631
FXUS61 KPHI 202310
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
710 PM EDT MON APR 20 2026
WHAT HAS CHANGED
ADDED COASTAL MONMOUTH TO A FREEZE WARNING AND UPDATED TIMING OF
FREEZE WARNINGS.
KEY MESSAGES
1. A WIDESPREAD FREEZE IS EXPECTED TO OCCUR TONIGHT AS AN UNUSUALLY
COLD AIRMASS SETTLES OVER THE AREA.
2. A RETURN TO ABOVE AVERAGE TEMPERATURES LATER THIS WEEK BEFORE
COOLING DOWN AGAIN OVER THE WEEKEND. WIDESPREAD RAINFALL POSSIBLE
OVER THE WEEKEND.
DISCUSSION
KEY MESSAGE 1...A WIDESPREAD FREEZE IS EXPECTED TO OCCUR TONIGHT AS
AN UNUSUALLY COLD AIRMASS SETTLES OVER THE AREA.
IN WAKE OF DEPARTING COLD FRONT, A RATHER STRONG AREA OF HIGH
PRESSURE QUICKLY BUILDS OVER CENTRAL PENNSYLVANIA TONIGHT. THIS HIGH
WILL CAUSE NORTHWEST WINDS TO DIMINISH QUICKLY THROUGH THE EVENING
HOURS AND LEAD TO AN EXCEPTIONAL NIGHT FOR RADIATIONAL COOLING UNDER
CLEAR SKIES. NOT ONLY WILL THE AIRMASS BE UNUSUALLY COLD, BUT IT
WILL BE QUITE DRY WITH DEW POINTS FALLING INTO THE LOW TEENS TO LOW
20S. UNDER THESE ATMOSPHERIC CONDITIONS, THE BOUNDARY LAYER SHOULD
DECOUPLE, SO HAVE OPTED TO BLEND IN SOME COLDER GUIDANCE, LOWERING
LOWS FOR TONIGHT INTO THE LOW 20S TO LOW 30S FOR AREAS AWAY FROM THE
COAST. FREEZE WARNINGS REMAIN IN EFFECT TONIGHT, AND HAVE ADDED
COASTAL MONMOUTH COUNTY INTO THE WARNING AS WELL. FOR MORE
INFORMATION REGARDING DAILY LOW TEMPERATURE RECORDS, PLEASE REFER TO
THE CLIMATE SECTION BELOW.
FOR REMAINING COASTAL LOCALES, FROM COASTAL OCEAN TO COASTAL SUSSEX,
THINKING THAT MAY BE ENOUGH OF A MARINE INFLUENCE TO KEEP TEMPS IN
THESE AREAS FROM FALLING BELOW FREEZING. WHILE SOME PATCHY FROST IS
POSSIBLE IN THESE AREAS, IT MAY NOT BE WIDESPREAD DUE TO WINDS
REMAINING ELEVATED. NONETHELESS, LOWS WILL FALL INTO IN THE MID TO
UPPER 30S IN THESE AREAS.
AS A REMINDER, ALL OF OUR COUNTIES NOW HAVE AN ACTIVE GROWING SEASON
DUE TO THE RECENT EXCESSIVE WARMTH. BLOOMS/VEGETATION HAVE QUICKLY
INITIATED AND IN SOME CASES ARE AHEAD OF SCHEDULE. FRUIT TREES AND
OTHER COLD SENSITIVE PLANTS ALREADY PLANTED ARE OF THE MOST CONCERN.
FROST FORMATION MIGHT BE SOMEWHAT LIMITED GIVEN A DRY LOW-LEVEL
AIRMASS IN PLACE TONIGHT.
KEY MESSAGE 2...A RETURN TO ABOVE AVERAGE TEMPERATURES LATER THIS
WEEK BEFORE COOLING DOWN AGAIN OVER THE WEEKEND. SOME SHOWERS
EXPECTED ON WEDNESDAY MORNING WITH MORE WIDESPREAD RAINFALL
POSSIBLE OVER THE WEEKEND.
IT IS NOT ANTICIPATED TO BE AS COLD TUESDAY NIGHT AS THE AIR
MASS CONTINUES TO MODIFY AND CLOUDS INCREASE WITH HIGH PRESSURE
NOW WELL OFFSHORE. A RETURN, SOUTHERLY, FLOW WILL ALSO BECOME
ESTABLISHED TUESDAY AND CONTINUE WEDNESDAY. THIS ALONG WITH AN
INCREASE IN WARM AIR ADVECTION AND RISING HEIGHTS WILL RESULT IN
TEMPERATURES CLIMBING BACK ABOVE AVERAGE WEDNESDAY THROUGH
FRIDAY. HIGHS FOR MOST OF THE AREA ARE FORECAST TO BE IN THE
MID/UPPER 60S WEDNESDAY, THEN INTO THE 70S FOR THURSDAY AND
FRIDAY. A FRONT MAY ARRIVE FRIDAY NIGHT INTO SATURDAY WITH SOME
SHOWERS, AND WITH THE LOW-LEVEL FLOW MORE ONSHORE IT WILL BRING
IN SOME COOLING STARTING FRIDAY ESPECIALLY CLOSER TO THE COAST.
