Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 292315
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
615 PM EST THU JAN 29 2015

.SYNOPSIS...
A FRONTAL SYSTEM WILL MOVE ACROSS THE AREA TONIGHT AS LOW
PRESSURE MOVES INTO NEW ENGLAND THEN SLOWLY DRIFTS INTO THE
CANADIAN MARITIMES THROUGH THE WEEKEND. HIGH PRESSURE BUILDS TO
OUR SOUTH THROUGH THE WEEKEND, FOLLOWED BY ANOTHER FRONTAL
BOUNDARY ON SUNDAY. AN AREA OF LOW PRESSURE IS FORECAST TO DEVELOP
ALONG THIS BOUNDARY AND PASS JUST TO OUR SOUTH ON MONDAY BUT STILL
AFFECT THE AREA. HIGH PRESSURE BUILDS IN ONCE AGAIN FOR MONDAY
NIGHT INTO TUESDAY. ANOTHER FRONTAL BOUNDARY IS EXPECTED WEDNESDAY
INTO WEDNESDAY NIGHT.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
THE GFS AND WRF-NMMB INITIALIZATION LOOKED PRETTY GOOD. AT 500MB
KILZ WINDS LOOKED OFF BASED ON WATER VAPOR IMAGERY. 850MB TEMPS IF
ANYTHING WERE INITIALIZED 1C TOO WARM AROUND OUR REGION, IT GETS
COLDER AT 925MB WITH A 1 TO 2C WARM BIAS. ACAR SOUNDINGS AT PHL
ARE ALL STILL BELOW ZERO CELSIUS. 12Z MORNING SOUNDINGS SHOWED
PLENTY OF DRY AIR BELOW 700MB.

THE ECMWF VERIFIED THE BEST WITH ITS 6HR QPF FORECAST. GIVEN IT
AND THE CAN GGEM ARE IN THE COMPROMISE POSN BETWEEN THE GFS WHICH
IS MOST BULLISH WITH PCPN AND THE MESOSCALE MODELS THAT LEAVE THE
I95 CORRIDOR SEWD HIGH AND DRY, WE HAVE OPTED FOR THE FORMER.

A SUB ADVISORY ONE-TWO PCPN PUNCH IS EXPECTED ACROSS OUR CWA
EARLY THIS EVENING AND THEN AGAIN LATE TONIGHT. ONE TO THREE
INCHES THROUGH FRIDAY MORNING WAS KEPT FROM A READING PA - TRENTON
NJ - NEW BRUNSWICK NJ LINE NORTHWESTWARD. I95 CORRIDOR WAS KEPT
UNDER AN INCH AND JUST A COATING POSSIBLE CLOSER TO THE COAST.

THE FIRST PCPN SHOT IS TIED TO A SHORT WAVE AND HAS THE BEST WAA
AS WELL AS MID LEVEL QVEC CONVERGENCE PREDICTED. THIS LOOKS LIKE A
QUICK 1 TO 3 HR SHOT. IN SPITE OF PCPN FIELD DIFFERENCES, THE
EVENING DEEP OMEGA BETWEEN THE WRF-NMM AND GFS ARE QUITE SIMILAR.
MESOSCALE MODELS ARE SIDING WITH THE DRIER WRF-NMMB COLLAPSING THE
PCPN BEFORE IT GETS TO PHL. BUT THE SOUTHERN EXTENSION WAS SOUTH
OF THEIR 6HR PREDICTIONS. WE WERE MORE BULLISH WITH POPS ALONG THE
MD EASTERN SHORE AS WELL INTO THE I95 CORRIDOR.

