789
FXUS61 KPHI 200531
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1231 AM EST FRI DEC 20 2024
SYNOPSIS
HIGH PRESSURE INFLUENCES THE REGION THROUGH TONIGHT. LOW PRESSURE
IMPACTS THE REGION FRIDAY/FRIDAY NIGHT; IMPACTS LASTING POSSIBLY
INTO SATURDAY MORNING. COLD AND STRONG SURFACE HIGH PRESSURE BEGINS
TO BUILD IN LATER SATURDAY, HOLDING INFLUENCE OVER THE REGION
THROUGH MONDAY. NEXT LOW PRESSURE SYSTEM COULD IMPACT THE REGION
MONDAY NIGHT INTO THE WEDNESDAY TIME FRAME.
NEAR TERM /UNTIL 6 AM THIS MORNING/
HIGH PRESSURE CENTERED WILL CONTINUE TO DRIFT NORTH AND EAST
THROUGH QUEBEC WHILE AN UPPER LEVEL TROUGH WILL BE DIGGING
TOWARDS THE EAST COAST. THE INITIAL SURFACE LOW WITH THIS SYSTEM
WILL BE MOVING THROUGH THE MIDWESTERN STATES WHILE A SECONDARY
LOW WILL BEGIN TO TAKE SHAPE BY MORNING NEAR THE CAROLINA COAST.
IT WILL REMAIN DRY ACROSS OUR AREA TONIGHT WITH THE BIGGEST
CHALLENGE BEING THE SKY COVER AND TEMPERATURE FORECAST. THE
OVERALL TREND WILL BE TOWARDS AN EVENTUALLY THICKENING AND
LOWERING OF THE CLOUD DECK BY MORNING HOWEVER THROUGH THIS
EVENING, IT MAY JUST BE MAINLY HIGH CLOUDS ACROSS THE AREA.
COMBINED WITH DECREASING WINDS, THIS COULD ALLOW OUR
TEMPERATURES TO DROP OFF FOR A TIME BEFORE THE CLOUDS THICKEN
AND LOWER AND WINDS START TO TURN MORE ONSHORE. THUS, FORECAST
LOWS ARE MAINLY IN THE 20S TO LOW 30S. ALSO, NEAR THE COAST
LOWS WILL BE A BIT WARMER DUE TO THE WINDS TURNING ONSHORE WITH
LOWS FORECAST HERE TO GENERALLY BE IN THE 35 TO 40 DEGREE RANGE.
SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/
THIS CONTINUES TO BE THE MOST CHALLENGING PART OF THE FORECAST DUE
TO A COMPLEX SYSTEM THAT WILL BE IMPACTING THE AREA FRIDAY THROUGH
EARLY SATURDAY. IN THE UPPER LEVELS, A FAIRLY STRONG, ROBUST UPPER
LEVEL TROUGH WILL CONTINUE TO DIG AS IT MOVES EASTWARD AND BECOMES
CENTERED NEAR THE COAST BY 0Z SATURDAY. AS THIS OCCURS, THE INITIAL
SURFACE LOW ASSOCIATED WITH THIS FEATURE WILL FIZZLE OUT NEAR OHIO
WHILE AS A SECONDARY LOW STRENGTHENS AND MOVES NORTH AND EAST OFF
THE NORTH CAROLINA COAST. ONE OF THE MAIN FORECAST CHALLENGES WILL
BE THE EXACT TRACK THIS LOW TAKES AND WHETHER AN INVERTED SURFACE
TROUGH DEVELOPS ON ITS NW FLANK HELPING FOCUS SOME POTENTIALLY
HEAVIER PRECIPITATION OVER OUR AREA. THERE CONTINUE TO BE SOME
DIFFERENCES IN OUR FORECAST GUIDANCE REGARDING HOW ALL THIS PLAYS
OUT. ALL GUIDANCE INDICATES WE'LL GET AT LEAST SOME PRECIP FROM THE
SYSTEM WITH THE NAM (ESPECIALLY THIS MORNING'S 6Z RUN) DEPICTING THE
LOW BEING FARTHEST WEST CLOSER TO THE COAST THAN OTHER GUIDANCE. THE
OTHER CHALLENGE WILL BE THE MARGINAL TEMPERATURES AROUND THE
FREEZING MARK MAKING FOR A TRICKY PRECIPITATION TYPE FORECAST.
