Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 251937 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 337 PM EDT MON MAY 25 2015 .SYNOPSIS...
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A HIGH PRESSURE SYSTEM WILL BE ANCHORED OFF THE EAST COAST THROUGH THE END OF THIS WEEK. A COLD FRONT WILL APPROACH FROM THE WEST WEDNESDAY AND EVENTUALLY DISSIPATE AS IT TRIES TO MOVE THROUGH THE FORECAST AREA THURSDAY. ANOTHER COLD FRONT IS FORECAST TO APPROACH THE AREA ON SUNDAY AND STALL IN OUR VICINITY ON MONDAY.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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HIGH PRES TO THE E WILL CONTINUE TO MOVE FURTHER OFFSHORE THRU TONIGHT. AS IT DOES, AN AREA OF LOW PRES WILL MOVE FROM THE UPR MS VLY INTO SERN CANADA, BRINGING ITS ASSOCD WMFNT WITH IT TONIGHT. THIS WILL PUT OUR REGION IN THE WARM SECTOR, COUPLED WITH THE S TO SWLY FLOW FROM THE AFOREMENTIONED HIGH. EXPECT DRY CONDS AND MAINLY HIGH CLOUDS OVERNIGHT. MOISTURE WILL SLOWLY BEGIN TO INCREASE, THOUGH TONIGHT SHOULD STILL BE RELATIVELY COMFORTABLE.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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ON TUE, THE WK CDFNT ASSOCD WITH THE LOW IN SERN CANADA WILL MOVE MAINLY N OF THE AREA DURG THE AFTN HOURS. THIS FRONT AND INCREASING MOISTURE WITH DAYTIME HEATING WILL BRING THE POTENTIAL FOR SHWRS/TSTMS, MAINLY OVER THE NWRN AREAS AND HIGHER TERRAIN. THE GFS IS A BIT MORE BULLISH ON THE PRECIP THAN THE ECMWF, NAM/WRF AND CMC. SO WHILE ITS PSBL FOR SOME PRECIP FURTHER S AND E, CONFIDENCE IS NOT HIGH ENOUGH TO MAKE CHANGES ATTM. WITH TEMPS FCST TO BE IN THE MID TO UPR 80S DEW POINTS STILL LOOK TO BE IN THE LOWER 60S, SO IT LOOKS TO BE HOT BUT COMFORTABLE.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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THE GFS AND WRF-NMMB/NAM INITIALIZATION LOOKED PRETTY GOOD WITH NO CLEAR CUT WINNER. HOWEVER, THE DP/DT ON THE GFS RUN SHOWED A SLOWER EVOLUTION OF THE PATTERN WHICH WE TOOK INTO CONSIDERATION. WE BASICALLY ARE GOING TO END MAY WITH TYPICAL JULY WEATHER, WARMER AND MORE HUMID WITH SHOWER AND THUNDERSTORM CHANCES. WHILE THERE ARE MODEL DIFFERENCES (NAM/EC PREFER WED OVER THU, GFS PREFERS SAT OVER SUN) AS TO THE MOST WIDESPREAD CONVECTIVE DAYS, WE ARE GOING TO TAKE A COMBINATION OF CONSENSUS AND BIAS ADJUSTING TO KEY ON THU AND SUN AS THE MOST CONVECTIVELY ACTIVE DAYS IN THE LONG TERM AND SATURDAY THE RELATIVE LULL. REGARDLESS AFTER NOT BEING ABLE TO BUY A THUNDERSTORM, ITS TOUGH TO FIND A DAY TO NOT INCLUDE A THUNDERSTORM. THERE IS ACTIVE CONVECTION IN THE GULF COASTS STATES AND THE MEAN FLOW IS GOING TO TAKE IT TOWARD THE WESTERN PART OF OUR CWA ON TUESDAY NIGHT. WE CARRY SOME LOW POPS ON TUESDAY NIGHT. IT WILL BE A MORE HUMID NIGHT WITH MIN TEMPS NOT AS LOW. ON WEDNESDAY, A COLD FRONT IS EXPECTED TO COME CLOSER TO OUR CWA. COUPLED WITH HIGHER DEW POINTS AND THE RELATIVE CORE OF WARMEST