USA Weather — Severe Weather Division
This outlook is expired and is no longer valid.
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS EXTENDING FROM THE UPPER MIDWEST INTO THE MIDDLE MISSISSIPPI VALLEY AND CENTRAL PLAINS...
...SUMMARY...
A REGIONAL SEVERE WEATHER OUTBREAK IS EXPECTED THIS AFTERNOON AND EVENING FROM THE WESTERN GREAT LAKES AND PARTS OF THE MIDWEST THROUGH THE MISSISSIPPI VALLEY AND SOUTHERN PLAINS. INITIAL SUPERCELL ACTIVITY WILL PRODUCE POTENTIAL FOR SEVERAL TORNADOES, SOME STRONG AND LONG TRACKED, AS WELL AS VERY LARGE TO GIANT HAIL. WIDESPREAD DAMAGING TO DESTRUCTIVE WINDS AND SEVERAL LINE-EMBEDDED TORNADOES ARE EXPECTED AS GRADUAL ORGANIZATION INTO A POWERFUL SQUALL LINE OCCURS.
...SYNOPSIS...
EARLY MORNING WATER VAPOR IMAGERY SHOWS A LARGE UPPER TROUGH EXTENDING SOUTHWARD THROUGH THE ROCKIES, WITH A SOUTHERN STREAM SHORTWAVE AND THE SUBTROPICAL JET NOTED TO BE PHASING WITH THE BASE OF THE PARENT TROUGH OVER THE DESERT SOUTHWEST REGION. THESE TWO FEATURES WILL CONTINUE TO PHASE AS THEY TRANSLATE EASTWARD INTO THE GREAT PLAINS, WITH A STRONG 500MB JET WITH 70-90KT MAXIMA SPREADING ACROSS MUCH OF THE CENTRAL CONUS. SURFACE CYCLOGENESIS IS ONGOING OVER THE NORTHERN PLAINS WITH A COLD FRONT EXTENDING SOUTHWESTWARD INTO THE CENTRAL ROCKIES, WHILE A DRYLINE EXTENDS SOUTHWARD OVER THE HIGH PLAINS. THE SURFACE LOW AND ASSOCIATED COLD FRONT WILL TRANSLATE EASTWARD INTO THE GREAT LAKES REGION TODAY AND TONIGHT, WITH GRADUAL DEEPENING EXPECTED. A SECONDARY SURFACE LOW WILL ALSO DEVELOP TODAY NEAR THE INTERSECTION OF THE SOUTHEASTWARD-ADVANCING COLD FRONT AND THE DRYLINE.
RAPID MOISTURE TRANSPORT IS ALREADY OCCURRING DUE TO A 40-60KT LOW-LEVEL JET, AND 60S DEWPOINTS ALREADY EXTEND INTO NORTHWESTERN IOWA AND EASTERN NEBRASKA. STRONG MOISTURE ADVECTION CONTINUES THROUGHOUT THE MORNING AND INTO EARLY AFTERNOON, BY WHICH TIME A LARGE WARM SECTOR WITH UPPER 60S TO LOW 70 DEWPOINTS SHOULD EXTEND WELL NORTHWARD INTO CENTRAL WISCONSIN. VERY STEEP MID-LEVEL LAPSE RATES ALREADY NOTED ACROSS THE GREAT PLAINS INTO THE MISSISSIPPI VALLEY AND MIDWEST WILL CONTRIBUTE TO STRONG TO EXTREME INSTABILITY BY THIS AFTERNOON WHEN ROBUST DIURNAL HEATING WILL HAVE TAKEN PLACE. GIVEN THE IMPRESSIVE KINEMATICS AND LIFT OVERSPREADING THE UNSTABLE WARM SECTOR TODAY, WIDESPREAD SEVERE THUNDERSTORMS WITH A REGIONAL SEVERE WEATHER OUTBREAK CAN BE EXPECTED THIS AFTERNOON AND EVENING.
...UPPER MISSISSIPPI VALLEY AND MIDWEST/GREAT LAKES...
