Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 250228
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
928 PM EST WED DEC 24 2014

.SYNOPSIS...
LOW PRESSURE STRENGTHENS AS IT LIFTS UP ACROSS THE GREAT LAKES
REGION INTO CANADA THROUGH TONIGHT. AN ASSOCIATED COLD FRONT WILL
SWEEP ACROSS OUR AREA EARLY THURSDAY MORNING. HIGH PRESSURE WILL
THEN SETTLE TO OUR SOUTH THURSDAY NIGHT AND FRIDAY, BEFORE SHIFTING
OFFSHORE INTO SATURDAY. A COLD FRONT IS FORECAST TO SETTLE THROUGH
OUR AREA SUNDAY, HOWEVER IT MAY THEN STALL NEARBY. LOW PRESSURE
SHOULD DEVELOP AND MOVE ALONG THIS FRONT SUNDAY NIGHT AND MONDAY,
TRACKING TO OUR SOUTH. HIGH PRESSURE NEAR THE CENTRAL PLAINS THEN
STARTS TO GRADUALLY BUILD TOWARD THE MID ATLANTIC TUESDAY AND
WEDNESDAY.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
WARM FRONT CONTINUES TO MAKE SLOW PROGRESS NORTH THROUGH THE REGION.
THE BIG STORY WILL BE THE COLD FRONT WHICH IS EXPECTED TO SWEEP
THROUGH THE REGION DURING THE VERY EARLY MORNING HOURS.

SHOULD CONTINUE TO SEE LIGHT TO MODERATE RAIN THROUGH THIS EVENING,
THEN AS THE FRONT APPROACHES, THE COMBINATION OF MODEST ELEVATED
INSTABILITY (ELEVATED CAPE VALUES AROUND 100 J/KG) AND VERY LARGE
SHEAR VALUES LEADS TO AN INCREASED CHANCE FOR ISOLATED
THUNDERSTORMS. GIVEN THE LARGE SHEAR VALUES, COULD SEE GUSTY WINDS
WITH ANY THUNDERSTORMS.

RADAR CONTINUES TO SHOW LULL IN PRECIP, THOUGH HRRR WANTS TO
REDEVELOP AROUND MIDNIGHT. WILL LOWER POPS OVER THE NEXT FEW HOURS
BEFORE RAMPING UP AGAIN. PRECIP SHOULD INCREASE WITH THE FROPA, IF
NOT BEFORE.

BEHIND THE COLD FRONT, THE RAIN SHOULD CLEAR OUT QUICKLY.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
FOR CHRISTMAS DAY, WE KEEP A RATHER TIGHT PRESSURE GRADIENT OVER THE
REGION LEADING TO BREEZY CONDITIONS THROUGH THE DAY TIME HOURS.
HOWEVER, WITH THE CONTINUED DRY AIR ADVECTION, SHOULD SEE MOSTLY DRY
CONDITIONS EXCEPT NEAR THE COAST WHERE RAIN MAY LINGER THROUGH MID
MORNING. DEPENDING ON HOW QUICKLY THE INVERSION BREAKS, COULD EVEN
SEE CLOUDS RAPIDLY DISSIPATING THROUGH THE MORNING.

