Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 292100 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 400 PM EST THU JAN 29 2015 .SYNOPSIS...
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A FRONTAL SYSTEM WILL MOVE ACROSS THE AREA TONIGHT AS LOW PRESSURE MOVES INTO NEW ENGLAND THEN SLOWLY DRIFTS INTO THE CANADIAN MARITIMES THROUGH THE WEEKEND. HIGH PRESSURE BUILDS TO OUR SOUTH THROUGH THE WEEKEND, FOLLOWED BY ANOTHER FRONTAL BOUNDARY ON SUNDAY. AN AREA OF LOW PRESSURE IS FORECAST TO DEVELOP ALONG THIS BOUNDARY AND PASS JUST TO OUR SOUTH ON MONDAY BUT STILL AFFECT THE AREA. HIGH PRESSURE BUILDS IN ONCE AGAIN FOR MONDAY NIGHT INTO TUESDAY. ANOTHER FRONTAL BOUNDARY IS EXPECTED WEDNESDAY INTO WEDNESDAY NIGHT.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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THE GFS AND WRF-NMMB INITIALIZATION LOOKED PRETTY GOOD. AT 500MB KILZ WINDS LOOKED OFF BASED ON WATER VAPOR IMAGERY. 850MB TEMPS IF ANYTHING WERE INITIALIZED 1C TOO WARM AROUND OUR REGION, IT GETS COLDER AT 925MB WITH A 1 TO 2C WARM BIAS. ACAR SOUNDINGS AT PHL ARE ALL STILL BELOW ZERO CELSIUS. 12Z MORNING SOUNDINGS SHOWED PLENTY OF DRY AIR BELOW 700MB. THE ECMWF VERIFIED THE BEST WITH ITS 6HR QPF FORECAST. GIVEN IT AND THE CAN GGEM ARE IN THE COMPROMISE POSN BETWEEN THE GFS WHICH IS MOST BULLISH WITH PCPN AND THE MESOSCALE MODELS THAT LEAVE THE I95 CORRIDOR SEWD HIGH AND DRY, WE HAVE OPTED FOR THE FORMER. A SUB ADVISORY ONE-TWO PCPN PUNCH IS EXPECTED ACROSS OUR CWA EARLY THIS EVENING AND THEN AGAIN LATE TONIGHT. ONE TO THREE INCHES THROUGH FRIDAY MORNING WAS KEPT FROM A READING PA - TRENTON NJ - NEW BRUNSWICK NJ LINE NORTHWESTWARD. I95 CORRIDOR WAS KEPT UNDER AN INCH AND JUST A COATING POSSIBLE CLOSER TO THE COAST. THE FIRST PCPN SHOT IS TIED TO A SHORT WAVE AND HAS THE BEST WAA AS WELL AS MID LEVEL QVEC CONVERGENCE PREDICTED. THIS LOOKS LIKE A QUICK 1 TO 3 HR SHOT. IN SPITE OF PCPN FIELD DIFFERENCES, THE EVENING DEEP OMEGA BETWEEN THE WRF-NMM AND GFS ARE QUITE SIMILAR. MESOSCALE MODELS ARE SIDING WITH THE DRIER WRF-NMMB COLLAPSING THE PCPN BEFORE IT GETS TO PHL. BUT THE SOUTHERN EXTENSION WAS SOUTH OF THEIR 6HR PREDICTIONS. WE WERE MORE BULLISH WITH POPS ALONG THE MD EASTERN SHORE AS WELL INTO THE I95 CORRIDOR. AS FOR PTYPE. THE SOUNDINGS ARE SO DRY BELOW 700MB THAT EVAPORATIONAL COOLING INITIALLY WILL TAKE PTYPE TO SNOW POSSIBLY IN ALL PLACES. ARE SEEING SOME SLEET (SNOW PELLETS?) IN OBSERVATIONS TO OUR WEST. NON-FREEZING RAIN PTYPE SEEMS MOST CONFIDENT AROUND AND TO THE NORTHWEST OF THE I95 CORRIDOR BECAUSE OF THE EVAP