985
FXUS61 KPHI 130639
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
139 AM EST SAT DEC 13 2025
SYNOPSIS
HIGH PRESSURE WILL SHIFT TO OUR SOUTH AND EAST TODAY. A WEAK
AREA OF LOW PRESSURE TRACKS NEARBY TONIGHT INTO SUNDAY MORNING,
WITH AN ARCTIC FRONT CROSSING OUR AREA. THE CENTER OF ARCTIC
HIGH PRESSURE SLIDES TO OUR SOUTH TUESDAY BEFORE WEAKENING AS IT
SHIFTS OFFSHORE WEDNESDAY. A WARM FRONT MAY SLIDE BY TO OUR
NORTH WEDNESDAY INTO THURSDAY, FOLLOWED BY A COLD FRONT THURSDAY
NIGHT.
NEAR TERM /THROUGH SUNDAY/
HIGH CLOUDS SPREADING OVERHEAD EARLY THIS MORNING THOUGH
RADIATIONAL COOLING HAS ALLOWED MANY AREAS TO GET QUITE COLD
ALREADY, WITH MID-TEENS HERE AT THE OFFICE AS OF 2 AM. THIS IS
DEFINITELY THE QUIET BEFORE THE STORM, HOWEVER.
FOR THE BALANCE OF TODAY, NOT MUCH WILL HAPPEN, WITH JUST PLENTY
OF MID AND HIGH CLOUDS AND A MILDER SOUTHWESTERLY BREEZE. AFTER
THE CHILLY START, WE'LL LIKELY REBOUND INTO THE 40S ACROSS MUCH
OF OUR REGION, PERHAPS EVEN APPROACHING 50 ACROSS THE SOUTHERN
DELMARVA, BUT LIKELY STAYING IN THE 30S NORTH OF I-78 AND WEST
OF I-287.
THE WEAK WAVE OF LOW PRESSURE WHICH WILL BRING SNOW TO THE
REGION BY THIS TIME TOMORROW MORNING IS STILL WELL TO OUR WEST-
NORTHWEST OVER THE WESTERN HIGH PLAINS OF MONTANA. AT THE
SURFACE THERE ACTUALLY IS VERY LITTLE REFLECTION OF A LOW
PRESSURE, AS THE FORCING FOR THIS SYSTEM IS NEARLY 100 PERCENT
ALOFT, DRIVEN BY A STRONG SHORTWAVE TROUGH, VORT MAX AND JET
STREAK HEADING SOUTHEASTWARD ACROSS THE PLAINS AND MIDWEST
TODAY BEFORE CROSSING OUR AREA ON SUNDAY. THAT'S NOT TO SAY
THERE ISN'T A SURFACE COMPONENT TO OUR INCOMING WEATHER, NAMELY
THE ARCTIC FRONT PLUNGING SOUTHEASTWARD ACROSS THE UPPER MIDWEST
PRESENTLY. THIS FRONT WILL ALSO REACH OUR REGION EARLY SUNDAY,
JUST IN TIME TO HAVE THE COLD AIR MEET THE FORCING ALOFT.
GUIDANCE IS RELATIVELY STABLE AT PRESENT, BRINGING LIGHT PRECIP
INTO THE AREA VERY LATE TODAY, THEN A MUCH MORE FOCUSED BAND OF
PRECIP DEVELOPS LATER THIS EVENING AND CONTINUES INTO EARLY
SUNDAY. AS MENTIONED, IT WILL WARM UP DECENTLY TODAY, SO
ESPECIALLY FROM I-95 SOUTH AND EAST, PRECIP STANDS A GOOD SHOT
AT STARTING AS RAIN BEFORE TRANSITIONING TO SNOW LATE THIS
EVENING INTO THE OVERNIGHT. THE HEAVIEST SNOW WILL DEFINITELY
OCCUR AFTER MIDNIGHT SATURDAY NIGHT, THE LEAST IMPACTFUL TIME WE
CAN THINK OF, SO THIS SYSTEM AT LEAST HAS THAT GOING FOR IT. AS
THE SYSTEM STARTS TO PULL EASTWARD EARLY SUNDAY, WE SHOULD SEE A
FAIRLY QUICK END TO THE SNOW VERY LATE TONIGHT INTO SUNDAY
MORNING FROM NORTHWEST TO SOUTHEAST. THAT HAVING BEEN SAID,
LINGERING INSTABILITY MAY CAUSE SPOTTY SNOW SHOWERS TO LINGER
INTO THE AFTERNOON, THOUGH ANY ADDITIONAL ACCUMULATION SHOULD BE
NEGLIGIBLE. WITH THE ARCTIC FRONT HAVING MOVED THROUGH, GUSTY
NORTHWEST WINDS WILL TAKE OVER, POSSIBLY CAUSING SOME BLOWING
AND DRIFTING SNOW ALONG WITH FALLING WIND CHILLS, BUT THE WORST
OF THAT WILL OCCUR SUNDAY NIGHT.