PUTTING ALL THIS TOGETHER IN TERMS OF WHAT IT MEANS FOR OUR SENSIBLE
WEATHER, EXPECT MAINLY LIGHT PRECIPITATION TO BEGIN OVERSPREADING
THE AREA FROM SOUTH TO NORTH THROUGH FRIDAY MORNING WITH THIS
CONTINUING THROUGH THE AFTERNOON. MODERATING TEMPERATURES SHOULD
ALLOW THIS TO BE MAINLY RAIN THROUGH THE DAY NEAR AND SOUTH OF THE I-
95 CORRIDOR WITH MIXED RAIN AND SNOW FARTHER NORTH INTO PORTIONS OF
BERKS COUNTY INTO THE LEHIGH VALLEY AND THEN RUNNING EAST INTO
PORTIONS OF NORTHERN NJ ALONG THE I-78 CORRIDOR. NORTH OF HERE,
PRECIPITATION SHOULD BE MAINLY SNOW ACROSS THE SOUTHERN POCONOS INTO
NW NJ (CARBON AND MONROE COUNTIES IN PA, SUSSEX COUNTY NJ). THESE
AREAS WILL SEE HIGHS ONLY IN THE LOW TO MID 30S WHILE FARTHER SOUTH,
NEAR AND SOUTH OF THE I-95 CORRIDOR, HIGHS GET INTO THE UPPER 30S
AND 40S. BY SUNSET FRIDAY, THERE MAY ALREADY BE SOME SNOW
ACCUMULATION ON THE GROUND NEAR AND NORTH OF THE I-78 CORRIDOR BUT
ESPECIALLY OVER THE HIGHER ELEVATIONS OF THE POCONOS AND NW NJ.
DON'T EXPECT ANY SNOW ON THE GROUND THROUGH THE DAYTIME HOURS
FARTHER SOUTH EVEN IF SOME FLAKES MIX IN AT TIMES.
THE FORECAST GETS A BIT MORE INTERESTING FARTHER SOUTH AS WE HEAD
INTO FRIDAY EVENING AND OVERNIGHT. THE LOW OFFSHORE WILL BE STARTING
TO PULL AWAY FROM THE AREA BUT AS ALLUDED TO ABOVE, THERE MAY BE A
SURFACE TROUGH EXTENDING BACK INTO THE AREA THAT LINGERS KEEPING
PRECIPITATION GOING MUCH OF THE NIGHT. ALSO WINDS WILL BE TURNING
MORE NORTHERLY WHICH, WHEN COMBINED WITH THE DIURNAL CYCLE, WILL
HELP TO COOL TEMPERATURES. THE UPSHOT OF ALL THIS IS THAT I EXPECT
THE RAIN/SNOW TRANSITION ZONE TO SHIFT SOUTHWARD WITH A CHANGE TO
SNOW LIKELY THROUGH THE EVENING ACROSS THE I-95 CORRIDOR AND
EVENTUALLY OVERNIGHT EVEN CLOSER TO THE COAST BEFORE PRECIP STARTS
TO WIND DOWN LATE. IT'S STILL NOT LOOKING LIKE A MAJOR SNOWSTORM FOR
THESE AREAS BUT IN OUR LATEST FORECAST WE ARE INDICATING A COATING
UP TO A HALF INCH OR SO OF ACCUMULATION NEAR THE URBAN
CORRIDOR...SPECIALLY ON GRASSY SURFACES. FARTHER NORTH AND WEST
EXPECT AROUND 1 TO 2 INCHES ACROSS THE LEHIGH VALLEY NORTH AND EAST
INTO NW NJ WITH 2 TO 3 INCHES LIKELY ACROSS THE POCONO PLATEAU. IT
SHOULD CONTINUE TO BE NOTED THOUGH THAT THIS IS A MORE CHALLENGING
FORECAST THAN AVERAGE AND THAT IF PRECIPITATION IS A BIT HEAVIER AND
A CHANGE TO SNOW OCCURS SOONER, AMOUNTS COULD BE HIGHER THAN
CURRENTLY FORECAST... POTENTIALLY 1 TO 2 INCHES IN THE URBAN
CORRIDOR FROM AROUND PHILLY TO TRENTON WITH UPWARDS OF 2 TO 4 INCHES
NORTH OF HERE. EXPECT LOWS BY SATURDAY MORNING MAINLY IN THE UPPER
20S TO LOW 30S EXCEPT LOW TO MID 20S OVER THE POCONO PLATEAU AND THE
HIGHER TERRAIN OF NW NJ.
