836
FXUS61 KPHI 311955
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
355 PM EDT MON MAR 31 2025
SYNOPSIS
A COLD FRONT WILL CROSS THROUGH THE REGION LATER THIS AFTERNOON INTO
THIS EVENING BRINGING WIDESPREAD SHOWERS AND THUNDERSTORMS. HIGH
PRESSURE RETURNS FOR TUESDAY AND WEDNESDAY. A WARM FRONT WILL LIFT
NORTH OF THE AREA ON THURSDAY BEFORE SINKING BACK TO OUR SOUTH ON
FRIDAY. A SEQUENCE OF LOWS AND DISTURBANCES WILL RIDE ALONG THIS
BOUNDARY CAUSING UNSETTLED CONDITIONS TO OCCUR LATE IN THE WEEK
THROUGH THE WEEKEND.
NEAR TERM /THROUGH TUESDAY/
LATEST SATELLITE IMAGERY SHOWS AN AREA OF AGITATED CUMULUS
STRETCHING FROM THE SOUTHERN SUSQUEHANNA VALLEY TO THE LEHIGH VALLEY
ALONG A CONVERGENCE BOUNDARY. THIS IS THE CORRIDOR MOST LIKELY TO
SEE THE FIRST SHOWERS AND THUNDERSTORMS OF THE AFTERNOON. IN FACT,
THE LATEST RADAR IS SHOWING A FEW SPOTTY SHOWERS ALREADY UNDERWAY,
SIGNALING THAT THE CONVECTIVE INITIATION PROCESS HAS BEGUN AND WILL
UNFOLD WITHIN THE NEXT FEW HOURS. THE LATEST MESOANALYSIS SHOWS SFC
CAPE HAS BUILT UP TO 500-1000 J/KG ACROSS MUCH OF THE REGION WITH
UPWARDS TO 1500 J/KG ACROSS THE SOUTHERN DELMARVA, ALL THANKS TO
STEADY DIURNAL HEATING THAT HAS TAKEN PLACE UNDER MOSTLY CLEAR
SKIES. WITH DEEP LAYER WIND SHEAR OF 40-50 KTS IN THE 0-6 KM LAYER
AND AROUND 30 KTS OF LOW-LEVEL SHEAR IN THE 0-3 KM LAYER, PARAMETERS
REMAIN FAVORABLE FOR STRONG TO SEVERE THUNDERSTORM DEVELOPMENT THIS
AFTERNOON INTO THE EARLY EVENING AS THE UPPER LEVEL TROUGH IS SLATED
TO PIVOT ACROSS THE MID ATLANTIC AND DRAG A STRONG COLD FRONT ACROSS
THE REGION OVERNIGHT. LOCALLY DAMAGING WIND GUSTS REMAIN THE MAIN
SEVERE WEATHER THREAT, BUT AN ISOLATED TORNADO OR TWO CANNOT BE
RULED OUT. THE BEST CHANCE FOR SEVERE THUNDERSTORMS WILL BE THROUGH
THE EARLY EVENING TIMEFRAME. THESE THUNDERSTORMS ARE EXPECTED TO
START OFF MORE DISCRETE IN NATURE, MAXIMIZING ON THE AVAILABLE
SEVERE PARAMETERS IN PLACE. THESE MORE DISCRETE CELLS ARE EXPECTED
TO BECOME MORE NUMEROUS THROUGH THE LATE AFTERNOON AND EARLY EVENING
BEFORE COALESCING INTO A MORE LINEAR STRUCTURE AFTER SUNSET. ONCE
THIS OCCURS, THE THREAT OF FLASH FLOODING INCREASES.