FOR THIS PACKAGE, MAIN CHANGES TO THE FORECAST WERE A MODEST
UPTICK IN SNOWFALL, WHICH RESULTED IN AN EXPANSION OF THE WINTER
WEATHER ADVISORY NORTHWARD AND SOUTHWARD. BOTH EXPANSIONS ARE
STILL A LITTLE MARGINAL, 2-4 INCHES ALONG THE I-78/I-287
CORRIDORS (CRITERIA IS 3 HERE) AND 1-3 INCHES IN SUSSEX COUNTY
DELAWARE (CRITERIA IS 2 HERE), BUT ENOUGH CONFIDENCE IS PRESENT
TO BRING THEM INTO THE FOLD. ACROSS A LARGE CENTRAL PORTION OF
THE ADVISORY, AREAS ALONG AND SOUTHEAST OF I-95 IN PA, NJ DE AND
MD, WE'RE NOW EXPECTING A WIDE AREA OF 3-5 INCHES, AND THERE ARE
SOME SNOWIER MODELS SUGGESTING A STRIPE OF WARNING CRITERIA
(WHICH IS MOSTLY 5 INCHES IN THIS AREA, THOUGH 6 IN CENTRAL NJ)
COULD OCCUR. NOT QUITE SOLD ON THAT YET GIVEN POTENTIAL FOR LOST
QPF FROM THE TRANSITION FROM RAIN TO SNOW, BUT ITS DEFINITELY ON
OUR MINDS FOR POTENTIAL CHANGES. FOR NOW HOWEVER, KEPT ADVISORY
LEVEL FORECAST ACROSS THIS REGION, THOUGH HIGH-END FOR SURE.
SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/
IN THE WAKE OF THE SNOW, A VERY COLD AIRMASS WILL ARRIVE WITH
GUSTY NORTHWESTERLY WINDS. AIR TEMPERATURES DROP INTO THE TEENS
SUNDAY NIGHT WITH SOME SINGLE DIGITS POSSIBLE IN THE POCONOS. A
BRISK WIND WILL DRIVE WIND CHILLS WELL DOWN INTO THE SINGLE
DIGITS TO NEAR ZERO THROUGH SUNDAY NIGHT WITH SOME BELOW ZERO
VALUES MOSTLY IN THE POCONOS. IF THE WIND REMAINS STRONG ENOUGH
COMBINED WITH EVEN COLDER TEMPERATURES, SOME AREAS MAY BE VERY
CLOSE TO COLD WEATHER ADVISORY CRITERIA LATER SUNDAY NIGHT AND
EARLY MONDAY MORNING.
HIGH PRESSURE WILL CONTINUE TO BUILD ACROSS THE EASTERN US,
KEEPING THE FORECAST GENERALLY DRY, BUT COLD TEMPERATURES
PERSIST INTO MONDAY, WITH NEARLY ALL LOCATIONS STAYING BELOW
FREEZING IN THE AFTERNOON. A STIFF WNW BREEZE WILL PERSIST,
KEEPING WIND CHILLS IN THE 20S WITH TEENS ACROSS THE HIGHER
ELEVATIONS.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
SUMMARY...ARCTIC AIR/BITTER COLD STARTS TO EASE DURING MID-
WEEK, THEN IT TURNS MUCH MILDER THURSDAY, WITH A CHANCE FOR
SHOWERS THURSDAY INTO THURSDAY NIGHT WITH A COLD FRONTAL PASSAGE
THAT WILL BRING BACK COOL WEATHER FOR FRIDAY.
SYNOPTIC OVERVIEW...AN UPPER-LEVEL TROUGH AND ITS ASSOCIATED
CYCLONIC FLOW WILL CONTINUE TO SHIFT EAST MONDAY NIGHT INTO
TUESDAY. FLOW WILL THEN BECOME MORE ZONAL ALOFT WEDNESDAY. THE
FLOW ALOFT THEN LOOKS TO BACK MORE THURSDAY AHEAD OF A
POTENTIALLY STRENGTHENING UPPER-LEVEL TROUGH ACROSS THE GREAT
LAKES REGION, THOUGH SIGNIFICANT MODEL DISCREPANCIES EXIST
REGARDING THE EVOLUTION OF THE UPPER-AIR PATTERN AT THIS RANGE.