FOR SATURDAY, DEEPENING LOW PRESSURE CONTINUES TO PULL AWAY FROM THE
AREA WITH A STRONG PRESSURE GRADIENT SETTING UP OVER THE AREA AS AN
ARCTIC HIGH BUILDS IN TO OUR WEST. THE RESULT WILL BE A VERY COLD,
BLUSTERY DAY WITH TEMPERATURES ONLY RISING A FEW DEGREES DUE TO THE
COLD ADVECTION PATTERN. EXPECT ANY LINGERING LIGHT SNOW TO COME TO
AN END THROUGH THE MORNING WITH LITTLE TO NO ADDITIONAL ACCUMULATION
WITH THE MAIN HAZARD BEING STRONG NW WINDS 15 TO 20 GUSTING UP TO 30
MPH. THIS WILL RESULT IN WIND CHILLS A GOOD 10 TO 15 DEGREES COLDER
THAN THE ACTUAL TEMPERATURES SO IN THE TEENS AND 20S!
LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/
SURFACE HIGH PRESSURE CENTERED JUST NORTH OF THE GREAT LAKES REGION
SATURDAY NIGHT WILL SLIDE SOUTHEASTWARDS WITH TIME. AS THIS SURFACE
HIGH SHIFTS OFFSHORE OF THE NORTHEASTERN CONUS AROUND THE TIME FRAME
OF MONDAY/MONDAY NIGHT, SURFACE LOW PRESSURE FROM THE WEST IS
INVITED TO APPROACH. A WEAK WARM FRONT ASSOCIATED WITH THE LOW COULD
LIFT THROUGH OUR REGION AFTER THE MONDAY PERIOD WITH A COLD FRONT TO
EVENTUALLY FOLLOW. THIS COLD FRONT COULD END UP PASSING THROUGH
DURING THE TUESDAY/WEDNESDAY TIME FRAME WITH SOME WEAK SURFACE HIGH
PRESSURE POSSIBLY BUILDING IN BEHIND.
COLD AND STRONG SURFACE HIGH PRESSURE WILL CONTROL THE REGION
SATURDAY NIGHT THROUGH AT LEAST MONDAY. THOUGH A FEW LINGERING
FLURRIES AND/OR LIGHT SNOW SHOWERS MAY OCCUR OFFSHORE DURING THE
SATURDAY NIGHT PERIOD, THE REGION IS MAINLY LOOKING AT A DRY AND
COLD FORECAST DURING THE TIME FRAME. THE COLD WILL BE THE MAIN STORY
DURING THE TIME FRAME. OVERNIGHT LOWS SATURDAY NIGHT ARE EXPECTED TO
BE IN THE TEENS ACROSS MUCH OF THE REGION, WITH HIGHS ON SUNDAY
ANTICIPATED TO BE MAINLY IN THE 20S. WITH SURFACE HIGH PRESSURE
CENTERED NEARLY OVERHEAD SUNDAY NIGHT, OVERNIGHT LOWS DURING THE
PERIOD ARE ANTICIPATED TO BE EVEN COLDER THAN THOSE SEEN DURING THE
PREVIOUS NIGHT; SINGLE DIGITS ARE POSSIBLE ACROSS AREAS KNOWN TO
RADIATE WELL AND THOSE LOCATED GENERALLY NORTHWESTWARDS OF THE I-95
CORRIDOR.
