USA Weather — Severe Weather Division
This outlook is expired and is no longer valid.
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER EASTERN MISSOURI INTO SOUTHWESTERN ILLINOIS...
...SUMMARY...
A REGIONAL SEVERE WEATHER OUTBREAK ACROSS THE MIDWEST, OHIO VALLEY, AND THE MID-SOUTH ON MONDAY IS BECOMING INCREASINGLY APPARENT. ALL SIGNIFICANT SEVERE HAZARDS, INCLUDING STRONG TORNADOES ARE POSSIBLE.
...SYNOPSIS...
AN IMPRESSIVE AND RAPID TROUGH EJECTION WILL OCCUR ON MONDAY ACROSS THE CENTRAL PLAINS INTO THE MIDWEST. AN ASSOCIATED MID-LEVEL JET MAX IN EXCESS OF 70-80KT WILL OVERSPREAD AREAS TO THE SOUTH AND EAST OF THE SHORTWAVE. STRONG UPPER-LEVEL DIVERGENCE AHEAD OF THE TROUGH AXIS WILL SUPPORT RAPID SURFACE CYCLOGENESIS TO CONTINUE MONDAY, WITH THE 990S MB LOW INITIALLY OVER EASTERN NE/KS CONTINUING TO DEEPEN INTO THE 980S WHILE LIFTING NORTHEAST. AHEAD OF A TRAILING COLD FRONT, A VERY LARGE OPEN WARM SECTOR WITH RICH LOW-LEVEL MOISTURE AND STEEP LAPSE RATES WILL ALLOW FOR A SIZABLE AREA FOR SIGNIFICANT SEVERE WEATHER POTENTIAL – POTENTIALLY A REGIONAL SEVERE WEATHER OUTBREAK.
...DISCUSSION...
A FAIR AMOUNT OF UNCERTAINTY REMAINS WITH HOW ONGOING CONVECTION THAT BEGINS OVERNIGHT IN THE D2 PERIOD WILL EVOLVE DURING THE MORNING HOURS MONDAY, WITH SOLUTIONS VARYING FROM GRADUAL WEAKENING DURING THE MID TO LATE MORNING (HRRR, NAM) TO STRONG CONVECTION TRAINING EASTWARD ACROSS CENTRAL TO NORTHERN ILLINOIS THROUGH THE MID-AFTERNOON (ECMWF, MPAS). DEPENDING ON WHICH SCENARIO EVOLVES WILL HAVE SIGNIFICANT IMPLICATIONS FOR THE NORTHWARD EXTENT OF STRONG DESTABILIZATION SUPPORTIVE FOR THE SIGNIFICANT SEVERE WEATHER POTENTIAL.
REGARDLESS, A LARGE AREA OF UPPER 60S TO LOW 70S DEWPOINTS WILL EXTEND NORTHWARD INTO THE OHIO VALLEY AND MID-MISSISSIPPI VALLEY REGION MONDAY MORNING, WITH NORTHWARD MOISTURE TRANSPORT EXPECTED TO OCCUR IN THE WAKE OF MORNING CONVECTION. VERY STEEP LAPSE RATES EXCEEDING 8.0 C/KM ACROSS THE WARM SECTOR ALONG WITH ROBUST DIURNAL HEATING WILL SUPPORT MLCAPE RISING INTO THE 2500-4000 J/KG RANGE. THE GREATEST CONFIDENCE IN DESTABILIZATION IS TO THE SOUTH OF CENTRAL INDIANA/ILLINOIS AND NORTHERN MISSOURI, THOUGH AFOREMENTIONED STIPULATIONS COULD YIELD THIS INSTABILITY EXTENDING FURTHER NORTH INTO THE UPPER MIDWEST. AS THE JET STREAK IMPINGES ON THE REGION BY THE AFTERNOON HOURS, A RAPID INCREASE IN DEEP-LAYER SHEAR TO OVER 65KT AND RAPIDLY ENLARGING HODOGRAPHS WILL SUPPORT SCATTERED STORM DEVELOPMENT ACROSS THE OPEN WARM SECTOR TO QUICKLY INTENSIFY AND BECOME SUPERCELLULAR IN NATURE. LOW-LEVEL JET WINDS EXCEEDING 50KT EVEN IN THE MID-AFTERNOON WILL CONTRIBUTE TO 300-450 M2/S2 SRH, WITH MESOSCALE FEATURES LEFT OVER FROM MORNING STORMS CAUSING CORRIDORS OF HIGHER VALUES. THIS WILL BE SUPPORTIVE FOR THE POTENTIAL OF MULTIPLE STRONG AND PERHAPS LONG-TRACKED TORNADOES AND WIDESPREAD LARGE TO VERY LARGE HAIL. THE HIGHEST CONFIDENCE IN INTENSE/LONG-TRACK TORNADO POTENTIAL EXISTS ACROSS EASTERN MISSOURI INTO SOUTHWESTERN ILLINOIS, WHERE A MODERATE RISK HAS BEEN OUTLINED, THOUGH THIS COULD NECESSITATE EXPANSIONS IN LATER OUTLOOKS AS CONFIDENCE GROWS REGARDING EARLY STORMS.
WITH TIME, INCREASING CONVECTIVE COVERAGE SHOULD SUPPORT THE DEVELOPMENT OF MULTIPLE ORGANIZED CLUSTERS AND BOWING SEGMENTS WITH WIDESPREAD DAMAGING WINDS AND LINE-EMBEDDED TORNADOES LIKELY AS THEY QUICKLY SPREAD EASTWARD. EVENTUALLY CONSOLIDATION INTO A LARGE AND POWERFUL QLCS IS POSSIBLE LATE IN THE EVENING PRODUCING WIDESPREAD DAMAGING WINDS INTO THE OVERNIGHT HOURS. ADDITIONAL STORM DEVELOPMENT SHOULD SPREAD SOUTHWARD INTO THE MID-SOUTH AND THE TENNESSEE VALLEY OVERNIGHT, WITH SCATTERED SUPERCELLS DEVELOPING IN A RATHER UNSTABLE AND SHEARED AIRMASS DRIVEN BY A STRONG LOW-LEVEL JET REMAINING IN PLACE. THIS SHOULD ALSO SUPPORT AN ALL-HAZARDS (POTENTIALLY SIGNIFICANT) SEVERE THREAT THROUGH THE END OF THE PERIOD.