149
FXUS61 KPHI 172105
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
405 PM EST FRI JAN 17 2025
SYNOPSIS
SURFACE HIGH PRESSURE FLEETS OFFSHORE TONIGHT AS A WARM FRONT
APPROACHES. A COLD FRONT APPROACHES SATURDAY LOOKING TO CROSS
THROUGH SATURDAY NIGHT. LOW PRESSURE LOOKS TO BRING WINTER WEATHER
IMPACTS TO THE REGION SUNDAY INTO SUNDAY NIGHT. THEREAFTER, COLD
ARTIC HIGH PRESSURE BUILDS IN HOLDING INFLUENCE THROUGH THE MIDDLE
OF NEXT WEEK. WELL BELOW NORMAL TEMPERATURES EXPECTED MONDAY INTO
THE MIDDLE OF NEXT WEEK.
NEAR TERM /THROUGH SATURDAY/
A TRANQUIL AND SEASONABLE FRIDAY WILL CONTINUE THIS EVENING AND INTO
TONIGHT. OVERNIGHT LOWS WILL BE IN THE MID TO UPPER 20S. HIGH
PRESSURE OFF THE SOUTHEAST COAST WILL SHIFT OFFSHORE, ALLOWING
CLOUDS TO BUILD BACK IN AHEAD OF THE WARM FRONT TOMORROW.
ON SATURDAY, OUR FOCUS IS ON THE WARM FRONT APPROACHING FROM THE
SOUTH. THE MAIN CONCERN WITH THIS SYSTEM WILL BE THE POTENTIAL FOR A
BRIEF PERIOD OF LOCALIZED LIGHT FREEZING RAIN OR DRIZZLE WITHIN A
FEW HOURS OF SUNRISE SATURDAY MORNING IN FAR NORTHERN DELAWARE AND
EXTREME SOUTHEASTERN PENNSYLVANIA. MODEL SOUNDINGS SHOW A COLD LAYER
WITHIN THE LOWEST 50 MB AT THE SURFACE LINGERING FOR A FEW HOURS
AFTER SUNRISE WHILE TEMPERATURES ALOFT WARM WITH THE ARRIVAL OF THE
FRONT, CREATING A WARM NOSE. THAT SAID, THERE WILL ALSO LIKELY BE A
VERY DEEP DRY LAYER ABOVE THIS, SO ANY PRECIP THAT FALLS MAY BE MORE
OF A FREEZING DRIZZLE SET UP. ALL THAT BEING SAID, THIS IS STILL
VERY CONDITIONAL AND FULLY DEPENDENT ON WHETHER TEMPERATURES WILL
STAY BELOW FREEZING FOR A FEW HOURS AFTER SUNRISE AND IF THE AIR
CLOSEST TO THE SURFACE BEING NEARLY SATURATED, ALLOWING FOR
PRECIPITATION TO REACH THE SURFACE. AT THIS TIME, DECIDED NOT TO
ISSUE A WINTER WEATHER ADVISORY FOR THIS GIVEN THE LIKELY LIMITED
COVERAGE AND OVERALL HIGH LEVEL OF UNCERTAINTY NEEDLESS TO SAY, WE
WILL BE WATCHING TRENDS CLOSELY OVER THE NEXT 12-18 HOURS FOR ANY
CHANGES. TEMPERATURES ARE EXPECTED TO WARM ABOVE FREEZING BY MID-
MORNING, ALLOWING ANY FREEZING RAIN TO BECOME MORE OF A BENIGN RAIN.
OTHERWISE, THIS SYSTEM SHOULD RESULT IN VERY LIGHT (GENERALLY ONLY A
FEW HUNDREDTHS OF AN INCH) RAIN DURING THE DAY TIME HOURS ON
SATURDAY. HOWEVER, IN THE HIGHER TERRAIN OF THE SOUTHERN POCONOS,
ANY PRECIPITATION COULD BE SNOW (NEW ACCUMULATION LESS THAN ONE
INCH). RAIN AND SNOW AMOUNTS WILL BE LIGHT AS THE LIFT ASSOCIATED
WITH THIS WILL BE WEAK. SOME RAIN MAY LINGER BY THE COAST SATURDAY
EVENING. AFTERNOON HIGHS ARE EXPECTED TO WARM INTO THE LOW-40S FOR
MOST WITH MID-30S FOR THE POCONOS.
SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/
THE STRONG ARCTIC COLD FRONT WILL BE APPROACHING FROM THE WEST ON
SATURDAY NIGHT AND WILL CROSS THROUGH THE REGION EARLY ON SUNDAY
MORNING. WITH A SUBSTANTIAL COLD AIR ADVECTION PUSH BEHIND THE
FRONT, THIS WILL USHER IN A MUCH COLDER AIRMASS. AS IT DOES SO, AN
AREA OF LOW PRESSURE WILL BE DEVELOPING OVER THE DEEP SOUTH ALONG
THE TAIL-END OF THE ARCTIC FRONT. THIS AREA OF LOW PRESSURE WILL
RIDE ALONG THE FRONTAL BOUNDARY AND DEEPEN AS IT MOVES OFF THE COAST
NEAR THE VIRGINIA/NORTH CAROLINA BORDER BY SUNDAY AFTERNOON.
FROM HERE, FORECAST GUIDANCE HAS COME INTO BETTER AGREEMENT THIS
AFTERNOON AND HAS SHOWN AN OVERALL NORTHWESTERN SHIFT TO THE TRACK
OF THE SURFACE LOW BY MOST GLOBAL AND ENSEMBLE GUIDANCE. THIS WILL
PLACE THE SURFACE LOW JUST OFF THE NEW JERSEY COAST ON SUNDAY
AFTERNOON. STILL EXPECT THAT THE 12Z CANADIAN/GEM GUIDANCE IS
UNDERDOING THE COLD AIR ADVECTION REGIME ON THE NORTHWEST SIDE OF
THE LOW, SO SUSPECT THAT THE LOW WILL REMAIN JUST OFF OUR COASTLINE
INSTEAD OF TRACKING DIRECTLY OVER SOUTHERN NEW JERSEY. HEADING INTO
SUNDAY NIGHT AS THE LOW EXITS, IT APPEARS THAT THE DEEPENING SURFACE
LOW WILL PASS RIGHT OVER OR JUST OFF TO THE NORTHWEST OF THE 40N/70W
BENCHMARK. ALSO, AVAILABLE GUIDANCE SUGGESTS AN OVERALL UPTICK IN
FORECAST QPF VALUES BY NEARLY 0.1-0.2", ESPECIALLY NORTH AND WEST OF
THE I-95 CORRIDOR. FACTORING IN RATHER HIGH SNOW-TO-LIQUID RATIOS TO
THE NORTH AND WEST, THERE AGAIN HAS BEEN AN INCREASE IN FORECASTER
CONFIDENCE IN PLOWABLE SNOWFALL FOR AREAS NORTHWEST OF THE I-95
CORRIDOR. THUS, OUR FORECAST THIS AFTERNOON GENERALLY INCORPORATES A
BLEND OF THE SITUATION DISCUSSED ABOVE. STILL, THIS DOES NOT MEAN
THAT AREAS SOUTH AND EAST, INCLUDING THE PHILADELPHIA METRO WILL SEE
SNOW THROUGH THE ENTIRE DURATION OF THE EVENT. SOME SHORT-RANGE
GUIDANCE DOES DEPICT A SUBTLE WARM LAYER AT 850MB SO THERE MAY BE AT
LEAST A BRIEF RAIN/SNOW MIX FOR AREAS DIRECTLY ALONG THE I-95
CORRIDOR AT THE ONSET. FOR THIS REASON, HAVE KEPT A RAIN/SNOW MIX
FOR THESE AREAS THROUGH SUNDAY MORNING AND EARLY AFTERNOON. HOWEVER,
AS THE COLD AIR BEGINS TO POUR INTO THE REGION AS THE LOW DEPARTS,
WE SHOULD SEE AN EVENTUAL CHANGEOVER FROM RAIN TO RAIN/SNOW MIX TO
ALL SNOW EVEN DOWN TO THE COAST BY SUNDAY NIGHT.
IN COORDINATION WITH NEIGHBORING FORECAST OFFICES AND WPC, HAVE OPTED
TO ISSUE WINTER STORM WATCHES FOR SUNDAY MORNING INTO SUNDAY EVENING
FOR ALL OF OUR PENNSYLVANIA COUNTIES EXCEPT FOR DELAWARE,
PHILADELPHIA AND LOWER BUCKS. ALSO, HAVE ISSUED WINTER STORM WATCHES
FOR HUNTERDON, WARREN, SUSSEX, AND MORRIS COUNTIES IN NEW JERSEY.
