160
FXUS61 KPHI 170843
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
343 AM EST FRI JAN 17 2025
SYNOPSIS
HIGH PRESSURE RETURNS TODAY AHEAD OF A WARM FRONT THAT WILL
CROSS THROUGH OUR REGION SATURDAY BRINGING. THIS WILL BRING A
BRIEF RETURN OF MILDER WEATHER AND SOME RAIN TO THE REGION. A
STRONG ARCTIC COLD FRONT WILL PASS THROUGH ON SUNDAY WHILE A
SECONDARY LOW DEVELOPS FOR SUNDAY NIGHT BRINGING THE POTENTIAL
FOR SNOW TO THE REGION. COLD ARTIC HIGH PRESSURE RETURNS ON
MONDAY AND PERSISTS THROUGH THE MIDDLE OF NEXT WEEK.
NEAR TERM /THROUGH SATURDAY NIGHT/
THE BIGGEST CONCERN IN THIS PERIOD IS A SMALL (20%) CHANCE FOR
VERY LIGHT FREEZING RAIN OR FREEZING DRIZZLE WITHIN A FEW HOURS
OF SUNRISE SATURDAY MORNING IN FAR NORTHERN DELAWARE AND EXTREME
SOUTHEASTERN PENNSYLVANIA.
FOR TODAY AND TONIGHT, TRANQUIL CONDITIONS AND NEAR NORMAL
TEMPERATURES ARE EXPECTED AS HIGH PRESSURE CENTERED TO THE
SOUTH OF OUR REGION SLIDES BY. EXPECT CLOUDS TO GRADUALLY CLEAR
THROUGH MID DAY, THOUGH CLOUDS WILL START TO BUILD BACK LATE
TONIGHT AHEAD OF THE WARM FRONT TOMORROW.
ON SATURDAY, OUR FOCUS IS ON THE WARM FRONT APPROACHING FROM THE
SOUTH. IN GENERAL, THIS 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.
AS MENTIONED ABOVE THOUGH, ONE CHANGE FROM THE PREVIOUS FORECAST
IS THAT THERE IS NOW A VERY SMALL CHANCE THAT LOW LEVEL MOISTURE
WILL INCREASE ENOUGH AHEAD OF THE WARM FRONT ARRIVING FOR
LOCALIZED LIGHT FREEZING RAIN IN FAR NORTHERN DELWARE 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. LOOKING AT THE MODEL SOUNDINGS THOUGH,
THERE WILL ALSO LIKELY BE A VERY DEEP DRY LAYER ABOVE THIS, SO
IT MAY BE MORE OF A FREEZING DRIZZLE SET UP. ALL THAT BEING
SAID, THIS IS STILL VERY CONDITIONAL ON THE AIR CLOSEST TO THE
SURFACE BEING NEARLY SATURATED AND STAYING BELOW FREEZING FOR A
FEW HOURS AFTER SUNRISE. WILL BE WATCHING TRENDS CLOSELY OVER
THE NEXT 24 HOURS.
IN THE WAKE OF THE WARM FRONT, HIGH TEMPERATURES ON SATURDAY
WILL BE A FEW DEGREES HIGHER THAN TODAY, IN THE 40S SOUTH AND
EAST OF THE FALL LINE, FROM THE MID 30S TO LOWER 40S NORTHWEST
OF THE FALL LINE. THOUGH THIS SYSTEM SHOULD BE OUT OF THE AREA
BY LATE EVENING SATURDAY EVENING, CLOUDS WILL START BUILDING IN
AGAIN SATURDAY NIGHT AHEAD OF THE COLD FRONT AND SUNDAY SYSTEM.
AS SUCH, TEMPERATURES MAY NOT DROP OFF MUCH SATURDAY NIGHT.
LOWS ARE GENERALLY EXPECTED TO RANGE FROM THE LOWER 20S TO LOWER
30S.
SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/
THE FOCUS OF THE SHORT TERM PERIOD WILL BE ON A SYSTEM
IMPACTING THE AREA ON SUNDAY IN THE FROM OF FROZEN
PRECIPITATION.
