Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 040827 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 427 AM EDT MON MAY 4 2015 .SYNOPSIS... HIGH PRESSURE WILL MOVE FARTHER OFFSHORE TODAY. A COLD FRONT MOVES ACROSS THE AREA TUESDAY AFTERNOON AND NIGHT. THE COLD FRONT IS FORECAST TO STALL SOUTH OF THE AREA THROUGH THE END OF THE WEEK WITH HIGH PRESSURE NOSING ITS WAY SOUTHWARD ACROSS THE AREA THROUGH FRIDAY. THE HIGH BUILDS OFFSHORE OVER THE WEEKEND, WITH RETURN FLOW DEVELOPING ACROSS THE AREA. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... RED FLAG WARNING IN EFFECT THIS AFTERNOON FOR OUR PENNSYLVANIA AND NEW JERSEY ZONES...EXCLUDING THE IMMEDIATE COASTAL AREAS. SURFACE RIDGING OFFSHORE WILL CONTINUE TO USHER IN A WARMER AIRMASS UNDER ITS STRENGTHENING SOUTHERLY FLOW IN THE LOW-LEVELS. THE MAIN CONCERN TODAY IS A SIGNIFICANT THREAT FOR FIRE SPREAD. THE REGION HAS BEEN VERY DRY THE PAST SEVERAL WEEKS AND THE FIRE FUELS HAVE HAD MORE THAN AMPLE TIME TO DRY OUT...ACTING LIKE KINDLING. WE SHOULD BE ABLE TO MIX UPWARDS OF 825 TO 700 MB THIS AFTERNOON WHERE AT LEAST 25 KNOTS OF BOUNDARY LAYER WINDS RESIDES...NORTH OF THE DELMARVA ZONES. THE DELMARVA ZONES WILL SEE MUCH LESS WIND THIS AFTERNOON WHERE THE PRESSURE GRADIENT IS BIT WEAKER. FREQUENT GUSTS INTO THE LOW-20 KNOTS RANGE IS EXPECTED ALLOWING DEWPOINTS TO DRY OUT...LOWER THAN WHAT GUIDANCE IS SHOWING, EVEN UNDER A SOUTHERLY FLOW. RELATIVE HUMIDITY VALUES SHOULD DROP CLOSE TO 20 PERCENT DURING THE PEAK HEATING HOURS THIS AFTERNOON HELPING TO PRIME CONDITIONS FOR RAPID FIRE SPREAD, SHOULD A FIRE OCCUR. TEMPERATURES TODAY WILL BE THE WARMEST OF THE YEAR, THUS FAR, AS WE TOP OUT CLOSE TO THE MID-80S IN A LOT OF PLACES UNDER SUNNY SKIES. IT IS POSSIBLE THAT A SEABREEZE MAY PUSH INLAND A BIT LATER THIS AFTERNOON, EVEN THOUGH THE SYNOPTIC FLOW IS RATHER STRONG BUT NOT AS AN OPPOSING FLOW...WEST OR NORTHWEST IS OPPOSING. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... STILL UNDER THE INFLUENCE OF SUBSIDENCE WITH THE RIDGING OFFSHORE, BUT ALOFT AN INCREASE IN MOISTURE IS EXPECTED...AHEAD OF AN APPROACHING COLD FRONT. AS THE FRONT SLIDES TOWARDS THE REGION IT IS EXPECTED TO SLOW SOME AS THE FLOW ALOFT BECOMES MORE PARALLEL ORIENTED TO ITS CONVERGENCE ZONE. WE HAVE SLOWED THE CHANCE POPS BACK BY A FEW HOURS AS WE EXPECT MOST OF THE NIGHT TO REMAIN DRY...ONLY THE EXTREME NORTHERN ZONES COULD SEE THE SHOWERS LATE TONIGHT. WITH MORE WARM AIR ADVECTION TAKING SHAPE TONIGHT AND SOME BOUNDARY LAYER MIXING OCCURRING, TEMPERATURES WILL NOT RADIATE MUCH. EXPECT OVERNIGHT LOWS TO BE SEVERAL DEGREES ABOVE NORMAL IN THE MID TO UPPER- 