Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 141334 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 934 AM EDT TUE APR 14 2015 .SYNOPSIS... A COLD FRONT WILL TRACK ACROSS THE REGION TODAY, WITH A WAVE OF LOW PRESSURE PASSING BY TO OUR SOUTH ALONG THE DEPARTING BOUNDARY LATE TODAY AND TONIGHT. AN AREA OF HIGH PRESSURE WILL THEN BUILD ACROSS THE NORTHEAST AND MID ATLANTIC STATES THROUGH MIDWEEK. THIS HIGH PRESSURE IS FORECAST TO MOVE OFFSHORE BY FRIDAY, ALLOWING UNSETTLED WEATHER TO RETURN FOR THE END OF THE WEEK AND THE WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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9:30 AM UPDATE: HOURLY TEMPERATURES TEMPERATURES AND DEWPOINTS WERE ADJUSTED THROUGH THE EARLY AFTERNOON BASED ON THE POSITION OF THE FRONT AND CURRENT OBS. WITH THE RAINFALL AND FRONTAL PASSAGE TEMPERATURES HAVE FALLEN OFF SEVERAL DEGREES ACROSS NORTHERN PORTIONS OF THE AREAS. RADAR TRENDS SHOW THE RAINFALL ENDING NORTHWEST OF THE PHILADELPHIA METRO AREA, SO HAVE REDUCED POPS IN THOSE LOCATIONS FOR THE AFTERNOON. QPF WAS UPDATED WITH THE LATEST GUIDANCE FROM THE MARFC. A COLD FRONT IS SLOWLY MOVING SOUTH TOWARD THE INTERSTATE 95 REGION. STILL EXPECTING IT TO SLOWLY SAG SOUTH THROUGH THE DAY. A LOW PRESSURE SYSTEM IS EXPECTED TO DEVELOP ON THE FRONT, BUT THIS SHOULD OCCUR ONCE IT IS SOUTH OF OUR REGION. THIS COULD ENHANCE PRECIP OVER THE FAR SOUTHEASTERN PORTIONS OF THE REGION FROM LATE MORNING THROUGH MID AFTERNOON. MODEL SOUNDINGS, ESPECIALLY THE NAM, ARE SHOWING MODEST ELEVATED INSTABILITY OVER DELMARVA AND EXTREME SOUTHERN NJ (UP TO 100 J/KG CAPE VALUES). THIS IS NOT SURPRISING GIVEN THE LATER ARRIVAL OF THE FRONT. STILL, AS SATURATED AS THE ENTIRE COLUMN WILL BE, AND AS ELEVATED AS THE INSTABILITY WILL BE, THUNDERSTORMS SEEM VERY UNLIKELY, SO WILL LEAVE OUT OF THE FORECAST FOR NOW.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... PRECIP COULD LINGER THROUGH THE EARLY EVENING HOURS ACROSS SOUTHERN DELMARVA, BUT OTHERWISE, SHOULD SEE DRY CONDITIONS ACROSS MUCH OF THE REGION. ABOUT THE ONLY SIGNIFICANT CHANGE TO THE FORECAST WAS TO INCREASE SKY COVER IN ANTICIPATION OF THICK CIRRUS DEVELOPMENT AS THE UPPER LEVEL JET SLIDES EAST. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... A QUIETER TREND IS EXPECTED AT THE BEGINNING OF THIS PERIOD AS SURFACE HIGH PRESSURE CENTERED OVER SOUTHEASTERN CANADA WILL BE BUILDING DOWN ACROSS THE NORTHEAST TO MID ATLANTIC STATES THROUGH WEDNESDAY AND THURSDAY. WITH THE HIGH PRESSURE CENTERED TO OUR NORTH THROUGH WEDNESDAY, AMPLE SUN WITH SLIGHTLY ABOVE AVERAGE TEMPERATURES AND MODEST NORTHERLY WINDS ARE EXPECTED. MAXIMUM TEMPERATURES ARE ANTICIPATED