Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 311349
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
949 AM EDT TUE MAR 31 2015

.SYNOPSIS...
LOW PRESSURE WILL QUICKLY TRACK SOUTHEASTWARD FROM THE GREAT LAKES
REGION, CROSSING OUR AREA LATER TODAY INTO THIS EVENING. HIGH
PRESSURE WILL THEN BUILD INTO OUR REGION WEDNESDAY BEFORE QUICKLY
SHIFTING OFFSHORE WEDNESDAY NIGHT INTO THURSDAY. THE NEXT COLD FRONT
IS SCHEDULED TO ARRIVE LATE FRIDAY, WITH A SECONDARY COLD FRONT
MOVING THROUGH LATE SATURDAY NIGHT AND SUNDAY MORNING. A HIGH
PRESSURE SYSTEM IS THEN NEARBY FOR MONDAY.

&&

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

9:30 AM UPDATE: WITH THIS UPDATE MADE SOME CHANGES TO ACCOUNT FOR
A PRETTY QUICK RISE IN TEMPERATURES ACROSS SOUTHERN PARTS OF THE
REGION. THIS WILL LIKELY CONTINUE INTO THIS AFTERNOON WITH DECENT
WAA SOUTH OF THE CLIPPER TRACK. ALSO WITH THE WAA, THE NAM AND
HRRR ARE SHOWING SOME INSTABILITY IN THE FORM OF STEEP LAPSE
RATES AND CAPE BETWEEN 200-500 J/KG ACROSS THE DELMARVA LATE THIS
AFTERNOON. THIS COULD BE THE TRIGGER FOR A THUNDERSTORM OR TWO, SO
HAVE ADDED THIS TO THE GRIDS SOUTH OF ILG. SNOW PART OF THE
FORECAST LOOKS MAINLY ON TRACK WITH THE CHANGEOVER FROM RAIN TO
SNOW OCCURRING EARLY AFTERNOON FOR THE POCONOS AND THE HIGHER
ELEVATIONS IN SUSSEX NJ. LIGHTER ACCUMULATIONS HAVE BEEN TRIMMED
BACK IN MORRIS NJ AND FOR THE LEHIGH VALLEY/READING. TEMPERATURES
IN THESE AREAS ARE ALREADY IN THE UPPER 30`S AND LOW 40`S WITH 1-2
OF ADDITIONAL WARMING BEFORE PRECIPITATION STARTS. WIND GUSTS
AROUND 20-25 MPH COUPLED WITH RH VALUES AROUND 35% ARE FORECASTED
IN THE SOUTHERN DELMARVA FOR A FEW HOURS, WITH RAIN IN THE
FORECAST THIS AFTERNOON DO NOT SEE ANY FIRE WEATHER CONCERNS ATTM.



8:00 AM: FORECAST STILL LOOKS ON TRACK FOR A LIGHT ACCUMULATING SNOWFALL
IN THE HIGHER TERRAIN OF SUSSEX NJ AND THE POCONOS TODAY WITH A
PERIOD OF RAIN OR RAIN/SNOW MIX ELSEWHERE. SLOWED THE INCREASE OF
CLOUDS SOMEWHAT OVER THE NEXT FEW HOURS THOUGH. THE PRECIPITATION
ONSET TIME MAY NEED TO BE PUSHED BACK BY 1-2 HOURS AS WELL BASED
ON THE LATEST RAP AND HRRR RUNS. ATTM DID NOT MAKE THIS
ADJUSTMENT WITH THE POSSIBILITY STILL PRESENT OF RAIN/ MIX
ENTERING THE WESTERN FRINGE OF THE CWA BY 16-17Z. IN THE POCONOS
AND NW NJ, THE PRECIPITATION MAY START AS A MIX BEFORE CHANGING TO
SNOW WITH EVAPORATIVE COOLING OCCURRING.


PREVIOUS: THE GFS INITIALIZATION LOOKED A LITTLE WEAK WITH THE
APPROACHING TROF AND MAYBE WHY ITS TIMING IS THE FASTEST. ITS
SLIGHTLY WARMER AT 925MB UPSTREAM THAN THE MODELS THINK. OVERALL
THE MODELS ARE MUCH CLOSER THAN THEY WERE YESTERDAY, BUT THERE
REMAINS DIFFERENCES AS TO THE NORTHERN EXTENT OF HEAVIER PCPN.
THEY HAVE TRENDED COLDER AND OVERALL WETTER. MODEL PREDICTED PWATS
HOWEVER ARE AROUND HALF AN INCH AND GIVEN THIS IS ABOUT A 6 TO 12
HR EVENT, BELIEVE QPF ABOVE HALF AN INCH ARE TOO ROBUST UNLESS A
FGEN BAND CONCENTRATES IN A NARROW AREA FOR A PROTRACTED PERIOD.
OUR FORECAST SOLUTION IS CLOSEST TO A COMBINATION OF THE UKMET`S
QPF FIELD, GFS PATH (COUPLE OF HOURS SLOWER) AND WRF-NMM`S BETTER
LLVL THERMALS AND SFC TEMPS FOR THE NORTHERN SNOWIER AREAS.