50S. && .LONG TERM /TUESDAY THROUGH SUNDAY/... A COLD FRONT IS EXPECTED TO MOVE SOUTHWARD THROUGH NORTHEAST PA/ NORTHWEST NJ TUESDAY AFTERNOON AND SOUTHEAST PA/CENTRAL AND SOUTHERN NJ/NORTHERN DELMARVA TUESDAY NIGHT. MOISTURE FLUX ALONG AND AHEAD OF THE FRONT WITH RESULT IN DEWPOINTS INCREASING TO NEAR 60F AND PWATS APPROACHING 1.5 INCHES. EXPECT SCATTERED SHOWERS TO BE MAINLY FOCUSED NEAR THE FRONT DURING THE DAY WITHOUT MUCH OF A LIFTING MECHANISM OTHER THAN LOW-LEVEL CONVERGENCE ALONG THE FRONT (THOUGH IT IS POSSIBLE A DIFFERENTIAL HEATING BOUNDARY MAY INITIATE CONVECTION FARTHER SOUTHEAST). THE 00Z NAM/GFS AND 03Z SREF ARE IN GOOD AGREEMENT, SHOWING A MODESTLY UNSTABLE ENVIRONMENT AHEAD OF THE COLD FRONT WITH MIXED-LAYER CAPE VALUES AVERAGING AROUND 500 J/KG. THIS, ALONG WITH SEVERAL OTHER CONVECTIVE PARAMETERS, SUPPORT THE POTENTIAL FOR ISOLATED THUNDERSTORMS DURING THE AFTERNOON/EVENING HOURS BUT THE FORECAST ENVIRONMENT IS NOT PARTICULARLY CONDUCIVE FOR SEVERE STORMS. A GRADUAL DECREASE IN INTENSITY OF CONVECTION IS EXPECTED WITH THE LOSS OF DAYTIME HEATING TUESDAY EVENING. SHOWERS MAY CONTINUE INTO THE NIGHT ONCE DEEPER LIFT ASSOCIATED WITH AN APPROACHING UPPER SHORTWAVE TROUGH ARRIVES. FAVORED THE WARMER MET GUIDANCE FOR TUESDAY`S HIGHS FROM THE I-95 CORRIDOR AND POINTS SOUTH, WHERE LESS CLOUD COVER AND STRONGER DAYTIME HEATING SHOULD OCCUR IN THE PRE-FRONTAL WARM SECTOR. MODEL GUIDANCE SEVERAL DAYS AGO SHOWED A MUCH SLOWER PROGRESSION OF THE COLD FRONT WITH SOME EVEN STALLING IT OVER THE AREA. THE LATEST 00Z GUIDANCE SHOWS THE FRONT PUSHING SOUTH OF DE/EASTERN MD WEDNESDAY MORNING. TRENDED DRIER WITH WEDNESDAY`S FORECAST DUE TO FASTER MOVEMENT OF THE FRONT AND A QUICKER ARRIVAL OF HIGH PRESSURE THAT WILL BE BUILDING IN FROM UPSTATE NY. EXPECT ANY LINGERING SHOWERS TO BE MAINLY CONFINED TO THE DELMARVA IN THE MORNING. EASTERLY FLOW IN BETWEEN THE HIGH CENTERED TO OUR NORTH AND THE LINGERING FRONTAL BOUNDARY TO OUR SOUTH WILL PRODUCE A LIGHT NELY WINDS. TRENDED LOWER WITH TEMPS WEDNESDAY BY SEVERAL DEGREES SINCE COOL MARINE AIR WILL ADVECT INLAND. HIGHS ON WEDNESDAY MAY ONLY BE IN THE 60S TOWARD THE COAST AND LOW 70S FARTHER INLAND. BERMUDA HIGH PRESSURE WILL EXTEND BACK TOWARD THE NORTHERN MID- ATLANTIC REGION LATE IN THE WEEK AND THIS WEEKEND. A CLOSED LOW IS FORECAST TO DEVELOP ALONG THE SOUTHEAST COAST THURSDAY. THE LOW IS NOT EXPECTED TO MOVE MUCH THROUGH THE WEEKEND SINCE IT DEVELOPED UNDERNEATH THE LARGE-SCALE RIDGE WHERE THERE IS MINIMAL STEERING FLOW. THIS WILL ALLOW THE FORECAST AREA TO REMAIN MAINLY DRY THROUGH THE WEEKEND. HOWEVER, WE COULD SEE WEAKLY-FORCED CONVECTION POP UP ACROSS THE HIGHER TERRAIN DURING THE PEAK HEATING HOURS BOTH SATURDAY AND SUNDAY. ABOVE NORMAL TEMPS WILL PERSIST WITH HIGHS IN THE MID 70S TO LOW 80S EACH DAY. