Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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489
FXUS61 KPHI 151722
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
122 PM EDT FRI MAY 15 2015

.SYNOPSIS...
A HIGH PRESSURE SYSTEM OVER THE COASTAL WATERS WILL EASE SLOWLY
OFFSHORE TODAY. A LOW PRESSURE SYSTEM FROM THE UPPER MISSISSIPPI
VALLEY WILL MOVE NORTHEAST, WITH ITS ASSOCIATED WARM FRONT CROSSING
OUR REGION TONIGHT. ITS COLD FRONT THEN WILL SETTLE SOUTH ACROSS
OUR AREA BEFORE STALLING LATER IN THE WEEKEND. THE NEXT LOW
PRESSURE SYSTEM FROM THE ROCKIES SHOULD TRACK NORTHEAST THROUGH
THE GREAT LAKES AND SAINT LAWRENCE VALLEY. ITS COLD FRONT WOULD
THEN PUSH ACROSS OUR AREA ON TUESDAY. A CANADIAN HIGH PRESSURE
SYSTEM WILL GRADUALLY BUILD IN FOR WEDNESDAY AND THURSDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

12:30 PM UPDATE: ANOTHER NICE DAY IN PROGRESS! THE ATMOSPHERE
APPEARS TO BE SLOW TO MOISTEN EVEN WITH THE WSW FLOW AHEAD OF THE
NEXT SYSTEM EVEN WITH SOME HIGHER CLOUDS THIS MORNING. MIXING IS
CONTRIBUTING TO THE LOWER DEWPOINTS (MOISTURE) ACROSS THE AREA AS
WELL AND PROMOTING SOME WIND GUSTS CLOSE TO 20 MPH THIS AFTERNOON
AS WELL.

PREVIOUS...

HIGH PRESSURE ACROSS THE AREA THIS MORNING WILL MOVE EAST THIS
AFTERNOON. MOSTLY SUNNY WEATHER EXPECTED TODAY WITH TEMPERATURES
NEAR NORMAL FOR MID-MAY. HUMIDITY LEVELS WILL REMAIN COMFORTABLE,
WINDS WILL BE MOSTLY SW OR S AT 5 TO 10 MPH. THE WINDS WILL BE
LOCALLY ONSHORE ACROSS SRN NJ AND NEAR THE DEL BAY.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
LOW PRESSURE ACROSS THE GREAT LAKES WILL CAUSE A WARM FRONT TO MOVE
BY TO THE NORTH OVERNIGHT. THERE WILL BE AN INCREASE IN CLOUDS AND A
CHC FOR SHOWERS MOSTLY N AFTER MIDNIGHT TONIGHT. THERE IS ENOUGH
ELEVATED INSTABILITY TO INCLUDE A SLGT CHC FOR THUNDER TOO. WE HAVE
CHC POPS FROM ABOUT KRDG-KVAY-KBLM AND NORTH AND SLGT CHC POPS JUST
SOUTH OF THAT. WE ARE KEEPING A DRY FCST FOR NOW OVER THE DELMARVA
AND SRN NJ. THE GFS MODEL DOES INDICATE SOME CHC FOR THESE SRN
AREAS...SO UPDATES ARE POSSIBLE. LOWS TONIGHT WILL BE MILD WITH
UPPER 50S AND LOW 60S MOST AREAS. AN INCREASE IN HUMIDITY WILL BE
NOTICEABLE OVERNIGHT. WINDS MOSTLY SRLY AT 5 TO 10 MPH.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
THE WRF-NMMB INITIALIZATION LOOKED BETTER THAN THE GFS AT 500MB
AS THE GFS UPPER MIDWEST TROF WAS TOO DEEP AND SOMEHOW FASTER.
BOTH MODELS WERE EQUALLY GOOD AT 850MB WITH SOME 1C WARM BIAS ERRORS
AND AT 925MB WRF-NMMB LOOKS BETTER AGAIN AS THE GFS HAS SOME 1C COLD
BIAS ERRORS.