AIR ALOFT (925MB ANALYSIS HAS IT OVER PA THIS MORNING, BUT MORE SOUTH GROWN HEAT WILL LIKELY KEEP A STATUS QUO IN 850/925MB TEMPS THRU WED) PASSING OVER OUR CWA WOULD BE MORE CONDUCIVE FOR TSTMS TO DEVELOP WITH CONVECTIVE TEMPS WITHIN REACH. THE LATEST ECMWF TAKES A SLIGHTLY FASTER TIMING THAN MOST OTHER MODELS. THIS BUCKS THE TREND OF AN OVERALL SLOWER EVOLUTION THAT THE MODELS HAVE THRU TODAY. LOOKING AT MODELING SIMILARITIES VS DIFFERENCES, ALL OF THEM HAVE THE MOST CONDUCIVE FOR CONVECTION THERMODYNAMIC FEATURES IN THE NWRN PART OF OUR CWA. THE GFS AND WRF-NMM AGREE ABOUT MID LEVEL DRY AIR MAKING STORMS PULSIER. BUT FROM THERE KINEMATICALLY THERE ARE TOO MANY DIFFERENCES WED VS THU TO RESOLVE AT THIS TIME AS TO MORE ORGANIZATIONAL/STRONGER STORMS. GIVEN THE NWRN CONSENSUS WE UPPED LATE POPS TO LIKELY, BUT ADDED NO ENHANCED WORDING. WHILE THUNDERSTORMS WILL BE STRONG, HIGH PWATS WILL ALSO PRODUCE LOCALLY HEAVY DOWNPOURS. TEMPERATURES, GIVEN DECENT WINDS ALOFT PLUS NO INDICATION OF A DEW POINT POOLING IN OUR CWA, WITH BREEZY CONDITIONS, STAT GUIDANCE (AND MODEL GUIDANCE MORE CONFIDENTLY) IS LIKELY TOO HIGH WITH AFTERNOON DEW POINTS, OR ANY SURPRISE WONT BE ON THE HIGH SIDE. THIS BRINGS HEAT INDEX VALUES CLOSE TO AIR TEMPERATURES AND LIKELY TOP IN THE LOWER 90S. WE ARE GOING WITH THE HIGHER NAM STAT GUIDANCE FOR MAX TEMPS GIVEN ONGOING GFS STAT GUIDANCE COOL BIAS WITH MAX TEMPS. ON WEDNESDAY NIGHT, CONVECTION WILL TRY TO SPREAD ACROSS OUR CWA. THERE ARE PREDICTIONS OF SHORT WAVES, SO WE WILL KEEP A CHANCE (NOT AS HIGH AS THE AFTERNOON THOUGH), GOING THRU THE NIGHT. THE COLD FRONT SHOULD BE ENTERING OUR CWA ON THURSDAY. WITH THE WEAKENING BOUNDARY, THE MODELS ARE OFFERING DIFFERING OPINIONS AS TO HOW ACTIVE THE FRONT CAN REMAIN. THE GFS IS MOST BULLISH AS IT HAS DEEPER QVEC CONVERGENCE, BULK SHEAR AND ENTRANCE REGION OF THE 250 MB JET. THE OTHER MODELS ARE A BIT MORE DIFFUSE. REGARDLESS, THE RELATIVELY HIGHER POPS ALONG THE BOUNDARY WILL BE CENTERED IN OUR CWA. AS THE MODELS ARE DIFFERING AS TO HOW ACTIVE, WE KEPT POPS AS CHANCE. COMBINATION OF MORE UPWIND DEBRIS AS FRONTAL PROXIMITY, AIR MASS IS SLIGHTLY COOLER ON THU. MAX TEMPS NUDGED DOWN SLIGHTLY. DEW POINTS THOUGH SHOULD POOL MORE EFFICIENTLY SO ZERO SUM GAIN WITH APPARENT TEMPS. THE FRONTAL BOUNDARY SHOULD LINGER AND DISSIPATE OVER OUR CWA ON THURSDAY NIGHT AND FRIDAY. IT COULD ACT AS A FOCUS FOR MORE CONVECTION. BUT GIVEN, ITS DISSIPATING, OVERALL POPS ARE LOWER THAN THURSDAY. WE WILL KEY ON SUNDAY VS SATURDAY AS THE CONVECTIVELY MORE ACTIVE DAY GIVEN THE BETTER MODEL CONSENSUS AND OVERALL TENDENCY FOR A SLOWER TIMING. POPS HIT A RELATIVE LOW ON SATURDAY BEFORE RAMPING UP AGAIN ON SUNDAY. ALSO GIVEN THE SLOWER FRONTAL TIMING, MAX TEMPS ARE MUCH CLOSER TO WPC GUIDANCE AND EC MOS GUIDANCE THAN GFS MOS. INITIAL LOOK AT MONDAY HAS THE FRONT STALLED JUST SOUTH OF OUR CWA, THIS SHOULD BE RELATIVELY COOLER WITH STILL SOME SHOWERS AND THUNDERSTORMS AROUND.