THE CENTER OF ARCTIC HIGH PRESSURE WILL SLIDE JUST TO OUR SOUTH
TUESDAY BEFORE SHIFTING OFFSHORE. A WARM FRONT MAY SLIDE BY TO
OUR NORTH DURING WEDNESDAY AS LOW PRESSURE GRADUALLY PIVOTS
ACROSS THE UPPER GREAT LAKES REGION AND INTO PORTIONS OF ONTARIO
AND QUEBEC. A TRAILING COLD FRONT LOOKS TO PASS THROUGH THE
REGION THURSDAY NIGHT INTO FRIDAY.
FOR MONDAY NIGHT INTO TUESDAY...AN UPPER-LEVEL TROUGH AND ITS
ASSOCIATED CYCLONIC FLOW IS EXPECTED TO REMAIN IN PLACE DURING
THIS TIME FRAME. IT COULD BE ENHANCED FOR A BRIEF TIME MONDAY
NIGHT OR TUESDAY AS A STRONGER SHORTWAVE DIVES SOUTHEASTWARD OUT
OF THE GREAT LAKES AND ACROSS OUR AREA. IT IS NOT OUT OF THE
QUESTION THAT A FEW SNOW SHOWERS COULD ACCOMPANY THIS SHORTWAVE,
WITH THE BEST CHANCES BEING ACROSS THE NORTHERN HALF OR SO OF
THE AREA. THE NBM FEATURES POPS MONDAY NIGHT AROUND 20%, WHICH
SEEMS REASONABLE SO HAVE OPTED NOT TO MAKE ANY CHANGES. HIGH
PRESSURE CENTERED TO OUR SOUTH TUESDAY WILL BEGIN TO SHIFT
OFFSHORE, THOUGH ITS AXIS WILL EXTEND NORTHWARD OVER OUR AREA.
THIS WILL RESULT IN MUCH LESS WIND ON TUESDAY. IT WILL STILL BE
RATHER COLD, HOWEVER THE HARSH CONDITIONS WILL START TO EASE
SLOWLY.
FOR WEDNESDAY THROUGH FRIDAY...A PATTERN CHANGE SHOULD RESULT
IN A SURGE OF MUCH MILDER AIR ACROSS OUR AREA AS WE GET INTO
THURSDAY. AS SURFACE HIGH PRESSURE BECOMES MORE ANCHORED IN THE
WESTERN ATLANTIC AND WE LOSE THE UPPER-LEVEL TROUGH, WARM AIR
ADVECTION WILL BE UNDERWAY. THIS SHOULD INCREASE MORE AS A WARM
FRONT SLIDES BY TO OUR NORTH DURING WEDNESDAY. AN UPPER-TROUGH
ACROSS THE GREAT LAKES LOOKS TO SLIDE TO OUR NORTH THURSDAY INTO
FRIDAY, THOUGH THERE IS DISAGREEMENT AMONGST THE MODELS AS TO
ITS EXACT EVOLUTION AND THE DEGREE OF AMPLIFICATION. FOR NOW,
THE EXPECTATION IS THAT A SURFACE LOW WILL SHIFT NORTHEASTWARD
FROM THE GREAT LAKES REGION THURSDAY AND INTO QUEBEC BY FRIDAY,
WITH A TRAILING COLD FRONT PASSING THROUGH THE REGION BY FRIDAY.
SOUTHWESTERLY FLOW WELL AHEAD OF THIS WILL BOOST THE WARM AIR
ADVECTION, WITH MUCH OF OUR AREA CURRENTLY FORECAST TO GET INTO
THE 50S ON THURSDAY. SHOWERS (RAIN FOR MOST, SOME SNOW IN THE
POCONOS) WILL BE POSSIBLE WITH THE PASSAGE OF THE COLD FRONT,
WITH POPS RIGHT NOW IN THE 40-50% RANGE AREAWIDE THURSDAY NIGHT.
TEMPERATURES LOOK TO RETURN TO NEAR NORMAL FOR FRIDAY.
AVIATION /06Z SATURDAY THROUGH WEDNESDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
THRU 12Z THIS MORNING...VFR. INCREASING MID AND HIGH LEVEL
CLOUDS. LIGHT AND VARIABLE WINDS GENERALLY 5 KT OR LESS. HIGH
CONFIDENCE.