THE DP/DT INITIALIZATION SHOWS THE GFS 500MB BIAS. GOING FORWARD
NEITHER THE GFS WITH ITS LIKELY FEEDBACK VORT MAX SATURDAY NIGHT
NOR THE PROGRESSIVE AND MORE UNSTABLE SOLUTION OF THE WRF-NMMB FOR
SUNDAY AND SUNDAY NIGHT FIT TOWARD THE CONSENSUS, CLOSER TO THE
ECMWF AND CAN GGEM. OVERALL THERE IS NO BIG CHANGE IN THE SOLUTION
AS THE UPPER MISSISSIPPI VALLEY TROF SHEARS AWAY, GETS FOLLOWED
BY A BACKDOORING TROF FROM NEW ENGLAND/CANADIAN MARITIMES CLOSED
LOW SUNDAY NIGHT AND MONDAY. FINALLY THE ANOMALOUSLY STRONG CLOSED
LOW OVER CALIFORNIA LIFTS INTO EASTERN CANADA, BUT NOT BEFORE A
COLD FRONT COMES THROUGH ON TUESDAY. TIMING WISE THE CURRENT GFS
RUN IS SLOWER AND CLOSER TO ITS ENSEMBLE MEAN AND THE LATEST
ECMWF. THUS THIS IS A LITTLE BIT OF THIS AND A LITTLE BIT OF THAT
FORECAST IN WHICH WE WILL INCORPORATE A MODEL BLEND. WHILE WE WILL
HAVE OUR FIRST DECENT CHANCES FOR MEASURABLE PCPN IN A WHILE, THE
HIGHEST CHANCES AND GREATEST LIKELIHOOD INTO MONDAY IS IN PA, WITH
THE EMPHASIS SWITCHING TO NORTH OF THE MASON/DIXON LINE ON MONDAY
NIGHT AND TUESDAY.

ON SATURDAY, THERE MIGHT BE SOME RESIDUAL PCPN EARLY ASSOCIATED WITH
THE WARM FRONT. THEN A SECOND SHOT IN THE AFTERNOON AS A SFC CDFNT
APPROACHES AND A LEE SIDE TROF PRECEDES IT. THE ONE SHIFT IN FCST
SOUNDINGS FROM YESTERDAY IS THE LACK OF DRY AIR ALOFT. NEVERTHELESS,
THIS IS THE DAY WHERE SYNOPTIC SCALE FORCING (MID LEVEL QVEC CONVERGENCE,
LEFT SIDE LOCATION OF LLJ, THETA E LLVL RDG, EXIT REGION OF THE
250MB JET AND INCREASING PWATS) CONVERGE WITH SLIGHTLY STRONGER
INSTABILITY. THE PREDICTED BULK SHEAR DOES GET CLOSER TO 30 KTS LATER
IN THE DAY AS THE JETS PASS THROUGH AND THE 500MB TEMPS ARE RELATIVELY
STILL COLD. THE PREDICTED MIXED LAYER CAPES ARE STILL HOVERING
AROUND 1K JOULES (MORE SO WEST THAN EAST) AND THE OVERALL
INSTABILITY (MID LEVEL LAPSE RATES, S.I(S), TT(S)) ARE NOT REALLY
BOISTEROUS. WHILE SHORT WAVES SHOULD HELP INITIALIZE, THE OVERALL
ENVIRONMENT DOES NOT CONDUCIVE TO SVR WEATHER AT THIS POINT. WITH
PWATS APPROACHING 1.75", A HEAVY RAIN POTENTIAL RANKS A BIT HIGHER
THAN SEVERE. WE WENT ABOVE STAT GUIDANCE FOR MAX TEMPS. LLJ
SHOULD PUSH THE WARM FRONT IN NEW ENGLAND AND MODELS ARE BANKING
TOO MUCH ON CLOUDS TO KEEP TEMPS DOWN. THE DAYS ARE LONG NOW AND
IT DOES NOT TAKE MUCH SUNSHINE TO MAKE UP FOR LOST TIME. POPS ARE
SLANTED WEST TOWARD HIGHER INSTABILITY.