TO REACH THE MIDDLE TO UPPER 60S ACROSS MOST OF THE REGION, WITH SOMEWHAT COOLER UPPER 50S TO NEAR 60 DEGREE READINGS INTO THE POCONOS AND ALONG THE COASTS OF NEW JERSEY AND DELAWARE. WHILE GENERALLY QUIET CONDITIONS ARE EXPECTED TO CONTINUE INTO THURSDAY, THE CENTER OF THE SURFACE HIGH PRESSURE IS PROGGED TO BE PASSING OFF THE COAST OF THE NORTHEAST STATES, AND THIS WILL ALLOW FOR MORE OF AN EASTERLY SURFACE FLOW TO SET-UP ACROSS OUR REGION, BRINGING A RETURN TO MORE CLOUDS AND DAYTIME TEMPERATURES NEAR TO SLIGHTLY BELOW MID-APRIL AVERAGES. MAX TEMPS FOR THURSDAY SHOULD BE MORE IN THE UPPER 50S TO LOWER 60S ACROSS THE REGION, WITH COOLER LOW/MID 50S POSSIBLE INTO THE POCONOS AND ALONG THE COAST. FROM HERE, A MORE UNSETTLED PATTERN IS EXPECTED TO CLOSE OUT THE WEEK AND EXTEND THROUGH THE WEEKEND AND POSSIBLY MONDAY. WITH THE PREVIOUSLY MENTIONED HIGH PRESSURE EAST AND OFFSHORE, A SHORTWAVE UPPER-LEVEL TROUGH IS PROGGED TO PASS OVER THE REGION FRIDAY, BRINGING SCATTERED RAIN SHOWERS. INTO THE WEEKEND AND MONDAY, THERE CONTINUES TO BE A RATHER LARGE SPREAD OF MODEL SOLUTIONS REGARDING THE TIMING, EVOLUTION, AND TRACK OF POSSIBLE LOW PRESSURE AND ITS ASSOCIATED FRONTAL BOUNDARIES DEVELOPING AND MOVING IN A SPLIT FLOW PATTERN. THIS LEADS TO GREATER UNCERTAINTY IN THE TIMING AND AMOUNT OF PRECIPITATION THAT COULD AFFECT OUR FORECAST AREA OVER THE WEEKEND AND INTO MONDAY. THEREFORE, WE MAINLY TOOK A BLEND OF WPC GUIDANCE WITH CONTINUITY FOR THIS TIMEFRAME, WITH MAINLY CHANCE POPS IN PLACE DURING THIS TIMEFRAME. FOR COMPARISON SAKE, THE LATEST ECMWF WOULD HAVE A RELATIVELY DRY WEEKEND, WITH THE MAIN PRECIPITATION EVENT GOING INTO MONDAY. MEANWHILE, THE GFS HAS DONE A BIT OF A FLIP-FLOP, WITH SUNDAY INTO MONDAY NOW BEING THE WETTER PERIOD AND SATURDAY BEING RELATIVELY DRY. AS WE GET CLOSER IN TIME TO THE UPCOMING WEEKEND, MODEL RUNS WILL HOPEFULLY SHOW MORE CONSISTENCY AND RESOLVE THE TIMING AND AMOUNT OF POTENTIAL PRECIP TO AFFECT OUR AREA IN THE SPLIT FLOW PATTERN. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. AS OF 07Z, COLD FRONT IS SLOWLY MOVING EAST OVER CENTRAL PA. IT SHOULD BE ARRIVING AT THE WESTERN TAF SITES (KRDG AND KABE) BEFORE DAY BREAK, THE DELAWARE VALLEY SITES (KPHL, KPNE, KILG, KTTN) AROUND OR JUST BEFORE 12Z, AND THE COASTAL SITES (KMIV AND KACY) BY MID TO LATE MORNING. WITH THE FRONT, EXPECT GENERALLY A 4 TO 6 HOUR WINDOW OF SHRA, WITH OCCASIONAL MVFR CONDITIONS. KMIV AND KACY COULD SEE A FEW HOURS OF IFR CONDITIONS, AND SHRA LINGERING FOR MUCH OF THE AFTERNOON. CONDITIONS SHOULD IMPROVE TO VFR BETWEEN 18 AND 00Z, AND REMAIN VFR FOR THE REST OF THE TAF PERIOD. OUTLOOK... WEDNESDAY...VFR CONDITIONS ARE EXPECTED