTHWARD FRIDAY AND FRIDAY NIGHT. AN EXPANSIVE AND HIGHLY UNSTABLE WARM SECTOR AHEAD OF THE SYSTEM EXTENDING INTO THE GREAT LAKES WILL LIKELY PRODUCE A WIDESPREAD SIGNIFICANT SEVERE WEATHER EVENT.
...EASTERN PLAINS, MISSISSIPPI VALLEY, MIDWEST, AND GREAT LAKES...
AN EXPANSIVE WARM SECTOR WILL ALREADY EXTEND ACROSS MOST OF THE PLAINS AND MISSISSIPPI VALLEY INTO THE MIDWEST AND GREAT LAKES REGION 12Z FRIDAY, WITH CONTINUED WARM AIR AND MOISTURE ADVECTION OCCURRING AHEAD OF THE APPROACHING TROUGH, AIDED BY A MODERATE TO STRONG SOUTHERLY LOW-LEVEL JET. DEWPOINTS IN THE MID-60S TO LOW 70S ARE EXPECTED TO SPREAD AS FAR NORTH AS SOUTHERN WISCONSIN BY EARLY FRIDAY AFTERNOON. NOTABLY, VERY STEEP LAPSE RATES POTENTIALLY NEAR 9.0 C/KM WILL ADVECT INTO THE REGION WHILE ROBUST SURFACE HEATING IS ONGOING. THIS SHOULD RESULT IN STRONG TO EXTREME INSTABILITY WITH MLCAPE OF 3000-4000 J/KG ACROSS A CORRIDOR FROM SOUTHERN WISCONSIN INTO NORTHERN AND WESTERN MISSOURI AND EASTERN KANSAS, WITH LESS BUT STILL SUBSTANTIAL INSTABILITY FURTHER EAST ACROSS PARTS OF THE GREAT LAKES INTO THE OHIO VALLEY. REMNANT CAPPING/CINH ACROSS THE REGION THOUGH EARLY AFTERNOON WILL SUPPRESS CONVECTIVE DEVELOPMENT. AS HEATING AND SIGNIFICANT HEIGHT FALLS OCCUR, HOWEVER, THIS WILL GRADUALLY BE ERODED INTO THE AFTERNOON HOURS, WITH CONVECTIVE TEMPERATURES BEING BREECHED AROUND 19-21Z AND EXPLOSIVE CONVECTIVE DEVELOPMENT QUICKLY OCCURRING ALONG THE COLD FRONT/DRYLINE AND POTENTIALLY ALONG SUBTLE SURFACE CONVERGENCE ZONES WITHIN THE OPEN WARM SECTOR.
EVEN IN THE MID-AFTERNOON, VERY STRONG DEEP-LAYER SHEAR EXCEEDING 50KT WITH STRONG SOUTHERLY LOW-LEVEL WINDS WILL FAVOR ENLARGED, FISHHOOK- SHAPED HODOGRAPHS, WITH SRH EXCEEDING 300-500 M2/S2. INITIAL DEVELOPMENT WILL QUICKLY INTENSIFY INTO SUPERCELLS, WITH WIDESPREAD VERY LARGE TO GIANT HAIL LIKELY TO BEGIN RATHER QUICKLY. SEVERAL TORNADOES ARE ALSO LIKELY WITHIN THESE SUPERCELLS. A RATHER CONCERNING AND POTENTIALLY HIGH-END ENVIRONMENT WITHIN THE WARM SECTOR, ESPECIALLY ACROSS SOUTHERN WISCONSIN INTO NORTHWEST ILLINOIS AND EASTERN IOWA WHERE SUBSTANTIAL OVERLAP OF STRONG INSTABILITY AND INTENSE LOW-LEVEL SHEAR OCCURS. THIS IS WELL ILLUSTRATED BY A LARGE AREA OF STP VALUES >5 ACROSS THIS AREA ON VARIOUS MODEL OUTPUTS. VARIOUS CAMS SUGGEST AN ARCING BAND OF DISCRETE SUPERCELLS COULD DEVELOP DURING THE AFTERNOON WITHIN THIS AREA IMMEDIATELY AHEAD OF THE SURFACE LOW, POTENTIALLY PRECEDED BY A FEW ADDITIONAL DISCRETE SUPERCELLS. ANY MATURE SUPERCELL WITHIN THIS ENVIRONMENT WILL HAVE THE POTENTIAL TO PRODUCE INTENSE AND POTENTIALLY LONG TRACKED TORNADOES. THERE ARE SOME UNCERTAINTIES IN THE OVERALL STORM MODE DUE TO VERY STRONG FORCING QUICKLY MOVING INTO THIS REGION, WHICH COULD RESULT IN RATHER QUICK UPSCALE GROWTH AND A LIMITED DURATION OF DISCRETE SUPERCELLS. EVEN IF THIS OCCURS, HOWEVER, THERE WOULD STILL BE POTENTIAL FOR A FEW INTENSE TORNADOES WITHIN SUPERCELLS WITH SEVERAL TORNADOES LIKELY ALONG THE EVENTUAL MCS. MDT RISK-LEVEL TORNADO PROBABILITIES HAVE THEREFORE BEEN INTRODUCED ACROSS CENTRAL AND SOUTHERN WISCONSIN INTO EASTERN IOWA. FURTHER UPGRADES COULD BECOME NECESSARY IF A LONGER DURATION DISCRETE SUPERCELL MODE BECOMES APPARENT.
