SPC AC 221931
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0231 PM CDT MON JUN 22 2009
VALID 222000Z - 231200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID MS/LOWER OH VALLEY
TO FL...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NRN PLAINS...
...LOWER OH/TN VALLEY TO FL...
LATEST WV IMAGERY...ALONG WITH RUC GUIDANCE...SUGGEST A WEAK
SHORTWAVE TROUGH MAY BE TOPPING THE UPPER RIDGE OVER IL. THIS
FEATURE SHOULD BEGIN TO TURN SHARPLY SEWD OVER THE NEXT FEW HOURS AS
IT DIGS TOWARD THE TN VALLEY. VIS SATELLITE ALSO SUPPORTS THIS
CONCEPT WITH CU FIELD EXPANDING ACROSS SRN IL...WITH ISOLATED
THUNDERSTORMS NOW EVOLVING ACROSS SERN MO. IT APPEARS THIS ACTIVITY
WILL GRADUALLY EXPAND IN AREAL COVERAGE AS BOUNDARY LAYER WARMS OVER
THE NEXT FEW HOURS.
DOWNSTREAM...A GRADUALLY EXPANDING CLUSTER OF THUNDERSTORMS FROM ERN
TN TO CNTRL GA SHOULD CONTINUE TO PROPAGATE SWD ALONG WRN FRINGE OF
STRONGER NWLY FLOW ALOFT. BOUNDARY LAYER HAS REALLY WARMED TO THE
SOUTH-WEST OF THIS ACTIVITY WITH SFC TEMPERATURES NOW ABOVE 100F
OVER PARTS OF SRN GA/AL/NRN FL. IF PRECIPITATION ASSOCIATED
THUNDERSTORM ACTIVITY OVER GA CAN CONTINUE TO EXPAND AND GENERATE A
COLD POOL THEN THERE APPEARS TO BE AN INCREASING CHANCE FOR VERY
STRONG WINDS ALONG LEADING EDGE OF DEVELOPING MCS. FOR THIS REASON
HAVE EXPANDED SLIGHT RISK TO ACCOUNT FOR MORE ORGANIZATION ACROSS
SRN HALF OF GA. OTHERWISE...ISOLATED DAMAGING DOWNBURSTS CAN BE
EXPECTED GIVEN THE SOMEWHAT LOWER RH BOUNDARY LAYER.
PER EARLIER DISCUSSION...THUNDERSTORM INITIATION SHOULD BE DELAYED
UNTIL LATER IN THE AFTERNOON ACROSS THE FL PENINSULA.
...NRN PLAINS...
LARGE SCALE ASCENT IS NOW BEGINNING TO SPREAD ACROSS THE NRN HIGH
PLAINS AS UPPER SPEED MAX BEGINS TO EJECT ACROSS ERN MT. SCATTERED
THUNDERSTORMS ARE ALSO INCREASING WITHIN VEERED FLOW ALONG ADVANCING
COLD FRONT. AS BOUNDARY LAYER CONTINUES TO DEEPEN AND LOW LEVEL
LAPSE RATES APPROACH DRY ADIABATIC...ADDITIONAL CONVECTION SHOULD BE
GENERATED ALONG COLD FRONT. EARLIER FORECAST APPEARS TO BE ON TRACK
ACROSS THIS REGION.
..DARROW.. 06/22/2009
.PREV DISCUSSION... /ISSUED 1123 AM CDT MON JUN 22 2009/
...NRN PLAINS...
STRONG SURFACE COLD FRONT ATTENDANT TO NRN STREAM SHORTWAVE TROUGH
NOW MOVING INTO THE NRN ROCKIES WILL ADVANCE EWD ACROSS THE DAKOTAS
LATER TODAY AND TONIGHT. ALTHOUGH FRONT WILL OUTRUN STRONGEST
ASCENT WELL EAST OF MAIN MID/UPPER LEVEL TROUGH...SUFFICIENT LIFT
ALONG FRONT SHOULD SUPPORT SCATTERED THUNDERSTORM DEVELOPMENT WITHIN
AXIS OF MODEST INSTABILITY OVER WRN ND THIS AFTERNOON.