WITH NORTHERLY WINDS. THURSDAY...CONTINUED VFR, WITH EASTERLY TO SOUTHEAST WINDS. THURSDAY NIGHT AND FRIDAY...CONDITIONS LOWERING TO MVFR WITH SCATTERED RAIN SHOWERS. SATURDAY...SUB-VFR POSSIBLE IN ISOLATED/SCATTERED SHOWERS. LOW CONFIDENCE. && .MARINE... SOUTHERLY WINDS WILL SHIFT ABRUPTLY TO NORTHWESTERLY WITH THE ARRIVAL OF A COLD FRONT LATER TODAY. WIND GUSTS NEAR OR ABOVE 20KT ARE POSSIBLE THROUGH THE EVENING AND OVERNIGHT HOURS. FOR THE COASTAL WATERS FROM FENWICK ISLAND UP TO ATLANTIC CITY, SCA CONDITIONS ARE LIKELY BEGINNING LATE TONIGHT. WAVES WILL SUBSEQUENTLY INCREASE WITH THE WIND SPEED INCREASE. OUTLOOK... WEDNESDAY...WIND GUSTS TO AROUND 20 KNOTS AND SEAS AROUND 5 FEET ARE EXPECTED TO CONTINUE FOR OUR SOUTHERN COASTAL WATERS FROM GREAT EGG INLET SOUTH TO FENWICK ISLAND DE, AND A SMALL CRAFT ADVISORY LASTS INTO EARLY AFTERNOON. OTHERWISE, WINDS AND SEAS ARE FORECAST TO BE SUB-ADVISORY FOR THE REST OF THE COASTAL WATERS AND DELAWARE BAY. THURSDAY...SUB-ADVISORY CONDITIONS ARE EXPECTED. FRIDAY AND SATURDAY...MORE UNCERTAINTY EXISTS DURING THIS PERIOD, BUT SEAS AT OR ABOVE 5 FT ARE POSSIBLE FOR THE COASTAL WATERS, ESPECIALLY ON SATURDAY. && .FIRE WEATHER... FOR TODAY...LOCATIONS NORTH AND WEST OF THE FALL LINE, INCLUDING LEHIGH VALLEY, NORTHWEST NJ, AND THE POCONOS, COULD SEE MINIMUM AFTERNOON RELATIVE HUMIDITY VALUES NEAR 30 PERCENT. HOWEVER, WITH WETTING RAINS EXPECTED THIS MORNING, AND WINDS GENERALLY LESS THAN 10 MPH, NO FIRE WEATHER CONCERNS ARE ANTICIPATED AT THIS TIME. FOR WEDNESDAY...WHILE RELATIVE HUMIDITY VALUES WILL LIKELY DROP INTO THE 20S ACROSS MUCH OF THE AREA, WINDS ARE NOT EXPECTED TO FREQUENTLY GUST ABOVE 20 MPH. IN ADDITION, MUCH OF THE REGION IS EXPECTED TO RECEIVE WETTING RAINS DURING TUESDAY AND TUESDAY NIGHT, WHICH SHOULD HELP TO MOISTEN THE FINE FUELS. && .HYDROLOGY... ACROSS DELMARVA AND SOUTHERN NEW JERSEY, GENERALLY ALONG AND SOUTHEAST OF THE I95 CORRIDOR, STILL WATCHING FOR HEAVY RAIN POTENTIAL FROM MID MORNING THROUGH LATE THIS AFTERNOON, ALTHOUGH TIMING IS HIGHLY DEPENDENT ON HOW QUICKLY AND HOW FAR THE FRONT WILL SLIDE SOUTH. NEAR THE FRONT, RELATIVELY HIGH MEAN RH, PWATS WELL ABOVE NORMAL, AND A DEEP WARM CLOUD LAYER WILL ENHANCE THE HEAVY RAIN THREAT. THE ONLY QUESTION IS HOW LONG THE THREAT WILL LAST. SO FOR NOW, WILL KEEP THE SAME WORDING IN THE HWO. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FROM 2 AM TO 2 PM EDT WEDNESDAY FOR ANZ453>455. && $$ SYNOPSIS...KLINE NEAR TERM...GAINES/JOHNSON SHORT TERM...JOHNSON LONG TERM...KLINE AVIATION...JOHNSON/KLINE MARINE...JOHNSON/KLINE FIRE WEATHER... JOHNSON HYDROLOGY...JOHNSON

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