AS MENTIONED BEFORE, VERY MOIST DEWPOINTS INTO THE UPPER 60S WILL SPREAD AS FAR NORTH AS CENTRAL WISCONSIN THIS AFTERNOON AHEAD OF THE COLD FRONT AND ASSOCIATED SURFACE LOW, WHICH SHOULD TRACK EASTWARD OVER NORTHERN MINNESOTA INTO LAKE SUPERIOR LATE THIS AFTERNOON AND INTO THE EVENING. MODEL SOUNDINGS ACROSS THIS REGION INDICATE >8.0-8.5 C/KM MID-LEVEL LAPSE RATES ADVECTING INTO THE AREA WILL CONTRIBUTE TO MLCAPE EXCEEDING 3000-3500 J/KG DURING THE AFTERNOON HOURS, WITH SURFACE TEMPERATURES IN THE UPPER 70S TO MID-80S. CONVECTIVE DEVELOPMENT IS EXPECTED BY 17-19Z OVER EASTERN MINNESOTA INTO CENTRAL IOWA, SPREADING EAST INTO WISCONSIN AND NORTHERN ILLINOIS DURING THE AFTERNOON AND EARLY EVENING HOURS.
IMPRESSIVE FISHHOOK SHAPED HODOGRAPHS WITH EFFECTIVE SRH EXCEEDING 300-350 M2/S2 WILL FAVOR QUICK INTENSIFICATION INTO MULTIPLE DISCRETE SUPERCELLS WITHIN THE HIGHLY VOLATILE ENVIRONMENT. SEVERAL TORNADOES ARE EXPECTED, SOME STRONG (EF2-EF3+). A LONG TRACKED TORNADO WILL BE POSSIBLE IF A DISCRETE SUPERCELL CAN REMAIN WITHIN THE BROADER PORTION OF THE WARM SECTOR, WHICH BEGINS TO PINCH OFF WITH NORTHWARD EXTEND OVER NORTHERN WISCONSIN. CAMS CONTINUE TO STRUGGLE WITH THE CONVECTIVE EVOLUTION, WITH RECENT HRRR RUNS SUGGESTING STORMS REMAIN DISCRETE OR SEMI-DISCRETE FOR SEVERAL HOURS BEFORE GROWING UPSCALE, WHILE OTHERS SUCH AS MPAS AND WRF INDICATE VERY QUICK UPSCALE GROWTH INTO WITH FEW DISCRETE SUPERCELLS OUT AHEAD OF THE MATURING MCS. EITHER WAY, THIS ENVIRONMENT WILL BE SUPPORTIVE FOR THE HIGHER-END TORNADO POTENTIAL, WITH POTENTIAL STORM MODE ISSUES CASTING ENOUGH UNCERTAINTY PRECLUDING HIGHER UNCONDITIONAL TORNADO PROBABILITIES AT THIS TIME. ADDITIONALLY, WIDESPREAD LARGE TO VERY LARGE HAIL IS LIKELY WITHIN THE STRONGER UPDRAFT CORES.
ONCE UPSCALE GROWTH DOES OCCUR, A LARGE MCS WITH EMBEDDED BOWING SEGMENTS AND MESOVORTICIES WILL SWEEP EASTWARD ACROSS PARTS OF THE MIDWEST AND GREAT LAKES REGION DURING THE EVENING HOURS. NUMEROUS TO WIDESPREAD DAMAGING WIND GUSTS AND MULTIPLE EMBEDDED TORNADOES WILL BE LIKELY AT LEAST FOR A FEW HOURS BEFORE THE STORMS GRADUALLY OUTRUN BETTER INSTABILITY DURING THE LATE EVENING AND OVERNIGHT HOURS.
...SOUTHERN/CENTRAL PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY...
