800
FXUS61 KPHI 171803
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
103 PM EST TUE DEC 17 2024
SYNOPSIS
A COLD FRONT CROSSES THROUGH THE AREA TODAY GIVING WAY TO BRIEF HIGH
PRESSURE BY TONIGHT. ANOTHER AREA OF LOW PRESSURE AND ASSOCIATED
COLD FRONT IMPACT THE AREA LATE WEDNESDAY INTO WEDNESDAY NIGHT.
HIGH PRESSURE RETURNS ON THURSDAY WITH A WEAK DISTURBANCE PASSING
THROUGH ON FRIDAY. OTHERWISE, COLD CANADIAN HIGH PRESSURE ARRIVES
FOR THE WEEKEND INTO EARLY NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
LOW CLOUDS AND PATCHY FOG ARE BEGINNING TO LIFT AND DISSIPATE
AS A COLD FRONT SHIFTS IS BEGINNING TO MOVE INTO THE AREA,
WHICH THEN SHIFT OFFSHORE THROUGH THIS AFTERNOON, AND BRING
DRIER AIR INTO THE AREA. TEMPERATURES WILL CLIMB INTO THE MID TO
UPPER 50S/LOW 60S WITH SUNSHINE IN THE AFTERNOON. SW WINDS
AROUND 10 MPH WITH GUSTS AS HIGH AS 20 MPH IN THE MORNING,
TURNING W IN THE AFTERNOON.
A MORE SEASONABLE AND CERTAINLY DRY NIGHT IS ON TAP FOR TUESDAY
NIGHT WITH WEAK HIGH PRESSURE IN CONTROL. LOWS WILL BE MOSTLY IN THE
30S, WHICH IS STILL A LITTLE ON THE WARMER SIDE OF CLIMO. WHILE
WINDS WILL BE RATHER CALM, HIGH CLOUDS WILL LIKELY LIMIT RUNAWAY
RADIATIONAL COOLING OVERNIGHT.
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/
HIGH PRESSURE WILL SCOOT OFF THE COAST EARLY ON WEDNESDAY AS A WEAK
LOW PRESSURE SYSTEM TRACKS OUT OF THE TENNESSEE RIVER VALLEY. THIS
SYSTEM WILL LIFT NORTHEAST OVER THE AREA BY WEDNESDAY NIGHT BEFORE
MOVING UP INTO THE CANADIAN MARITIMES ON THURSDAY MORNING. SO WHILE
THE START OF WEDNESDAY WILL BE MOSTLY DRY WITH A MIX OF SUN/CLOUDS,
CLOUDS ARE EXPECTED TO STEADILY INCREASE THROUGHOUT THE DAY.
FORECAST GUIDANCE CONTINUES TO TAKE THE PATH OF THE LOW DIRECTLY
OVER THE I-95 CORRIDOR, SO IF THIS IS TO OCCUR, THERE WOULD BE A
SHARP GRADIENT WITH RESPECT TO TEMPERATURES AND PRECIPITATION ON
EITHER SIDE OF THE LOW ACROSS THE AREA. WITH THIS SCENARIO, AREAS
NORTH/WEST OF PHILADELPHIA WILL ENCOUNTER PERIODS OF RAIN ON
WEDNESDAY AFTERNOON CONTINUING INTO WEDNESDAY NIGHT WITH HIGH TEMPS
MAINLY IN THE 40S. FOR AREAS SOUTH/EAST OF PHILADELPHIA, THESE AREAS
WILL LIKELY BE IN THE WARM-SECTOR, SO RAIN MAY ENTIRELY HOLD OFF
UNTIL WEDNESDAY NIGHT AS TEMPERATURES RAISE INTO THE 50S, WITH
EVEN NEAR 60 DEGREES OVER THE DELMARVA!
LOW PRESSURE WILL DEPART ON WEDNESDAY NIGHT AS A TRAILING COLD FRONT
TRACKS ACROSS THE AREA ALLOWING ALL PRECIPITATION TO CEASE BY
THURSDAY MORNING. AS COLD AIR USHERS IN ON THE BACKSIDE OF THE LOW,
THERE MAY BE A SLIGHT CHANGEOVER TO SNOW ACROSS THE HIGHER TERRAIN,
BUT THE COLD AIR ADVECTION SURGE ISN'T ALL THAT STRONG, SO THIS
POTENTIAL DOESN'T LOOK ALL THAT LIKELY. IN TERMS OF RAINFALL
AMOUNTS, LOOKING LIKE ANYWHERE BETWEEN 0.25-0.75" WITH THE HEAVIEST
AMOUNTS NORTH AND WEST AND LESSER AMOUNTS SOUTH AND EAST.
OTHERWISE, HIGH PRESSURE WILL RETURN ON THURSDAY AND PERSIST THROUGH
THURSDAY NIGHT. TEMPERATURES WILL RETURN TO NEAR SEASONABLE LEVELS
WITH HIGHS IN THE 40S AND LOWS IN THE 20S/30S.