THE TEMPERATURE GRADIENT ACROSS THE COLD FRONT IS SOMEWHAT MODEST.
THEREFORE, EXPECT HIGHS TOMORROW TO BE 5 TO 10 DEGREES ABOVE NORMAL
(RANGING FROM THE LOWER 40S TO LOWER 50S), A FAR CRY FROM THE UPPER
60S THAT DELMARVA HAS THIS AFTERNOON, BUT STILL QUITE A WARM
CHRISTMAS DAY.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
THE SYNOPTIC SETUP IS COMPRISED OF AN UPPER-LEVEL TROUGH LIFTING OUT
OF NEW ENGLAND THURSDAY NIGHT AS ENERGY RELOADS ACROSS THE WEST AND
CENTRAL PLAINS. THIS ENERGY WILL AMPLIFY A TROUGH WELL TO OUR WEST
FRIDAY THROUGH SUNDAY. THE INITIAL ENERGY EJECTS NORTHEASTWARD
BETWEEN A RIDGE OFF THE SOUTHEASTERN U.S. COAST AND BUSIER FLOW
ACROSS CANADA. THIS SETUP HAS THE POTENTIAL TO BE AN OVERRUNNING
EVENT LATE SUNDAY AND MONDAY FOLLOWING A SECONDARY COLD FRONTAL
PASSAGE. THESE TYPES OF SETUPS ESPECIALLY FARTHER OUT IN TIME CARRY
MORE UNCERTAINTY AS THE TIMING AND TRACK OF THE ENERGY AND
ASSOCIATED SURFACE LOW EJECTING NORTHEASTWARD ARE KEY. AS ENERGY
CONTINUES TO DIVE INTO THE WEST AND PLAINS, THE TROUGH CONTINUES TO
EXPAND EASTWARD AND THIS APPEARS TO BE THE START OF A TURN TO COLDER
WEATHER IN THE EAST. WE USED A MODEL BLEND APPROACH FOR THURSDAY
NIGHT THROUGH SATURDAY, THEN WENT WITH THE 12Z WPC GUIDANCE
THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING ADDITIONAL
COLLABORATION WITH OUR NEIGHBORING OFFICES.

FOR THURSDAY NIGHT...HIGH PRESSURE IS FORECAST TO BUILD INTO OUR
AREA FROM THE SOUTHWEST. THIS WILL ALLOW THE PRESSURE GRADIENT TO
RELAX AND AS THE CAA WANES WITH EVEN SOME MODERATION AT 850 MB, THE
MIXING WILL WEAKEN AND THUS THE WINDS ARE EXPECTED TO DIMINISH
FAIRLY QUICKLY DURING THE EVENING. THIS WILL SET THE STAGE FOR A
COLDER NIGHT.

FOR FRIDAY AND SATURDAY...THE CENTER OF HIGH PRESSURE SLIDES TO OUR
SOUTH FRIDAY AND THEN OFFSHORE INTO SATURDAY. AS THIS OCCURS, SOME
RIDGING ALOFT IS FORECAST TO BUILD ACROSS THE EAST DOWNSTREAM OF AN
AMPLIFYING TROUGH ACROSS THE WEST AND INTO THE PLAINS. THIS IS
DIVIDED BY A COLD FRONT THAT IS FORECAST TO BE APPROACHING OUR AREA
SATURDAY NIGHT. THIS FRONT MAY NOT HAVE MUCH IN THE WAY OF MOISTURE
WITH IT AS THE MAIN SURFACE LOW TRACKS FAR TO OUR NORTH. OVERALL, A
DRY AND MILD TIME FRAME WITH PERHAPS SOME INCREASE IN CLOUDS LATE
SATURDAY.

FOR SUNDAY AND MONDAY...THE POTENTIAL REMAINS FOR AN OVERRUNNING
SETUP. THIS IS DUE TO THE MAIN UPPER-LEVEL TROUGH SITTING BACK WELL
TO OUR WEST WITH THE EAST UNDER MORE OF A SOUTHWESTERLY FLOW ALOFT
BETWEEN THE SOUTHEASTERN RIDGE AND THE MORE BUSY FLOW ACROSS CANADA.
THE FORECAST CHALLENGE IS A SURFACE LOW THAT DEVELOPS OUT OF THE
MAIN TROUGH THEN IS EJECTED NORTHEASTWARD ALONG A STALLED FRONTAL
BOUNDARY. WHILE THE SIGNAL IS THERE FOR AN OVERRUNNING EVENT, THE
TRACK AND ASSOCIATED PRECIPITATION SHIELD IS LESS CERTAIN. OF COURSE
THE TRACK WILL ALSO DETERMINE THE THERMAL PROFILES AS WELL, PLUS A
BUILDING SURFACE HIGH TO THE NORTH COULD COMPLICATE THINGS SOME. WE
FAVORED MORE OF THE WPC GUIDANCE DUE TO UNCERTAINTY IN THE
TRACK/DETAILS. THIS RESULTS IN AN AREA OF LOW LIKELY POPS ACROSS THE
SOUTHERN AREAS LATER SUNDAY WHERE THERE IS ENOUGH CONSENSUS, AND
ALSO TO PRESERVE SOME CONTINUITY. THE POPS THEN DECREASE SOME
NORTHWARD. THERE IS THE POTENTIAL FOR SOME SNOW ON THE NORTHERN
PORTION OF THE PRECIPITATION SHIELD, HOWEVER ANY AMOUNTS AND
ASSOCIATED THERMAL PROFILES WILL BE DETERMINED BY THE TRACK OF THE
SURFACE FEATURE GIVEN MOSTLY AN OVERRUNNING SCENARIO. THERE IS A CHC
THIS FEATURE TRACKS EVEN FARTHER SOUTH IF HIGH PRESSURE TO THE NORTH
IS STRONGER WITH ITS SOUTHWARD PUSH.