THE HEAVY RAIN AND FLASH FLOODING THREAT WILL BE HIGHEST THROUGH THE
EVENING INTO THE EARLY OVERNIGHT HOURS AS STORMS TEND TO GROW
UPSCALE AND INSTABILITY BECOMES MORE ELEVATED. A STRENGTHENING LOW-
LEVEL JET DURING THE EVENING AND NIGHTTIME HOURS WILL SUPPORT PWAT
VALUES SURGING INTO THE 1.5+ INCH RANGE, NEAR THE CLIMATOLOGICAL
MAXIMUM FOR THIS TIME OF YEAR. AS A RESULT, FORECAST STORM TOTAL
RAINFALL IS GENERALLY AROUND 1 TO 2 INCHES ACROSS THE AREA WITH THE
HIGHEST AMOUNTS (1.5 TO 2 INCHES) EXPECTED TO BE RIGHT OVER THE I-95
URBAN CORRIDOR. DESPITE OUR ONGOING DROUGHT, THIS WILL POSE A THREAT
FOR FLASH FLOODING SINCE RAIN RATES WILL BE HIGH AS IT WILL ALL FALL
WITHIN JUST A FEW HOURS. EXPECT THE COLD FRONT TO CROSS THE URBAN
CORRIDOR ROUGHLY AROUND 11PM - MIDNIGHT AND THEN MOVE OFFSHORE NEAR
OR SHORTLY AFTER 6Z. AS THIS IS OCCURRING, GUIDANCE CONTINUES TO
SUPPORT THE IDEA OF A WAVE OF LOW PRESSURE TRYING TO FORM ALONG IT
SO THIS COULD LEAD TO LINGERING POST FRONTAL MORE STRATIFORM TYPE
RAIN LASTING INTO THE OVERNIGHT, ESPECIALLY FOR AREAS NEAR AND
SOUTH/EAST OF THE URBAN CORRIDOR. ALL PRECIP SHOULD BE OVER THOUGH
BY TUESDAY MORNING WITH SHARPLY COLDER TEMPERATURES IN THE FRONT'S
WAKE. EXPECT LOWS RANGING FROM THE LOW TO MID 30S NORTH TO THE
MIDDLE TO UPPER 40S SOUTH.
WE WILL STILL BE IN A POST FRONTAL, COLD ADVECTION REGIME FOR MUCH
OF TUESDAY WITH 850 MB TEMPERATURES DROPPING TO AROUND -4C TO 2C.
THIS WILL TRANSLATE TO HIGH TEMPERATURES NEAR NORMAL, MAINLY IN THE
MID TO UPPER 50S FOR MOST AREAS (COOLER IN THE HIGHER ELEVATIONS).
BREEZY NORTHWEST WINDS AROUND 10-15 MPH WITH GUSTS UP TO 25 MPH AND
SUNNY SKIES.
SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/
UPPER TROUGHING WILL PUSH OFFSHORE BY TUESDAY NIGHT, FOLLOWED BY
ZONAL FLOW FOR WEDNESDAY AND UPPER RIDGING FOR WEDNESDAY NIGHT INTO
THURSDAY. AT THE SURFACE, COOL AND DRY CANADIAN HIGH PRESSURE WILL
BUILD INTO THE REGION TUESDAY NIGHT INTO WEDNESDAY. A WARM FRONT
WILL THEN LIFT NORTH THROUGH THE AREA WEDNESDAY NIGHT AS A STRONG
LOW PASSES THROUGH THE NORTHERN GREAT LAKES ON THURSDAY.
HIGH PRESSURE WILL BEGIN SHIFTING EAST ON TUESDAY NIGHT WHICH WILL
LEAD TO SURFACE WINDS BECOMING MORE NORTHEASTERLY. WINDS SHOULD
REMAIN ELEVATED ENOUGH ON THE OUTER PERIPHERY OF THE HIGH AROUND 5-
10 MPH, BUT THE USUAL SHELTERED SPOTS WILL LIKELY GO CALM AND
RADIATE WELL UNDER MOSTLY CLEAR SKIES. THIS IS NOTEWORTHY BECAUSE
THE FROST/FREEZE PROGRAM BEGINS APRIL 1 FOR OUR DELMARVA COUNTIES.