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&& .AVIATION /20Z MONDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDS ARE EXPECTED THRU THE TAF PD, WITH HIGH PRES OFF THE CST AND SWLY FLOW TODAY BECOMING MORE SLY AND THEN SWLY ON TUE AGAIN. WIND CUD GUST TO AROUND 20 KT THRU EVE, BEFORE DECREASING TO LESS THAN 10 KTS OVERNIGHT. ON TUE, THERE CUD BE SOME DIURNAL SHRA/TSRA MAINLY FOR KABE/KRDG, BUT POPS ARE TOO LOW TO INCLUDE IN INDIVIDUAL TAF FCSTS. ALSO, TIMING IS UNCERTAIN. OUTLOOK... TUESDAY NIGHT...PATCHY RADIATIONAL FOG IS POSSIBLE LATE. WEDNESDAY THROUGH THURSDAY...WHILE PREDOMINATELY VFR, SCATTERED SHOWERS AND TSTMS WILL PRODUCE SOME MVFR TO BRIEFLY IFR CONDITIONS AT TIMES. THURSDAY NIGHT THROUGH SATURDAY...OVERALL COVERAGE OF SHOWERS AND TSTMS (THUS MVFR TO BRIEF IFR CONDITIONS) SHOULD BE LESS. THERE COULD STILL BE SOME PATCHY RADIATIONAL FOG EACH MORNING.
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&& .MARINE...
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A SCA REMAINS IN EFFECT FOR THE NRN WATERS THRU TONIGHT. WIND CUD GUST TO AROUND 25 KT AND SEAS CUD REACH AROUND 5 FT, THOUGH RIGHT NOW BOTH WIND AND SEAS ARE BELOW CRITERIA. BASED ON LATEST GUIDANCE, WILL NOT BE EXTENDING ENDING TIME. OUTLOOK... TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...A STRONG SOUTHERLY FLOW MIGHT PRODUCE SMALL CRAFT ADVISORY GUSTS AND SEAS REACHING 5 FEET ON THE OCEAN WATERS. USUALLY IN THESE SCENARIOS, THE MODELS TEND TO BE TOO BULLISH. WE WILL CONTINUE TO MONITOR, BUT NOT CONFIDENT TO EXTEND CURRENT ADVISORY. THURSDAY THROUGH SATURDAY...WINDS AND WAVES SHOULD BE BELOW SCA THRESHOLD AS A WEAKER PRESSURE PATTERN SHOULD PREVAIL.
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&& .CLIMATE...
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A TOP 10 WARMEST MAY WILL OCCUR IN LARGE PORTIONS OF OUR FORECAST AREA. THE FIRST 24 DAYS OF MAY IN OUR FORECAST AREA WERE AVERAGING ABOUT 5 TO 6 DEGREES ABOVE NORMAL. RUNNING THE NUMBERS FROM THE FCST THROUGH THE END OF THE MONTH WE FIND THE FOLLOWING. FOR PHILADELPHIA...PERIOD OF RECORD (POR) BACK TO 1874. PROJECTING A MONTHLY AVERAGE TEMPERATURE OF 69 TO 70 RISING FROM THE CURRENT VALUE OF 67.8, AT LEAST 5 TO 6 DEGREES ABOVE NORMAL. HEADING FOR MOST LIKELY THE THIRD WARMEST MAY ON RECORD. WARMEST AVERAGE TEMPERATURE IN MAY ON RECORD WAS 70.8 IN 1991. THEN 69.2 2004 AND 68.2 IN 2012. FOR ALLENTOWN...PERIOD OF RECORD (POR) BACK TO 1922. THE MONTHLY AVERAGE TEMPERATURE IS CURRENTLY 63.9 DEGREES. IT IS LIKELY TO INCREASE BY A DEGREE OR TWO LATER THIS WEEK, LEADING TO A TOP 10 WARMEST MAY THIS YEAR AT ALLENTOWN. THE WARMEST AVERAGE TEMPERATURE IN MAY WAS 67.2 BACK IN 1991. FOR WILMINGTON.... THE MONTH OF MAY IS LIKELY TO END UP IN THE TOP 5- 10 WARMEST. THE CURRENT MONTHLY TEMPERATURE IS 65.8 DEGREES AND SHOULD RISE A DEGREE OR TWO BY MONTHS END. THE WARMEST MAY WAS IN 1896 WHERE THE MONTHLY TEMPERATURE WAS 70.1 DEGREES. IN 1991 THE MONTHLY TEMPERATURE WAS 69.1 