COOLING POWER OF THIS DRY AIR MASS STILL IN PLACE OVER OUR CWA. IN THE REST OF OUR CWA, GIVEN THAT INITIALIZED 925MBS WERE TOO WARM, FORECAST SOUNDINGS THAT EDGE ABOVE 3C SHOULD EVAP COOL BELOW AS SNOW STARTS FALLING. THIS GIVES SOUNDINGS THERE MORE THE ICE PELLET LOOK TO IT AND IF INTENSITIES ARE EXTREMELY LIGHT POSSIBLY SOME RAIN WAY SOUTH. WHILE THE THREAT FOR FREEZING RAIN SOUTHEAST IS NOT ZERO, IT REMAINS TOO LOW TO INCLUDE AT THIS TIME. A COUPLE OF FACTORS ARE ON OUR SIDE, SURFACE ROAD TEMPS HAVE RESPONDED TO AROUND 40 TODAY IN DE AND AIR TEMPS ARE NOT EXPECTED TO FALL MUCH BELOW IF TO FREEZING THIS EVENING AS CLOUDS ARE ALREADY HERE. LASTLY MOST ROADWAYS ARE HEAVILY SALTED AND ARE NOT STARTING FROM A CLEAN SLATE. REGARDLESS WE WILL CONTINUE TO MONITOR THIS EVENING. WHERE POPS ARE LIKELY WE HAVE ISSUED AN SPS. THERE SHOULD BE A LULL IN THE PCPN DURING THE MIDDLE OF THE NIGHT, EXCEPT FOR FAR NORTH. THEN LATER TONIGHT AS A COLD FRONT AND ANOTHER SHORT WAVE APPROACHES FROM THE WEST, PRECIPITATION IS EXPECTED TO RE-ENERGIZE. THIS IS MOST LIKELY TO OCCUR IN THE NORTHERN AND NORTHEASTERN PART OF OUR CWA. TEMPERATURES. BECAUSE OF THE LIGHT SOUTH TO SOUTHEAST FLOW AND CLOUDINESS, THEY SHOULD REMAIN NEARLY STATIONARY IF NOT RISE SLIGHTLY OVERNIGHT AFTER THE INITIAL SHOT OF PCPN. WE ARE HIGHER THAN STAT GUIDANCE WITH MINS.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
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ANY COLD FRONTAL RELATED PCPN SHOULD MOVE OFFSHORE EARLY FRIDAY MORNING. BUT THAT MIGHT NOT BE THE END OF PCPN CHANCES AS ANOTHER SHORT WAVE AT THE BASE OF THE TROF WILL BE MOVING THROUGH. IN FACT SOME OF OUR WINDEX/SNOW SQUALL TOOLS ARE GIVING THE SOUTHERN HALF OF OUR CWA THE CHANCE FRIDAY AFTERNOON. SOME OF THE OLDER WINDEX PROCEDURES ARE SLIGHTLY MORE SUBDUED BECAUSE OF THE LACK OF EVEN STEEPER LAPSE RATES AND NO REAL FOCUSING BOUNDARY OR CAPES ABOVE 70J. THE FORECAST SOUNDINGS HAVE THE CAP HIGH ENOUGH TO SUPPORT SNOW SHOWERS EVERYWHERE. FOR NOW WE HAVE PUT IN A LOW CHANCE FOR SNOW SHOWERS AND SEE HOW THE GUIDANCE PROGRESSES. SNOW SHOWERS OR NOT, THE NORTHWEST GRADIENT WILL BE TIGHTENING AS THE AFTERNOON PROGRESSES. WE ARE APPROACHING WIND ADVY CRITERIA LATE IN THE DAY AS MIXING BECOMES DEEPER. BECAUSE WE ARE NOT DEEP INTO THE CRITERIA AND PMDHMD RECOMMENDED THAT THE NAM/WRF IS TOO TUCKED INTO THE COAST WITH THE SFC LOW, WE HELD OFF WITH ISSUING IT FOR NOW. THE KATABATIC NORTHWEST FLOW WILL BE ABLE TO MAINTAIN TEMPS FOR A WHILE AND GIVEN A RELATIVELY HIGH START, WE WERE AT THE HIGH END FOR MAX TEMPS. NOT THAT IT WILL FEEL WARM.
