USA Weather — Severe Weather Division
This outlook is expired and is no longer valid.
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL INTO NORTHERN ILLINOIS AND INDIANA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ALONG THE NORTHWESTERN GULF COAST...
...SUMMARY...
A SEVERE WEATHER OUTBREAK IS POSSIBLE WEDNESDAY AFTERNOON INTO WEDNESDAY NIGHT ACROSS PARTS OF THE MIDWEST INTO MUCH OF THE OHIO VALLEY. SEVERAL INTENSE TORNADOES, WIDESPREAD DAMAGING WINDS, AND VERY LARGE HAIL ARE ALL EXPECTED. A FEW TORNADOES ARE ALSO POSSIBLE ACROSS PARTS OF THE NORTHWESTERN GULF COAST.
...MIDWEST/OHIO VALLEY...
A STRONG SHORTWAVE TROUGH INITIALLY OVER THE NORTHERN WILL RAPIDLY TRANSLATE EAST-SOUTHEAST INTO THE GREAT LAKES AND OHIO VALLEY REGION BY WEDNESDAY EVENING. AN ASSOCIATED 500MB JET STREAK OF >80-90 KT (WHICH UNUSUALLY INTENSE FOR THIS TIME OF YEAR) WILL MOVE INTO THE MIDWEST, OHIO VALLEY, AND GREAT LAKES AS A RESULT, LIKELY WITH 500MB JET WINDS INTENSIFYING TO OVER 100KT WITH TIME. AS THE JET STREAK RAPIDLY SHIFTS EASTWARD, AN IMPRESSIVE 50-70+KT SOUTHERLY LOW-LEVEL WILL OVERSPREAD THE UPPER MIDWEST AND OHIO VALLEY. A SUB 990MB CYCLONE AHEAD OF THE SHORTWAVE WILL QUICKLY MOVE EAST-NORTHEAST WEDNESDAY INTO THE GREAT LAKES BY WEDNESDAY NIGHT, GRADUALLY INTENSIFYING INTO THE MID-980S MILLIBAR RANGE. A WARM FRONT DRAPED FROM A TRIPLE POINT INTO THE MIDDLE APPALACHIANS INITIALLY WILL RAPIDLY SURGE NORTHWARD WITH THE INTENSIFYING LOW-LEVEL JET, RESULTING IN A SURGE OF UPPER 60S TO MID 70S DEWPOINTS SPREADING ACROSS THE OHIO VALLEY BY THE AFTERNOON HOURS.
A LARGE AND LIKELY ELEVATED STORM CLUSTER WITH STRATIFORM RAIN EXTENDING NORTHWARD WILL INITIALLY BE LOCATED OVER IOWA DURING THE START OF THE PERIOD, SPREADING EASTWARD DURING THE DAY. THE EXACT TRACK OF THIS CLUSTER IS SOMEWHAT UNCERTAIN AND THIS WILL STRONGLY INFLUENCE THE NORTHWARD PROPAGATION OF THE WARM FRONT AND THEREFORE EXTENT OF ROBUST SURFACE-BASED INSTABILITY. NOTABLY, A FEW STRONGER UPDRAFTS WITHIN THIS CLUSTER COULD PRODUCE A THREAT FOR LARGE HAIL AS FAIRLY ROBUST ELEVATED MUCAPE AND VERY STRONG DEEP-LAYER SHEAR ARE OVERLAPPED. IN THE WAKE OF THESE STORMS AND TO THE SOUTH OF THE WARM FRONT, RAPID LOW-LEVEL MASS RESPONSE WITH THE NORTHWARD SURGE OF HIGH SURFACE DEWPOINTS WILL BE ACCOMPANIED BY A PLUME OF STEEP MID-LEVEL LAPSE RATES IN THE 7.5 TO 8.5 C/KM RANGE. WITH SURFACE TEMPERATURES LIKELY HEATING INTO THE 80S DURING THE AFTERNOON, A PLUME OF FAIRLY STRONG INSTABILITY SHOULD DEVELOP WITH WIDESPREAD MLCAPE OF 2500-4000 J/KG EXPECTED TO EXTEND ACROSS THE MIDWEST AND INTO PARTS OF THE OHIO VALLEY BY MID AFTERNOON, WITH NORTHWARD AND EASTWARD EXTENT OF THESE VALUES DEPENDENT ON THE WARM FRONT.
