Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 310953
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
453 AM EST SAT JAN 31 2015

.SYNOPSIS...
LOW PRESSURE WILL DEPART EASTERN NEW ENGLAND AND GIVE WAY
TO HIGH PRESSURE APPROACHING FROM THE OHIO VALLEY TODAY. THIS HIGH
PRESSURE WILL MOVE TO THE MID-ATLANTIC STATES TONIGHT AND THEN
OFFSHORE ON SUNDAY. BY SUNDAY NIGHT, LOW PRESSURE WILL MOVE INTO THE
OHIO VALLEY THEN WILL TRACK INTO OUR REGION ON MONDAY. ANOTHER AREA
OF HIGH PRESSURE WILL MOVE INTO THE REGION TUESDAY AND WEDNESDAY
WITH LOW PRESSURE TRACKING JUST OFFSHORE FOR THE LATER HALF OF THE
WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
WITH THE SURFACE HIGH PROPAGATING EAST, PRESSURE GRADIENT ACROSS THE
REGION WILL DECREASE, AND WITH THAT, WINDS WILL SLOWLY SUBSIDE BUT
REMAIN OUT OF THE NORTHWEST. WITH THE CONTINUED NORTHWESTERLY FLOW,
WILL SEE COLD AIR ADVECTION THROUGH THE DAY SO TEMPERATURES WILL BE
QUITE LOW, EVEN FOR LATE JANUARY. HIGHS TODAY SHOULD BE 15 TO 20
DEGREES BELOW NORMAL AND 15 TO 20 DEGREES LESS THAN YESTERDAY/S
HIGHS. SUBTLE SHORT WAVE RIDGING IN THE MID AND UPPER LEVELS ALONG
WITH DRY AIR STILL IN PLACE IN THE BOUNDARY LAYER, SHOULD HELP TO
KEEP SKIES MOSTLY SUNNY, ALTHOUGH CURRENT SATELLITE IMAGERY SHOWS A
MID LAYER CLOUD DECK (AROUND 4000 FT AGL) WHICH COULD ADVECT OVER
THE REGION FROM THE NORTHWEST THROUGH THE DAY.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
AS THE SURFACE LOW SHIFTS EVEN FURTHER EAST, PULLING AWAY FROM THE
COAST, WINDS IN OUR REGION WILL SHIFT TO WESTERLY, BUT WILL
GENERALLY BE NEAR OR BELOW 10KT. DESPITE THE LIGHT WINDS, THE SLIGHT
DOWNSLOPE, ALONG WITH INCREASING MID AND HIGH LEVEL CLOUDS SHOULD
HELP TO AT LEAST SOMEWHAT LIMIT RADIATIONAL COOLING OVERNIGHT.
THEREFORE, LOWS TONIGHT, WHILE STILL SLIGHTLY BELOW NORMAL, SHOULD
BE 5 TO 10 DEGREES HIGHER THAN LOWS LAST NIGHT. TOWARDS THE EARLY
MORNING HOURS ON SUNDAY, THE COLD FRONT SHOULD BEGIN TO APPROACH THE
REGION FROM THE NORTHWEST. HOWEVER, AT THIS POINT, EXPECT IT TO
REMAIN NORTHWEST OF THE REGION THROUGH THE EARLY MORNING HOURS.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...

SUNDAY: LOOKS TO BE FAIRLY QUIET DAY WITH HIGH PRESSURE MOVING
OFFSHORE. THIS WILL BRING SOUTHERLY FLOW AND A MODERATING TREND TO
THE REGION. STAYED CLOSE TO MET AND MAV WHICH ARE A FEW DEGREES
WARMER THAN MODELED NAM/ECMWF TWO METER TEMPERATURES WHICH SEEM TO
COOL.