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&& .LONG TERM /FRIDAY THROUGH THURSDAY/...
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AS THE LOW PULLS AWAY FROM THE AREA AND INTO THE NEW ENGLAND COASTAL WATERS FRIDAY NIGHT, PRECIPITATION IS EXPECTED TO END ACROSS MOST OF THE AREA. THE EXCEPTION TO THIS WOULD BE ACROSS THE POCONOS AREAS WHERE SOME LINGERING LAKE EFFECT SHOWERS MAY CONTINUE INTO THE NIGHT. OTHERWISE, BITTERLY COLD AIR WILL FILTER DOWN ACROSS THE AREA ALONG WITH STRONG WINDS AS THE PRESSURE GRADIENT TIGHTENS BETWEEN THE DEPARTING LOW AND HIGH PRESSURE BUILDING TO OUR WEST. WINDS COULD GUST 35-40 MPH DURING FRIDAY NIGHT AS WELL. THE COMBINATION OF THE LOW TEMPERATURES AND STRONG WINDS WILL CREATE DANGEROUSLY LOW WIND CHILLS ACROSS MUCH OF THE AREA. SUB-ZERO WIND CHILLS WILL OCCUR ALMOST EVERYWHERE, WITH THE POCONOS -15 TO -20. WE HAVE ISSUED A WIND CHILL ADVISORY FOR CARBON AND MONROE SINCE THEY ARE EXPECTED TO REACH WELL INTO THE ADVISORY RANGE. ELSEWHERE, WIND CHILLS AS OF NOW ARE EXPECTED TO FALL JUST SHORT. SATURDAY WILL CONTINUE TO BE WINDY AND COLD, BUT WIND CHILLS WILL BE ABLE TO REBOUND SOME AS TEMPERATURES WARM DURING THE DAY. DRY WEATHER IS CONTINUED TO BE EXPECTED THROUGH THE DAY SATURDAY. WINDS WILL CONTINUE TO BE GUSTY WITH GUSTS IN THE 25-30 MPH RANGE. WINDS SHOULD DIMINISH LATE IN THE DAY INTO THE NIGHT AS THE PRESSURE GRADIENT WEAKENS. ON SUNDAY, A COLD FRONT IS FORECAST TO SAG DOWN ACROSS THE AREA FROM THE NORTH. IT LOOKS LIKE THE ACTUAL FRONT SHOULD BE DRY AS IT DIPS ACROSS THE AREA. HOWEVER, AN AREA OF LOW PRESSURE IS FORECAST TO DEVELOP ALONG THIS FRONT ACROSS THE MID-MISSISSIPPI VALLEY DURING THE DAY, AND MAKE ITS WAY ACROSS THE CENTRAL APPALACHIANS AND OFF THE MID-ATLANTIC COAST SUNDAY NIGHT INTO MONDAY MORNING. AS THIS HAPPENS, A SHORT WAVE ALOFT APPROACHING FROM THE WEST WILL HELP STRENGTHEN THE LOW AS IT PASSES JUST TO OUR SOUTH OVERNIGHT AND LIFT TO OUR NORTHEAST MONDAY MORNING. MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT THAT SNOW WILL OVERSPREAD THE AREA ON THE NORTHERN SIDE OF THE SYSTEM OVERNIGHT SUNDAY INTO MONDAY MORNING. WITH THE LOW BEING TO OUR SOUTH, AND COLD HIGH PRESSURE TO OUR NORTH, IT LOOKS LIKE THE PRECIPITATION SHOULD BE ALL SNOW. AN ACCUMULATING SNOWFALL IS BECOMING MORE LIKELY, FOR MOST, IF NOT ALL OF OUR AREA SUNDAY NIGHT INTO