WINTER WEATHER ADVISORY FOR OUR THREE NORTHERN COUNTIES.

IF THIS WAS NIGHTTIME THIS WOULD BE MORE OF A CONFIDENT SNOWFALL
FCST, BUT GIVEN THIS IS A TIMING REPEAT OF MARCH 20TH, THERE REMAINS
UNCERTAINTY AS TO HOW MUCH SNOW CAN ACCUMULATE. MARCH 20TH SHOWED
INTENSITY CAN TRUMP THE LATE MARCH SUN. THE HOURLY RATES
AT PEAK TIME DURING THIS AFTERNOON IS NEARING .1 WATER EQUIVALENT
PER HOUR. THIS SHOULD BE ENOUGH TO START ACCUMULATING.
BUT THIS OVERALL WINDOW IS SMALLER THAN THAT PREVIOUS EVENT.
ALSO THE INITIAL BOUNDARY LAYER CAN WARM THIS MORNING AND THIS
WILL PROLONG THE CHANGE TO SNOW AT LOWER TERRAIN LOCATIONS.
THE HIGHER TERRAIN OF THE POCONOS AND WESTERN SUSSEX COUNTY NJ
IT WILL BE PRETTY MUCH COLD ENOUGH FOR SNOW.
THE UNCERTAINTY IS TO WILL  THE HEAVIER PCPN REACH THAT FAR
NORTH. THE GENERAL CONSENSUS IS YES, BUT THERE IS NOT UNIFORMITY.
THE GFS DIAGS DO SHOW FGEN BANDING IN THAT AREA, BUT THE EXIT REGION
OF THE 250MB JET AND BEST MID LEVEL QVEC CONVERGENCE IS A BIT FTHR
TO THE SOUTH. THERE WILL BE A 45 KT LLJ FEEDING ACROSS THIS
BOUNDARY AND THERE IS A BROAD 200MB OF LIFT PREDICTED AT 290K
ACROSS OUR CWA THIS AFTERNOON.

HERE GOES, PCPN MOVES IN NORTH LATE THIS MORNING AND EARLY THIS
AFTERNOON AND LATER IN THE AFTERNOON THE REST OF OUR CWA. THE
SOUNDINGS ARE DRY ABOVE THE SFC AND EVAP COOLING SHOULD CHANGE ANY
BRIEF START OF RAIN IN THE HIGHER TERRAIN OF THE POCONOS TO SNOW.
ELSEWHERE ITS THE LESS EFFICIENT DYNAMIC COOLING THAT IS EXPECTED TO
DO THE TRICK. OBVIOUSLY ELEVATION HELPS AS THE GFS PREDICTED
FREEZING LEVEL AT ABE DROPPING TO 800 FEET SHOWS. ALL THE MODELS
LOWER SFC TEMPS AND WBZS TO AROUND FREEZING IN THE POCONOS, BUT
STRUGGLE ELSEWHERE. SO THERE IS GREATER UNCERTAINTY FARTHER EAST
IN SUSSEX COUNTY NJ. THE NEXT TIER SOUTHWARD, THERE COULD BE SOME
HIGHER TERRAIN LOCATIONS THAT DO GET A COUPLE OF INCHES, NOT AS
WIDESPREAD AS THE ADVISORY AREA  WE BELIEVE. WE WILL HAVE TO WATCH
IF THE FGEN BANDING ESTABLISHES ITSELF IN THIS LOCATION LATER
TODAY, BUT CONFIDENCE IS NOT HIGH ENOUGH TO ISSUE AN ADVISORY.
WE WILL KEEP MENTION IN THE HWO.

TEMPERATURES ARE ALSO PROBLEMATICAL AS THE GFS LOWER TEMPS ARE
BANKING ON A FASTER PCPN ARRIVAL TIME. GIVE ITS ARRIVAL
UNTIL THE AFTERNOON AND NAM MOS MAY BE RIGHT FOR THE WRONG
REASON. WE COMPROMISED BETWEEN THE DATASETS.