FOR TUESDAY AND WEDNESDAY...IT APPEARS ADDITIONAL ENERGY WILL BE
EJECTING NORTHEASTWARD AND WHILE THE EARLIER SURFACE LOW SHOULD BE
GONE TO START, A FRONTAL BOUNDARY MAY LINGER NEARBY TUESDAY. AS THE
UPPER-LEVEL TROUGH MIGRATES EAST SOME, THERE COULD BE SOME ENERGY
STILL SLIDING NORTHEASTWARD ALONG THE FRONT. AS OF NOW, WE FAVORED
MORE OF THE WPC GUIDANCE WHICH INDICATES A COLD FRONT SHIFTING
EAST TUESDAY AS STRONG HIGH PRESSURE BUILDS TOWARD THE CENTRAL
PLAINS AND ALSO EXPANDS TOWARD THE MID ATLANTIC INTO WEDNESDAY. THIS
RESULTS IN COLDER AIR SEEPING SOUTH AND EASTWARD.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

IFR CONDITIONS WILL PERSIST IN OUR REGION INTO TONIGHT. CONDS HAVE
BEEN VARIABLE FROM LIFR TO MVFR. THERE HAS BEEN A LULL IN THE PRECIP
IN THE NEAR TERM AND THIS SHOULD CONTINUE THRU THE EVE.
UNFORTUNATELY, IN SOME OF THESE AREAS, VSBYS HAVE DROPPED QUITE A
BIT, BUT FOR NOW THESE DROPS DON`T SEEM TO LAST ALL THAT LONG.
THEREFORE, WILL KEEP PREVAILING IFR CONDITIONS. THIS EVENING AND
LATE TONIGHT COULD ALSO SEE ISOLATED TSRA. WITH ANY TSRA COULD SEE
VRB AND GUSTY WINDS. HOWEVER, COVERAGE IS TOO LIMITED TO INCLUDE
IN THE TAFS AT THIS TIME.

A LOW LEVEL SOUTHERLY JET AS DEPICTED BY THE VAD WIND PROFILE FROM
KDIX CONTINUES OVER THE COASTAL PLAIN AND SHOULD PERSIST THROUGH AT
LEAST 06Z. AS A RESULT, WE HAVE CONTINUED THE MENTION OF LOW LEVEL WIND
SHEAR AT KTTN, KPNE, KPHL, KILG, KMIV AND KACY. BOTH KRDG AND KABE
SHOULD BE ENOUGH WEST OF THE LOW LEVEL JET.

AT THE SURFACE, GENERALLY LIGHT SOUTHERLY WINDS WILL CONTINUE UNTIL
THE COLD FRONT ARRIVES. THE COLD FRONT AND ASSOCIATED ABRUPT SHIFT
TO WESTERLY WINDS IS EXPECTED TO ARRIVE BETWEEN 06 AND 09Z. BEHIND
THE FRONT, EXPECT CONDITIONS TO IMPROVE TO MVFR, THEN VFR.

OUTLOOK...
THURSDAY NIGHT...VFR. WEST-NORTHWEST WINDS 10-15 KNOTS EARLY,
DIMINISHING TO LESS THAN 10 KNOTS.

FRIDAY AND SATURDAY...VFR, ALTHOUGH CLOUDS MAY INCREASE LATE
SATURDAY AS A COLD FRONT APPROACHES. SOUTHWEST WINDS MAINLY AROUND
10 KNOTS.

