Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 192246 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 646 PM EDT SUN APR 19 2015 .SYNOPSIS... HIGH PRESSURE WILL MOVE FARTHER OFF THE NEW ENGLAND COAST THROUGH TONIGHT. MEANWHILE, LOW PRESSURE OVER THE MIDWEST THIS AFTERNOON WILL STRENGTHEN AS IT TRACKS NORTHWARD INTO THE GREAT LAKES TONIGHT. THE LOW WILL LIFT INTO ONTARIO CANADA EARLY IN THE WEEK. A WARM FRONT IS FORECAST MOVE NORTHWARD INTO THE MID ATLANTIC ON MONDAY BEFORE A COLD FRONT MOVES THROUGH MONDAY NIGHT. THE LOW PRESSURE SYSTEM OVER ONTARIO WILL SLOWLY MOVE EASTWARD MIDWEEK BEFORE STALLING OVER EASTERN CANADA AND NEW ENGLAND THROUGH NEXT WEEKEND. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... HIGH PRESSURE WILL BE MOVING TO THE EAST EARLY TONIGHT. LOW PRESSURE AND ITS ASSOCIATED FRONT WILL BE MOVING IN FROM THE OHIO VALLEY OVERNIGHT. CLOUDS WILL OVERSPREAD THE AREA AND RAIN WILL ARRIVE IN MANY AREAS AFTER MIDNIGHT...MAYBE A FEW HOURS EARLIER FAR S. THE RAINS WILL BECOME STEADY OVERNIGHT AND PATCHY FOG IS POSSIBLE. LOW TEMPERATURES WILL BE IN THE LOW/MID 40S NORTH AND UPPER 40S TO LOW 50S SOUTH. WINDS WILL INCREASE FROM THE EAST AT 10 TO 15 MPH WITH GUSTS 20 TO 25 MPH OVERNIGHT. QPF WILL BE AROUND A TENTH OF AN INCH N/E TO A QUARTER INCH S/W. BASED ON LATEST RADAR TRENDS HAVE LOWERED POPS IN THE IMMEDIATE NEAR TERM S AND W. OTHERWISE NO SIGNIFICANT CHANGES TO FCST. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... A LARGE BATCH OF STEADY RAINS WILL BE ACROSS THE AREA DURING THE MORNING AND A DECENT QPF UP AROUND AN INCH OR SO WILL OCCUR IN MANY AREAS. TOTALS UP TO 1.5 INCHES ARE POSSIBLE IN A FEW LOCALIZED AREAS. WHILE THESE TOTALS ARE ROBUST...THE DRY CONDITIONS ACROSS THE AREA PRESENTLY SHOULD KEEP ANY FLOODING CONCERNS AT BAY. IT IS POSSIBLE THAT SOME LOCALIZED POOR DRAINAGE FLOODING MAY OCCUR...BUT THE LACK OF ANY WIDESPREAD THREAT WILL KEEP US FROM ISSUING ANY FLOOD FLAGS ATTM. THE RAIN SHIELD WILL PULL TO THE NORTH BY LATE MORNING AND PRECIP SHOULD BE MORE SHOWERY FOR THE AFTERNOON. CLOUDS WILL LIKELY REMAIN OVC N/W DURING THE AFTERNOON...BUT BREAKS WILL DEVELOP ACROSS THE DELMARVA AND SRN NJ. THE MOST RECENT SPC DAY2 OUTLOOK HAS PUSHED THE SLIGHT RISK AREA ACROSS MOST OF THE S/W 2/3RDS OF THE CWA FOR TOMORROW INTO TOMORROW NIGHT. A COLD FRONT WILL BEGIN TO APPROACH LATE AND THIS SHOULD TOUCH OFF SCT-NUMEROUS TSTMS ACROSS THE AREA. CAPE VALUES SHOULD INCREASE INTO THE 1000-2000 J/KG RANGE ACROSS THE SRN AREAS...ESPECIALLY IN AREAS WHERE BREAKS IN THE CLOUDS DEVELOP. HIGH TEMPS WILL BE TRICKY ALSO...SINCE A SHORT BREAK IN THE CLOUDS WILL HAVE A PROFOUND IMPACT ON TEMPS. WE HAVE A MAV FCST FOR THE MOST PART...WITH A FEW DEGREES LOWER IN FEW AREAS. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... AN UPPER LOW IS FORECAST TO DEEPEN OVER THE UPPER MIDWEST/LAKE SUPERIOR ON MONDAY NIGHT. THE SURFACE REFLECTION OF THE UPPER LOW IS FORECAST TO MEANDER OVER ONTARIO. THERE WILL ALSO BE A NEGATIVELY- TILTED TROUGH/OCCLUDED COLD FRONT EXTENDING SOUTHEASTWARD FROM THE LOW WHILE A WARM FRONT IS EXPECTED TO RESIDE SOMEWHERE NEAR CENTRAL PORTIONS OF PA AND NJ MONDAY EVENING. A SAMPLE OF MODEL FORECAST SOUNDINGS ACROSS THE AREA SHOW MODEST INSTABILITY BEING SUSTAINED IN THE WARM SECTOR DURING THE EVENING IN RESPONSE TO A S-SWLY LOW-LEVEL JET HELPING TO MOISTEN THE LOW LEVELS AND 700-500 MB LAPSE RATES NEAR 7 C/KM BEING CONDITIONALLY UNSTABLE. WILL MENTION A CHANCE FOR THUNDER SOUTH OF THE WARM FRONT FROM THE DELMARVA TO THE GREATER PHILLY AREA WHERE MUCAPE VALUES BETWEEN 750-1250 J/KG ARE FORECAST. FARTHER NORTH, LIMITED THUNDER TO SLIGHT CHANCE WITH FORECAST MUCAPE AROUND 500 J/KG AND WITH MORE CIN FOR CONVECTION TO OVERCOME IN THE COOL SECTOR. EVEN IN OUR MOST SOUTHERN ZONES THAT ARE DEEPER INTO THE WARM SECTOR, FORECAST SOUNDINGS INDICATE INSTABILITY BEING NON- SURFACE BASED AFTER SUNSET. THE UPPER LOW IS FORECAST TO CUT OFF JUST NORTH OF THE GREAT LAKES MIDWEEK. THE COLD FRONT IS EXPECTED TO MOVE THROUGH THE COASTAL MID- ATLANTIC LATE MONDAY NIGHT INTO EARLY TUESDAY MORNING. WINDS TURN WESTERLY POST-FRONTAL AND COLDER/DRIER AIR ADVECTS INTO THE AREA. TRENDED SLIGHTLY FASTER WITH AN END TO THE PRECIP. THE FORECAST IS NOW DRY FOR TUESDAY EXCEPT FOR SOME ISOLATED SHOWERS/SPRINKLES IN THE HIGHER TERRAIN OF NORTHEAST PA/NORTHWEST NJ AS THE MID-LEVEL SHORTWAVE TROUGH PIVOTS THRU. A ZONAL FLOW/NEUTRAL THERMAL ADVECTION PATTERN WILL ENSUE TUESDAY AFTERNOON AND NIGHT AS THE MID ATLANTIC BECOMES SITUATED BETWEEN THIS LOW AND HIGH PRESSURE OVER THE SOUTHEAST COAST. SEASONABLE TEMPS ARE EXPECTED DURING THIS PART OF THE FORECAST. SHORTWAVE ENERGY IS FORECAST TO DIG SOUTHEASTWARD TOWARD THE BASE OF THE UPPER TROUGH ON WEDNESDAY. CONSENSUS FROM THE 12Z GUIDANCE SHOW PRECIP EXPANDING FROM THE MIDWEST INTO THE MID ATLANTIC WEDNESDAY AFTERNOON AND EVENING AHEAD OF A COLD FRONT. THE COLD FRONT IS CURRENTLY FORECAST TO MOVE THRU THE AREA LATE WEDNESDAY NIGHT. THE 12Z GFS SHOWED A MORE AGGRESSIVE SOLUTION WITH RESPECT TO HOW QUICKLY THE UPPER-LEVEL JET STREAK STRENGTHENS AT THE BASE OF THE TROUGH. IN THIS SCENARIO, THE UPPER DIVERGENCE IN THE LEFT EXIT REGION WOULD ENHANCE BOTH LIFT OVER OUR AREA AND COVERAGE OF PRECIP. HOWEVER, THERE IS STILL DECENT SPREAD IN THE GUIDANCE WITH THIS SYSTEM, SO POPS WERE ONLY INCREASED SLIGHTLY FROM THE PREVIOUS FORECAST. THE UPPER LOW SHOULD WILL EVENTUALLY PROGRESS EASTWARD INTO EASTERN CANADA/NORTHERN NEW ENGLAND LATE THIS WEEK AND NEXT WEEKEND. CYCLONIC FLOW AROUND