06Z MODELS PRETTY MUCH HELD THEIR OWN. E.G. ABE FREEZING LEVEL
LATE THIS AFTERNOON AT 800 TO 900 FEET. 06Z MODEL QPF VERIFICATION
GEOGRAPHICALLY WAS GOOD WITH THE GFS AND NAM A BIT WET. GFS
ENSEMBLE MEAN WAS SLIGHTLY SLOWER THAN THE OP.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
OPTING FOR THE SLOWER MODEL TIMING, WE CARRIED PCPN INTO THIS
EVENING, ESPECIALLY IN NJ. EVENT SHOULD BE DONE BY ABOUT MIDNIGHT.
THE PREDICTED VORT MAX OVERNIGHT BECOMES QUITE CHANNELIZED AND
MODELS PREDICTED MOISTURE OVERALL MEAGER. WE CLEARED SKIES OVERNIGHT.
WE OPTED FOR A STAT GUIDANCE COMPROMISE FOR MINS.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
THE OVERALL SYNOPTIC SETUP IS AN ACTIVE ONE BUT ALSO COMPRISED OF A
FAST FLOW REGIME. AN UPPER-LEVEL TROUGH ACROSS THE NORTHEAST TO
START WEDNESDAY WILL SHIFT EAST WITH A RIDGE BUILDING IN THURSDAY AS
SHORT WAVE ENERGY MOVES ACROSS THE MIDWEST. THIS SHORT WAVE ENERGY
WILL HELP TO AMPLIFY AN UPPER-LEVEL TROUGH ACROSS THE GREAT LAKES
AND OHIO VALLEY LATE FRIDAY, THEN INTO THE EAST SATURDAY. IT APPEARS
THIS TROUGH REMAINS THROUGH MONDAY, ALTHOUGH IT SHOULD START TO
RETREAT NORTHWARD WITH TIME. WE USED A MODEL BLEND FOR WEDNESDAY
THROUGH FRIDAY, THEN INCORPORATED THE 00Z WPC GUIDANCE IN WITH
CONTINUITY THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING
ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES.

FOR WEDNESDAY AND THURSDAY...AN UPPER-LEVEL TROUGH AXIS IS FORECAST
TO PIVOT ACROSS THE AREA WEDNESDAY. A SHORT WAVE ROUNDING THE BASE
OF THIS TROUGH MAY HAVE SOME SHOWERS WITH IT TO OUR NORTHWEST,
HOWEVER IT MAY END UP DAMPENING OUT AS IT TRACKS SOUTHEAST AND EAST.
THEREFORE, WE WILL CONTINUE WITH A DRY FORECAST. SOME CAA AT LEAST
DURING THE FIRST HALF OF THE DAY WILL RESULT IN A COOLER DAY.

HIGH PRESSURE SHIFTS OFFSHORE WEDNESDAY NIGHT INTO THURSDAY ALLOWING
FOR A RETURN FLOW. AS THIS OCCURS, WAA WILL INCREASE AHEAD OF OUR
NEXT SYSTEM. THIS WILL BE IN THE FORM OF A COLD FRONT THAT WILL BE
APPROACHING LATE THURSDAY NIGHT. AHEAD OF THIS, A NOTABLE INCREASE
IN AFTERNOON TEMPERATURES ARE EXPECTED THURSDAY /ALTHOUGH PROBABLY
COOLER ALONG THE COAST DUE TO A SOUTHERLY FLOW OFF THE COLDER
OCEAN/. IT APPEARS THAT A LEAD SHORT WAVE GENERATES SOME SHOWERS
WELL OUT AHEAD OF THE COLD FRONT THURSDAY AND THESE MAY START TO
MOVE INTO OUR WESTERN ZONES LATER THURSDAY NIGHT. IT APPEARS THAT IT
WILL TAKE AWHILE FARTHER EAST THEREFORE WE SLOWED DOWN THE POP
INCREASE AT NIGHT FROM WEST TO EAST. IN ADDITION, THE FORECAST
SOUNDINGS GENERALLY SHOW A DEEPENING MOIST PROFILE AS A LOW-LEVEL
JET INCREASES THE THETA-E ADVECTION. THIS RESULTS IN A DECREASE IN
THE SHOWALTER VALUES, HOWEVER NO REAL INSTABILITY LOOKS TO BE
PRESENT. AS A RESULT THERE IS A QUESTION WHETHER OR NOT CHARGE
SEPARATION CAN TAKE PLACE AND THEREFORE WE REMOVED THE SLIGHT CHC OF
THUNDER ATTM. AS MIXING INCREASES THURSDAY, A BREEZY AFTERNOON
SHOULD RESULT.