WITH THE DRY AIRMASS IN PLACE AND A COOL NORTHEAST BREEZE, THIS
SHOULD LIMIT/PREVENT ANY FROST DEVELOPMENT DESPITE THE LOW TEMPS IN
THE MID TO UPPER 30S. FURTHER NORTH, LOWS WILL BE IN THE UPPER 20S
TO MID 30S, BUT THE GROWING SEASON IS NOT ACTIVE YET IN THESE
LOCATIONS TO WARRANT ANY FREEZE HEADLINES.
FOR WEDNESDAY, THE HIGH WILL CONTINUE TO EXIT AND SHIFT OFF THE
COAST OF NEW ENGLAND. SHOULD SEE MOSTLY CLEAR SKIES EARLY IN THE
DAY, BECOMING MORE CLOUD-FILLED IN THE AFTERNOON. WINDS WILL BECOME
SOUTHEASTERLY DUE TO THE POSITIONING OF THE HIGH, CAUSING A MORE
ONSHORE COMPONENT. IT WILL ALSO BECOME BREEZY ON WEDNESDAY WITH
WINDS INCREASING TO 10-20 MPH WITH GUSTS LOCALLY UP TO 30 MPH. HIGH
TEMPERATURES SHOULD RANGE FROM THE UPPER 40S TO UPPER 50S FROM NORTH
TO SOUTH.
BY WEDNESDAY NIGHT AND THURSDAY, WE WILL BEGIN TO SEE SIGNIFICANT
CHANGES AROUND THE AREA. A WARM FRONT EXTENDING EASTWARD FROM A
STRONG AREA OF LOW PRESSURE TRACKING INTO THE GREAT LAKES WILL SURGE
NORTHWARD ACROSS OUR AREA ON WEDNESDAY NIGHT. THIS WILL RESULT IN A
RAMP UP IN WARM AIR AND MOISTURE ADVECTION TO OCCUR. COULD SEE A FEW
WARM AIR ADVECTION SHOWERS OCCUR ESPECIALLY NORTH AND WEST OF THE I-
95 CORRIDOR WITH THE FRONTAL PASSAGE, BUT OVERALL ANY QPF SHOULD BE
LIMITED. LOWS WILL BE MUCH WARMER THAN THE NIGHT BEFORE WITH LOWS IN
THE UPPER 30S TO MID 40S. FOR THURSDAY, WILL HAVE SOME UPPER LEVEL
ENERGY AROUND OFF TO OUR NORTH AND WEST, SO HAVE KEPT A CHANCE OF
SHOWERS AND ISOLATED THUNDERSTORMS IN THE FORECAST CONTINUING INTO
THURSDAY. CHANCES FOR ANY SEVERE THREAT DO NOT APPEAR TO BE ALL THAT
GREAT WITH BETTER FORCING DISPLACED WELL AWAY FROM THE AREA. DESPITE
MOSTLY CLOUDY TO OVERCAST SKIES AROUND, STRONG SOUTHERLY WINDS
ADVECTING WARMER AIR NORTHWARD SHOULD ALLOW HIGHS TO RANGE FROM THE
UPPER 60S TO UPPER 70S.
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
LITTLE IN THE WAY OF CHANGES WERE MADE TO THE LONG TERM PERIOD AS
RIDGING OVER THE EASTERN US WILL BE IN PLACE LATE WEEK THROUGH THE
WEEKEND WITH AN UPPER LEVEL TROUGH MOVING BACK INTO THE REGION EARLY
NEXT WEEK.