NOT GOING WITH THE WETTER GFS SOLUTION FOR SATURDAY NIGHT AS THERE IS
NO RUN TO RUN CONTINUITY NOR OTHER MODEL CORROBORATION. FCST IS
MORE IN LINE WITH LEFTOVER CONVECTION WITHERING AWAY AS THE NIGHT
PROGRESSES.

ON SUNDAY AS THE TROF DIGS INTO NEW ENGLAND AND THE RIDGE AMPLIFIES
TO OUR WEST, THE FRONT WILL START BACKDOORING INTO OUR CWA. THE
PREDICTED ENVIRONMENT IS OVERALL A PEG MORE STABLE THAN SATURDAY.
WHILE THE WRF-NMMB IS MORE UNSTABLE, IT TOO IS A LEVEL BELOW
SATURDAY`S PREDICTED INSTABILITY. WITH WARMER AIR MOVING IN ALOFT
AT 500MB, OVERALL INSTABILITY IS LESS AND PREDICTED BULK SHEAR
VALUES ARE LESS THAN 20 KNOTS. THIS HAS THE LOOK OF SLOWER MOVING
SHOWERS AND TSTMS WITH THE EMPHASIS AGAIN TOWARD HEAVIER RAIN AND
IN THE WESTERN PART OF OUR CWA. MAX TEMPS, SOUNDINGS SUGGEST A
1-2F BUMP UP FROM SATURDAY. STILL PRETTY HUMID FOR MAY.

SUNDAY NIGHT INTO MONDAY STILL LOOKS TO BE A POP LULL. THERE ARE
DIFFERENCES AS TO HOW MUCH WILL THE HI PRES NOSE INTO OUR CWA FROM
NEW ENGLAND AND THUS UNCERTAINTIES TO THE DEGREE OF THE LULL AND THE
IMPACT ON TEMPS WITH THE ONSHORE FLOW. KEEPING WITH THE THEME OF THIS
PACKAGE HIGHEST POPS ARE IN THE WESTERN PART OF OUR CWA. WE WILL
HAVE TO WATCH FOR SOME MINOR COASTAL FLOODING POTENTIAL AS THE ONSHORE
FLOW WILL AUGMENT THE SPRING TIDES ASSOCIATED WITH THE NEW MOON.

THEN THE OVERALL HIGHEST CHANCES FOR PCPN COME MONDAY NIGHT AND TUESDAY
AS A NEW COLD FRONT MOVES THROUGH OUR AREA. WHILE PREDICTED PWATS REACH
NORTH OF 1.5", OVERALL INSTABILITY REMAINS SUBDUED FOR LATE MAY. THIS
WOULD BE ESPECIALLY TRUE IF THE CALIFORNIA CLOSED LOW TAKES THAT MUCH
OF A NORTHWARD PASS FROM OUR CWA. WE WILL BE FAIRLY REMOVED FROM THE
COLD POOL.

FOLLOWING THE CFP, ANOTHER CANADIAN HIGH PRESSURE SYSTEM DROPS INTO THE
CONUS AND WOULD GIVE US A PAIR OF DRY DAYS TO END THE LONG TERM. WEDNESDAY
WOULD BE BREEZY WITH THURSDAY A REPEAT OF YESTERDAY. BOTH DAYS WOULD
FEATURE SLIGHTLY BELOW NORMAL TEMPS, ESPECIALLY WITH MINS.