AS FOR PTYPE. THE SOUNDINGS ARE SO DRY BELOW 700MB THAT
EVAPORATIONAL COOLING INITIALLY WILL TAKE PTYPE TO SNOW POSSIBLY
IN ALL PLACES. ARE SEEING SOME SLEET (SNOW PELLETS?) IN
OBSERVATIONS TO OUR WEST. NON-FREEZING RAIN PTYPE SEEMS MOST
CONFIDENT AROUND AND TO THE NORTHWEST OF THE I95 CORRIDOR BECAUSE
OF THE EVAP COOLING POWER OF THIS DRY AIR MASS STILL IN PLACE OVER
OUR CWA. IN THE REST OF OUR CWA, GIVEN THAT INITIALIZED 925MBS
WERE TOO WARM, FORECAST SOUNDINGS THAT EDGE ABOVE 3C SHOULD EVAP
COOL BELOW AS SNOW STARTS FALLING. THIS GIVES SOUNDINGS THERE MORE
THE ICE PELLET LOOK TO IT AND IF INTENSITIES ARE EXTREMELY LIGHT
POSSIBLY SOME RAIN WAY SOUTH. WHILE THE THREAT FOR FREEZING RAIN
SOUTHEAST IS NOT ZERO, IT REMAINS TOO LOW TO INCLUDE AT THIS TIME.
A COUPLE OF FACTORS ARE ON OUR SIDE, SURFACE ROAD TEMPS HAVE
RESPONDED TO AROUND 40 TODAY IN DE AND AIR TEMPS ARE NOT EXPECTED
TO FALL MUCH BELOW IF TO FREEZING THIS EVENING AS CLOUDS ARE
ALREADY HERE. LASTLY MOST ROADWAYS ARE HEAVILY SALTED AND ARE NOT
STARTING FROM A CLEAN SLATE. REGARDLESS WE WILL CONTINUE TO
MONITOR THIS EVENING.

WHERE POPS ARE LIKELY WE HAVE ISSUED AN SPS. THERE SHOULD BE A
LULL IN THE PCPN DURING THE MIDDLE OF THE NIGHT, EXCEPT FOR FAR
NORTH.

THEN LATER TONIGHT AS A COLD FRONT AND ANOTHER SHORT WAVE APPROACHES
FROM THE WEST, PRECIPITATION IS EXPECTED TO RE-ENERGIZE. THIS IS
MOST LIKELY TO OCCUR IN THE NORTHERN AND NORTHEASTERN PART OF OUR
CWA.

TEMPERATURES. BECAUSE OF THE LIGHT SOUTH TO SOUTHEAST FLOW AND
CLOUDINESS, THEY SHOULD REMAIN NEARLY STATIONARY IF NOT RISE
SLIGHTLY OVERNIGHT AFTER THE INITIAL SHOT OF PCPN. WE ARE HIGHER
THAN STAT GUIDANCE WITH MINS.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
ANY COLD FRONTAL RELATED PCPN SHOULD MOVE OFFSHORE EARLY FRIDAY
MORNING. BUT THAT MIGHT NOT BE THE END OF PCPN CHANCES AS ANOTHER
SHORT WAVE AT THE BASE OF THE TROF WILL BE MOVING THROUGH. IN FACT
SOME OF OUR WINDEX/SNOW SQUALL TOOLS ARE GIVING THE SOUTHERN HALF
OF OUR CWA THE CHANCE FRIDAY AFTERNOON. SOME OF THE OLDER WINDEX
PROCEDURES ARE SLIGHTLY MORE SUBDUED BECAUSE OF THE LACK OF EVEN
STEEPER LAPSE RATES AND NO REAL FOCUSING BOUNDARY OR CAPES ABOVE
70J. THE FORECAST SOUNDINGS HAVE THE CAP HIGH ENOUGH TO SUPPORT
SNOW SHOWERS EVERYWHERE. FOR NOW WE HAVE PUT IN A LOW CHANCE FOR
SNOW SHOWERS AND SEE HOW THE GUIDANCE PROGRESSES.

