091
FXUS61 KPHI 180536
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1236 AM EST SAT JAN 18 2025
SYNOPSIS
SURFACE HIGH PRESSURE IS USHERED OFFSHORE TONIGHT AS A WARM
FRONT APPROACHES. A STRONG COLD FRONT THEN CROSSES OUR REGION
SATURDAY NIGHT. LOW PRESSURE LOOKS TO BRING A ROUND OF WINTRY
PRECIPITATION TO THE REGION SUNDAY INTO SUNDAY NIGHT.
THEREAFTER, A BITTERLY COLD AIRMASS BUILDS IN THROUGH THE
MIDDLE OF NEXT WEEK.
NEAR TERM /THROUGH TODAY/
AS OF 1230 AM, HIGH LEVEL CLOUDS ARE INCREASING ACROSS THE
REGION AS SOUTH TO SOUTHWESTERLY FLOW ALOFT INCREASES. A LOW-
LEVEL JET ON THE ORDER OF 40 KNOTS IS FORECAST TO ARRIVE CLOSER
TO DAYBREAK AND THIS WILL RAMP-UP THE LOW-LEVEL WARM AIR
ADVECTION AND ALSO START TO BRING IN ADDITIONAL LOW-LEVEL
MOISTURE. TEMPERATURES HAVE RISEN SOME IN SPOTS ESPECIALLY
ACROSS THE COASTAL PLAIN, WHILE TANKING IN SOME OTHER AREAS
(MORE SHELTERED). THE HOURLY TEMPERATURE GRIDS WERE ADJUSTED TO
REFLECT THIS AND THE LOW TEMPERATURES WERE ALSO ADJUSTED
DOWNWARD BASED ON THIS. DEW POINTS ARE RUNNING A LITTLE LOWER
THAN FORECAST SO FAR MOSTLY ACROSS THE NORTHERN AREAS THEREFORE
ADJUSTED THIS AS WELL.
OTHERWISE FOR SATURDAY, A WARM FRONT WILL BE APPROACHING FROM
THE SOUTH. A LOW-LEVEL JET WILL BE MOVING ACROSS THE AREA
THROUGH ABOUT EARLY AFTERNOON AND THIS WILL INCREASE THE LOW-
LEVEL WARM AIR ADVECTION. SOME MOISTENING TAKES PLACE IN THE
LOWER LEVELS EARLY IN THE MORNING, HOWEVER THERE IS A DRY LAYER
ABOVE IT. THE SOUNDINGS OVERALL LOOK TOO DRY FOR PRECIPITATION
TO OCCUR EARLY ON AND THIS WILL GIVE TEMPERATURES MORE TIME TO
INCREASE PRIOR TO SHOWERS DEVELOPING. TEMPERATURES ARE EXPECTED
TO WARM ABOVE FREEZING BY MID-MORNING FOR NEARLY ALL AREAS,
ALLOWING ANY SPOTTY VERY LIGHT FREEZING RAIN/DRIZZLE TO BECOME
RAIN SHOWERS. THE SHOWERS SHOULD BE MOST WIDESPREAD ACROSS THE
NORTHERN AREAS ASSOCIATED WITH SOME BETTER LIFT WITH THE LOW-
LEVEL JET AND THEREFORE INCREASED THE POPS THERE FOR A TIME.
THIS SYSTEM SHOULD RESULT IN LIGHT RAINFALL AMOUNTS (GENERALLY
LESS THAN A TENTH OF OF AN INCH) DURING THE DAY TIME HOURS.
HOWEVER, IN THE HIGHER TERRAIN OF THE SOUTHERN POCONOS AND
IMMEDIATE VICINITY, PRECIPITATION LOOKS TO BE LIGHT SNOW SHOWERS
AND EVEN SOME SLEET MAY MIX IN BEFORE SOME CHANGE TO RAIN
SHOWERS. ANY SNOW/SLEET ACCUMULATIONS LOOK TO BE LESS THAN ONE
INCH. AFTERNOON HIGHS ARE EXPECTED TO WARM INTO THE LOW-40S FOR
MOST WITH MID-30S FOR THE POCONOS.
SHORT TERM /TONIGHT 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 /05Z SATURDAY THROUGH WEDNESDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
OVERNIGHT...VFR WITH INCREASING CLOUDS. SOUTHERLY WINDS NEAR 5
KNOTS BECOMING LIGHT AND VARIABLE TO LOCALLY CALM. HIGH CONFIDENCE.
SATURDAY...CEILINGS LOWER TO A PERIOD OF MAINLY MVFR FROM ABOUT
MID-MORNING ONWARD ALONG WITH SOME RAIN SHOWERS. SOME IFR
CEILINGS CANNOT BE RULED OUT. VISIBILITIES LOWER TO MVFR AT
TIMES WITH THE RAIN SHOWERS. LIGHT AND VARIABLE WINDS BECOMING
SOUTH OR SOUTHEAST 5-10 KNOTS, THEN BECOMING SOUTHWEST THIS
AFTERNOON. LOW-LEVEL WIND SHEAR THIS MORNING THROUGH ABOUT EARLY
AFTERNOON AS WINDS NEAR 2,000 FEET AGL INCREASE OUT OF THE
SOUTH-SOUTHWEST AROUND 40 KNOTS. LOW CONFIDENCE REGARDING
TIMING DETAILS.
OUTLOOK...
SATURDAY NIGHT THROUGH SUNDAY NIGHT...SUB-VFR CONDITIONS
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 SATURDAY MORNING AND CONTINUE THROUGH EARLY SATURDAY
AFTERNOON FOR WINDS GUSTING TO 25 KTS. ELSEWHERE, CONDITIONS ARE
EXPECTED TO REMAIN BELOW SCA CRITERIA.
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 EARLY THIS MORNING TO 1 PM EST
THIS AFTERNOON FOR ANZ450-451.
SYNOPSIS...WUNDERLIN
NEAR TERM...GORSE/MJL
SHORT TERM...DESILVA
LONG TERM...WUNDERLIN
AVIATION...DESILVA/GORSE/MJL
MARINE...DESILVA/MJL/WUNDERLIN
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