SPC AC 301949
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0249 PM CDT SAT MAY 30 2009
VALID 302000Z - 311200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE MID-MS
VALLEY AND OH VALLEY...
THE MAIN CHANGE WAS TO ADJUST THE SLIGHT RISK SLIGHTLY FURTHER NORTH
INTO CNTRL IL. THIS AREA IS LOCATED ALONG THE NERN EDGE OF MODERATE
INSTABILITY WHERE VERTICAL SHEAR IS FAVORABLE FOR A SEVERE THREAT.
IF AN ISOLATED STORM OR TWO CAN INITIATE IN NW IL AND MOVE SEWD
ALONG THE GRADIENT...THEN LARGE HAIL AND ISOLATED WIND DAMAGE WOULD
BE POSSIBLE...REF MCD 899. ANOTHER CHANGE WAS TO DOWNGRADE THE
SLIGHT IN LOWER MI TO A SEE TEXT. INSTABILITY REMAINS VERY WEAK AND
THE CONVECTION IN ERN LOWER MI SHOULD MOVE EWD INTO SW ONTARIO THIS
AFTERNOON...REF MCD 898.
OTHERWISE...NO CHANGES FROM THE 1630Z OUTLOOK.
..BROYLES.. 05/30/2009
.PREV DISCUSSION... /ISSUED 1122 AM CDT SAT MAY 30 2009/
...SYNOPSIS...
AN INTENSE LATE SPRING COLD UPPER LOW MOVES SEWD ACROSS ONTARIO
BRINGING A STRONG POLAR JET THRU GREAT LAKES INTO NERN STATES THIS
FORECAST PERIOD. BROAD UPPER RIDGE PERSISTS WRN U.S. WITH WEAK UPPER
LOW INTERIOR SRN CA FORECASTED TO DRIFT SLOWLY ENEWD INTO NRN AZ
TONIGHT.
PRIMARY FRONTAL BAND HAS PUSHED ANY SOURCE OF RICH LOW LEVEL
MOISTURE OFFSHORE OF ATLANTIC COAST AND GULF COAST WITH ONLY S TX
AND FL PENINSULA REMAINING SEASONABLY MOIST.
SECONDARY FRONTAL ZONE AHEAD OF ONTARIO VORTEX WILL SWEEP EWD ACROSS
MI BY LATE AFTERNOON AND INTO NEW ENGLAND OVERNIGHT. FRONT ALSO
TRAILS SWWD FROM CENTRAL IA TO NWRN KS/NERN CO THIS AM AND BY
EVENING WILL EXTEND FROM CENTRAL IL THEN WWD...LIKELY STALLING
ACROSS KS INTO ERN CO.
...MID MS AND OH VALLEYS...
CONVECTIVE CLOUDS NOW ACROSS THIS AREA WILL THIN ALLOWING STRONG
HEATING AHEAD OF APPROACHING COLD FRONT THIS AFTERNOON. IN ADDITION
AN EML WITH LAPSE RATES AROUND 8C/KM IS SPREADING EWD FROM CENTRAL
PLAINS ON A 30-40KT WLY LLJ ACROSS LWR MO VALLEY WHICH WILL ENHANCE
DESTABILIZATION ACROSS MID MS VALLEY WHERE PWS AOA 1 INCH HAVE
POOLED. BY MID AFTERNOON MLCAPES GIVEN SUFFICIENT SURFACE HEATING
COULD CLIMB TO AOA 1500 J/KG MID MS VALLEY. WITH 40-50KT OF DEEP
LAYER SHEAR...THE THERMODYNAMICS WOULD SUPPORT A FEW SEVERE
THUNDERSTORMS DEVELOPING ALONG/AHEAD OF COLD FRONT MID MS VALLEY
THEN SPREADING EWD DURING THE EVENING INTO OH VALLEY. THERE ALSO IS
A THREAT OF SUPERCELLS WHICH WOULD ENHANCE THE WIND/HAIL POTENTIAL
AS WELL AS ISOLATED TORNADOES UNTIL LATE EVENING EWD INTO CENTRAL
KY/SRN IN. THIS SCENARIO IS CONTINGENT ON SUFFICIENT CLEARING OF
MORNING CLOUDINESS TO ALLOW THE SURFACE HEATING THAT WOULD BE
NEEDED.
...LWR MI...
STEEP LAPSE RATES AND COLD AIR ALOFT WILL LEAD TO DEVELOPMENT OF
MLCAPES AOA 500 J/KG BY EARLY THIS AFTERNOON ACROSS LOWER MI AS GOOD
SURFACE HEATING IS CURRENTLY OCCURRING. LOW TOPPED THUNDERSTORMS
WILL DEVELOP EWD ACROSS LWR MI ALONG/AHEAD OF COLD FRONT THIS
AFTERNOON AND GIVEN THE 40-50KT OF SHEAR AND THERMODYNAMIC
ENVIRONMENT...STRONGER UPDRAFTS/TSTMS WOULD HAVE HAIL POTENTIAL
ALONG WITH GUSTY WINDS. HAVE UPGRADED MUCH OF LWR MI EWD INTO LH
FOR THE HAIL POTENTIAL WHICH WILL END BY LATE AFTERNOON AS
POST-FRONTAL SUBSIDENCE AND DRYING SPREAD EWD IN WAKE OF COLD FRONT.
...S FL...
STRONG HEATING WILL OCCUR AHEAD OF REMNANT COLD FRONTAL SEGMENT
CROSSING N CNTRL FL ATTM. VERY MOIST PRE-FRONTAL AIR AND MODEST
...LARGELY UNIDIRECTIONAL WLY FLOW SHOULD SUPPORT DEVELOPMENT OF
STRONG TSTM CLUSTERS/LINES ALONG AND AHEAD OF FRONT. THESE WILL
HAVE THE POTENTIAL TO PRODUCE ISOLD DMGG WIND GUSTS...ESPECIALLY S
OF A FMY-VRB LINE.
...ORE/NRN ID...
ANOTHER ROUND OF SCTD STRONG DIURNAL STORM CLUSTERS EXPECTED OVER
THE ORE CASCADES...SISKIYOUS...BLUES AND WALLOWAS TODAY.
REGION WILL REMAIN IN AREA OF ENHANCED FLOW BETWEEN LWR CO VLY UPR
LOW AND AN IMPULSE CROSSING SRN BC. SETUP MAY RESULT IN
MULTICELL/BRIEF SUPERCELL STRUCTURES WITH ISOLD LARGE HAIL AND DMGG
WINDS.
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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