SNOW SHOWERS OR NOT, THE NORTHWEST GRADIENT WILL BE TIGHTENING AS
THE AFTERNOON PROGRESSES. WE ARE APPROACHING WIND ADVY CRITERIA
LATE IN THE DAY AS MIXING BECOMES DEEPER. BECAUSE WE ARE NOT DEEP
INTO THE CRITERIA AND PMDHMD RECOMMENDED THAT THE NAM/WRF IS TOO
TUCKED INTO THE COAST WITH THE SFC LOW, WE HELD OFF WITH ISSUING
IT FOR NOW. THE KATABATIC NORTHWEST FLOW WILL BE ABLE TO MAINTAIN
TEMPS FOR A WHILE AND GIVEN A RELATIVELY HIGH START, WE WERE AT
THE HIGH END FOR MAX TEMPS. NOT THAT IT WILL FEEL WARM.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
AS THE LOW PULLS AWAY FROM THE AREA AND INTO THE NEW ENGLAND
COASTAL WATERS FRIDAY NIGHT, PRECIPITATION IS EXPECTED TO END
ACROSS MOST OF THE AREA. THE EXCEPTION TO THIS WOULD BE ACROSS THE
POCONOS AREAS WHERE SOME LINGERING LAKE EFFECT SHOWERS MAY
CONTINUE INTO THE NIGHT. OTHERWISE, BITTERLY COLD AIR WILL FILTER
DOWN ACROSS THE AREA ALONG WITH STRONG WINDS AS THE PRESSURE
GRADIENT TIGHTENS BETWEEN THE DEPARTING LOW AND HIGH PRESSURE
BUILDING TO OUR WEST. WINDS COULD GUST 35-40 MPH DURING FRIDAY
NIGHT AS WELL. THE COMBINATION OF THE LOW TEMPERATURES AND STRONG
WINDS WILL CREATE DANGEROUSLY LOW WIND CHILLS ACROSS MUCH OF THE
AREA. SUB-ZERO WIND CHILLS WILL OCCUR ALMOST EVERYWHERE, WITH THE
POCONOS -15 TO -20. WE HAVE ISSUED A WIND CHILL ADVISORY FOR
CARBON AND MONROE SINCE THEY ARE EXPECTED TO REACH WELL INTO THE
ADVISORY RANGE. ELSEWHERE, WIND CHILLS AS OF NOW ARE EXPECTED TO
FALL JUST SHORT.

SATURDAY WILL CONTINUE TO BE WINDY AND COLD, BUT WIND CHILLS WILL
BE ABLE TO REBOUND SOME AS TEMPERATURES WARM DURING THE DAY. DRY
WEATHER IS CONTINUED TO BE EXPECTED THROUGH THE DAY SATURDAY.
WINDS WILL CONTINUE TO BE GUSTY WITH GUSTS IN THE 25-30 MPH RANGE.
WINDS SHOULD DIMINISH LATE IN THE DAY INTO THE NIGHT AS THE
PRESSURE GRADIENT WEAKENS.

ON SUNDAY, A COLD FRONT IS FORECAST TO SAG DOWN ACROSS THE AREA
FROM THE NORTH. IT LOOKS LIKE THE ACTUAL FRONT SHOULD BE DRY AS IT
DIPS ACROSS THE AREA. HOWEVER, AN AREA OF LOW PRESSURE IS FORECAST
TO DEVELOP ALONG THIS FRONT ACROSS THE MID-MISSISSIPPI VALLEY
DURING THE DAY, AND MAKE ITS WAY ACROSS THE CENTRAL APPALACHIANS
AND OFF THE MID-ATLANTIC COAST SUNDAY NIGHT INTO MONDAY MORNING.
AS THIS HAPPENS, A SHORT WAVE ALOFT APPROACHING FROM THE WEST WILL
HELP STRENGTHEN THE LOW AS IT PASSES JUST TO OUR SOUTH OVERNIGHT
AND LIFT TO OUR NORTHEAST MONDAY MORNING. MEDIUM RANGE GUIDANCE IS
IN GOOD AGREEMENT THAT SNOW WILL OVERSPREAD THE AREA ON THE
NORTHERN SIDE OF THE SYSTEM OVERNIGHT SUNDAY INTO MONDAY MORNING.
WITH THE LOW BEING TO OUR SOUTH, AND COLD HIGH PRESSURE TO OUR
NORTH, IT LOOKS LIKE THE PRECIPITATION SHOULD BE ALL SNOW. AN
ACCUMULATING SNOWFALL IS BECOMING MORE LIKELY, FOR MOST, IF NOT
ALL OF OUR AREA SUNDAY NIGHT INTO MONDAY, WITH THE SOUTHERN HALF
LOOKING TO RECEIVE THE MOST. WE MAY RUN INTO AN INSTANCE WHERE
EXTREME SOUTHERN AREAS MAY HAVE MORE QPF BUT LOWER RATIOS, AND
NORTHERN AREAS HAVING LESS QPF AND HIGHER RATIOS, AND IN BETWEEN
HAVING A LITTLE OF BOTH. AS USUAL, WE`LL REFINE SNOW AMOUNTS IN
SUBSEQUENT FORECASTS.