DEGREES. FOR ATLANTIC CITY... THE MONTH IS LIKELY TO END UP IN THE TOP THREE WARMEST MAYS. CURRENTLY, THE AVERAGE TEMPERATURE FOR THE MONTH IS 64.5 DEGREES AND IS LIKELY TO RISE A DEGREE TOR TWO BY MONTHS END. THE WARMEST MAY WAS BACK IN 2004 WHERE THE AVERAGE TEMPERATURE REACHED 66.9 DEGREES. IN 1991 THE MONTHLY AVERAGE TEMPERATURE WAS 66 DEGREES. BOTH 2011 AND 2012 SAW A MONTHLY AVERAGE TEMPERATURE OF 65 DEGREES. NORMAL FIRST DATE OF 90 OR HIGHER. PHILADELPHIA MAY 29 ALLENTOWN MAY 30 WILMINGTON JUNE 4 ATLANTIC CITY JUNE 11. ************************************************************* HERE IS OUR ANNUAL LOOK AS TO HOW HOT, HOT, HOT THE SUMMER WILL BE BASED ON PAST PERFORMANCES. A FULL FLEDGED EL NINO IS UNDERWAY IN THE TROPICAL PACIFIC. ALL DYNAMICAL AND STATISTICAL MODELS KEEP IT GOING, THE DIFFERENCES THAT EXIST ARE TO ITS STRENGTH THROUGH THIS UPCOMING SUMMER. THE DYNAMICAL AND STATISTICAL MODELS ARE AVERAGING A MODERATE EL NINO FOR THE COMBINED SUMMER MONTHS. SOME MODELS, INCLUDING THE CFS2 AND ECMWF ARE PREDICTING A STRONG EL NINO. IN THE CPC MONITORING EL NINO ERA STARTING SINCE 1950, THE HIGHEST (WARMEST) SUMMER ANOMALY RECORDED WAS +1.5C (NEAR OR AT THE THRESHOLD FOR STRONG EL NINOS) DURING THE SUMMER OF 1997. THIS UPCOMING WEEK WILL REALLY SEAL THE DEAL THAT THIS MAY WILL BE UNSEASONABLY WARM IN PHILADELPHIA. IT "MAY" EVEN BE A TOP THREE WARMEST. THIS FOLLOWS ON THE HEELS OF AN UNSEASONABLY WARM APRIL. SINCE 1872, THE COMBINATION OF BOTH WARM (TOP THIRD OF ALL YEARS) APRILS AND MAYS HAS ONLY OCCURRED TWENTY-THREE TIMES. BUT IT HAS OCCURRED ELEVEN TIMES SINCE 1990 AND SIX OF THE LAST SEVEN SPRINGS. SO WE SCOURED THE CLIMATE RECORDS TO FIND BUDDING OR IN PROGRESS EL NINOS THAT COINCIDED WITH BOTH WARM APRILS AND MAYS LOCALLY IN THE CPC MONITORING ERA. WE FOUND THREE PAST SUMMERS THAT MET THE CRITERIA. THE ONE SIGN IS THAT ALL THREE ANALOG SUMMERS WERE WETTER THAN NORMAL, HOPEFULLY KEEPING DROUGHT CONDITIONS FROM INTENSIFYING FURTHER. THE NORTH AMERICAN MULTI MODEL ENSEMBLE PREDICTIONS FOR THIS UPCOMING SUMMER HAS WARMER AND DRIER THAN NORMAL WEATHER EXPECTED IN OUR AREA. THE INTERNATIONAL MULTI MODEL ENSEMBLE FORECASTS ARE SLIGHTLY MORE OPTIMISTIC PREDICTING NEAR NORMAL TEMPERATURES AND PRECIPITATION. THE ANALOGS FOR PHILADELPHIA ARE: YEAR JUNE AVG JULY AVG AUGUST AVG SUMMER AVG SUMMER PCPN 1969 73.4 75.1 75.2 74.6 18.30 1977 68.6 77.8 76.2 74.2 15.50 1991 75.7 79.0 79.0 77.9 12.01 AVG 72.6 77.3 76.8 75.6 15.27 1981- 2010 73.3 78.1 76.6 76.0 11.28 NORMAL THE OFFICIAL CPC OUTLOOK FOR OUR FORECAST AREA IS FOR EQUAL CHANCES OF ABOVE AND BELOW NORMAL TEMPERATURES AS WELL AS EQUAL CHANCES OF ABOVE AND BELOW NORMAL PRECIPITATION.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ450>452. $$ SYNOPSIS...GIGI/KLEIN NEAR TERM...NIERENBERG SHORT TERM...NIERENBERG LONG TERM...GIGI AVIATION...GIGI/KLEIN/NIERENBERG MARINE...GIGI/KLEIN/NIERENBERG CLIMATE...DRAG/GAINES/GIGI/LAGUARDIA

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