THE LOW WILL KEEP A COOL AIRMASS OVER THE AREA ALONG WITH PERIODS OF STRATOCU. MAY EVEN SEE SNOW SHOWERS IN THE POCONOS EARLY THURSDAY. TEMPS WILL BE BELOW NORMAL WITH HIGHS EACH DAY RANGING FROM THE UPPER 40S IN THE POCONOS TO NEAR 60F IN THE COASTAL PLAIN THURSDAY THROUGH SUNDAY. DEEP MIXING WILL ALSO YIELD GUSTY WEST-NORTHWEST WINDS DURING THE DAYTIME HOURS. THERE IS ALSO A POTENTIAL FOR FROST TO DEVELOP AT THE SOME OF COOLER SPOTS IN EASTERN PA AND NORTHWEST NJ EACH NIGHT IF WINDS IN THE BOUNDARY LAYER ARE ABLE TO DECOUPLE AND SKIES CLEAR OUT. THE GROWING SEASON STARTS FOR NORTHEAST PA (EXCEPT CARBON AND MONROE) AND NORTHWEST NJ IN THE NEXT COUPLE OF DAYS, SO FROST ADVISORIES MAY BE NEEDED. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY, AND SURROUNDING AREAS. VFR CONDITIONS INTO THE EARLY EVENING. THE DEEP ERLY FLOW AND THE APPROACHING WARM FRONT WILL COMBINE TO PRODUCE A QUICK INCREASE IN MOISTURE ACROSS THE AREA THIS EVENING AND CONDITIONS WILL QUICKLY DETERIORATE OVERNIGHT. WE EXPECT THAT CONDITIONS WILL GO IFR AFTER MIDNIGHT IN MOST AREAS AND A 6 TO 8 HOUR PERIOD OF LOW CONDITIONS, RAIN AND LLWS WILL BE ACROSS THE TERMINALS UNTIL 12Z-14Z MONDAY. THIS WILL HAVE BIG IMPACTS ON TRAVEL ACROSS THE AREA MONDAY...ESPECIALLY PHL MON MORNING. A WARM FRONT WILL CROSS THE AREA MONDAY AND CONDITIONS MAY IMPROVE BEHIND IT MON AFTERNOON. RATHER LOW CONFID IN THE FCST LATER MON MORNING. WINDS WILL BE ERLY TONIGHT AND MONDAY MORNING AND THEN VEER SE TO S DURING THE AFTERNOON. OUTLOOK... MONDAY NIGHT...ANOTHER ROUND OF SHRA AND POSSIBLY TSRA AHEAD OF A COLD FRONT. IFR CONDITIONS IN HEAVIER PRECIP BUT WE MAY ALSO SEE CIGS/VSBYS TRY TO IMPROVE TO MVFR/VFR IN STRETCHES OF NO PRECIP. TUESDAY AND TUESDAY NIGHT...VFR. W-NW WINDS GUST BETWEEN 20 AND 30 KT DURING THE DAY AND SUBSIDE AT NIGHT. WEDNESDAY AND WEDNESDAY NIGHT...CHANCES FOR SHRA INCREASE DURING THE AFTERNOON AND NIGHT AHEAD OF A COLD FRONT. PREDOMINATELY VFR THOUGH LOCALIZED MVFR RESTRICTIONS POSSIBLE IN STEADIER PRECIP. THURSDAY...VFR. W-NW WILL BE GUSTY AGAIN. && .MARINE... WINDS AND SEAS WILL CONTINUE TO BUILD ON THE WATERS TONIGHT AS LOW PRESSURE AND A WARM FRONT APPROACH. WE HAVE DECIDED TO RAISE THE REST OF THE SCA FLAG WITH THE 330 PM CWF ISSUANCE. WINDS GUSTS WILL BEGIN TO REACH 20 TO 25 KNOTS THIS EVENING AND INCREASE OVERNIGHT. THE GFS GUIDANCE WAS QUITE BULLISH WITH THE WINDS WITH CLOSE TO GALES OVERNIGHT...BUT WE WILL NOT COMPLETELY BUY THIS ATTM AND KEEP THE NUMBERS A BIT LOWER. THE GFS SEEMS TO HAVE A MESOLOW CROSSING THE AREA OVERNIGHT. RAIN/FOG OVERNIGHT WITH LOW VSBYS POSSIBLE. A CONTINUATION OF POOR CONDITIONS MONDAY WITH WINDS AND SEAS BEGINNING TO SUBSIDE LATE. THE PCPN SHOULD BECOME MORE SHOWERS IN THE AFTERNOON WITH TSTMS POSSIBLE. AREAS