ALL SNOW IS EXPECTED TO HAVE ENDED BY MONDAY EVENING AS THE LOW
PULLS AWAY FROM THE AREA. VERY COLD AIR, NEAR RECORD LOW
TEMPERATURES FOR SOME AREAS, ONCE AGAIN FILTERS DOWN INTO THE AREA
OVERNIGHT ACROSS THE AREA AS COLD CANADIAN HIGH PRESSURE BUILDS
DOWN INTO THE REGION AGAIN. WINDS SHOULD WEAKEN SOME OVERNIGHT AS
THE PRESSURE GRADIENT SLACKENS WHEN THE HIGH STARTS TO BUILD INTO
THE AREA. HOWEVER, THERE SHOULD BE ENOUGH WIND AND IT WILL BE COLD
ENOUGH FOR WIND CHILLS TO FALL WELL BELOW ZERO MONDAY NIGHT INTO
TUESDAY.

HIGH PRESSURE ACROSS THE AREA TUESDAY WILL PUSH OFFSHORE TUESDAY
NIGHT, AND DRY AND COLD CONDITIONS ARE EXPECTED THROUGH THIS
PERIOD.

ANOTHER FRONTAL BOUNDARY IS EXPECTED TO APPROACH THE AREA
WEDNESDAY INTO WEDNESDAY NIGHT. THIS COULD BRING ANOTHER ROUND OF
PRECIPITATION TO THE AREA, WHICH WOULD END UP BEING MOSTLY SNOW
WITH THE CURRENTLY EXPECTED TEMPERATURES.

&&

.AVIATION /23Z THURSDAY THROUGH TUESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

THIS EVENING BECOMING IFR/MVFR IN SNOW FROM THE PHL METRO AREA
TERMINALS AND AIRPORTS NWWD. MVFR CIGS AND VSBYS IN MIXED PCPN AT
KMIV AND KACY. LIGHT SOUTH TO SOUTHEAST WINDS. CONDITIONS SHOULD
IMPROVE TO VFR LATER IN THE EVENING.

OVERNIGHT AS THE COLD FRONT APPROACHES. CONDITIONS COULD LOWER TO
MVFR AGAIN AS SNOW SHOWERS PRECEDE AND ACCOMPANY THE COLD FRONT.
HIGHER CONFIDENCE NORTHERN AIRPORTS AND TERMINALS. THERE MIGHT
EVEN BE BRIEF IFR CONDITIONS. SOUTH WINDS 5 TO 10 KNOTS WILL
BECOME WEST AT AROUND 10 KNOTS.

FRIDAY MORNING. VFR. A LIKELY STRATOCU DECK CIG AROUND 4K. WIDELY
SCATTERED SNOW SHOWERS ARE POSSIBLE, BUT TOO ISOLATED TO INCLUDE
IN TAFS FOR NOW. NORTHWEST WINDS WILL INCREASE TO AROUND 20 KNOTS
SUSTAINED WITH GUSTS BETWEEN 30 AND 35 KNOTS. SOME HIGHER GUSTS
ARE POSSIBLE FRIDAY AFTERNOON.

