Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 271714
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
114 PM EDT WED MAY 27 2015

.SYNOPSIS...
THE EAST COAST REMAINS ON THE WESTERN PERIPHERY OF AN ATLANTIC
HIGH PRESSURE SYSTEM TODAY. A COLD FRONT WILL MOVE ACROSS THE AREA
THURSDAY INTO THURSDAY NIGHT. HIGH PRESSURE REESTABLISHES ITSELF
OFF THE EAST COAST FRIDAY INTO SATURDAY. A COLD FRONT IS FORECAST
TO MOVE ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY. HIGH PRESSURE
WILL RETURN TO THE NORTHEAST EARLY NEXT WEEK WHILE THE FRONTAL
BOUNDARY STALLS TO OUR SOUTH.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A SEVERE THUNDERSTORM WATCH IS IN EFFECT FOR THE AREA UNTIL 700
PM.

WITH THE UPDATE, HOURLY TEMPERATURES AND DEWPOINTS WERE ADJUSTED
SOMEWHAT USING THE LAV/LAMP GUIDANCE TO MORE CLOSELY MATCH THE
LATEST OBS AND TRENDS, BUT MAX TEMPERATURES LOOK ON TRACK BASED ON
THIS MORNINGS 12Z REGIONAL SOUNDINGS. WE CONTINUE TO MONITOR SOME
LINGERING STRATUS ACROSS THE REGION AS THIS WILL PLAY A ROLE IN
WHEN/HOW MUCH THE ATMOSPHERE DESTABILIZES LATER TODAY. THE HRRR
AND OTHER GUIDANCE CONTINUES TO REFLECT CONVECTION MOVING INTO OUR
AREA FOR MID-AFTERNOON TO EVENING, AND WE KEPT HIGHER POPS IN
PLACE FOR THIS PERIOD.

OTHERWISE, SURFACE HIGH PRESSURE AND ASSOCIATED UPPER RIDGE WILL
CONTINUE TO PARK OFF THE EAST COAST TODAY. THE MID-ATLANTIC REGION
WILL BE POSITIONED IN BETWEEN THIS DOWNSTREAM RIDGE AND AN
APPROACHING UPPER TROUGH OVER THE MIDWEST/GREAT LAKES. SOUTH-
SOUTHWEST WINDS THROUGHOUT THE TROPOSPHERE WILL BACK AND
STRENGTHEN SLIGHTLY AS THE PRESSURE/GEOPOTENTIAL HEIGHT GRADIENT
BETWEEN THESE TWO SYSTEMS TIGHTENS OVER THE EASTERN SEABOARD.

A NOTICEABLE CHANGE IN THE SENSIBLE WX TODAY COMPARED TO RECENT
DAYS WILL BE THE INCREASE IN HUMIDITY WITH DEWPOINTS RISING INTO
THE MID 60S TO NEAR 70F THIS AFTERNOON.

THE ATMOSPHERE IS FORECAST TO BECOME MODERATELY UNSTABLE THIS
AFTERNOON AS A DIRECT RESULT OF THE THE INCREASING MOISTURE AND
STRONG DIABATIC HEATING. MEAN MLCAPE VALUES FROM BOTH THE 00Z
NCAR/MMM HI-RES ENSEMBLES AND 03Z SREF ARE AROUND 1500 J/KG FOR
OUR INLAND AREAS. WHILE FORECAST 0-6 KM BULK SHEAR OF 20-25 KT
WILL BE MODEST, A 35-40 KT JET AT 500 MB WILL ENHANCE SHEAR
PROFILES IN THE 0-5 KM LAYER LATE IN THE DAY. THE MAIN QUESTION
LEADING UP TO TODAY WAS WHETHER THERE WAS GOING TO BE A LIFTING
MECHANISM TO INITIATE CONVECTION. IT APPEARS THAT THERE WILL BE
SOME FORCING. THE HIRES GUIDANCE HAS COME INTO BETTER AGREEMENT,
FOCUSING THE INITIAL CONVECTIVE DEVELOPMENT ALONG A LEE SURFACE
TROUGH TO OUR WEST DURING THE EARLY AFTERNOON. A BROKEN LINE OF
STORMS SHOULD PROGRESS EASTWARD INTO EASTERN PA DURING THE MID TO
LATE AFTERNOON WITH ADDED UPPER FORCING BROUGHT TO YOU BY AN
APPROACHING MID-LEVEL SHORTWAVE TROUGH. POPS ARE HIGHEST (LIKELY)
WEST OF THE PHILLY METRO WHERE THE ARRIVAL OF THE LINE SHOULD
COINCIDE WITH PEAK HEATING. OVERALL, THE FORECAST ENVIRONMENT
SUPPORTS A POTENTIAL FOR LOCALLY DAMAGING STRAIGHT-LINE WIND GUSTS.
THE LATEST D1 CONVECTIVE OUTLOOK FROM SPC HAS PLACED AREAS ALONG
AND WEST OF I-95 IN A SLIGHT RISK THIS AFTERNOON.

