Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 260827
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
427 AM EDT TUE MAY 26 2015

.SYNOPSIS...
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.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
FOR THE THIRD STRAIGHT DAY, HIGH PRESSURE WILL REMAIN PARKED OFF THE
MID-ATLANTIC COAST TODAY. ALTHOUGH THE HUMIDITY WILL INCREASE
SLIGHTLY TODAY OWING TO THE CONTINUED SOUTHERLY RETURN FLOW AROUND
THE HIGH, IT WON`T BE ON PAR WITH A QUINTESSENTIAL MUGGY SUMMER DAY
IN THE MID ATLANTIC. OFFICIAL TEMP FORECAST FALLS ON THE WARMER
ENVELOPE OF GUIDANCE AFTER TAKING INTO ACCOUNT THE RECENT COOL BIAS
EXHIBITED BY THE MODELS. EXPECT HIGHS TODAY TO BE IN THE MID TO
UPPER 80S WHICH IS GENERALLY ON PAR WITH YESTERDAY, IF NOT A DEGREE
OR TWO WARMER. DID NOT QUITE GO HIGH ENOUGH TO FORECAST THE FIRST 90
DEGREE DAY OF THE SEASON FOR PHILADELPHIA, BUT THE POSSIBILITY
CANNOT BE COMPLETELY RULED OUT.

THE UPPER RIDGE AXIS IS FORECAST TO SHIFT JUST EAST OF THE EAST
COAST TODAY. THE LARGE-SCALE SUBSIDENCE ASSOCIATED WITH THIS RIDGE
WILL WEAKEN OVERHEAD A BIT, WHICH MAY RESULT IN SOME POP UP SHOWERS
AND STORMS FORMING OVER THE HIGHER TERRAIN OF NE PA AND NW NJ. THE
WINDOW FOR CONVECTION APPEARS TO BE MID TO LATE AFTERNOON WHEN
DIURNAL INSTABILITY PEAKS AND A SUBTLE SHORTWAVE TROUGH THAT IS
CURRENTLY OVER THE SOUTHERN APPALACHIANS MOVES AROUND THE RIDGE AND
INTO EASTERN PA. MLCAPE PROFILES BELOW 1000 J/KG AND DEEP-LAYER BULK
SHEAR BELOW 25 KT ARE NOT SUPPORTIVE OF INTENSE/ORGANIZED STORMS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
A MILD NIGHT IS IN STORE TONIGHT WITH PERSISTENT SOUTHERLY FLOW
AROUND THE OFFSHORE HIGH. HOURLY POPS FOR TONIGHT EXHIBIT A SEMI-
DIURNAL TREND; DECREASING AFTER SUNSET DUE TO THE LOSS OF DAYTIME
INSTABILITY. HOWEVER, ISOLATED SHOWERS MAY LAST INTO PART OF THE
NIGHT OVER THE HIGHER TERRAIN AS A WEAK DISTURBANCE MOVES THROUGH
THE AREA.

AT THE VERY LEAST, THE AFOREMENTIONED DISTURBANCE WILL RESULT IN AN
INCREASE IN MID AND HIGH CLOUDS OVER A MAJORITY OF THE FORECAST
AREA. THE CLOUDS WILL LIMIT RADIATIONAL COOLING AND KEEP TEMPS
WARMER THAN IN PREVIOUS NIGHTS. FORECAST LOWS ARE GENERALLY IN THE
MID TO UPPER 60S. CLOUDS WILL LIMIT THE FOG POTENTIAL, BUT THERE MAY
BE PATCHY FOG THAT DEVELOPS TOWARD DAWN AT INLAND LOCATIONS THAT
RECEIVE ANY RAINFALL TODAY.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
5-WAVE MODEL GUIDANCE SHOWS EAST COAST RIDGING AS THE DOMINANT FORCE
THROUGH MOST OF THE LONGTERM PERIOD, WITH A RIPPLE OR TWO. BY THE
WEEKEND THE RIDGING BEGINS TO BREAK DOWN, MOVES OFF TOWARDS THE
NORTHEAST, WHILE GREAT LAKES TROUGHING STARTS TO PUSH IN EARLY NEXT
WEEK.

OVERALL THE LONGTERM REMAINS IN TACT FROM THE PREVIOUS SHIFT WITH
DAILY CHANCES FOR SHOWERS AND THUNDERSTORMS EACH AFTERNOON TIME
PERIOD...BETTER WEST THAN EAST WITH LEE TROUGHING POSSIBLE AND
DIFFERENTIAL HEATING ALONG THE RIDGE TOPS.

WEDNESDAY...COLD FRONT MOVES CLOSER TO THE REGION FROM THE
NORTHWEST. EXPECTING A THERMAL/LEE SIDE TROUGH TO DEVELOP TO OUR
IMMEDIATE WEST DURING THE PEAK HEATING HOURS AND SLOWLY MOVE IT TO
THE EAST THROUGH THE EVENING HOURS. BETTER HEATING ALONG THE RIDGE
TOPS SHOULD BE THE PRIME FOCUS FOR CONVECTIVE INITIATION DURING THE
AFTERNOON HOURS WHERE HIGHER SURFACE BASED CAPE VALUES SETUP AND
SOMEWHAT BETTER 0-4KM SHEAR VALUES...AROUND 35 KNOTS. ONE ISSUE IS
STRICTLY TIED TO THE TIMING OF THE TROUGHS PASSAGE AS THE SHEAR
VALUES ARE EXPECTED TO DECREASE THROUGH THE AFTERNOON. NONE-THE-LESS
POP-UP/AIRMASS THUNDERSTORMS ARE EXPECTED WITH BETTER ORGANIZED
CONVECTION TO OUR SOUTHWEST AND NORTH. WHILE THUNDERSTORMS WILL BE
STRONG, HIGH PWATS WILL ALSO PRODUCE LOCALLY HEAVY DOWNPOURS.
TEMPERATURES STILL RUNNING WELL ABOVE NORMAL THOUGH COULD END UP A
DEGREE OR TWO COOLER THAN TUESDAY WITH A BIT MORE CLOUD COVER IN
PLACE.