FOR FRIDAY AND SATURDAY...A COLD FRONT WILL GRADUALLY SETTLE
SOUTHEAST ACROSS OUR AREA LATER FRIDAY INTO SATURDAY. A WARM
SOUTHWESTERLY FLOW WILL BE IN PLACE AND THIS COMBINED WITH LARGE
SCALE LIFT FROM THE INCOMING COLD FRONT, UPPER-LEVEL TROUGH AND AN
UPPER-LEVEL JET SHOULD RESULT IN SHOWERS OR EVEN BANDS OF SHOWERS.
IF ENOUGH INSTABILITY CAN BE REALIZED, SOME THUNDER COULD OCCUR ON
FRIDAY AHEAD OF THE COLD FRONT. WE WILL MAINTAIN CONTINUITY AND
INCLUDE A SLIGHT CHC OF THUNDER IN THE FORECAST DATABASE. LOW
PRESSURE SHOULD BE TRACKING TO OUR NORTH AND NORTHEAST FRIDAY NIGHT,
PULLING THE COLD FRONT TO OUR EAST EARLY SATURDAY. AS SOME ENERGY
ROTATES AROUND THE BASE OF THE TROUGH, A COUPLE OF WAVES OF LOW
PRESSURE SHOULD DEVELOP ALONG THE COLD FRONT. THE FIRST ONE SHOULD
DELAY THE COLD FRONTAL PASSAGE ACROSS OUR AREA AND THEN THE SECOND
ONE TRACKS WELL TO OUR SOUTH AND EAST AFTER THE FRONT CLEARS OUR
AREA EARLY SATURDAY. THE TIMING AND POSITIONING OF THE COLD FRONT
FRIDAY WILL IMPACT TEMPERATURES, HOWEVER OUR ENTIRE CWA SHOULD
REMAIN IN THE WARM SECTOR. WE THEN KEPT LOW CHC POPS FOR SHOWERS IN
FOR SATURDAY THEN DRYING OVERTAKES THE AREA. A SECONDARY COLD FRONT
LOOKS TO DROP INTO THE AREA LATE SATURDAY NIGHT.

FOR SUNDAY AND MONDAY...A COLD FRONT SHOULD MOVE ACROSS THE AREA
SUNDAY MORNING, HOWEVER THIS LOOKS MOISTURE STARVED. HIGH PRESSURE
THEN SLIDES TO OUR EAST LATE SUNDAY INTO MONDAY, ALTHOUGH THE
TAILEND OF THE AFOREMENTIONED COLD FRONT MAY REMAIN FROM THE OHIO
VALLEY WESTWARD TO THE NORTHERN PLAINS. FOR NOW, KEPT THIS TIMEFRAME
DRY WITH MODERATION IN TEMPERATURES ON MONDAY.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY, AND SURROUNDING AREAS.

THE 12Z TAFS STILL BRING ALL OF OUR SITES TO LOW MVFR OR IFR
CONDITIONS THIS AFTERNOON WITH A HIGH DEGREE OF UNCERTAINTY ABOUT
THE WIND DIRECTIONS THIS AFTERNOON AND EARLY EVENING.

THIS MORNING A MID LEVEL CIG ARRIVING, SOME RAIN POSSIBLE LATE AT
KABE AND KRDG. SOUTH TO SOUTH WEST WINDS AVERAGING 5 TO 10 KNOTS.

THIS AFTERNOON AT KABE AND KRDG CIGS AND VSBYS LOWERING TO IFR.
RAIN MAY MIX WITH OR CHANGE TO SNOW LATE. ESP KABE. TARMAC ACCUMS
NOT EXPECTED. LOCAL KPHL AIRPORTS RAIN ARRIVES AND CIGS AND VSBYS
LOWERING TO THE BORDER BETWEEN MVFR AND IFR CONDITIONS. KMIV AND
KACY SIMILAR EVOLUTION, BUT LATER IN THE AFTERNOON.

WINDS WILL BE TRICKY AS IT DEPENDS UPON THE TRACK OF THE LOW.
WE ARE EXPECTING IT TO PASS TO THE SOUTH OF ALL THE TERMINALS
ACROSS DELMARVA. THERE WILL BE A SLOW BACKING OF THE WINDS FROM
SOUTH TO NORTHEAST AS THE AFTERNOON PROGRESSES. SPEEDS SHOULD BE
AROUND 10 KNOTS.

THIS EVENING, CONDITIONS BOTTOMING EAST OT IFR EARLY AND THEN
IMPROVING CONDITIONS THE REST OF THE EVENING. PCPN SHOULD END BY
04Z ALL TERMINALS. WINDS WILL CONTINUE TO BACK TOWARD THE NORTH
AND THEN NORTHWEST WITH AVERAGE SPEEDS AROUND 10 KNOTS, BUT SOME
GUSTINESS TO AROUND 20 KNOTS FROM THE KPHL AIRPORTS
SOUTHEASTWARD.