OUTLOOK...
FRIDAY NIGHT-SATURDAY NIGHT...IMPROVING TO VFR DURING THE EVENING
AND CONTINUING INTO SATURDAY. GUSTY NORTHWEST WINDS 25-30 KNOTS
POSSIBLE FRIDAY NIGHT INTO SATURDAY, DIMINISHING SATURDAY NIGHT.

SUNDAY...VFR EARLY, MVFR POSSIBLE DEVELOPING BY LATE AFTERNOON
WITH SNOW SHOWERS POSSIBLE. GUSTY WEST WINDS 15-20 KNOTS.

SUNDAY NIGHT...DIMINISHING CONDITIONS TO IFR WITH SNOW LIKELY,
ESPECIALLY SOUTHERN AREAS. GUSTY NORTHEAST WINDS 20-25 KNOTS.

MONDAY...IFR WITH SNOW LIKELY EARLY, IMPROVING TO MVFR THEN VFR
BY LATE AFTERNOON. GUSTY NORTH WINDS EARLY, BECOMING NORTHWEST BY
AFTERNOON AROUND 20-25 KNOTS.

MONDAY NIGHT-TUESDAY...GENERALLY VFR.

&&

.MARINE...
WE MADE A SLIGHT ADJUSTMENT TO THE START OF THE GALE WARNING ON
FRIDAY MORNING. THE MODELS ARE TRENDING WEAKER WITH THE GRADIENT
AND CONSEQUENTLY THE SEAS FOR MOST OF TONIGHT. WITH JUST
BORDERLINE SCA CONDITIONS NOW EXPECTED TONIGHT, WE OPTED TO SINGLE
HEADLINE THIS PACKAGE AND WILL MAKE MENTION IN THE MWW. GALE
CONDITIONS BECOMING LIKELIER AS FRIDAY PROGRESSES.

OUTLOOK...
FRIDAY NIGHT-SATURDAY...GALE CONDITIONS CONTINUING THROUGH
SATURDAY AFTERNOON. FREEZING SPRAY ADVISORY FRIDAY NIGHT INTO
SATURDAY.

SATURDAY NIGHT...CONDITIONS DROP TO SMALL CRAFT ADVISORY LEVELS
BY EVENING AND MAY DROP BELOW ADVISORY CONDITIONS OVERNIGHT. LIGHT
FREEZING SPRAY POSSIBLE.

SUNDAY-SUNDAY NIGHT...SUB-SMALL CRAFT ADVISORY CONDITIONS
EXPECTED.

MONDAY-MONDAY NIGHT...SMALL CRAFT ADVISORY CONDITIONS
LIKELY...GALE CONDITIONS POSSIBLE DURING THE DAY MONDAY. FREEZING
SPRAY LIKELY MONDAY NIGHT.

TUESDAY...SUB-SMALL CRAFT ADVISORY CONDITIONS EXPECTED.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...WIND CHILL ADVISORY FROM MIDNIGHT FRIDAY NIGHT TO 11 AM EST
     SATURDAY FOR PAZ054-055.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...FREEZING SPRAY ADVISORY FROM MIDNIGHT FRIDAY NIGHT TO 6 PM EST
     SATURDAY FOR ANZ430-431-450>455.
     GALE WARNING FROM 9 AM FRIDAY TO 6 PM EST SATURDAY FOR ANZ430-
     431-450>455.

&&

$$

SYNOPSIS...ROBERTSON
NEAR TERM...GIGI
SHORT TERM...GIGI/IOVINO
LONG TERM...ROBERTSON
AVIATION...GIGI/ROBERTSON/IOVINO
MARINE...GIGI/ROBERTSON






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