WITH THE RAPID APPROACH OF THE MID-LEVEL JET STREAK DURING THE AFTERNOON, POSSIBLY WITH A TRANSLATION SPEED OF 35-45KT, RAPID HEIGHT FALLS AND CONFLUENCE BANDS OVER THE WARM SECTOR, WITH INTENSIFYING CONVERGENCE ALONG A TRAILING SURFACE COLD, SHOULD SUPPORT CONVECTIVE INITIATION DURING THE AFTERNOON HOURS. THE GREATEST COVERAGE SHOULD BE ALONG THE COLD FRONT, THOUGH SCATTERED WARM SECTOR DEVELOPMENT IS EXPECTED AS WELL ALONG THE CONFLUENCE BANDS AND ANY DIFFERENTIAL HEATING ZONES. VERY STRONG SHEAR WILL RESULT IN UPPER-ECHELON HODOGRAPHS BECOMING INCREASINGLY ENLARGED AS THE LOW-LEVEL JET AXIS OF 50-70KT MOVES OVERHEAD. THE RESULT WILL BE SCATTERED INTENSE SUPERCELLS MOVING NORTHEAST ACROSS THE WARM SECTOR, WITH HIGH-END, EFFECTIVE SRH OVER 350-500 M2/S2 SUPPORTING A RATHER CONCERNING AND POTENTIALLY HIGH-END TORNADO THREAT, WITH MULTIPLE INTENSE TORNADOES LIKELY, ESPECIALLY ACROSS CENTRAL TO NORTHERN ILLINOIS AND INDIANA WHERE THE BEST INSTABILITY/SHEAR OVERLAP APPEARS TO BE. GIVEN FAST STORM MOTIONS, THE SIZE OF THE WARM SECTOR, AND THE HIGH-END PARAMETER SPACE, THERE MAY BE A CORRIDOR FOR POTENTIAL OF MULTIPLE INTENSE TO VIOLENT, LONG-TRACKED TORNADOES THAT OCCURS DURING THE AFTERNOON AND EVENING HOURS. FOR NOW, 15% CIG2 OUTLINES ARE MADE WITH THIS OUTLOOK GIVEN THE UNCERTAINTIES THAT REMAIN WITH THE EXTENT AND LOCATION OF THE GREATEST THREAT, THOUGH IT IS QUITE POSSIBLE THAT HIGHER PROBABILITIES/CIG LEVELS AND THEREFORE A CATEGORICAL UPGRADE IS MADE WHEN THESE UNCERTAINTIES ARE SORTED OUT.
IN ADDITION, A THREAT FOR SCATTERED VERY LARGE HAIL AND NUMEROUS TO WIDESPREAD DAMAGING WINDS, SOME IN EXCESS OF 75-80MPH, SHOULD EVOLVE WITH MANY OF THE STORMS TOMORROW AFTERNOON AND EVENING GIVEN THE INTENSITY OF THE ENVIRONMENT. DURING THE EVENING HOURS, STORMS COULD BEGIN TO ORGANIZE ALONG THE COLD FRONT INTO A BROKEN LINE OF SEMI-DISCRETE SUPERCELLS AND BOWING SEGMENTS, WHICH WILL SUPPORT A CONTINUED THREAT FOR A FEW STRONG TORNADOES AND WIDESPREAD DAMAGING WINDS AS IT RAPIDLY SURGES EAST INTO THE LATE EVENING AND OVERNIGHT HOURS.
...GULF COAST...
A TROPICAL DISTURBANCE DUBBED 90L WILL BE LOCATED OVER THE NORTHWEST GULF TOMORROW, POSSIBLY AS A TROPICAL CYCLONE. REGARDLESS OF CLASSIFICATION, A LARGE PLUME OF DEEP TROPICAL MOISTURE WILL SURGE NORTHWARD ON THE EAST SIDE OF THE LOW. INCREASING LOW-LEVEL WIND SHEAR WILL BE NOTED THROUGHOUT THE PERIOD AS A LOW-LEVEL JET DEVELOPS IN ADDITION TO 150-250 M2/S2 SRH GIVEN THE CLOCKWISE TURNING OF WINDS WITH HEIGHT. DESPITE WEAK LAPSE RATES, FAVORABLY STRONG INSTABILITY DUE TO THE DEEP TROPICAL MOISTURE, WITH HIGH THETA-E MOVING INLAND DURING THE PERIOD, SHOULD SUPPORT SCATTERED LOW-TOPPED SUPERCELLS AND AS A RESULT THE THREAT FOR A COUPLE TORNADOES AND PERHAPS LOCALIZED STRONG TO MARGINALLY SEVERE GUSTS SHOULD EVOLVE. THE EXTENT AND LOCATION OF THE GREATEST TORNADO THREAT WILL DEPEND ON THE TRACK AND STRENGTH OF THE LOW, THOUGH THE ENVIRONMENT SHOULD BE FAVORABLE ENOUGH TO WARRANT 2 AND 5% TORNADO PROBABILITIES AT THIS TIME.