SYNOPSIS

THE LARGE SCALE PATTERN OVER THE CONUS CONTINUES TO BE CHARACTERIZED BY AN EASTERN RIDGE/WESTERN TROUGH…WITH A SURFACE QUASI-STATIONARY FRONT EXTENDING FROM THE NORTHERN GREAT LAKES INTO THE CENTRAL PLAINS. AS OF WEDNESDAY MORNING…A SW TROUGH WAS RAPIDLY SHEARING OUT OVER ONTARIO…AS IT ENCOUNTERED THE STRONGLY CONFLUENT FLOW OVER EASTERN NORTH AMERICA.

GREAT LAKES/UPPER MISS VALLEY

THE AFTERNOON CONVECTIVE FORECAST IS SOMEWHAT COMPLICATED BY THE PRESENCE OF ONGOING WARM SECTOR CONVECTION FROM EXTREME EASTERN IA INTO EASTERN WI AND MI. OVERALL…THIS ACTIVITY HAS BEEN GRADUALLY TRENDING DOWNWARD IN TERMS OF COVERAGE/INTENSITY DURING THE PAST TWO HOURS. MEANWHILE…THERE IS A NARROW CORRIDOR BETWEEN THE FRONT AND THE BACK EDGE OF THIS CONVECTION THAT IS DESTABILIZING QUITE NICELY FROM SOUTH CENTRAL IA INTO NORTHERN WI (MLCAPE VALUES WERE ALREADY IN THE 2500-3000 J/KG RANGE IN THIS AREA AS OF 1600 UTC). lOW LEVEL SOUTHWEST FLOW IN THIS REGION SHOULD MAINTAIN SURFACE DEWPOINTS IN THE MID/UPPER 60S…WHILE AFTERNOON TEMPS SHOULD SOAR WELL INTO THE 90S. A CONSENSUS OF MODEL GUIDANCE SUGGESTS MLCAPE SHOULD EASILY EXCEED 3500 J/KG JUST AHEAD OF THE FRONT BY LATE AFTERNOON. THIS REGION IS ALONG THE SOUTHERN EDGE OF THE WESTERLIES…SO SHEAR PARAMETERS RANGE FROM FAIRLY STRONG ACROSS NORTHERN WI…TO RELATIVELY WEAK ACROSS SOUTHERN IA. THIS IS UNLIKELY TO CHANGE SIGNIFICANTLY THROUGHOUT THE DAY.

AS THE FRONT SLOWLY SAGS SOUTHEAST ACROSS THE REGION… SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON. LACK OF SIGNIFICANT LARGE-SCALE FORCING SHOULD LIMIT THE OVERALL COVERAGE. HOWEVER…CLUSTERING OF CONVECTION ALONG COLD POOLS COULD OCCUR…PARTICULARLY IN THE MORE WEAKLY SHEARED AIRMASS ACROSS EASTERN IA. ACROSS WI…STORMS MAY TEND TO BE MORE DISCRETE/SUPERCELLULAR IN NATURE. HOWEVER…WITH THE VEERED LOW-LEVEL FLOW…THE THREAT OF TORNADOES SEEMS TO BE LOW…UNLESS WINDS BACK LOCALLY IN THE VCNY OF LINGERING OUTFLOW/DIFF HEATING BOUNDARIES. OTHERWISE…THE MAIN THREATS WILL BE IN THE FORM OF LARGE HAIL…SOME OF WHICH COLD BE VERY LARGE…AND DAMAGING DOWNBURSTS IN ASSOCIATION WITH THE MORE ACTIVE MULTICELLULAR COLD POOLS.

NORTHEAST/NRN NEW ENGLAND

ALTHOUGH THE AIRMASS OVER THE NORTHEAST WILL BECOME QUITE UNSTABLE THIS AFTERNOON…THE PRESENCE OF THE UPPER RIDGE OVER THE EASTERN CONUS SUGGESTS THE LARGE SCALE PATTERN IS GENERALLY UNFAVORABLE FOR SIGNIFICANT CONVECTIVE DEVELOPMENT. THE SURFACE FRONT WILL ALSO REMAIN TOO FAR TO THE WEST OF THE REGION TO PROVIDE A FOCUS FOR CONVECTION THIS AFTERNOON. ALTHOUGH DIFF HEATING SHOULD RESULT IN INITIATION ACROSS THE HIGHER TERRAIN OF NORTHERN NY/NORTHERN NE THIS AFTERNOON…IT APPEARS COVERAGE IS LIKELY TO BE TOO ISOLATED TO WARRANT EWP OPERATIONS IN THIS REGION. (A HIGHER THREAT MAY EXIST IN THIS AREA AFTER 00Z…ESPECIALLY IF CONVECTION ORGANIZES ALONG THE FRONT ACROSS SOUTHEAST ONTARIO/SRN QUEBEC THIS AFTERNOON).

CENTRAL HIGH PLAINS

VERTICAL WIND SHEAR WILL LIKELY BE SUPPORTIVE OF A ROTATING STORM OR TWO BY EARLY EVENING…IF SUFFICIENT DESTABILATION CAN OCCUR IN THE WAKE OF DEPARTING SURFACE RIDGE OVER CENTRAL AND NORTHERN PLAINS.  AT THIS TIME…RETURN FLOW OF INCREASINGLY MOIST UPSLOPE FLOW SUGGESTS ONLY MODEST DESTABILIZATION TODAY AND EXPECT VERY ISOLATED STORM COVERAGE THROUGH 03Z. THUS…BELIEVE EWP OPERATIONS SHOULD BE FOCUSED FARTHER EAST OVER GREAT LAKES/UPPER MISSISSIPPI VALLEY REGION.