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...VFR. LIGHT AND VARIABLE WINDS TO START THE DAY BECOMING MORE SOUTHERLY BY LATE MORNING. GUSTS INTO THE LOW TO MID-20 KNOTS RANGE EXPECTED STARTING MID-AFTERNOON THROUGH SUNSET. COULD SEE A SEABREEZE PUSH INTO ACY BY LATE AFTERNOON. TONIGHT...VFR. LIGHT SOUTHERLY WINDS DECREASE TO LESS THAN 10 KNOTS WITH THE MORE SHELTERED TERMINALS DROPPING TO LESS THAN 6 KNOTS. OUTLOOK... TUESDAY AND TUESDAY NIGHT...PREDOMINATELY VFR. VSBY/CIG RESTRICTIONS POSSIBLE DURING THE AFTERNOON AND NIGHT FROM SCT SHOWERS AND ISO STORMS. RESTRICTIONS WOULD BE LOCALIZED/TEMPORARY. WEDNESDAY...MVFR CIGS POSSIBLE, ESPECIALLY IN THE MORNING WITH ONSHORE FLOW DEVELOPING. SHOWERS EXPECTED TO PUSH SOUTH OF THE TERMINALS IN THE MORNING. WEDNESDAY NIGHT THROUGH FRIDAY...VFR AND LIGHT WINDS WITH HIGH PRESSURE IN CONTROL. && .MARINE... TODAY - TONIGHT...SUB-SCA CONDITIONS EXPECTED. STRENGTHENING SOUTHERLY FLOW TODAY AND TONIGHT WILL HELP TO PUSH SEAS CLOSE TO 4 FEET ON THE OCEAN FRONT TODAY WITH 20 KNOTS OF WIND EXPECTED. OUTLOOK... TUESDAY AND TUESDAY NIGHT...SWLY WINDS INCREASE TO 15-20 KT AHEAD OF A COLD FRONT. ISOLATED TSTMS DEVELOPING ON LAND MAY MOVE OVER THE WATERS TUESDAY DURING THE LATE AFTERNOON AND EVENING. WEDNESDAY THROUGH FRIDAY...WINDS AND SEAS BELOW SCA CRITERIA. && .FIRE WEATHER... VERY DRY FINE FUELS, INCREASING WINDS AND GUSTS, COMBINED WITH LOWERING DEWPOINT THIS AFTERNOON WILL PRIME THE REGION FOR A HIGH RISK IN THE SPREAD OF FIRS THIS AFTERNOON. WHILE THE CONCERN MAY EXIST ACROSS THE ENTIRE REGION, THE WINDS ARE FORECAST TO BE STRONGER ACROSS NEW JERSEY AND PENNSYLVANIA TODAY SO WE HAVE UPGRADED THOSE STATES TO A RED FLAG WARNING. ACROSS THE DELMARVA IT DOES NOT LOOK LIKE WE WILL REACH THE SUSTAINED 20 MPH WINDS NEEDED FOR RED FLAG, BUT AGAIN THIS DOES NOT MEAN THAT CONDITIONS ARE NOT ALREADY ELEVATED. WE WILL COORDINATE WITH OUR DELAWARE AND MARYLAND STATE PARTNERS LATER THIS MORNING. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...RED FLAG WARNING FROM 1 PM THIS AFTERNOON TO 8 PM EDT THIS EVENING FOR PAZ054-055-060>062-070-071-101>106. NJ...RED FLAG WARNING FROM 1 PM THIS AFTERNOON TO 8 PM EDT THIS EVENING FOR NJZ001-007>010-012-013-015>023-027. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...KLEIN NEAR TERM...HEAVENER SHORT TERM...HEAVENER LONG TERM...KLEIN AVIATION...HEAVENER/KLEIN MARINE...HEAVENER/KLEIN FIRE WEATHER...HEAVENER

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