TODAY...VFR BUT WITH SLOWLY THICKENING AND LOWERING CIGS.
SOUTH-SOUTHWEST WINDS AROUND 5-10 KT. MODERATE-HIGH CONFIDENCE.
TONIGHT...SNOW WILL ENVELOP NORTHWESTERN TERMINALS IN THE
EVENING, WITH PRECIP STARTING AS RAIN PHL SOUTH AND EAST, BUT
TRANSITIONING TO SNOW OVERNIGHT FROM NORTHWEST TO SOUTHEAST.
THUS, EXPECT ANY LINGERING VFR EARLY TO FALL TO IFR IF NOT LIFR
OR EVEN BRIEFLY VLIFR ACROSS THE BOARD BY 6Z OR SHORTLY
THEREAFTER. WINDS LIGHT/VARIABLE. MODERATE CONFIDENCE.
OUTLOOK...
SUNDAY...THE CONDITIONS IMPROVE TO VFR. WEST-NORTHWEST WINDS
INCREASE DURING SUNDAY WITH GUSTS UP TO 30 KNOTS.
MONDAY...VFR. WEST-NORTHWEST WIND GUSTS UP TO 30 KNOTS.
MONDAY NIGHT...PRIMARILY VFR. SLIGHT CHANCE FOR SNOW SHOWERS
(AROUND 20%) FOR THE LEHIGH VALLEY TERMINALS.
TUESDAY THROUGH WEDNESDAY...VFR. NO SIGNIFICANT WEATHER.
MARINE
MARGINAL SMALL CRAFT ADVISORY CONDITIONS EXPECTED TO DEVELOP FOR
A TIME AROUND MIDDAY TODAY FOR THE NORTHERN TWO OCEAN ZONES,
WITH GUSTS UP TO 25 KTS. GUSTS SHOULD STAY LIGHTER ELSEWHERE.
OTHERWISE, NO MARINE HEADLINES THROUGH EARLY SUNDAY, THOUGH A
PERIOD OF RAIN CHANGING TO SNOW IS EXPECTED TONIGHT INTO SUNDAY
MORNING. WINDS PICK UP QUICKLY SUNDAY AFTERNOON, WITH GALES
POSSIBLE BY DAY'S END.
OUTLOOK...
SUNDAY NIGHT...GALE FORCE WIND GUSTS PROBABLE. AREAS OF
FREEZING SPRAY POSSIBLE.
MONDAY...GALE FORCE WIND GUSTS POSSIBLE IN THE MORNING,
OTHERWISE SMALL CRAFT ADVISORY CONDITIONS PROBABLE. AREAS OF
FREEZING SPRAY POSSIBLE DURING THE MORNING.
MONDAY NIGHT...SMALL CRAFT ADVISORY CONDITIONS COULD LINGER
INTO THE NIGHT WITH WESTERLY WIND 15-20 KT AND GUSTS PERHAPS
NEAR 25 KT. SEAS 2-4 FEET.
TUESDAY THROUGH TUESDAY NIGHT...NO MARINE HEADLINES ARE
CURRENTLY ANTICIPATED WITH WINDS REMAINING BELOW 25 KT AND SEAS
BELOW 5 FEET.
WEDNESDAY...SMALL CRAFT ADVISORY CONDITIONS POSSIBLE WITH
SOUTHWESTERLY WIND 15-25 KT. SEAS 2-4 FEET.
PHI WATCHES/WARNINGS/ADVISORIES
PA...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 1 PM EST
SUNDAY FOR PAZ070-071-101>106.
WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
SUNDAY FOR PAZ060>062.
NJ...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 1 PM EST
SUNDAY FOR NJZ009-010-012>027.
WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST
SUNDAY FOR NJZ007-008.
DE...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 1 PM EST
SUNDAY FOR DEZ001-002.
WINTER WEATHER ADVISORY FROM 1 AM TO 1 PM EST SUNDAY FOR
DEZ003-004.
MD...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 1 PM EST
SUNDAY FOR MDZ012-015-019-020.
MARINE...GALE WATCH FROM SUNDAY AFTERNOON THROUGH MONDAY MORNING FOR
ANZ430-431-450>455.
SMALL CRAFT ADVISORY FROM 6 AM THIS MORNING TO 6 PM EST THIS
EVENING FOR ANZ450-451.
SYNOPSIS...COOPER/RCM
NEAR TERM...RCM
SHORT TERM...MJL
LONG TERM...COOPER/GORSE
AVIATION...COOPER/MJL/RCM
MARINE...COOPER/MJL/RCM
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