ALTHOUGH FORECAST 925/850 MB TEMPS ARE AROUND 1C HIGHER TODAY THAN
WHAT WAS OBSERVED ON MONDAY AND TUESDAY, CLOUD COVER IS EXPECTED
TO ALSO BE HIGHER TODAY (ESPECIALLY INLAND). THE MOST LIKELY
OUTCOME IS MAX TEMPS TODAY THAT ARE VERY SIMILAR TO THE PREVIOUS
TWO DAYS. OVERALL, THE OFFICIAL FORECAST TEMPS ARE ON THE HIGHER
SIDE OF GUIDANCE AFTER ACCOUNTING FOR A PERSISTENT COOL BIAS SEEN
IN THE MODELS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
LATEST HI-RES MODEL SIMULATIONS SHOW A BROKEN LINE OF SHOWERS AND
STORMS OVER EASTERN PA THAT CROSS THE I-95 CORRIDOR AROUND SUNSET
AND DISSIPATE BEFORE IT REACHES THE COAST. CONVECTION IS EXPECTED
TO BECOME SEPARATED FROM THE CONVERGENCE/SOURCE OF LIFT NEAR THE
LEE TROUGH AND INSTABILITY WILL WANE WITH THE LOSS OF DAYTIME
HEATING, RESULTING IN A GENERALLY WEAKENING TREND AS IT MOVES
EASTWARD. HOWEVER, THERE COULD STILL BE A FEW STRONG TO SEVERE
STORMS EARLY. POPS DECREASE SHARPLY FROM WEST TO EAST ACCORDINGLY.

CLOUD COVER AND MUGGY CONDITIONS WILL KEEP TEMPS MILD TONIGHT.
FORECAST MIN TEMPS ARE GENERALLY IN THE MID TO UPPER 60S. IF WE
ARE ABLE TO CLEAR OUT OVERNIGHT, WE MAY SEE PATCHY FOG DEVELOP.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
ON THURSDAY, A COLD FRONT IS FORECAST TO APPROACH THE AREA AND MOVE
ACROSS THE AREA LATE IN THE DAY INTO THE EVENING HOURS. A SHORT WAVE
ALOFT IS FORECAST TO MOVE ACROSS THE AREA ALONG WITH THE FRONTAL
BOUNDARY DURING THE AFTERNOON AND INTO THE EVENING AS WELL. WITH AN
INCREASE IN INSTABILITY DURING THE DAY, SCATTERED SHOWERS AND
THUNDERSTORMS SHOULD BE ABLE TO DEVELOP ACROSS THE AREA. WHILE QPF
AMOUNTS ARE NOT HIGH, 0.10-0.25 INCHES, PW VALUES ARE NEAR 1.5
INCHES, SO IT IS POSSIBLE FOR SOME HEAVY DOWNPOURS. WITH A LACK OF
STRONG SHEAR, THE POTENTIAL FOR SEVERE WEATHER IS LOW, ALTHOUGH ANY
THUNDERSTORMS THAT DO DEVELOP COULD PRODUCE STRONG GUSTY WINDS AND
HEAVY RAIN.