MONDAY, WITH THE SOUTHERN HALF LOOKING TO RECEIVE THE MOST. WE MAY RUN INTO AN INSTANCE WHERE EXTREME SOUTHERN AREAS MAY HAVE MORE QPF BUT LOWER RATIOS, AND NORTHERN AREAS HAVING LESS QPF AND HIGHER RATIOS, AND IN BETWEEN HAVING A LITTLE OF BOTH. AS USUAL, WE`LL REFINE SNOW AMOUNTS IN SUBSEQUENT FORECASTS. ALL SNOW IS EXPECTED TO HAVE ENDED BY MONDAY EVENING AS THE LOW PULLS AWAY FROM THE AREA. VERY COLD AIR, NEAR RECORD LOW TEMPERATURES FOR SOME AREAS, ONCE AGAIN FILTERS DOWN INTO THE AREA OVERNIGHT ACROSS THE AREA AS COLD CANADIAN HIGH PRESSURE BUILDS DOWN INTO THE REGION AGAIN. WINDS SHOULD WEAKEN SOME OVERNIGHT AS THE PRESSURE GRADIENT SLACKENS WHEN THE HIGH STARTS TO BUILD INTO THE AREA. HOWEVER, THERE SHOULD BE ENOUGH WIND AND IT WILL BE COLD ENOUGH FOR WIND CHILLS TO FALL WELL BELOW ZERO MONDAY NIGHT INTO TUESDAY. HIGH PRESSURE ACROSS THE AREA TUESDAY WILL PUSH OFFSHORE TUESDAY NIGHT, AND DRY AND COLD CONDITIONS ARE EXPECTED THROUGH THIS PERIOD. ANOTHER FRONTAL BOUNDARY IS EXPECTED TO APPROACH THE AREA WEDNESDAY INTO WEDNESDAY NIGHT. THIS COULD BRING ANOTHER ROUND OF PRECIPITATION TO THE AREA, WHICH WOULD END UP BEING MOSTLY SNOW WITH THE CURRENTLY EXPECTED TEMPERATURES.
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&& .AVIATION /20Z THURSDAY THROUGH TUESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. 18Z TAFS BROUGHT MOST TERMINALS DOWN TO IFR THIS EVENING IN SNOW. VFR BUT VERY WINDY ON FRIDAY. REST OF THIS AFTERNOON VFR WITH LOWERING CIGS. LIGHT SOUTHEAST WINDS 5 TO 10 KNOTS. PCPN IS PREDICTED TO ARRIVE AT KRDG LATE THIS AFTERNOON. THIS EVENING BECOMING IFR VSBY IN SNOW WITH MVFR CIGS FROM THE PHL METRO AREA TERMINALS AND AIRPORTS NWWD. MVFR CIGS AND VSBYS IN MIXED PCPN AT KMIV AND KACY. LIGHT SOUTH TO SOUTHEAST WINDS. CONDITIONS SHOULD IMPROVE TO VFR LATER IN THE EVENING. OVERNIGHT AS THE COLD FRONT APPROACHES. CONDITIONS COULD LOWER TO MVFR AGAIN AS SNOW SHOWERS PRECEDE AND ACCOMPANY THE COLD FRONT. HIGHER CONFIDENCE NORTHERN AIRPORTS AND TERMINALS. THERE MIGHT EVEN BE BRIEF IFR CONDITIONS. SOUTH WINDS 5 TO 10 KNOTS WILL BECOME WEST AT AROUND 10 KNOTS. FRIDAY MORNING. VFR. A LIKELY STRATOCU DECK CIG AROUND 4K. WIDELY SCATTERED SNOW SHOWERS ARE POSSIBLE, BUT TOO ISOLATED TO INCLUDE IN TAFS FOR NOW. NORTHWEST WINDS WILL INCREASE TO AROUND 20 KNOTS SUSTAINED WITH GUSTS BETWEEN 30 AND 35 