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June 21-24 Severe Obs/Disc.


Ellinwood

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...MID ATLANTIC STATES...

INITIAL AREA OF LIKELY CONCERN FOR SEVERE STORM DEVELOPMENT IS THE

LEE TROUGH FROM PA TO VA WHERE CONVERGENCE WILL FOCUS INITIATION

WITHIN A VERY MOIST POTENTIALLY MDTLY UNSTABLE AIR MASS. MID LEVEL

STRONGER FLOW WILL BE INCREASING EWD ACROSS THIS AREA DURING THE

AFTERNOON...SUPPORTING DEVELOPMENT OF COLD POOLS AND A DAMAGING WIND

THREAT.

FURTHER S INTO CAROLINAS HAVE INCREASED THE SEVERE THREAT FOR LATER

THIS AFTERNOON/EVENING AS COLD POOLS SHOULD EVOLVE FROM THE STORMS

FURTHER W AND THEN MOVE INTO EXPECTED STRONG INSTABILITY OVER

CAROLINAS WITH STEEP LOW LEVEL LAPSE RATES FROM THE STRONG DAYTIME

HEATING. AGAIN OVERALL SHEAR PROFILES OF 25KT OR SO SUFFICIENT TO

MAINTAIN FORWARD PROPAGATING COLD POOLS THRU THE EVENING GIVEN THE

PRESENCE OF MLCAPES AOA 1500 J/KG AND DCAPES IN EXCESS OF 1000 J/KG.

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MESOSCALE DISCUSSION 1357

NWS STORM PREDICTION CENTER NORMAN OK

0103 PM CDT WED JUN 22 2011

AREAS AFFECTED...ERN PA/MD/VA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 221803Z - 222000Z

STORMS ARE EXPECTED TO INCREASE IN COVERAGE AND INTENSITY THROUGH THE AFTERNOON AS DIURNAL DESTABILIZATION OCCURS. CONVECTIVE TRENDS WILL BE MONITORED FOR A POSSIBLE WW. STORMS ARE CURRENTLY FORMING OVER THE HIGHER TERRAIN OF PA WITH MORE DEVELOPMENT EXPECTED FARTHER SOUTH INTO VA LATER THIS AFTERNOON OVER THE TERRAIN AND INVOF LEE SURFACE TROUGH. WITH SURFACE DEWPOINTS AROUND 70F...THE ATMOSPHERE WILL BECOME MODERATELY UNSTABLE WITH MLCAPE VALUES AOA 1000 J/KG. AS THE UPPER LOW SLOWLY APPROACHES FROM THE WEST...DEEP-LAYER SHEAR WILL REMAIN AROUND 30-35 KTS...WHICH WILL BE SUFFICIENT FOR STORM ORGANIZATION. GIVEN THE RELATIVELY WEAK LAPSE RATES...THE GREATEST SEVERE THREAT APPEARS TO BE DAMAGING WINDS...ESPECIALLY AS STORMS MATURE AND COLD POOLS MERGE IN THE PRESENCE OF FAVORABLE LOW-LEVEL SHEAR /I.E. 0-3 KM SHEAR AROUND 30 KTS PER AREA VWP DATA/.

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AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC

232 PM EDT WED JUN 22 2011

.SYNOPSIS... A COLD FRONT WILL APPROACH THE MID-ATLANTIC FRIDAY...BUT MAY NOT PUSH SOUTH OF THE AREA UNTIL LATE SATURDAY. HIGH PRESSURE CROSSES THE REGION SUNDAY...WITH THE POTENTIAL FOR UNSETTLED WEATHER RETURNING FOR EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH THURSDAY/... SO FAR...CONVECTION TODAY HAS BEEN UNDERWHELMING AND LESS THAN EVEN SHORT-RANGE MODELS EARLIER TODAY INDICATED. THIS IS...AS WE WERE CONCERNED ABOUT EARLIER...DUE TO THE CLOUDS THAT HAVE SUPPRESSED HEATING EVER SO SLIGHTLY. WE STILL EXPECT MORE INITIATION DURING THE LATE AFTERNOON AND EARLY EVENING...WITH THE FAVORED AREA EAST OF INTERSTATE 81 AND ESPECIALLY EAST OF THE BLUE RIDGE. THE WINDOW OF OPPORTUNITY FOR STORMS THIS AFTERNOON IS PRETTY SHORT...BUT SOME TORRENTIAL RAIN AND ISOLATED STRONG/SEVERE STORMS ARE STILL POSSIBLE.

ACTIVITY SHOULD WANE...BUT PERHAPS NOT COMPLETELY DISSIPATE...WITH THE LOSS OF DAYTIME HEATING. I THINK MOST PLACES WILL BE DRY TONIGHT BUT A STRAY SHOWER CANNOT BE RULED OUT...ESPECIALLY LATE TONIGHT IN THE WEST AS ANOTHER WEAK SHORTWAVE MOVES TOWARD THE AREA.

THOUGH IT IS A BIT HARDER TO FIND A TRIGGER FOR CONVECTION TOMORROW...WITH THE AREA REMAINING IN A VERY SIMILAR AIRMASS...I ALMOST HAVE TO GO WITH A PERSISTENCE FORECAST OF SCATTERED AFTERNOON AND EARLY EVENING CONVECTION AGAIN. ALSO WITH A SIMILAR AIRMASS IN PLACE...STRONG TO SEVERE STORMS WILL AGAIN BE POSSIBLE. CONVECTIVE INITIATION TIME WILL PROBABLY BE A BIT EARLIER THAN TODAY...GIVING ACTIVITY MORE TIME TO FIRE AND ORGANIZE. MOST OF THE AREA IS IN THE SPC DAY 2 SLIGHT RISK.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... CNVCTN SHUD DIURNALLY WANE THU NGT...THO CLOSER TO SFC BNDRY ACRS POTOMAC HIGHLANDS CHC POPS WILL BE CONTD OVNGT. FRI SFC CDFNT DRAGS THRU MID-ATLC AS UPR TROF AXIS APPROACHES FROM WEST. FAVORABLE SPEED AND DIRECTIONAL DEEP LYR SHEAR...STEEPENING LAPSE RATES...AND HIGH INSTABILITY WILL SUPPORT RISK FOR AT LEAST SCATTERED STRONG/SVR TSTMS...ESPECIALLY DURG THE AFTN/EVE. WITH BNDRY IN VCNTY FRI NGT...WILL KEEP LOW CHC POPS...AND CONT THEM INTO SAT AS UPR TROF GRADUALLY LIFTS NWD INTO SE CANADA. TEMPS SHUD RMN ABV NRML THRU FRI NGT...BUT FROPA SHUD ALLOW FOR DROP IN TEMPS TO SEASONAL LEVELS BY SAT.

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