LOW PRESSURE EXITS THE REGION THURSDAY NIGHT INTO THE CANADIAN
MARITIMES, WITH A LEFTOVER BOUNDARY REMAINING SITUATED TO THE NORTH
OF OUR AREA. THE BOUNDARY WILL GRADUALLY SINK SOUTHWARD DURING THE
DAY ON FRIDAY INTO FRIDAY NIGHT, WHILE REMAINING WELL SOUTH OF THE
AREA THROUGH THE WEEKEND. SEVERAL WEAK DISTURBANCES WILL RIDE ALONG
THIS BOUNDARY ACCOMPANIED WITH UPPER LEVEL ENERGY PULSES THAT WILL
OCCUR LATE WEEK AND THROUGH THE WEEKEND. THIS WILL CAUSE A RATHER
UNSETTLED WEATHER PERIOD TO OCCUR LATE IN THE WEEK INTO THE WEEKEND
WHERE SEVERAL ROUNDS OF SHOWERS ARE EXPECTED.
GIVEN THE NATURE OF THE PATTERN, ISOLATED THUNDERSTORMS WILL BE
POSSIBLE FOR THURSDAY NIGHT, BUT NOTHING IN TERMS OF SEVERE WEATHER
IS EXPECTED. A FEW RUMBLES OF THUNDER HERE OR THERE AT MOST. HEADING
INTO FRIDAY THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK, THE CHANCE
FOR THUNDERSTORMS BECOMES LESS LIKELY AS THE AIRMASS BECOMES MORE
STABLE NORTH OF THE BOUNDARY. ALL IN ALL, HAVE KEPT A CHANCE OF
SHOWERS ACROSS THE ENTIRE FORECAST AREA FRIDAY THROUGH MONDAY. NOT
EXPECTING A WASHOUT BY ANY MEANS AS THERE WILL BE SEVERAL
BREAKS/LULLS IN BETWEEN THE ROUNDS OF SHOWERS, BUT LONG STORY SHORT,
IT WILL BE UNSETTLED INTO EARLY NEXT WEEK.
IN TERMS OF TEMPERATURES, ANOTHER WARM DAY IS TO OCCUR ON FRIDAY
BEFORE THE BOUNDARY PASSES THROUGH THE AREA. WILL BECOME COOLER OVER
THE WEEKEND INTO EARLY NEXT WEEK WITH TEMPERATURES GENERALLY +/- 5
DEGREES COMPARED TO NORMAL FOR EARLY APRIL.
AVIATION /20Z MONDAY THROUGH SATURDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
REST OF TODAY (THROUGH 00Z)...PREVAILING VFR THIS AFTERNOON BEFORE
SHOWERS/STORMS ARRIVE LATE DAY (MAINLY AFTER 20Z) PRODUCING
ADDITIONAL RESTRICTIONS, POSSIBLY AS LOW AS IFR WITH STRONGEST TSRA.
WINDS VEERING TO SW AND GENERALLY INCREASING TO 10 TO 15 GUSTING 20
TO 25 KNOTS. LOW CONFIDENCE IN STORM COVERAGE LATE
AFTERNOON; MODERATE CONFIDENCE OTHERWISE.
TONIGHT...SUB VFR PREDOMINATING IN THE EVENING DUE TO HEAVY
SHOWERS/STORMS WITH AT LEAST PERIODS OF IFR LIKELY...ESPECIALLY
DURING THE EVENING TIME FRAME. SHOWERS/STORMS WINDING DOWN OVERNIGHT
WITH CONDITIONS IMPROVING TO VFR AND WINDS SHIFTING TO NW 10 TO 15
GUSTING TO AROUND 20 KTS. MODERATE CONFIDENCE.
TUESDAY...PREVAILING VFR CONDITIONS WITH BREEZY NW WINDS 10 TO 15
KTS GUSTING TO AROUND 20 KTS EARLY, SUBSIDING IN THE AFTERNOON. HIGH
CONFIDENCE.
OUTLOOK...
TUESDAY NIGHT THROUGH WEDNESDAY...VFR. NO SIGNIFICANT WEATHER
EXPECTED.
WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...MAINLY VFR EXPECTED WITH
OCCASIONAL SUB-VFR CONDITIONS POSSIBLE AT NIGHT. SLIGHT CHANCE OF
RAIN SHOWERS AND AN ISOLATED THUNDERSTORM.
FRIDAY THROUGH SATURDAY...SUB-VFR CONDITIONS POSSIBLE WITH A CHANCE
FOR RAIN SHOWERS.
MARINE
SMALL CRAFT ADVISORY CONDITIONS CONTINUING THROUGH TUESDAY DUE TO
ELEVATED WINDS AND SEAS. TONIGHT, SW WINDS GENERALLY GUSTING TO 20-
25 KNOTS WITH SEAS 4 TO 6 FEET. WIDESPREAD HEAVY RAIN AND STORMS
EXPECTED TONIGHT. WINDS SHIFT TO NORTHWEST OVERNIGHT BEHIND A COLD
FRONT AND WILL RETURN TO GUSTING AROUND 25 KTS WITH SEAS LINGERING
AT 4 TO 6 FEET. WINDS AND SEAS WILL BEGIN TO DIMINISH TUESDAY
AFTERNOON, FALLING BELOW ADVISORY CRITERIA LATE AFTERNOON.
OUTLOOK...
TUESDAY NIGHT THROUGH WEDNESDAY...SCA CONDITIONS MAY LINGER INTO
TUESDAY NIGHT, BUT OVERALL NO MARINE HEADLINES EXPECTED. FAIR
WEATHER.
WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...SCA CONDITIONS PROBABLE DUE
TO WIND GUSTS UP TO 30 KT AND SEAS AROUND 5-7 FEET. SHOWERS AND
ISOLATED THUNDERSTORMS LIKELY.
FRIDAY THROUGH SATURDAY...NO MARINE HEADLINES EXPECTED. PERIODS OF
RAIN SHOWERS LIKELY.
TIDES/COASTAL FLOODING
CONTINUED ONSHORE WINDS AND ELEVATED ASTRONOMICAL TIDES FROM THE
RECENT NEW MOON COULD LEAD TO SOME SOME SPOTTY MINOR COASTAL
FLOODING WITH TONIGHT'S HIGH TIDE, MAINLY FOR MIDDLESEX,
MONMOUTH, OCEAN COUNTIES, AS WELL AS DELAWARE BAY AND THE TIDAL
DELAWARE RIVER. HOWEVER, ANY IMPACTS ARE ANTICIPATED TO BE
LIMITED AT MOST, AND NO ADVISORIES ARE CURRENTLY ANTICIPATED.
CLIMATE
LOCALLY HEAVY RAINFALL IS FORECAST ACROSS THE FORECAST AREA
TODAY. BELOW IS A LIST OF THE DAILY PRECIPITATION RECORDS FOR
MARCH 31ST.
ALLENTOWN (ABE) 1.80" IN 2022
AC AIRPORT (ACY) 1.46" IN 2017
AC MARINA (55N) 1.22" IN 1958
GEORGETOWN (GED) 1.70" IN 2002
MOUNT POCONO (MPO) 1.41" IN 2022
PHILADELPHIA (PHL) 1.57" IN 1980
READING (RDG) 1.50" IN 1934
TRENTON (TTN) 1.48" IN 1997
WILMINGTON (ILG) 1.75" IN 2017
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 PM EDT TUESDAY FOR ANZ430-431.
SMALL CRAFT ADVISORY UNTIL 6 PM EDT TUESDAY FOR ANZ450>455.
SYNOPSIS...DESILVA/STAARMANN
NEAR TERM...MJL
SHORT TERM...DESILVA/STAARMANN
LONG TERM...DESILVA/STAARMANN
AVIATION...DESILVA/MJL
MARINE...DESILVA/MJL
TIDES/COASTAL FLOODING...WFO PHI
CLIMATE...WFO PHI
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