FURTHER SOUTH ACROSS THE MIDDLE MISSISSIPPI VALLEY INTO EAST KANSAS, INITIAL SUPERCELL ACTIVITY WILL LIKELY PRODUCE A THREAT FOR AT LEAST A FEW TORNADOES, WHICH COULD BE STRONG DUE TO SIMILAR INTENSITY OF SHEAR AND EXTREME INSTABILITY. RATHER QUICK UPSCALE GROWTH IS EXPECTED OVER THIS REGION DUE TO A SLIGHTLY LESS FAVORABLY ORIENTED NE TO SW INITIATING BOUNDARY COMPARED TO N TO S FURTHER NORTH, AND THE DEVELOPMENT OF A POWERFUL QLCS IS EXPECTED BY EARLY EVENING, SWEEPING EASTWARD ACROSS THE REGION. WITH THE MAGNITUDE OF INSTABILITY IN ADDITION TO A DRY EML, WIDESPREAD DAMAGING WINDS ARE EXPECTED ALONG THE LINE, WITH EMBEDDED BOWING SEGMENTS AND MESOVORTICIES PRODUCING A THREAT FOR DESTRUCTIVE GUSTS AND SEVERAL QLCS TORNADOES. SOME GUIDANCE HAS HINTED AT A CORRIDOR OF PARTICULARLY INTENSE DAMAGING WINDS (POTENTIALLY ABOVE 80-85MPH) ASSOCIATED WITH A WELL-DEFINED BOW ECHO DEVELOPING OVER NORTHERN MISSOURI INTO WESTERN ILLINOIS, AND TRENDS WILL BE MONITORED FOR HIGHER WIND PROBABILITIES AND/OR CIG LEVELS. THE QLCS WILL CONTINUE EASTWARD INTO THE EVENING AND OVERNIGHT HOURS ACROSS PARTS OF THE MISSISSIPPI VALLEY, MIDWEST AND GREAT LAKES, THOUGH WEAKENING WITH TIME/EASTWARD EXTENT DUE TO BOUNDARY LAYER STABILIZATION.
...SOUTHERN PLAINS...
A MORE CONDITIONAL THREAT FOR SEVERE WEATHER IS EXPECTED OVER PARTS OF THE SOUTHERN PLAINS (I.E. WEST OKLAHOMA INTO CENTRAL TEXAS) WITH WEAKER SYNOPTIC FORCING AND STRONG CINH. NONETHELESS, VERY STEEP LAPSE RATES OF 8.5-9.0 C/KM WITHIN A VERY HOT/MOIST AIRMASS WILL SUPPORT STRONG TO LOCALLY EXTREME DESTABILIZATION BY THE AFTERNOON HOURS. STRONG DEEP-LAYER SHEAR >50KT WITH ELONGATED, CURVING HODOGRAPHS SUPPORTING EFFECTIVE SRH >250-300 M2/S2. A FEW INTENSE SUPERCELLS SHOULD DEVELOP AT LEAST OVER WESTERN OKLAHOMA ALONG THE DRYLINE WHERE GREATEST CINH EROSION AND STRONGER CONVERGENCE OCCURS. THESE STORMS WILL BE ACCOMPANIED BY GIANT HAIL AND POTENTIAL FOR A COUPLE OF TORNADOES, WHICH COULD BE STRONG TO INTENSE GIVEN THE MAGNITUDE OF SHEAR. EVENTUALLY, UPSCALE GROWTH SHOULD OCCUR WITH THIS DEVELOPMENT INTO A QLCS, POTENTIALLY BEING THE SOUTHERN END OF A LARGE QLCS EXTENDING WELL TO THE NORTH. DAMAGING WINDS AND EMBEDDED TORNADOES WOULD BE A CONCERN AS IT SPREADS EASTWARD, WITH GRADUAL WEAKENING OVERNIGHT.
DEVELOPMENT FURTHER SOUTH IS QUITE UNCERTAIN AND WOULD BE ISOLATED AT BEST DURING THE LATE AFTERNOON AND EARLY EVENING. IF ANY SUPERCELL CAN DEVELOP, VERY LARGE TO GIANT HAIL AND A STRONG TORNADO WOULD BE POSSIBLE.