STRONG TO EXTREME DESTABILIZATION WILL OCCUR FURTHER SOUTH ACROSS PARTS OF THE GREAT PLAINS INTO THE MID-MISSISSIPPI VALLEY. LAPSE RATES >8.5 C/KM WITH TEMPERATURES IN THE 80S WILL SUPPORT MLCAPE OF 3000-4000 J/KG OVER A FAIRLY BROAD CORRIDOR ALONG AND AHEAD OF THE COLD FRONT AND DRYLINE. WHILE MODEL GUIDANCE HAS STRUGGLED PROJECTING THE SPEED THE COLD FRONT SURGES SOUTHEASTWARD, THE MORE NORTHEAST TO SOUTHWEST ORIENTATION ACROSS THE CENTRAL PLAINS WITH WEST-SOUTHWESTERLY SHEAR VECTORS WILL TEND TO FAVOR A MESSIER STORM MODE WITH RAPID UPSCALE GROWTH WHEN CONVECTIVE INITIATION OCCURS EARLY THIS AFTERNOON. REGARDLESS, WITH BULK SHEAR >50KT AND LENGTHY HODOGRAPHS, INITIAL ACTIVITY CONSISTING OF SUPERCELLS AND INTENSE CLUSTERS WILL POSE A THREAT FOR WIDESPREAD VERY LARGE TO GIANT HAIL ESPECIALLY OVER EAST KANSAS INTO WESTERN AND NORTHERN MISSOURI. A FEW TORNADOES ALSO APPEAR LIKELY, AND ANY INTENSE SUPERCELL THAT CAN FAVORABLY INTERACT WITH THE ENVIRONMENT AND/OR NEARBY STORMS COULD PRODUCE A STRONG TORNADO.
BY MID TO LATE AFTERNOON, A POWERFUL QLCS WILL ORGANIZE ALONG THE COLD FRONT AND BEGIN RAPIDLY PROPAGATING EASTWARD ACROSS THE CENTRAL PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY. WIDESPREAD DAMAGING WINDS OF 60-80MPH ARE EXPECTED, PARTICULARLY WITHIN EMBEDDED BOWING SEGMENTS AND MESOVORTICIES. VARIOUS CAMS HAVE SUGGESTED POTENTIAL FOR A SIGNIFICANT COLD POOL AND REAR INFLOW JET DEVELOPING WHEN THE STORMS ARE IN THE VICINITY OF CENTRAL OR NORTHWESTERN MISSOURI. THIS DEVELOPMENT WOULD BE ACCOMPANIED BY THE POTENTIAL FOR WIDESPREAD INTENSE SURFACE WIND GUSTS PERHAPS EXCEEDING 85MPH. SHOULD A DEFINED MESOSCALE CORRIDOR BE REALIZED, GREATER WIND PROBABILITY AND INTENSITY OUTLINES COULD BECOME REQUIRED. INTENSIFYING SHEAR BY EARLY EVENING AS THE LOW-LEVEL JET STRENGTHENS WILL ALSO SUPPORT HIGHER EFFECTIVE SRH, WITH SEVERAL EMBEDDED TORNADOES LIKELY. THE QLCS WILL PROGRESS QUICKLY INTO THE MIDWEST AND PERHAPS PARTS OF THE OHIO VALLEY DURING THE EVENING INTO THE OVERNIGHT HOURS. GRADUALLY WANING INSTABILITY WITH EASTWARD EXTENT SHOULD SUPPORT A SLOW WEAKENING TREND DURING THIS TIME, THOUGH ISOLATED TO SPORADIC SEVERE WINDS COULD PERSIST UNTIL FAIRLY LATE.
ANOTHER CORRIDOR FOR ISOLATED, INTENSE DEVELOPMENT COULD MATERIALIZE LATE THIS AFTERNOON AND EVENING OVER THE SOUTHERN PLAINS NEAR THE DRYLINE/COLD FRONT INTERSECTION AND POTENTIALLY FURTHER SOUTH INTO CENTRAL TEXAS. FAIRLY ROBUST CINH THROUGHOUT MUCH OF THE DAY SHOULD WORK TO LIMIT WIDESPREAD DEVELOPMENT AND ALLOW FOR MLCAPE EXCEEDING 3500-4000 J/KG WITHIN A HIGHLY SHEARED (>55-60KT) AIRMASS. IF ISOLATED DEVELOPMENT IS REALIZED, LENGTHY HODOGRAPHS WOULD FAVOR SPLITTING SUPERCELLS OR LINE SEGMENTS, WITH VERY LARGE HAIL AND DAMAGING WINDS THE PRIMARY CONCERN.