ONCE THE FRONT MOVES THROUGH, HIGH PRESSURE IS FORECAST TO
REESTABLISH ITSELF ACROSS THE ATLANTIC, WITH OUR AREA ON THE WESTERN
EDGE. SLIGHT RIDGING ALOFT BUILDS ACROSS THE AREA AS WELL, WHICH
SHOULD HELP KEEP THE WEATHER MOSTLY DRY INTO FRIDAY. WITH RETURN
FLOW ACROSS THE AREA, INSTABILITY IS FORECAST TO DEVELOP ACROSS THE
WESTERN AREAS. THIS DAYTIME INSTABILITY COULD LEAD TO A FEW ISOLATED
SHOWERS/THUNDERSTORMS ACROSS OUR WESTERN AREAS.

THE RIDGING ALOFT PUSHES EASTWARD SLIGHTLY SATURDAY, WITH SOUTHWEST
FLOW ALOFT DEVELOPING, ALLOWING FOR A COUPLE OF SHORT WAVE/VORTICITY
IMPULSES TO MOVE ACROSS THE AREA LATE SATURDAY. WITH DAYTIME
INSTABILITY DEVELOPING ACROSS THE AREA, AN INCREASE IN
SHOWER/THUNDERSTORM ACTIVITY IS POSSIBLE, ESPECIALLY FOR THE WESTERN
HALF OF THE AREA.

A COLD FRONT IS THEN FORECAST TO MOVE ACROSS THE AREA SATURDAY
NIGHT INTO SUNDAY SUNDAY NIGHT. HOWEVER, THERE REMAINS TIMING
DIFFERENCES BETWEEN THE GFS AND ECMWF REGARDING THIS FRONT. THE
GFS HAS THE FRONT AND ITS PRECIPITATION MOVING THROUGH SATURDAY
NIGHT INTO SUNDAY. THE ECMWF HAS THE FRONT MOVING THROUGH SUNDAY
INTO SUNDAY NIGHT. WE`LL CONTINUE WITH ENHANCED POPS DURING THE
TIME PERIOD, GENERALLY CENTERED AROUND SUNDAY AND WILL BE ABLE TO
BETTER FINE TUNE TIMING AS MODELS COME TO AN AGREEMENT. PW VALUES
INCREASE TO NEAR 2 INCHES, SO THERE COULD BE A PERIOD OF HEAVY
RAINFALL WITH ANY SHOWERS THAT DEVELOP DURING THE TIME PERIOD.

HIGH PRESSURE RETURNS TO THE NORTHEAST EARLY NEXT WEEK AS THE
FRONTAL BOUNDARY PUSHES SOUTH AND LIKELY STALLS JUST SOUTH OF OUR
AREA. AGAIN, THERE ARE DIFFERENCES BETWEEN THE GFS AND ECMWF. THE
GFS KEEPS HIGH PRESSURE ACROSS THE AREA, KEEPING MOSTLY DRY
WEATHER INTO THE EARLY PART OF THE WEEK. THE ECMWF STARTS TO LIFT
THE FRONT BACK NORTH TOWARD THE AREA, BRINGING AN INCREASE IN
SHOWER CHANCES. WE`LL KEEP A SMALL CHANCE OF SHOWERS INTO TUESDAY,
BECAUSE THE GFS HAS DOES HAVE A FEW SHORT WAVE/VORTICITY IMPULSES
FORECAST TO CROSS THE AREA. SO THIS COULD STILL PRODUCE SOME
SCATTERED SHOWERS/THUNDERSTORMS WITH DAYTIME INSTABILITY.

&&

.AVIATION /17Z WEDNESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

SOME STRATUS WITH CIGS AROUND 1500 FT WILL CONTINUE TO LINGER
ACROSS MUCH OF THE REGION THROUGH MID-MORNING, BEFORE LIFTING AND
DISSIPATING BY LATE MORNING.