LONG TERM /FRIDAY THROUGH MONDAY/
LITTLE CHANGES WERE MADE TO THE LONG TERM PERIOD AS HIGH PRESSURE
REMAINS LARGELY IN CONTROL. THE EXCEPTION REMAINS A WEAK "CLIPPER"
SYSTEM THAT WILL PASS THROUGH THE AREA FRIDAY INTO FRIDAY NIGHT
WHICH MAY BRING A CHANCE FOR SOME SNOW OR A WINTRY MIX TO THE
REGION. GUIDANCE THIS MORNING CONTINUES TO SHOW A LACK OF MOISTURE
ASSOCIATED WITH THIS SYSTEM SO HAVE MAINTAINED GENERALLY SLIGHT
CHANCE/CHANCE POPS (~20-40%) ACROSS THE AREA DURING THIS TIMEFRAME.
FORTUNATELY, WITH THE INITIAL LOW WEAKENING AND STRONG LOW PRESSURE
DEVELOPING SEVERAL HUNDRED MILES OFFSHORE, THERE DOES NOT LOOK TO BE
ANY SIGNIFICANT IMPACTS TO THE AREA AT THIS TIME.
OTHERWISE, BEHIND THIS SYSTEM WILL BE THE WELCOMING OF A STRONG
CANADIAN HIGH THAT WILL BUILD INTO THE REGION FOR THE WEEKEND INTO
THE START OF NEXT WEEK. A COUPLE OF DRY SECONDARY COLD FRONTS WILL
USHER IN COLDER AIR AT TIMES, WITH THE "PEAK" OF THE COLD AIR
OCCURING SATURDAY NIGHT THROUGH SUNDAY NIGHT. DURING THIS TIME,
TEMPERATURES WILL RANGE ANYWHERE BETWEEN 10-15 DEGREES BELOW NORMAL.
SOME MODERATING IS THEN EXPECTED ON MONDAY, BUT OVERALL THE LONG
TERM PERIOD WILL REMAIN BELOW-NORMAL AND DRY.
AVIATION /18Z TUESDAY THROUGH SUNDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS...
REST OF TODAY...THE LOW CLOUDS AND FOG HAVE BEGUN TO LIFT AND
DISSIPATE, AND ALL SITES WILL IMPROVE TO VFR BETWEEN 18Z-19Z.
WEST TO SOUTHWEST WINDS AROUND 5 TO 10 KTS WILL BECOME WEST TO
NORTHWEST THROUGH THIS AFTERNOON. OCCASIONAL GUSTS AROUND 15-20
KNOTS POSSIBLE. HIGH CONFIDENCE.
TONIGHT...VFR CONDITIONS EXPECTED. THERE IS A SMALL CHANCE OF
PATCHY FOG LATE IN THE NIGHT, HOWEVER THIS HAS BEEN KEPT OUT OF
THE TAFS AT THIS TIME. HIGH CONFIDENCE.
WEDNESDAY...VFR (UNLESS PATCHY FOG DOES DEVELOP) WILL REMAIN FOR
MUCH OF THE DAY. HOWEVER, LOWER CLOUDS AND LOWER VISIBILITY
(LIKELY IFR) WILL MOVE IN LATER IN THE DAY AS RAIN MOVES INTO
THE AREA. MODERATE CONFIDENCE.
WEDNESDAY NIGHT...LOWER CLOUDS AND LOWER VISIBILITY (LIKELY IFR)
WILL BEGIN THE PERIOD DURING THE EVENING HOURS, BEFORE IMPROVING
TO MVFR OR VFR OVERNIGHT AS THE RAIN EXITS. MODERATE CONFIDENCE.
OUTLOOK...
THURSDAY THROUGH THURSDAY NIGHT...VFR. NO SIGNIFICANT WEATHER.
FRIDAY THROUGH FRIDAY NIGHT...SUB-VFR CONDITIONS POSSIBLE WITH A
CHANCE FOR RAIN/SNOW SHOWERS.
SATURDAY...VFR. NO SIGNIFICANT WEATHER.
MARINE
A SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL OCEAN ZONES THROUGH THE
AFTERNOON AND EVENING HOURS. SEAS OF 4 TO 6 FEET ARE EXPECTED THOUGH
WIND GUSTS OUT OF THE SOUTHWEST COULD GET NEAR 25 KT AT TIMES
TUESDAY MORNING, DIMINISHING TO AROUND 15 KT BY THE AFTERNOON.
CONDITIONS WILL REMAIN BELOW ADVISORY CRITERIA TUESDAY NIGHT.
OUTLOOK...
WEDNESDAY...FAIR WEATHER. NO MARINE HEADLINES EXPECTED. WINDS UP TO
20 KT AND SEAS OF 2-3 FEET.
WEDNESDAY NIGHT THROUGH THURSDAY...SCA CONDITIONS PROBABLE. WIND
GUSTS UP TO 25-30 KT AND SEAS AROUND 5 FEET. RAIN LIKELY.
THURSDAY NIGHT THROUGH FRIDAY...FAIR WEATHER. NO MARINE HEADLINES
EXPECTED. WINDS UP TO 15 KT AND SEAS OF 3-4 FEET.
FRIDAY NIGHT THROUGH SATURDAY...SCA CONDITIONS PROBABLE. WIND GUSTS
UP TO 25 KT AND SEAS AROUND 5 FEET.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ450-
451.
SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR
ANZ452>455.
SYNOPSIS...DESILVA
NEAR TERM...MJL/ROBERTSON
SHORT TERM...DESILVA
LONG TERM...DESILVA
AVIATION...DESILVA/MJL/ROBERTSON
MARINE...DESILVA/MJL
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