191
FXUS61 KPHI 181608
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1108 AM EST WED DEC 18 2024
SYNOPSIS
HIGH PRESSURE MOVES OFFSHORE TODAY GIVING WAY TO AN AREA OF LOW
PRESSURE AND ASSOCIATED COLD FRONT LATER THIS AFTERNOON INTO
TONIGHT. HIGH PRESSURE BRIEFLY RETURNS ON THURSDAY AHEAD OF
ANOTHER AREA OF LOW PRESSURE WHICH PASSES BY ON FRIDAY AS
SECONDARY LOW PRESSURE DEVELOPS OFFSHORE. IN ITS WAKE, COLD
CANADIAN HIGH PRESSURE ARRIVES FOR THE WEEKEND THROUGH THE
MIDDLE OF NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
THE PATCHY FOG HAS DISSIPATED. THE MOSTLY SUNNY SKIES WILL GIVE
WAY TO INCREASING CLOUDS THIS AFTERNOON. HIGH PRESSURE WILL
SHIFT OFFSHORE THROUGH THE DAY AS A WARM FRONT LIFTS NORTH
ACROSS THE REGION AHEAD OF OUR NEXT AREA OF LOW PRESSURE
ADVANCING IN FROM THE WEST. TEMPERATURES WILL BE RATHER WARM
ONCE AGAIN WITH HIGHS EXPECTED IN THE 40S TO UPPER 50S, BUT
INCREASING AFTERNOON CLOUDS AND RAIN CHANCES WILL LIKELY HELP
PREVENT TEMPERATURES FROM GETTING ANY HIGHER. WE EXPECT THE RAIN
TO BEGIN TO MOVE IN, WEST TO EAST, DURING THE 1 TO 4 PM TIME
FRAME, BEFORE SPREADING ACROSS THE ENTIRE AREA THIS EVENING AS
THE LOW PRESSURE MOVES ACROSS THE AREA. THE RAINFALL COULD
BECOME MODERATE TO HEAVY AT TIMES, BUT RAINFALL AMOUNTS ARE
FORECAST TO BE AROUND 0.25-0.50 INCHES ACROSS THE AREA. THE RAIN
SHOULD BEGIN TO END DURING THE OVERNIGHT HOURS AS THE LOW LIFTS
TO OUR NORTHEAST AND A COLD FRONT SHIFTS ACROSS THE AREA. SOME
SNOW MAY MIX IN ACROSS THE POCONO PLATEAU AND ELEVATIONS OVER
1000FT OVERNIGHT BEFORE PRECIP ENDS, THOUGH MOST ACCUMULATIONS
ARE NOT EXPECTED TO BE MEASURABLE. WNW WINDS BEHIND THE COLD
FRONT WILL BE A BIT BREEZY AROUND 10 MPH EARLY THURSDAY MORNING
AND COULD ALSO BRING AN ISOLATED LIGHT SNOW SHOWER OR FLURRY TO
THE POCONOS IN THE MORNING. OVERNIGHT TEMPERATURES ARE EXPECTED
TO FALL INTO THE LOW-TO-MID 30S.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
TRANQUIL AND SEASONABLE WEATHER CONDITIONS ARE EXPECTED ON THURSDAY
INTO THURSDAY NIGHT AS HIGH PRESSURE SETTLES OVER SOUTHERN QUEBEC.
MOSTLY CLEAR SKIES ARE EXPECTED DURING THE DAY, WITH AN INCREASE IN
CLOUDS AT NIGHT. HIGHS WILL BE IN THE 40S WITH LOWS IN THE 20S/30S.
OUR ATTENTION THEN TURNS FOR THE FRIDAY THROUGH FRIDAY NIGHT PERIOD
AS OUR NEXT WEATHER SYSTEM TAKES AIM AT THE AREA. A DEEPENING UPPER
TROUGH WILL BE APPROACHING THE AREA TO CLOSE THE WEEK, WHICH WILL BE
ACCOMPANIED WITH SEVERAL SHORTWAVES EMBEDDED IN THE FLOW. AT THE
SURFACE, LOW PRESSURE ORIGINATING OVER THE HIGH PLAINS WILL TRAVERSE
ACROSS THE SOUTHERN GREAT LAKES REGION AND APPROACH OUR REGION BY
FRIDAY AFTERNOON. FORECAST GUIDANCE CONTINUES TO TREND A LITTLE
DEEPER WITH THE PRIMARY SHORTWAVE, SO AS THE LOW APPROACHES, SOME
PRECIPITATION IS EXPECTED TO OVERSPREAD THE AREA. AT THE SAME TIME,
A SECONDARY LOW WILL BE DEVELOPING A COUPLE HUNDRED MILES OFF THE
MID-ATLANTIC COAST AND DEEPEN RAPIDLY AS IT LIFTS NORTHEAST;
ENHANCED BY SPEED MAX ROUNDING BASE OF THE UPPER TROUGH.
WITH THE LOW OFFSHORE REMAINING IN 'CLOSE ENOUGH' PROXIMITY TO THE
AREA, IT IS LOOKING MORE LIKELY THAT THERE WILL BE SOME AREAS OF
LIGHT RAIN AND SNOW ACROSS THE AREA ON FRIDAY INTO FRIDAY NIGHT AS
THE INITIAL LOW TRANSITIONS ITS ENERGY TO THE OFFSHORE LOW. AS A
RESULT, POPS HAVE INCREASED SLIGHTLY (~40-60%). IN ADDITION, SOME
FORECAST GUIDANCE INDICATES THE DEVELOPMENT OF AN INVERTED /
NORLUN TROUGH SET-UP ON THE NORTHWEST SIDE OF THE OFFSHORE LOW.