SUNDAY AND MONDAY...CLOUDS POTENTIALLY LOWER TO SUB-VFR AS A SYSTEM
TRACKS TO OUR SOUTH. THIS COULD RESULT IN SOME RAIN OR SNOW, HOWEVER
CONFIDENCE IS ON THE LOW SIDE. WINDS SHOULD TURN NORTHERLY.

&&

.MARINE...
SOUTHERLY WINDS WILL BE INCREASING SHORTLY, AND SHOULD SEE GUSTS
ABOVE 25KT ON ALL THE WATERS THROUGH THE EVENING HOURS. WITH THE
INCREASING WINDS, SEAS SHOULD ALSO BUILD BACK ABOVE 5 FT. AFTER
MIDNIGHT TONIGHT, LIKELY BETWEEN 2 AND 6 AM LST, A COLD FRONT WILL
PUSH THROUGH, BRINGING AN ABRUPT SHIFT TO WESTERLY WINDS. IN
ADDITION, COULD SEE ISOLATED THUNDERSTORMS WITH THE FRONT. UNDER ANY
THUNDERSTORMS, EXPECT VERY GUSTY WINDS. THE STRONG WESTERLY WINDS
WILL CONTINUE ON ALL THE WATERS THROUGH THE DAY TOMORROW. ALONG THE
OCEAN WATERS, ESPECIALLY THE NORTHERN NEW JERSEY COASTAL WATERS,
COULD SEE A FEW GUSTS ABOVE 30KT. HOWEVER, VERY UNCERTAIN IF WE WILL
REACH GALE FORCE GUSTS. THEREFORE, HAVE CANCELED THE GALE WATCH,
BUT AN SCA IS IN EFFECT FOR ALL THE WATERS THROUGH EARLY TOMORROW
EVENING. HOWEVER, WILL MONITOR WHEN THE NEW GUIDANCE COMES IN THIS
EVENING TO SEE IF THE THREAT FOR GALES FOR TOMORROW CHANGES.

OUTLOOK...
THURSDAY NIGHT...AS THE PRESSURE GRADIENT RELAXES, THE WINDS WILL AS
WELL. IT APPEARS THAT THE WINDS AND SEAS DECREASE FAIRLY QUICKLY,
THEREFORE A SMALL CRAFT ADVISORY WAS NOT EXTENDED AS OF NOW.

FRIDAY AND SATURDAY...THE CONDITIONS SHOULD BE BELOW SMALL CRAFT
ADVISORY CRITERIA AS HIGH PRESSURE BUILDS TO OUR SOUTH AND THEN
OFFSHORE. A WEAK COLD FRONT APPROACHES SATURDAY NIGHT.

SUNDAY AND MONDAY...A COLD FRONT SETTLES SOUTHEASTWARD ACROSS THE
AREA SUNDAY BUT THEN MAY STALL NEARBY. THE SOUTHWESTERLY FLOW MAY
INCREASE SOME AHEAD OF IT, THEN TURN NORTHWESTERLY IN ITS WAKE.
OVERALL, IT APPEARS THAT THE CONDITIONS REMAIN BELOW ADVISORY
CRITERIA. A WEAK LOW PRESSURE SYSTEM SHOULD DEVELOP ON THE FRONT AND
TRACK TO OUR SOUTH DURING THIS TIME FRAME.

&&

.TIDES/COASTAL FLOODING...
THIS EVENING`S COASTAL FLOOD ADVISORY HAS BEEN LOWERED AS IT
APPEARS NOBODY ON CHESAPEAKE BAY HAS HIT TIDAL FLOODING CRITERIA.

TO A LESSER EXTENT THERE IS A SMALL THREAT AGAIN TOMORROW MORNING
ALONG THE CHESAPEAKE. IT LOOKS LIKE WE SHOULD HAVE THE SHIFT TO
WESTERLY WINDS WELL BEFORE THE HIGH TIDE CYCLE, AND THE ASTRONOMICAL
TIDE IS LOWER, SO THE THREAT IS TOO LOW TO MENTION IN THE HWO FOR
NOW, BUT WILL CONTINUE TO MONITOR.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...DENSE FOG ADVISORY UNTIL 4 AM EST THURSDAY FOR ANZ450>453.
     SMALL CRAFT ADVISORY UNTIL 7 PM EST THURSDAY FOR ANZ430-431-
     450>455.

&&

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





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