FOR SUNDAY INTO SUNDAY NIGHT, THE STRONG ARCTIC COLD FRONT WILL
CROSS THROUGH THE REGION EARLY SUNDAY MORNING ADVECTING A MUCH
COLDER AIRMASS INTO THE REGION DURING THE DAY. AS IT DOES SO, AN
AREA OF LOW PRESSURE WILL ALSO BE DEVELOPING OVER THE DEEP SOUTH
NEAR THE TAIL-END OF THE ARCTIC FRONT. THIS AREA OF LOW PRESSURE
WILL RIDE ALONG THE FRONTAL BOUNDARY AND STRENGTHEN AS IT MOVES OFF
OF THE CAROLINA COASTLINE BY SUNDAY AFTERNOON.
FROM HERE, FORECAST GUIDANCE VARIES GREATLY AND ULTIMATELY WILL
DETERMINE WHAT WILL OCCUR SUNDAY AFTERNOON INTO SUNDAY NIGHT. IF THE
TRACK OF THE LOW IS CLOSE ENOUGH TO THE COAST, A LARGE PORTION OF
THE REGION IS LIKELY TO OBSERVE ACCUMULATING SNOWFALL (SIMILAR TO
WHAT THE 12Z/GFS DEPICTS). IF THE TRACK OF THE LOW IS SUPPRESSED
FURTHER SOUTH AND EAST (SIMILAR TO THE 12Z/ECMWF), THEN ACCUMULATING
SNOW MAY ONLY BE CONFINED TO COASTAL AREAS. WHEREAS IF THE TRACK OF
THE LOW, HUGS THE IMMEDIATE COASTLINE, THEN THE MOST SIGNIFICANT
SNOWS WILL BE FOCUSED NORTH AND WEST (DEPICTED BY THE 12Z/CANADIAN).
REGARDLESS OF THE VARIANCE IN GLOBAL GUIDANCE, HAVE SEEN AN INCREASE
IN OVERALL QPF VALUES AND IN SNOW PROBS. THUS, THERE IS AN INCREASE
IN FORECASTER CONFIDENCE THAT ACCUMULATING SNOW IS ON THE TABLE
SUNDAY AFTERNOON/EVENING ESPECIALLY SINCE COLD AIR WILL BE
ADVECTING IN FROM THE NORTHWEST. SO WITH THIS BEING SAID, THE
GREATEST POTENTIAL FOR HIGHER ACCUMULATIONS ARE FOR AREAS ALONG
THE I-95 CORRIDOR AND POINTS NORTH AND WEST WHERE THE INITIAL
FORECAST CALLS FOR 2-4" OF SNOW THROUGH 00Z MONDAY. LESSER
AMOUNTS UPWARDS OF 1-2" ARE FORECAST NEAR COASTAL AREAS THROUGH
THE SAME TIMEFRAME. OBVIOUSLY, A LOT CAN CHANGE OVER THE NEXT
60-72 HOURS AS WE OBTAIN MORE HI-RES/SHORT RANGE FORECAST
GUIDANCE AND STORM TOTAL SNOWFALL COVERS THE 'FULL DURATION' OF
THE EVENT, SO STAY TUNED FOR THE LATEST DETAILS TO THE FORECAST
OVER THE COMING DAYS!
LONG TERM /MONDAY THROUGH THURSDAY/
IN THE WAKE OF THE DEPARTING SYSTEM AND ARCTIC COLD FRONT, THE EARLY
TO MIDDLE PORTION OF THE WEEK WILL FEATURE BY FAR THE COLDEST
AIRMASS OF THE SEASON. STRONG, EXPANSIVE AND COLD, CANADIAN HIGH
PRESSURE WILL SINK SOUTHWARD OUT OF THE HIGH PLAINS ON MONDAY BEFORE
GRADUALLY SHIFTING SOUTHEAST TOWARD THE MID-ATLANTIC REGION BY
WEDNESDAY AND THURSDAY. WITH SUCH A COLD/DRY AIRMASS IN PLACE, THERE
DOES NOT APPEAR TO BE ANY REAL CHANCE FOR SOME PRECIPITATION DURING
THIS PERIOD, HOWEVER THERE IS A SLIGHT CHANCE FOR SOME LIGHT SNOW ON
TUESDAY NIGHT AS A SYSTEM OFFSHORE SKIRTS ON BY.