OVERNIGHT IMPROVING CONDITIONS CONTINUING WITH A VFR CIG BECOMING
CLEAR AND NORTHWEST WINDS AVERAGING AROUND 10 TO 15 KNOTS.

OUTLOOK...
WEDNESDAY AND THURSDAY...VFR OVERALL. AN INCREASE IN CLOUDS SHOULD
OCCUR LATE THURSDAY AHEAD OF A COLD FRONT WITH SHOWERS LURKING NOT
TO FAR TO OUR WEST LATE AT NIGHT. GENERALLY LIGHT WINDS WEDNESDAY
DUE TO HIGH PRESSURE IN PLACE, THEN A SOUTHERLY FLOW DEVELOPS
WEDNESDAY NIGHT AND THURSDAY WITH SOME GUSTINESS DURING THURSDAY.

FRIDAY AND SATURDAY...MVFR TO POTENTIALLY IFR CONDITIONS WITH
SHOWERS. A THUNDERSTORM CANNOT BE RULED OUT AHEAD OF A COLD FRONT
FRIDAY. POTENTIALLY GUSTY SOUTHWESTERLY WINDS FRIDAY, SHIFTING TO
THE NORTHWEST FRIDAY NIGHT INTO SATURDAY. SHOWERS SHOULD END
SATURDAY MORNING FOLLOWED BY CONDITIONS RETURNING TO VFR. THERE IS
LOWER CONFIDENCE REGARDING THE TIMING OF THE CLEARING SATURDAY.

&&

.MARINE...
RIGHT NOW CONDITIONS ARE BELOW SCA CRITERIA ON THE OCEAN. HOWEVER
BOTH SEAS AND GUSTS ARE EXPECTED TO INCREASE SOME THIS AFTERNOON.
WE WILL KEEP THE SCA UP FOR THE POTENTIAL OF WIND GUSTS AROUND 25
KNOTS THIS AFTERNOON AND LOCALIZED SEAS NEAR FIVE FEET.

THE ADVISORY IS NOT IN EFFECT FOR DELAWARE BAY, ALTHOUGH THERE COULD
BE A FEW GUSTS TO 25 KNOTS THIS MORNING AND AGAIN LATER TONIGHT WITH
THE DOWN THE BAY FLOW. WE WILL REACCESS THE BAY LATER TODAY.

OUTLOOK...
WEDNESDAY...HIGH PRESSURE BUILDS OVER THE AREA BUT THEN BEGINS TO
SHIFT OFFSHORE AT NIGHT. AS A RESULT, THE WINDS AND SEAS WILL
DECREASE AND BE BELOW ADVISORY CRITERIA.

THURSDAY AND FRIDAY...A SOUTH TO SOUTHWEST FLOW WILL INCREASE AS THE
PRESSURE GRADIENT TIGHTENS AHEAD OF A COLD FRONT. A MUCH WARMER
AIRMASS HOWEVER WILL BE MOVING OVER THE COLDER WATERS, AND THIS WILL
LIMIT THE MIXING. AS A RESULT, THE HIGHEST GUSTS WILL PROBABLY BE
CLOSER TO THE COAST. THE INCREASING SOUTHERLY FLOW WILL BUILD THE
SEAS AND THEREFORE A SMALL CRAFT ADVISORY LOOKS TO BE NEEDED. THE
WAVEWATCH GUIDANCE IS PROBABLY OVERDONE SOME WITH THE SEAS AS THE
GFS IS A BIT TO STRONG WITH THE SURFACE WINDS, THEREFORE WE STAYED
CLOSER TO CONTINUITY WHICH HAD THIS FACTORED IN.

SATURDAY...A COLD FRONT SHOULD BE EAST OF OUR AREA WITH A WIND SHIFT
TO THE NORTHWEST, AND THE WINDS COULD BE A BIT GUSTY AS SOME COOLING
TAKES PLACE. THE SEAS SHOULD BE AT OR ABOVE 5 FEET ON THE OCEAN, BUT
TENDING TO SUBSIDE WITH THE OFFSHORE FLOW.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...WINTER WEATHER ADVISORY UNTIL 10 PM EDT THIS EVENING FOR
     PAZ054-055.
NJ...WINTER WEATHER ADVISORY UNTIL 10 PM EDT THIS EVENING FOR
     NJZ001.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT WEDNESDAY FOR ANZ450>455.

&&

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


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