THESE ARE THE AREAS WHICH ARE LIKELY TO OBSERVE WARNING LEVEL
SNOWFALL WITH LESSER AMOUNTS EXPECTED ELSEWHERE. IN TERMS OF
AMOUNTS, GENERALLY EXPECTING A WIDESPREAD 5-8" SNOWFALL IN THE WATCH
AREA WITH LOCALIZED AMOUNTS UP TO 10" POSSIBLE (ESPECIALLY ACROSS
THE HIGHER TERRAIN). STEPPING SOUTHEAST INTO AND ALONG THE IMMEDIATE
I-95 CORRIDOR, EXPECTING A 3-5" SNOWFALL EVENT DUE TO POTENTIAL
MIXING AT THE ONSET. OF COURSE, THESE TOTALS CAN BE HIGHER OR LOWER
DEPENDING ON THE DURATION OF MIXED PRECIPITATION. CLOSER TO THE
COAST WHERE PROLONGED PERIODS OF MIXING AND AT TIMES PLAIN RAIN IS
TO OCCUR BEFORE THE CHANGEOVER, A 1-3" EVENT IS EXPECTED. AS ALWAYS,
THE FORECAST CAN VARY OVER THE NEXT 36-48 HOURS AS MORE HI-RES
GUIDANCE BECOMES AVAILABLE. SO STAY TUNED FOR THE LATEST UPDATES TO
THE FORECAST THROUGH THE HOLIDAY WEEKEND!
IN WAKE OF THE SYSTEM ON SUNDAY NIGHT, WE'LL START TO SEE THE
BEGINNING OF THE COLD AIR MASS TAKE AIM AT THE AREA. SKIES WILL
BEGIN TO GRADUALLY CLEAR LATE SUNDAY NIGHT INTO MONDAY MORNING, AND
WITH A FRESH SNOWPACK IN PLACE, THIS SHOULD RESULT IN LOW
TEMPERATURES FALLING INTO THE SINGLE DIGITS/TEENS AREAWIDE. WITH A
STIFF NORTHWEST WIND FILLING IN ON THE BACKSIDE OF THE DEPARTING
LOW, SHOULD SEE WIND CHILLS IN THE SINGLE DIGITS FOR MOST. MOSTLY
CLEAR SKIES WILL BE ON TAP FOR MONDAY AS STRONG CANADIAN HIGH
PRESSURE BUILDS OVER THE NORTHERN PLAINS. HIGH TEMPERATURES WILL BE
LIMITED TO THE TEENS/20S WITH WIND CHILLS PRIMARILY IN THE TEENS.
ENHANCED NORTHWEST WINDS COULD POSE A BLOWING SNOW IN AREAS WHERE
HEAVIER SNOWFALL OCCURS.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
A STRONG ARTIC AIRMASS WILL DOMINATE THE REGION FOR THE MAJORITY OF
THE LONG TERM. DANGEROUSLY COLD TEMPERATURES WILL BE THE MAIN FOCUS
OF THE FORECAST. THESE DANGEROUSLY COLD TEMPERATURES ARE ANTICIPATED
AT LEAST THROUGH THE FIRST HALF OF THE LONG TERM (I.E., MONDAY NIGHT
THROUGH WEDNESDAY NIGHT). GRADUAL IMPROVEMENTS IN TEMPERATURES ARE
POSSIBLE BY THURSDAY/FRIDAY.
COLD WEATHER HEADLINES ARE NEARLY CERTAIN FOR SEVERAL PERIODS OF THE
LONG TERM. DANGEROUSLY COLD TEMPERATURES COULD RESULT IN IMPACTS TO
PEOPLE, ANIMALS, AND INFRASTRUCTURE. DANGEROUSLY COLD CONDITIONS FOR
PEOPLE AND ANIMALS ARE POSSIBLE RESULTING IN AN INCREASED RISK OF
HYPOTHERMIA AND FROST BITE. FOR INFRASTRUCTURE, IMPACTS COULD
INCLUDE FREEZING WATER PIPES AND HIGH DEMAND FOR HEATING ENERGY.
STAY TUNED TO THE LATEST FORECAST FOR ADDITIONAL INFORMATION AS WE
GET CLOSER.
WHILE STRONG SURFACE HIGH PRESSURE WILL INFLUENCE AND DOMINATE OVER
THE REGION FOR THE MAJORITY OF THE TERM, DETERMINISTIC GUIDANCE
CONTINUES TO SUPPORT STRONG BAROCLINIC INSTABILITY OVER THE GULF OF
MEXICO AND OFFSHORE OF THE EASTERN CONUS TUESDAY/WEDNESDAY. THIS
WILL LIKELY LEAD TO THE DEVELOPMENT A STRONG CYCLONE OVER OR IN THE
VICINITY OF THE AFOREMENTIONED AREAS. HOWEVER, GUIDANCE CONTINUES TO
INDICATE THIS CYCLONE WILL REMAIN MOSTLY OFFSHORE OF THE NORTHEASTERN
CONUS AS IT TRACKS NORTHEASTWARDS TUESDAY NIGHT THROUGH WEDNESDAY
NIGHT. IT IS WORTH MENTIONING THIS SYNOPTIC PATTERN AND WATCHING
FOR CHANGES AS WE GO FORWARD IN TIME; A SLIGHT SHIFT IN TRACK COULD
LEAD TO ANOTHER SNOWFALL EVENT FOR THE REGION DURING THE TUESDAY
NIGHT THROUGH WEDNESDAY TIMEFRAME.