LOW PRESSURE AND ASSOCIATED FRONTS COULD BRING SOME PRECIPITATION TO
THE REGION STARTING LATE MONDAY NIGHT ONWARDS, BUT THE FORECAST
REMAINS OVERALL UNCERTAIN THIS FAR OUT GIVEN THE PATTERN.
TEMPERATURES TUESDAY ONWARDS ARE ANTICIPATED TO BE MUCH MORE MILD;
A RETURN TO NEAR AVERAGE CAN BE EXPECTED.
AVIATION /06Z FRIDAY THROUGH TUESDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS...
REST OF TONIGHT (THROUGH 12Z)...VFR WITH LOWERING AND THICKENING
CEILINGS. NE WINDS AROUND 5 KT. HIGH CONFIDENCE.
FRIDAY...VFR CONDITIONS EARLY, DETERIORATING TO MVFR BY 16-18Z
AND EVENTUALLY IFR BY 20-22Z. RAIN EXPECTED EARLY, TRANSITIONING
TO A RAIN/SNOW MIX IN THE AFTERNOON. N-NE WINDS AROUND 5-10 KT.
LOW CONFIDENCE, ESPECIALLY WITH RESPECT TO TIMING OF
RESTRICTIONS.
FRIDAY NIGHT...MAINLY IFR/LIFR CONDITIONS EXPECTED WITH PERIODS
OF LIGHT SNOW AND/OR A RAIN/SNOW MIX. NW-N WINDS AROUND 5-10 KT.
LOW CONFIDENCE OVERALL.
OUTLOOK...
SATURDAY THROUGH MONDAY...AFTER CEILINGS LIFT EARLY ON SATURDAY,
VFR CONDITIONS ARE EXPECTED THROUGH AT LEAST MONDAY NIGHT. NO
SIGNIFICANT WEATHER IS EXPECTED.
TUESDAY...MVFR CONDITIONS POSSIBLE WITH A SYSTEM MOVING IN FROM THE
GREAT LAKES.
MARINE
NO MARINE HEADLINES ARE IN EFFECT THROUGH TONIGHT. NORTHEAST
WINDS AROUND 10-15 KT AND SEAS AROUND 3 FEET.
NORTHEAST WINDS WILL INCREASE THROUGH THE DAY FRIDAY AND REACH
AT LEAST SMALL CRAFT ADVISORY LEVELS BY FRIDAY NIGHT. THESE
CONDITIONS WILL CONTINUE SATURDAY WITH WINDS SHIFTING TO
NORTHWESTERLY. IT'S POSSIBLE THAT WE COULD EVEN SEE SOME PERIODS
OF GALE FORCE WIND GUSTS FRIDAY NIGHT AND/OR SATURDAY.
OUTLOOK...
SATURDAY NIGHT...SCA FLAG CONTINUES AS CRITERIA LINGERS INTO
THE PERIOD.
SUNDAY THROUGH TUESDAY...NO MARINE HEADLINES ANTICIPATED.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 6 AM SATURDAY TO MIDNIGHT EST
SATURDAY NIGHT FOR ANZ430-431.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 6 AM EST
SUNDAY FOR ANZ450>455.
SYNOPSIS...WUNDERLIN
NEAR TERM...DESILVA/FITZSIMMONS
SHORT TERM...FITZSIMMONS
LONG TERM...WUNDERLIN
AVIATION...DESILVA/FITZSIMMONS/KRUZDLO
MARINE...DESILVA/FITZSIMMONS/WUNDERLIN
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