ADDITIONALLY...MORE ISOLATED THUNDERSTORMS ARE EXPECTED NEARER THE
MID LEVEL COOL POCKET OVER CENTRAL MT... AND AHEAD OF STRONG
HEATING/MIXING ALONG SFC TROUGH INTO PORTIONS OF NRN/ERN SD.
LOW LEVEL SHEAR IS FORECAST TO REMAIN RELATIVELY WEAK AS STORMS
SHIFT EWD ACROSS ND AND THE RED RIVER VALLEY REGION THIS
EVENING/OVERNIGHT. HOWEVER...DEEP LAYER SHEAR SHOULD REMAIN
SUPPORTIVE OF ORGANIZED STORMS...INCLUDING SUPERCELLS AND
LINES/CLUSTERS. ISOLATED LARGE HAIL/DAMAGING WINDS CAN BE EXPECTED
WITH THE STRONGER CORES.
...CENTRAL/SRN FL...
ANOMALOUS PATTERN WILL REMAIN OVER FL TODAY...WITH EXTREMELY
WARM/MOIST BOUNDARY LAYER OVERRIDDEN BY WARM/DRY MID LEVEL AIR UNDER
MODEST NLY FLOW ALOFT. SUBSIDENCE EVIDENT ON WV IMAGERY HAS LIKELY
HINDERED CU DEVELOPMENT INTO THE EARLY AFTERNOON...ALTHOUGH AIRMASS
IS ALREADY VERY UNSTABLE AND WEAKLY CAPPED. EXPECT THUNDERSTORMS
WILL DEVELOP LATER THIS AFTERNOON ALONG EAST COAST...WHERE
SEA-BREEZE WILL MAKE LITTLE INLAND PUSH...AND ALONG E-W SURFACE COOL
FRONT PUSHING SSWWD LATE TODAY AND TONIGHT INTO CENTRAL FL.
ISOLATED THUNDERSTORMS CAN ALSO BE EXPECTED LATE TODAY INVOF SUBTLE
CONVERGENCE AXES FROM W-CENTRAL INTO S-CENTRAL PORTIONS OF THE
PENINSULA.
DESPITE WARM MID LEVEL TEMPERATURES...VERY UNSTABLE AIR MASS WILL BE
IN PLACE THIS AFTERNOON ALONG WITH MODEST SFC-6 KM SHEAR. THIS MAY
SUPPORT POTENTIAL FOR MORE ORGANIZED CLUSTERS PERSISTING AS THEY
SHIFT SWD...WITH PRIMARY THREAT OF STRONG/DAMAGING WINDS AND
ISOLATED LARGE HAIL.
...MID MS RIVER VALLEY INTO THE SRN APPALACHIANS...
REFERENCE SWOMCD 1271 FOR SHORT TERM FORECAST FOR ACTIVITY NOW
PERSISTING ACROSS CENTRAL KY. OVERALL PATTERN WILL REMAIN CONDUCIVE
FOR SSEWD MOVING CLUSTERS OF STORMS ALONG STALLED SURFACE FRONT
THROUGH MUCH OF THE PERIOD. STRONG INSTABILITY WITHIN WARM SECTOR
AND SEASONABLY STRONG NNWLY FLOW ALOFT SHOULD ENHANCE THE POTENTIAL
FOR DAMAGING WINDS/LARGE HAIL AS ACTIVITY EVOLVES INTO BOWING
SEGMENTS...WITH ADDITIONAL RISK OF SUPERCELLS WITH ANY
PERSISTENT/ISOLATED CELL.
...CHESAPEAKE BAY REGION...
UNSEASONABLY COLD MID LEVEL COLD POCKET EVIDENT AT ALB THIS MORNING
WILL SHIFT INTO THIS REGION THIS AFTERNOON...WHERE MODEST SFC
HEATING WILL SUPPORT WEAK INSTABILITY. SMALL CLUSTERS/BANDS OF
LOW-TOPPED MOIST CONVECTION SUFFICIENTLY DEEP FOR ISOLATED THUNDER
AND HAIL ARE EXPECTED INTO THE EARLY EVENING FROM ERN MD/DE INTO NE
NC.
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