AVIATION /21Z FRIDAY THROUGH WEDNESDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
REST OF TODAY...PREVAILING VFR. W WINDS 5-10 KTS BECOMING MORE
SW/SSW WITH TIME. HIGH CONFIDENCE.
TONIGHT...VFR. LIGHT S WINDS 5-10 KTS. SOME SITES MAY SEE WINDS
BECOME LIGHT AND VARIABLE DURING THE FIRST HALF OF THE PERIOD.
CIRRUS BUILDING IN WITH TIME. HIGH CONFIDENCE.
SATURDAY...BRIEF PERIODS OF MVFR OR EVEN IFR POSSIBLE WITH MOSTLY
RAIN. WINDS MAINLY 10 KTS OR LESS. LLWS POSSIBLE IN THE MORNING.
OUTLOOK...
SATURDAY NIGHT THROUGH SUNDAY NIGHT...SUB-VFR CONDITIONS LIKELY
ESPECIALLY ON SUNDAY INTO SUNDAY NIGHT. FOR KRDG, KABE, KTTN, KPNE,
KPHL, AND KILG, SNOW LIKELY. FOR KMIV AND KACY, A MIX OF RAIN OF
SNOW IS LIKELY BEFORE A CHANGEOVER TO RAIN.
MONDAY THROUGH TUESDAY...VFR. NO SIGNIFICANT WEATHER EXPECTED.
TUESDAY NIGHT THROUGH WEDNESDAY...SUB-VFR CONDITIONS POSSIBLE.
WATCHING LOW PRESSURE DEVELOPMENT, WHICH COULD WINTER PRECIPITATION
TO THE REGION.
MARINE
SMALL CRAFT ADVISORY CONDITIONS RESUME FOR THE NORTHERN COASTAL
WATERS OVERNIGHT FRIDAY INTO SATURDAY MORNING, CONTINUING THROUGH
EARLY SATURDAY AFTERNOON FOR WINDS GUSTING TO 25 KTS. ELSEWHERE,
CONDITIONS ARE EXPECTED TO REMAIN BELOW SCA CRITERIA WITH WIND GUSTS
AROUND 15-20 KTS.
OUTLOOK...
SATURDAY NIGHT THROUGH SUNDAY...NO MARINE HEADLINES EXPECTED. RAIN
AND/OR SNOW LIKELY ON SUNDAY.
SUNDAY NIGHT THROUGH MONDAY...SCA CONDITIONS LIKELY DUE TO WIND
GUSTS UP TO 30 KT AND SEAS AROUND 5 FEET.
MONDAY NIGHT...SCA CONDITIONS LIKELY. DUE TO THE COMBINATION OF COLD
AIR/WATER TEMPERATURES, GUSTY WINDS, AND SEAS, FREEZING SPRAY
ACCRETION IS LIKELY.
TUESDAY THROUGH WEDNESDAY...SCA CONDITIONS NOT CURRENTLY
ANTICIPATED. WATCHING LOW PRESSURE DEVELOPMENT OFFSHORE. SOME
FREEZING SPRAY ACCRETION POSSIBLE AT TIMES DUE TO COMBINATION OF
COLD AIR/WATER TEMPERATURES, GUSTY WINDS, SEAS.
PHI WATCHES/WARNINGS/ADVISORIES
PA...WINTER STORM WATCH FROM SUNDAY MORNING THROUGH LATE SUNDAY
NIGHT FOR PAZ054-055-062.
WINTER STORM WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING
FOR PAZ060-061-101>105.
NJ...WINTER STORM WATCH FROM SUNDAY MORNING THROUGH LATE SUNDAY
NIGHT FOR NJZ001-007>009.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 AM TO 1 PM EST SATURDAY FOR ANZ450-
451.
SYNOPSIS...WUNDERLIN
NEAR TERM...MJL
SHORT TERM...DESILVA
LONG TERM...WUNDERLIN
AVIATION...DESILVA/MJL/WUNDERLIN
MARINE...DESILVA/MJL/WUNDERLIN
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