EXPECT SHRA AND TSRA TO DEVELOP OVER THE HIGHER ELEVATIONS OF
CENTRAL/EASTERN PA THIS AFTERNOON. KEPT A TSRA PROB30 GROUP IN THE
06Z FOR RDG AND ABE AND ADDED IT TO THE 09Z PHL TAF FOR THE MID
TO LATE AFTERNOON. FARTHER EAST, THERE IS HIGHER UNCERTAINTY IF
STORMS WILL BE MAINTAINED BY THE TIME IT REACHES THE COASTAL PLAIN SO
NO MENTION OF TSRA AT THIS TIME. STORMS UNLIKELY TO REACH ACY THIS
EVENING.

S-SW WINDS 5-10 KT THIS MORNING INCREASE TO 10-15 KT THIS AFTERNOON
WITH GUSTS NEAR 20 KT.

OUTLOOK...

THURSDAY-THURSDAY NIGHT...GENERALLY VFR. SCATTERED
SHOWERS/THUNDERSTORMS POSSIBLE DURING THE DAY WHICH MAY LOCALLY
REDUCE CIGS/VSBYS.

FRIDAY...GENERALLY VFR. ISOLATED SHOWERS/THUNDERSTORMS POSSIBLE FOR
WESTERN TAFS.

FRIDAY NIGHT...VFR EARLY, THEN LOWERING CIGS/VSBYS POSSIBLE
OVERNIGHT.

SATURDAY...LOWER CONDITIONS POSSIBLE EARLY, THEN BECOMING VFR DURING
THE DAY. SCATTERED SHOWERS AND THUNDERSTORMS POSSIBLE WHICH MAY
LOCALLY REDUCE CIGS/VSBYS. GUSTY SOUTH-SOUTHWEST WINDS AROUND 20
KNOTS.

SATURDAY NIGHT-SUNDAY...SUB-VFR CONDITIONS POSSIBLE, ESPECIALLY WITH
SHOWERS/THUNDERSTORMS.

&&

.MARINE...
SCA WAS CANCELLED FOR THIS MORNING AS WINDS AND SEAS HAVE FALLEN TO
BELOW SCA LEVELS. THE WINDS WILL INCREASE THIS AFTERNOON AND EARLY
EVENING. EXPECT GUSTS TO 25 KT, ESPECIALLY NEAR THE COAST. SEAS WILL
RESPOND TO THE STRENGTHENING WINDS WITH WAVE HEIGHTS FORECAST TO
INCREASE TO NEAR 5 FT. ACCORDINGLY, THE SCA REMAINS IN EFFECT FOR
THIS AFTERNOON AND TONIGHT.

OUTLOOK...

THURSDAY-SATURDAY...SUB-SMALL CRAFT ADVISORY CONDITIONS CURRENTLY
EXPECTED, ALTHOUGH WINDS MAY GUST AROUND 20 KNOTS AT TIMES.

SATURDAY NIGHT...SEAS MAY RETURN TO 5 FEET OR GREATER OVERNIGHT
AHEAD OF AN APPROACHING COLD FRONT.

&&

.RIP CURRENTS...
BASED ON IN HOUSE REGRESSION GUIDANCE, HAVE INCLUDED A MODERATE
RISK OF RIP CURRENTS TODAY FOR THE NJ BEACHES UNDER A BREEZY
SOUTH WIND.

&&

.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...SMALL CRAFT ADVISORY UNTIL 6 AM EDT THURSDAY FOR ANZ450>455.

&&

$$
SYNOPSIS...ROBERTSON
NEAR TERM...KLEIN/KLINE
SHORT TERM...KLEIN
LONG TERM...ROBERTSON
AVIATION...KLEIN/KLINE/ROBERTSON
MARINE...KLEIN/ROBERTSON
RIP CURRENTS...
CLIMATE...


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