THIS WOULD ENHANCE PRECIPITATION ACROSS PORTIONS OF THE AREA,
HOWEVER, IT IS UNCERTAIN WHERE OR IF THIS FEATURE IS TO EVEN
DEVELOP AT THIS TIME. FOR NOW, THE BEST CHANCE OF OBSERVING
ACCUMULATING SNOW WILL BE ACROSS THE LEHIGH VALLEY, NORTHERN NEW
JERSEY AND IN THE POCONOS WHERE TEMPERATURES WILL BE COOLER
THROUGH THE DURATION OF THE EVENT. SNOW TOTALS IN THESE AREAS
WILL RANGE BETWEEN 1-2", LOCALLY UP TO 3". LIGHT ACCUMULATIONS
OF A DUSTING UP TO 1" ARE POSSIBLE ACROSS THE REMAINDER OF NEW
JERSEY, PENNSYLVANIA AND NORTHERN DELAWARE AS RAIN TRANSITIONS
TO SNOW ON FRIDAY NIGHT AS TEMPERATURES COOL BELOW/NEAR
FREEZING.
PRECIPITATION WILL TAPER OFF FROM WEST TO EAST BY EARLY SATURDAY
MORNING AS THE LOW EXITS TOWARD NOVA SCOTIA.
LONG TERM /SATURDAY THROUGH TUESDAY/
OVERALL, LITTLE CHANGES WERE MADE TO THE LONG TERM PERIOD AS THE
REGION WILL BE SITUATED WITHIN A DEEP LONGWAVE TROUGH. BEHIND THE
DEEPENING LOW OFFSHORE, A STRONG AREA OF CANADIAN HIGH PRESSURE WILL
BUILD OVER THE GREAT LAKES OVER THE WEEKEND BEFORE SHIFTING EAST
OVER THE MID-ATLANTIC AND NEW ENGLAND BY EARLY NEXT WEEK. A COUPLE
OF DRY SECONDARY COLD FRONTS WILL USHER IN SIGNIFICANTLY COLDER AIR
AT TIMES, WITH THE PEAK OF THE COLD AIR OCCURING SUNDAY INTO MONDAY.
DURING THIS TIME, TEMPERATURES WILL RANGE GENERALLY 10-15 DEGREES
BELOW NORMAL. THIS APPEARS TO BE THE "COLDEST" AIRMASS OF THE SEASON
THUS FAR, WITH 850 MB TEMPS FALLING TO AROUND -12C TO -18C ON
SUNDAY. THIS IS EXPECTED TO RESULT IN DAYTIME HIGH TEMPERATURES TO
REMAIN BELOW-FREEZING. OTHERWISE, SOME MODERATION IS EXPECTED INTO
EARLY NEXT WEEK AS THE HIGH SHIFTS EAST, BUT OVERALL THE LONG TERM
PERIOD WILL REMAIN BELOW-NORMAL AND DRY.
AVIATION /16Z WEDNESDAY THROUGH SUNDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS...
WEDNESDAY...VFR FOR ALL SITES UNTIL 20Z. MVFR CONDS THEN
DEVELOP IN RA. POTENTIAL FOR IFR CONDS JUST PRIOR TO 00Z.
LGT/VRB WINDS MOST OF THE DAY, THEN SE WINDS AROUND 5 KT AFTER
18Z. LOW CONFIDENCE.
WEDNESDAY NIGHT...IFR CONDS IN RA/STRATUS. IMPROVEMENT TO VFR
AFTER 06Z AS RAIN ENDS AND A COLD FRONT PASSES THROUGH THE
TERMINALS. WINDS BECOME W-NW AROUND 10 KT AFTER 00Z. MODERATE
CONFIDENCE.
OUTLOOK...
THURSDAY THROUGH THURSDAY NIGHT...VFR. NO SIGNIFICANT WEATHER
EXPECTED.
FRIDAY THROUGH FRIDAY NIGHT...SUB-VFR LIKELY WITH A CHANCE OF RAIN
AND/OR SNOW.
SATURDAY THROUGH SUNDAY...VFR. NO SIGNIFICANT WEATHER EXPECTED.
MARINE
A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE COASTAL WATERS AND
DELAWARE BAY BEGINNING WEDNESDAY NIGHT THROUGH THURSDAY MORNING. A
COLD FRONT WILL BRING RAIN BEGINNING LATE AFTERNOON INTO THE
NIGHTTIME HOURS. SEAS WILL BE MARGINAL AROUND 3-5 FEET, BUT NW WINDS
WILL GUST TO 25 KTS BEHIND THE COLD FRONT TONIGHT.
OUTLOOK...
THURSDAY THROUGH THURSDAY NIGHT...VFR. NO SIGNIFICANT WEATHER
EXPECTED.
FRIDAY THROUGH FRIDAY NIGHT...SUB-VFR LIKELY WITH A CHANCE OF RAIN
AND/OR SNOW.
SATURDAY THROUGH SUNDAY...VFR. NO SIGNIFICANT WEATHER EXPECTED.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 1 AM TO 10 AM EST THURSDAY FOR
ANZ430-431.
SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 10 AM EST
THURSDAY FOR ANZ450>455.
SYNOPSIS...DESILVA/STAARMANN
NEAR TERM...KRUZDLO/MJL
SHORT TERM...DESILVA
LONG TERM...DESILVA/STAARMANN
AVIATION...DESILVA/MJL
MARINE...DESILVA/MJL
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