SUNDAY NIGHT THROUGH MONDAY NIGHT:
* WINTER STORM POTENTIAL FOR AT LEAST THE NORTHERN HALF OF THE REGION*

LOW PRESSURE WILL TRACK INTO THE OHIO VALLEY BY SUNDAY NIGHT AND
TOWARD OUR REGION ON MONDAY. THIS LOW PRESSURE SYSTEM WILL TRACK
ALONG A COLD FRONT MOVING IN FROM THE NORTHWEST. HOWEVER, SOUTHERLY
FLOW WILL CONTINUE TO THE SOUTH OF THIS COLD FRONT ALLOWING FOR WARM
ENOUGH TEMPERATURES TO WHERE MIXED PRECIPITATION OR RAIN ARE MORE
LIKELY THAN SNOW SOUTH OF THE LOW TRACK AS THE FRONT STALLS OVER
THE REGION. THE PAST FEW MODEL CYCLE RUNS A SHORTWAVE WHICH
DEVELOPS THE LOW PRESSURE SYSTEM HAS COME INTO THE NATIONAL UPPER
AIR NETWORK. THIS INCREASES FORECASTER CONFIDENCE TO SOME DEGREE.
THE SHORTWAVE HAS ALSO TRENDED STRONGER AND SHARPER WHICH IN TURN
HAS SHIFTED THE TRACK OF THE LOW FURTHER NORTH OVER THE PAST FEW
MODEL CYCLES. THE UKMET, NAM AND SREF HAVE BEEN THE MORE AMPLIFIED
WHILE THE ECMWF IS MOST SOUTH OF THE MODELS WITH DEEPER LOW LEVEL
COLD AIR.

PLENTY OF MOISTURE IS DRAWN NORTH AND RUNG OUT ALONG THE FRONTAL
BOUNDARY WITH THE POTENTIAL FOR PERIODS OF MODERATE AND HEAVY
PRECIPITATION. WENT CLOSE TO MAV GUIDANCE ON TEMPERATURES
THROUGHOUT THE STORM. THE NAM SEEMS TO WARM AT THIS JUNCTURE AND
THE ECMWF TO COOL.

PERIODS OF SNOW DEVELOP FOR MOST OF THE REGION WITH RAIN IN THE
DELMARVA AROUND 00Z MONDAY. THIS GRADUALLY TRANSITIONS TO RAIN FOR
PHILADELPHIA METRO AND A WINTRY MIX JUST NORTHWEST OF
PHILADELPHIA. FURTHER NORTH SNOW, MODERATE TO HEAVY AT TIMES
CONTINUES FOR THE OVERNIGHT AND MONDAY MORNING HOURS. A VERY SHARP
CUTOFF IS LIKELY WITH SNOW ACCUMULATIONS TO OCCUR BASED ON THE VERY SLOW
MOVEMENT OF THE CHANGEOVER LINE NORTH. ACCUMULATIONS RANGE FROM AN
INCH OR TWO IN PHL TO SIX TO TEN INCHES IN THE LEHIGH VALLEY AND
EVEN CLOSE TO A FOOT FOR THE POCONOS. WHERE THIS CUTOFF SETS UP
WILL BE DETERMINED ON THE EVENTUAL LOCATION OF THE FRONT AND THE
LOW TRACK. ANY SHIFTS IN TRACK COULD ALTER AMOUNTS WITH FUTURE
FORECAST UPDATES. A WINTER STORM WATCH HAS BEEN FOR THE LEHIGH
VALLEY INTO NORTHERN NJ AND THE POCONOS FOR MODERATE TO HIGH
CONFIDENCE IN SNOWFALL OVER SIX INCHES FOR THE SUNDAY NIGHT AND
MONDAY PERIOD.

TUESDAY AND WEDNESDAY: BEHIND THE SYSTEM, A PRETTY POTENT BLAST OF
COLD COMES INTO THE REGION BY TUESDAY. 925 AND 850 MB BOTH WILL BE
WELL BELOW -10C COUPLED WITH STRONG NORTHWESTERLY WINDS. THIS
QUICKLY MODIFIES BY WEDNESDAY AHEAD OF ANOTHER COLD FRONTAL BOUNDARY
WITH A RETURN TO SOUTHERLY WINDS. SNOWCOVER LEADS TO GREATER
UNCERTAINTY IN TEMPERATURES. OVERALL THINKING IS ECMWF/ MEX MOS
AND ENSEMBLE GUIDANCE MAY BE A TOUCH TO WARM TUESDAY THEN TO COOL
WEDNESDAY.

WEDNESDAY NIGHT THROUGH FRIDAY NIGHT: POTENTIAL EXISTS FOR AN AREA
OF LOW PRESSURE TO DEVELOP IN THE GULF OF MEXICO AND TRACK NORTHEAST
ALONG THE COLD FRONT  WHICH PASSES THROUGH WEDNESDAY NIGHT. LIMITED
TIME TO FOCUS ON THIS PERIOD BUT LEFT IN CHANCE OF SNOW THURSDAY
INTO FRIDAY. THE ECMWF IS FURTHEST EAST WITH THE GFS, CMC AND
UKMET HINTING AT THIS THREAT.