FOR NOW, THE PEAK OF THE COLD LOOKS TO OCCUR DURING THE MONDAY NIGHT
THROUGH WEDNESDAY NIGHT TIMEFRAME, AS 850 MB TEMPERATURES ARE
FORECAST TO BE BETWEEN -20C TO -24C DURING THIS TIME! SO IN TERMS
HIGH TEMPS, EXPECTING MOSTLY MID TEENS/LOW 20S WITH LOW TEMPS IN THE
SINGLE DIGITS (NEGATIVES IN THE HIGHER TERRAIN AREAS). FEEL-LIKE
TEMPERATURES WILL MOSTLY BE IN THE SINGLE DIGITS DURING THE DAY AND
IN THE NEGATIVES AT NIGHT, SO COLD WEATHER ADVISORIES/WARNINGS MAY
BE WARRANTED IN THE COMING DAYS.
THERE IS QUITE HIGH CONFIDENCE THAT THIS RELATIVELY PROLONGED PERIOD
OF DANGEROUSLY COLD TEMPERATURES WILL OCCUR, RESULTING 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.
AVIATION /08Z FRIDAY THROUGH TUESDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
THROUGH TODAY...PREVAILING VFR. BRIEF REDUCTIONS IN VISIBILITY
TO MVFR ARE POSSIBLE THROUGH SUNRISE, BUT OTHERWISE, VFR SHOULD
PREVAIL. WINDS BECOMING WEST- NORTHWEST 5-10 KTS. HIGH
CONFIDENCE.
TONIGHT...VFR. WINDS SHIFTING TO SW AND EVENTUALLY S THROUGH THE
NIGHT, BUT SHOULD BE LIGHT (GENERALLY LESS THAN 10 KT.
OUTLOOK...
SATURDAY THROUGH SATURDAY NIGHT...BRIEF PERIODS OF MVFR OR EVEN
IFR POSSIBLE WITH MOSTLY RAIN.
SUNDAY THROUGH SUNDAY NIGHT...SUB-VFR CONDITIONS PROBABLE,
ESPECIALLY SUNDAY AFTERNOON AND EVENING. LIGHT TO MODERATE SNOW
EXPECTED.
MONDAY THROUGH TUESDAY...VFR. NO SIGNIFICANT WEATHER EXPECTED.
MARINE
SCA FOR WINDS GUSTING ABOVE 25 KT CONTINUES THROUGH MID MORNING.
AFTER THAT, WINDS AND SEAS ARE EXPECTED TO STAY BELOW SCA
CONDITIONS THROUGH SATURDAY NIGHT. ON THE WATERS, WIND GUSTS
ABOVE 20 KT ARE POSSIBLE SATURDAY, BUT AT THIS POINT LOOKS LIKE
THEY SHOULD STAY JUST BELOW 25 KT.
OUTLOOK...
SUNDAY...NO MARINE HEADLINES EXPECTED.
SUNDAY NIGHT THROUGH TUESDAY...SCA CONDITIONS LIKELY AS WIND GUSTS
WILL RANGE BETWEEN 25-30 KT WITH SEAS AROUND 5 FEET. DUE TO THE
COMBINATION OF COLD AIR/WATER TEMPERATURES, GUSTY WINDS, AND
ENHANCED SEAS, FREEZING SPRAY ACCRETION IS LIKELY.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 9 AM EST THIS MORNING FOR
ANZ451>455.
SYNOPSIS...JOHNSON/STAARMANN
NEAR TERM...JOHNSON
SHORT TERM...DESILVA
LONG TERM...DESILVA/JOHNSON
AVIATION...DESILVA/JOHNSON
MARINE...DESILVA/JOHNSON
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