KNOTS. SOME HIGHER GUSTS ARE POSSIBLE FRIDAY AFTERNOON. OUTLOOK... FRIDAY NIGHT-SATURDAY NIGHT...IMPROVING TO VFR DURING THE EVENING AND CONTINUING INTO SATURDAY. GUSTY NORTHWEST WINDS 25-30 KNOTS POSSIBLE FRIDAY NIGHT INTO SATURDAY, DIMINISHING SATURDAY NIGHT. SUNDAY...VFR EARLY, MVFR POSSIBLE DEVELOPING BY LATE AFTERNOON WITH SNOW SHOWERS POSSIBLE. GUSTY WEST WINDS 15-20 KNOTS. SUNDAY NIGHT...DIMINISHING CONDITIONS TO IFR WITH SNOW LIKELY, ESPECIALLY SOUTHERN AREAS. GUSTY NORTHEAST WINDS 20-25 KNOTS. MONDAY...IFR WITH SNOW LIKELY EARLY, IMPROVING TO MVFR THEN VFR BY LATE AFTERNOON. GUSTY NORTH WINDS EARLY, BECOMING NORTHWEST BY AFTERNOON AROUND 20-25 KNOTS. MONDAY NIGHT-TUESDAY...GENERALLY VFR.
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&& .MARINE...
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WE MADE A SLIGHT ADJUSTMENT TO THE START OF THE GALE WARNING ON FRIDAY MORNING. THE MODELS ARE TRENDING WEAKER WITH THE GRADIENT AND CONSEQUENTLY THE SEAS FOR MOST OF TONIGHT. WITH JUST BORDERLINE SCA CONDITIONS NOW EXPECTED TONIGHT, WE OPTED TO SINGLE HEADLINE THIS PACKAGE AND WILL MAKE MENTION IN THE MWW. GALE CONDITIONS BECOMING LIKELIER AS FRIDAY PROGRESSES. OUTLOOK... FRIDAY NIGHT-SATURDAY...GALE CONDITIONS CONTINUING THROUGH SATURDAY AFTERNOON. FREEZING SPRAY ADVISORY FRIDAY NIGHT INTO SATURDAY. SATURDAY NIGHT...CONDITIONS DROP TO SMALL CRAFT ADVISORY LEVELS BY EVENING AND MAY DROP BELOW ADVISORY CONDITIONS OVERNIGHT. LIGHT FREEZING SPRAY POSSIBLE. SUNDAY-SUNDAY NIGHT...SUB-SMALL CRAFT ADVISORY CONDITIONS EXPECTED. MONDAY-MONDAY NIGHT...SMALL CRAFT ADVISORY CONDITIONS LIKELY...GALE CONDITIONS POSSIBLE DURING THE DAY MONDAY. FREEZING SPRAY LIKELY MONDAY NIGHT. TUESDAY...SUB-SMALL CRAFT ADVISORY CONDITIONS EXPECTED.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...WIND CHILL ADVISORY FROM MIDNIGHT FRIDAY NIGHT TO 11 AM EST SATURDAY FOR PAZ054-055. NJ...NONE. DE...NONE. MD...NONE. MARINE...FREEZING SPRAY ADVISORY FROM MIDNIGHT FRIDAY NIGHT TO 6 PM EST SATURDAY FOR ANZ430-431-450>455. GALE WARNING FROM 9 AM FRIDAY TO 6 PM EST SATURDAY FOR ANZ430- 431-450>455.
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&& $$ SYNOPSIS...ROBERTSON NEAR TERM...GIGI SHORT TERM...GIGI LONG TERM...ROBERTSON AVIATION...GIGI/ROBERTSON MARINE...GIGI/ROBERTSON

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