&&

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

VFR CONDITIONS THROUGH MOST OF THE TAF PERIOD. THIS AFTERNOON,
SOME WIND GUSTS FROM THE S OR SSW MAY APPROACH 15-20 KNOTS AT
TIMES BEFORE DIMINISHING THIS EVENING. ANOTHER WINDOW IS PRESENT
FOR SSW WIND GUSTS AROUND 20 KNOTS SATURDAY AFTERNOON. CEILINGS
OVER 10,000 FEET THROUGH MOST OF TODAY WILL LOWER SOME OVERNIGHT
TO AROUND 5,000 FEET OVERNIGHT. SOME SHOWERS AND PERHAPS
THUNDERSTORMS ARE POSSIBLE TOMORROW AFTERNOON. STILL TO EARLY TO
HONE IN ON AN EXACT TIMEFRAME BROAD -SHRA GROUP INCLUDED AT PHL
ATTM.

OUTLOOK...
SATURDAY NIGHT THROUGH SUNDAY...SOME TIMES OF MVFR/IFR WITH
SCATTERED SHOWERS AND THUNDERSTORMS ESPECIALLY SATURDAY NIGHT,
OTHERWISE VFR. THERE IS LOWER CONFIDENCE REGARDING THE COVERAGE OF
THE PRECIPITATION, BUT MOST SHOULD BE IN THE AFTERNOON AND EVENING
HOURS WITH A GREATER IMPACT AT WESTERN TERMINALS AND AIRPORTS.

SUNDAY NIGHT AND MONDAY...SOME LOW CLOUDS AND SHOWERS POSSIBLE,
OTHERWISE MORE WIDESPREAD VFR CONDITIONS EXPECTED.

MONDAY NIGHT AND TUESDAY...MVFR/IFR CONDITIONS OCCURRING DURING
SHOWERS AND THUNDERSTORMS.

&&

.MARINE...
A GOOD DAY TO BE OUT ON THE WATERS. HIGH PRESSURE ACROSS THE AREA
THIS MORNING WILL MOVE EAST THIS AFTERNOON. WINDS WILL BE SWRLY THIS
MORNING AND THEN TREND MORE SRLY TONIGHT. WINDS NEAR THE SHORE WILL
TENS ONSHORE AND ACROSS DEL BAY WINDS WILL BE MOSTLY SERLY. WIND
SPEEDS WILL BE MOSTLY AROUND 10 KTS TODAY AND TONIGHT. FAIR WEATHER
TODAY AND SCT SHOWERS PSBL TSTM AFTER MIDNIGHT TONIGHT...MAINLY
ACROSS THE NRN NJ COASTAL WATERS.

OUTLOOK...
SATURDAY AND SATURDAY NIGHT...SOUTHWEST FLOW PRECEDING THE COLD
FRONT MIGHT BRING OUR OCEAN MARINE ZONES CLOSE TO SMALL CRAFT
ADVISORY CRITERIA. WHILE WE ARE CARRYING SEAS AS HIGH AS 5 FEET,
NOT CONFIDENT ENOUGH ABOUT IT OCCURRING TO ISSUE AN ADVISORY.

SUNDAY AND SUNDAY NIGHT...WITH OVERALL WEAKER WINDS, MORE
CONFIDENT ABOUT SUB SMALL CRAFT ADVISORY CONDITIONS OCCURRING.

MONDAY THROUGH TUESDAY...THE WINDS AND SEAS MAY NEAR ADVISORY CRITERIA
ON THE COASTAL WATERS AS THE FLOW TURNS ONSHORE MONDAY, THEN WEAKENS
SOME TUESDAY AS A COLD FRONT ARRIVES. ALSO, GUIDANCE IS NOT OUTLOOKING
AS MUCH FOG AS OCCURRED LAST WEEKEND.


&&

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

&&

$$
SYNOPSIS...GIGI/GORSE
NEAR TERM...GAINES/O`HARA
SHORT TERM...O`HARA
LONG TERM...GIGI
AVIATION...GAINES/GIGI/GORSE/O`HARA
MARINE...GIGI/GORSE/O`HARA



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