USA Weather — Severe Weather Division
This outlook is expired and is no longer valid.
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE WESTERN GREAT LAKES...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE MID-ATLANTIC...
...SUMMARY...
SCATTERED TO NUMEROUS SEVERE THUNDERSTORMS ARE EXPECTED ACROSS THE UPPER MISSISSIPPI VALLEY, GREAT LAKES, PORTIONS OF THE OHIO VALLEY, AND INTO THE MID-ATLANTIC THURSDAY AND THURSDAY NIGHT. A FEW STRONG TORNADOES, VERY LARGE HAIL, AND SIGNIFICANT SEVERE WIND GUSTS ARE ALL POSSIBLE.
...SYNOPSIS...
A NEGATIVELY TILTED UPPER-LEVEL TROUGH INITIALLY OVER THE CENTRAL GREAT PLAINS IS EXPECTED TO EJECT NORTHEASTWARD INTO THE UPPER MISSISSIPPI VALLEY AND GREAT LAKES ON THURSDAY, CLOSING OFF INTO AN UPPER LEVEL LOW DURING THE PERIOD. STRONG SOUTHWESTERLY FLOW WILL SPREAD AHEAD OF THE TROUGH AXIS DURING THE PERIOD. A MID-LEVEL RIDGE OVER THE GULF OF AMERICA EXTENDING INTO THE SOUTHEAST WILL RESULT IN NORTHWESTERLY FLOW ROUNDING THE TOP OF THE RIDGE EXTENDING INTO THE MID-ATLANTIC. AT THE SURFACE, A DEEPENING CYCLONE OVER THE UPPER MISSISSIPPI VALLEY AT 12Z THURSDAY WILL SLOWLY DRIFT NORTHWARD, WITH SIGNIFICANT HEIGHT FALLS AND UPPER LEVEL DIVERGENCE RESULTING IN CONSIDERABLE DEEPENING INTO THE LOWER 980S MILLIBAR RANGE BY THURSDAY AFTERNOON. A DRYLINE/PACIFIC COLD FRONT EXTENDING SOUTHWARD THROUGH THE EASTERN GREAT PLAINS WILL GRADUALLY ADVANCE EASTWARD ACROSS THE WESTERN GREAT LAKES AND OHIO VALLEY DURING THE PERIOD, WHILE BECOMING STALLED/STRETCHED OUT SOUTHWEST OF THIS REGION ACROSS THE OZARKS INTO THE SOUTHERN PLAINS.
...UPPER MISSISSIPPI VALLEY/WESTERN GREAT LAKES...
A CORRIDOR OF SUBSTANTIAL LOW-LEVEL MOISTURE AHEAD OF THE ADVANCING COLD FRONT IS EXPECTED TO ADVANCE EASTWARD ACROSS THE UPPER MISSISSIPPI VALLEY AND WESTERN GREAT LAKES THURSDAY INTO THURSDAY EVENING, WITH DEWPOINTS IN THE MID TO UPPER 60S AND POSSIBLY LOW 70S EXPECTED. SUBSTANTIAL SURFACE HEATING WITH TEMPERATURES REACHING THE 80S AND LOW 90S ACROSS MUCH OF THE WARM SECTOR UNDERNEATH VERY STEEP MID-LEVEL LAPSE RATES IN EXCESS OF 8.0-9.0 C/KM WILL FOSTER STRONG DESTABILIZATION BY THURSDAY AFTERNOON. A PLUME OF 3000-4000 J/KG MLCAPE WILL PRECEDE THE COLD FRONT, SPREADING EASTWARD WITH TIME.