OF FOG MAY LINGER WITH THE WATER TEMPS REMAINING VERY COLD AND DEW POINTS OVER THE WATERS QUITE HIGH. OUTLOOK... MONDAY NIGHT...SW WINDS 15-20 KT IN THE EVE WILL SHIFT OUT FROM THE W-NW OVERNIGHT BEHIND A COLD FRONT. GIVEN SST IN THE UPPER 40S AND LOWER 50S AND A WARM THE AIRMASS ABOVE, THE SETUP DOES NOT FAVOR MUCH MIXING OF HIGHER GUSTS ALOFT DOWN TO THE SURFACE. EVEN IF GUSTS TO 25 KT WILL BE INFREQUENT, SEAS WILL STILL BE 5-7 FT OFF THE NJ AND DE COAST. THEREFORE, A SCA IS IN EFFECT. TUESDAY...SCA MAY BE NEEDED FOR TUESDAY AS DEEPER MIXING ON LAND WILL YIELD GUSTY WLY WINDS OF 20-25 KT NEAR THE COAST. MEANWHILE, WINDS FARTHER OFFSHORE WILL LIKELY NOT SEE THESE GUSTS. SEAS WILL BE AROUND 4-6 FT IN THE MORNING, DIMINISHING TO 2-4 FT LATE IN THE DAY AND AT NIGHT. WILL HOLD OFF ON A FOURTH PERIOD SCA IN THIS MARGINAL SETUP. WEDNESDAY...SW WINDS INCREASE TO NEAR SCA LEVELS LATE WEDNESDAY. THURSDAY AND FRIDAY...SCA MAY BE NEEDED DUE TO A GUSTY W-NW. AIRMASS LOOKS COLD ENOUGH FOR GUSTY WINDS TO BE SUSTAINED EVEN OUT TO 20 NM MILES OFFSHORE. && .FIRE WEATHER... RH HAS INCREASED GRADUALLY THRUOUT THE DAY HAS INCREASED AS A RESULT OF ONSHORE FLOW. THE ONLY LOCATIONS WITH RH BELOW 30 PERCENT IN FAR NW NJ AND THE POCONOS BUT WINDS ARE LIGHT THERE. NOT EXPECTING CONDITIONS TO MEET RED FLAG WARNING CRITERIA THRU THE REMAINDER OF THE DAY. && .TIDES/COASTAL FLOODING... 630 PM: STATUS FOR TONIGHTS HIGH TIDE CYCLE. RECENT TRENDS SUGGEST WE`LL BE ABLE TO SQUEAK BY WITH NO EXCEEDANCE OF THE HIGHER THRESHOLD VALUES. LATEST NAM DBOFS AND GFS ETSS CONTINUE BLO FLOOD. SITAND OUR IN-HOUSE PHI CHECK`S SAY MARGINAL. WE`LL CHECK BACK AROUND 8 PM. A STRENGTHENING SOUTHEAST FLOW TONIGHT COMBINED WITH INFLUENCE FROM THE RECENT NEW MOON, MAY CAUSE SOME MINOR COASTAL FLOODING TO OCCUR WITH TONIGHTS HIGH TIDE CYCLE IN COASTAL DELAWARE AND SOUTHERN NEW JERSEY, MAINLY FROM CAPE MAY COUNTY SOUTHWARD AND UP THE ALONG THE DELAWARE BAY AND INTO THE DELAWARE RIVER. THE GUIDANCE MAY STILL BE RUNNING A BIT ON THE LOW SIDE AND WE WILL CONTINUE TO MONITOR THE SITUATION AND ANY NEED FOR A COASTAL FLOOD ADVISORY. AS A WARM FRONT LIFTS NORTHWARD INTO THE REGION MONDAY, THE WINDS WILL SHIFT TO MORE OF A SOUTHERLY DIRECTION. THE WINDS ACROSS THE NORTHERN AREAS MAY REMAIN MORE EAST OR SOUTHEAST AHEAD OF THE FRONT AND THIS MAY INCREASE THE POTENTIAL FOR SOME MINOR TIDAL FLOODING FROM ATLANTIC CITY NORTHWARD TO SANDY HOOK MONDAY MORNING. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL 10 AM EDT MONDAY FOR ANZ430-431. && $$ SYNOPSIS...KLEIN NEAR TERM...NIERENBERG/O`HARA SHORT TERM...O`HARA LONG TERM...KLEIN AVIATION...KLEIN/O`HARA MARINE...KLEIN/O`HARA FIRE WEATHER... TIDES/COASTAL FLOODING...646

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