NOT EXPECTING TO HAVE ISSUES WITH HEAT INDEX VALUES AS WE SHOULD BE
ABLE TO MIX OUT THE DEWPOINTS A BIT, THOUGH MUCH LESS THAN PREVIOUS
DAYS, AND KEEP VALUES SLIGHTLY STICKIER THAN PREDICTED AFTERNOON
MAXES.

THURSDAY - FRIDAY...COLD FRONT LOOKS TO STALL AND EVENTUALLY
DISSIPATE ACROSS THE REGION BY FRIDAY. THE FORCING WITH THE FRONT
DECREASES WITH TIME BECOMING NIL BY FRIDAY. AGAIN, WITH A WARM
AIRMASS IN PLACE, THOUGH SLIGHTLY COOLER THAN PREVIOUS DAYS, WE WILL
HAVE PLENTY OF DEWPOINT POOLING OCCURRING TO KEEP THE CHANCE POPS
BOTH DAYS...DIFFUSE FRONT WILL ACT AS A MOISTURE CONDUIT WITH
POCKETS OF HEAVIER RAIN BEING THE BIGGER ISSUE COMPARED TO SEVERE
STORMS.

SATURDAY - SUNDAY...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.

MONDAY...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. EASTERLY ONSHORE FLOW WILL HELP TO KEEP
MOISTURE STREAMING INTO THE REGION WHICH MAY PRODUCE A MUCH NEEDED
WIDESPREAD SOAKING RAIN WITH SUPPORT FROM THE UPPER LEVEL
DYNAMICS...JET INTERACTION AND PASSING SHORTWAVES.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

PREDOMINATELY VFR TODAY AND THIS EVENING. SOUTHERLY WINDS 5-10 KT
THIS MORNING WILL INCREASE THIS AFTERNOON WITH GUSTS UP TO 20 KT
POSSIBLE. MAY SEE AN ISOLATED SHRA OR TSRA IN VC OF ABE/RDG BUT
COVERAGE TOO LOW TO INCLUDE IN THE 06Z TAF ISSUANCE.

MOST TAF SITES SHOULD REMAIN AT VFR OVERNIGHT BUT PATCHY FOG MAY
DEVELOP AT THE USUAL FOG-PRONE TERMINALS.

OUTLOOK...
WEDNESDAY...POSSIBLE MORNING MVFR FOG. NUMEROUS SHOWERS AND
THUNDERSTORMS EXPECTED DURING THE AFTERNOON/EARLY EVENING
HOURS...BETTER CHANCES ACROSS RDG/ABE.

THURSDAY-SATURDAY...EARLY MORNING FOG/STRATUS FOLLOWED BY
SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS.

&&

.MARINE...
THE SCA THAT WAS IN EFFECT FOR PORTIONS OF THE COASTAL WATERS EARLY
THIS MORNING WAS CANCELLED AS WINDS ARE BELOW 20 KT AND SEAS 4 FT OR
LESS.

DEBATED ON WHETHER OR NOT TO ISSUE A SCA FOR THIS AFTERNOON AND
TONIGHT AS WINDS WILL BE GUSTY FOR A PERIOD LATE IN THE DAY TODAY
AND WAVES WILL RESPOND ACCORDINGLY. OPTED TO HOLD OFF ON ANY MARINE
HEADLINE SINCE THE WIND FIELD WILL BE SLIGHTLY WEAKER THIS AFTERNOON
THAN YESTERDAY, SO NEAR-SHORE GUSTS SHOULD GENERALLY BE BELOW 25 KT.
WINDS WILL BE STRONGER A FEW MILES OFFSHORE BUT MIXING WILL BE
SIGNIFICANTLY WEAKER DUE TO THE COOLER WATERS. SEAS TONIGHT SHOULD
GENERALLY BE AROUND 4 FT IN THE COASTAL ATLANTIC.

OUTLOOK...

WEDNESDAY...POSSIBLE SCA CONDITIONS WITH A STRONG SOUTHERLY FLOW
INPLACE. GUSTS MAY REACH 25 KNOTS WITH SEAS REACHING 5 FEET ON
THE OCEAN WATERS. STILL DO NOT HAVE THE CONFIDENCE TO ISSUE A SCA
ON THIS SHIFT. WE WILL CONTINUE TO MONITOR.

THURSDAY THROUGH SATURDAY...WINDS AND WAVES SHOULD BE BELOW SCA
THRESHOLD AS A WEAKER PRESSURE PATTERN SHOULD PREVAIL.

&&

.CLIMATE...
A TOP 10 WARMEST MAY WILL OCCUR IN LARGE PORTIONS OF OUR FORECAST
AREA.

THE FIRST 25 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.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...GIGI/KLEIN
NEAR TERM...KLEIN
SHORT TERM...KLEIN
LONG TERM...GIGI/HEAVENER
AVIATION...HEAVENER/KLEIN
MARINE...HEAVENER/KLEIN
CLIMATE...


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