AS LOW-LEVEL CONVERGENCE INCREASES ALONG THE FRONT IN TANDEM WITH INCREASING HEIGHT FALLS, EXPLOSIVE CONVECTIVE DEVELOPMENT APPEARS PROBABLE ALONG THE COLD FRONT BY EARLY THURSDAY AFTERNOON, EXTENDING FROM EAST CENTRAL MINNESOTA INTO WESTERN WISCONSIN. THIS CONVECTION WILL QUICKLY DEVELOP INTO AN ARCING BAND OF SUPERCELLS SPREADING EAST NORTHEASTWARD. LONG, CURVING HODOGRAPHS AND INTENSE DEEP-LAYER SHEAR WILL FAVOR A THREAT FOR VERY LARGE HAIL OF 2 TO 3 INCHES IN DIAMETER. VERY STEEP LOW-LEVEL LAPSE RATES AND A WELL-MIXED BOUNDARY LAYER WILL ALSO SUPPORT POTENTIAL FOR 60-80MPH CONVECTIVE WIND GUSTS. A FEW TORNADOES ARE ALSO LIKELY.
THE NORTHERN END OF THE CONVECTIVE BAND WILL EVENTUALLY BECOME LINEAR, WITH EMBEDDED BOWING SEGMENTS FAVORING SWATHS OF SIGNIFICANT WIND DAMAGE AND EMBEDDED TORNADOES. FURTHER SOUTH ACROSS SOUTHERN WISCONSIN/MICHIGAN AND NORTHERN PARTS OF ADJACENT STATES, RESIDUAL CAPPING AND SLIGHTLY WEAKER FORCING WILL CONTINUE TO SUPPORT SUPERCELLS SPREADING EASTWARD. INCREASING LOW-LEVEL JET WINDS BY THURSDAY EVENING WILL SUPPORT AN INCREASE IN LOW-LEVEL HELICITY TO OVER 250-300 M2/S2, SUPPORTING AN INCREASING THREAT FOR STRONG TORNADOES, AS WELL AS CONTINUED VERY LARGE HAIL POTENTIAL.
...MIDWEST/OHIO VALLEY...
MORE SUBSTANTIAL LOW-LEVEL MOISTURE WITH LOW TO MID 70S DEWPOINTS ARE EXPECTED ACROSS THE MIDWEST AND OHIO VALLEY, WITH MLCAPE OVER 3500-4500 J/KG DEVELOPING BY THURSDAY AFTERNOON AS A RESULT. WEAKER FORCING FOR ASCENT AND A RESIDUAL LOW-LEVEL CAP MAY HINDER CONVECTIVE DEVELOPMENT ACROSS THIS AREA. A CONDITIONAL THREAT FOR SIGNIFICANT SEVERE DOES EXIST ACROSS THIS AREA DURING THE AFTERNOON AND EVENING HOURS, HOWEVER, WITH LONG HODOGRAPHS AND 200-300 M2/S2 SRH FAVORING ANY CONVECTION THAT DEVELOPS TO QUICKLY BECOME SUPERCELLS, WITH VERY LARGE TO GIANT HAIL AND A STRONG TORNADO POTENTIAL. CONFIDENCE IS LOW IN SUBSTANTIAL CONVECTIVE DEVELOPMENT, HOWEVER.
...MID-ATLANTIC...
A MODERATE NORTHWESTERLY FLOW ACROSS THE MID-ATLANTIC REGION ESTABLISHED OVER THE REGION WILL CONTINUE TO SUPPORT A SHEARED ENVIRONMENT. AS A RESULT OF RICH LOW-LEVEL MOISTURE AND SUBSTANTIAL SURFACE HEATING, DEVELOPMENT OF 2500-3500 J/KG MLCAPE BY THE AFTERNOON HOURS IS EXPECTED, WITH A WELL-MIXED BOUNDARY LAYER. A SUBTLE FRONTAL BOUNDARY DRAPED OVER THE REGION WILL FOSTER DEVELOPMENT OF SCATTERED CONVECTION INITIALLY OVER WEST VIRGINIA, SPREADING SOUTHEASTWARD ACROSS CENTRAL VIRGINIA AND INTO NORTH-CENTRAL NORTH CAROLINA. LONG HODOGRAPHS WILL SUPPORT SUPERCELLS AND MULTICELL CLUSTERS, WITH SEVERE WIND GUSTS AND LARGE HAIL POSSIBLE WITH MORE INTENSE STORMS. GREATEST POTENTIAL EXISTS WITHIN THE AFOREMENTIONED CORRIDOR WHERE GREATER CONVECTIVE COVERAGE IS EXPECTED.