&&

.AVIATION /10Z SATURDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

GENERALLY VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. A MID
LEVEL CLOUD DECK AROUND 4000 FT AGL COULD ADVECT IN FROM THE
NORTHWEST THROUGH THE DAY TIME HOURS. THERE IS A SMALL CHANCE THAT
AS IT DOES, THE CEILING COULD LOWER TO MVFR AT KABE, BUT THAT IS TOO
UNLIKELY TO INCLUDE IN THE TAF AT THIS TIME.

NORTHWEST WINDS WILL BEGIN TO DECREASE AFTER 12Z. BY LATE THIS
AFTERNOON, WINDS SHOULD BE NEAR 10KT WITH FEW GUSTS. AFTER 00Z,
EXPECT THE LIGHT WINDS TO SHIFT TO WESTERLY THROUGH THE EVENING
HOURS.

OUTLOOK...

SUNDAY: VFR, INCREASING CLOUDS.

SUNDAY NIGHT AND MONDAY: MVFR AND IFR CEILINGS IN RAIN AND SNOW.
MAINLY SNOW FOR KRDG, KTTN AND KABE WITH MAINLY RAIN AT OTHER TAF
SITES.

MONDAY NIGHT THROUGH WEDNESDAY: VFR, NORTHWEST WIND GUSTS AROUND
25 KNOTS MONDAY NIGHT.

&&

.MARINE...
ALTHOUGH WINDS WILL SLOWLY SUBSIDE AFTER SUNRISE THIS MORNING, BUT
MAY NOT DROP BELOW GALE CONDITIONS UNTIL LATE THIS AFTERNOON. ONCE
GUSTS DO DROP BELOW GALES, A SCA MAY BE NEEDED THROUGH AT LEAST THE
EVENING HOURS AS WINDS AND SEAS CONTINUE TO SLOWLY FALL.

OUTLOOK...

SUNDAY AND SUNDAY NIGHT: SUB SCA SEAS AND WINDS WITH SEAS BUILDING
TOWARD SUNRISE MONDAY.

MONDAY THROUGH TUESDAY: SCA SEAS THROUGH TUESDAY MORNING AND NORTHWEST
SCA WIND GUSTS LATE MONDAY AFTERNOON AND NIGHT.

TUESDAY NIGHT AND WEDNESDAY: SUB SCA SEAS AND WINDS.


.TIDES/COASTAL FLOODING...
ISSUED A LOW WATER ADVISORY FOR THE UPPER DELAWARE BAY AND THE TIDAL
DELAWARE RIVER AS WATER LEVELS AT REEDY POINT ARE CURRENTLY ABOUT 2
FT BELOW MLLW. THIS WILL LIKELY ALSO RESULT IN WATER LEVELS WELL
BELOW NORMAL ON THE TIDAL PORTIONS OF THE DELAWARE RIVER FOR THIS
MORNINGS LOW TIDE. WINDS SHOULD BEGIN TO SUBSIDE AFTER SUNRISE.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...WIND ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR PAZ054-055-
     060>062-070-071-101>106.
     WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY
     AFTERNOON FOR PAZ054-055-060>062.
     WIND CHILL ADVISORY UNTIL 11 AM EST THIS MORNING FOR PAZ054-
     055.
NJ...WIND ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR NJZ001-
     007>010-012>027.
     WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY
     AFTERNOON FOR NJZ001-007>010.
     WIND CHILL ADVISORY UNTIL 11 AM EST THIS MORNING FOR NJZ001.
DE...WIND ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR DEZ001>004.
MD...WIND ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR MDZ008-012-
     015-019-020.
MARINE...FREEZING SPRAY ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ430-
     431-450>455.
     GALE WARNING UNTIL 6 PM EST THIS EVENING FOR ANZ430-431-
     450>455.
     LOW WATER ADVISORY UNTIL 7 AM EST THIS MORNING FOR ANZ430.

&&

$$
SYNOPSIS...GAINES
NEAR TERM...JOHNSON
SHORT TERM...JOHNSON
LONG TERM...GAINES
AVIATION...GAINES/JOHNSON
MARINE...GAINES/JOHNSON
TIDES/COASTAL FLOODING...






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