IF THE MARINE INFLUENCE ENDS UP BEING STRONGER FRIDAY INTO
SATURDAY, THEN MORE LOW CLOUDS MAY COME INTO PLAY ALONG WITH
EVEN COOLER TEMPERATURES.
IN TERMS OF RAINFALL, A WEAK AREA OF LOW PRESSURE SLIDES BY
WEDNESDAY MORNING BRINGING SOME SHOWERS. RAINFALL AMOUNTS
GENERALLY UP TO A TENTH OF AN INCH ARE EXPECTED. ANOTHER AREA
OF LOW PRESSURE MAY ARRIVE DURING THE WEEKEND, ESPECIALLY FOR
SUNDAY, BRINGING THE POTENTIAL FOR WIDESPREAD SHOWERS OR A
PERIOD OF RAIN. THE STRENGTH AND TIMING OF THE INVOLVED FEATURES
FOR THE WEEKEND HOWEVER IS LOWER CONFIDENCE. THE PATTERN THAT
IS CURRENTLY INDICATED AMONG THE MODEL GUIDANCE HOWEVER WOULD
RESULT IN TEMPERATURES DROPPING TO AVERAGE OR BELOW AVERAGE OVER
THE WEEKEND, WITH AN INCREASED CHANCE FOR RAINFALL.
AVIATION /00Z TUESDAY THROUGH SATURDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
TONIGHT...VFR WITH MOSTLY CLEAR SKIES. NORTH WINDS AROUND 4-8
KT BECOMING LIGHT AND VARIABLE AT TIMES. HIGH CONFIDENCE.
TUESDAY...VFR WITH INCREASING CLOUDS IN THE AFTERNOON. NORTH WINDS
IN THE MORNING, TRANSITION TO SOUTHWEST AROUND 5-10 KT IN THE
AFTERNOON. HIGH CONFIDENCE.
OUTLOOK...
TUESDAY NIGHT...VFR. NO SIGNIFICANT WEATHER.
WEDNESDAY...MVFR/IFR CONDITIONS EXPECTED ESPECIALLY IN THE
MORNING WITH SHOWERS AND LOW CLOUDS AROUND.
WEDNESDAY NIGHT THROUGH FRIDAY...VFR. NO SIGNIFICANT WEATHER.
FRIDAY NIGHT THROUGH SATURDAY...SUB-VFR CONDITIONS LIKELY AT
TIMES WITH SHOWERS AND LOW CLOUDS MOVING THROUGH.
MARINE
NO MARINE HEADLINES ARE IN EFFECT THROUGH TUESDAY. NORTH-NORTHWEST
WINDS AROUND 10-20 KT ARE EXPECTED TO CONTINUE THROUGH TONIGHT
BEFORE DIMINISHING TO 5-10 KT BY TUESDAY MORNING. WINDS WILL
GRADUALLY SHIFT TO SOUTH-SOUTHEAST AROUND 10 KT BY TUESDAY
AFTERNOON. SEAS AROUND 2-3 FEET.
ASIDE FOR SOME RAIN/GRAUPEL SHOWERS EXPECTED THIS AFTERNOON, FAIR
WEATHER IS EXPECTED THROUGH TUESDAY.
OUTLOOK...
TUESDAY NIGHT/WEDNESDAY MORNING...SMALL CRAFT ADVISORY
CONDITIONS POSSIBLE (30-40%) WITH WIND GUSTS NEAR 25 KT.
WEDNESDAY AFTERNOON THROUGH SATURDAY...NO MARINE HEADLINES
EXPECTED.
CLIMATE
RECORD LOW TEMPERATURES ARE POSSIBLE AT SOME CLIMATE SITES FOR
TUESDAY, APRIL 21ST. BELOW ARE THE DAILY LOW TEMPERATURE
RECORDS FOR 4/21:
DAILY RECORD LOW TEMPERATURES
APRIL 21
SITE RECORD/YEAR
ALLENTOWN (ABE) 28/1925 & 1956 & 2018
AC AIRPORT (ACY) 25/1981
AC MARINA (55N) 26/1875
GEORGETOWN (GED) 27/1961
MOUNT POCONO (MPO) 11/1908
PHILADELPHIA (PHL) 27/1875
READING (RDG) 26/1982
TRENTON (TTN) 30/1907 & 1925
WILMINGTON (ILG) 28/1925
PHI WATCHES/WARNINGS/ADVISORIES
PA...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT TUESDAY FOR
PAZ060>062-070-071-101>106.
FREEZE WARNING UNTIL 10 AM EDT TUESDAY FOR PAZ054-055.
NJ...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT TUESDAY FOR
NJZ007>010-012>023-027.
FREEZE WARNING UNTIL 10 AM EDT TUESDAY FOR NJZ001.
DE...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT TUESDAY FOR
DEZ001.
FREEZE WARNING FROM 2 AM TO 9 AM EDT TUESDAY FOR DEZ002-003.
MD...FREEZE WARNING FROM 2 AM TO 9 AM EDT TUESDAY FOR MDZ012-015-
019-020.
MARINE...NONE.
DISCUSSION...DESILVA/HOEFLICH
AVIATION...DESILVA/HOEFLICH/MJL
MARINE...DESILVA/HOEFLICH
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