434
FXUS61 KPHI 311751
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
151 PM EDT MON MAR 31 2025
SYNOPSIS
A WARM FRONT WILL LIFT NORTH OF THE AREA THIS MORNING, THEN A
COLD FRONT WILL IMPACT THE REGION LATE THIS AFTERNOON AND
EVENING WITH WIDESPREAD SHOWERS AND THUNDERSTORMS. COOL AND DRY
HIGH PRESSURE WILL SETTLE INTO THE AREA THROUGH WEDNESDAY, THEN
MOVES OFFSHORE. SEVERAL ROUNDS OF SHOWERS EXPECTED LATE IN THE
WEEK AND THROUGH THE WEEKEND. A WARM FRONT WILL LIFT NORTH
WEDNESDAY NIGHT INTO THURSDAY. THIS FRONT WILL RETURN SOUTH
THROUGH THE AREA LATE FRIDAY, THEN LOW PRESSURE WILL PASS
OFFSHORE OVER THE WEEKEND.
NEAR TERM /THROUGH TONIGHT/
145 PM...LATEST SATELLITE SHOWS SKIES MOSTLY CLEAR NOW ACROSS
THE FORECAST AREA WITH CU FIELDS BEGINNING TO BUBBLE UP.
TEMPERATURES CONTINUE TO OVER-PERFORM ACROSS THE REGION. LATEST
MESOANALYSIS SHOWS INSTABILITY BUILDING ACROSS MUCH OF THE
REGION, WITH 500-1500 J/KG OF SFC CAPE ALREADY IN PLACE.
PREVIOUS DISCUSSION...AS WE GET INTO THE DAY TODAY, THE MAIN
FOCUS CONTINUES TO BE ON THE SEVERE WEATHER AND FLOODING THREAT
BEGINNING IN THE MID TO LATE AFTERNOON AND CONTINUING INTO
TONIGHT. THIS WILL OCCUR AS A STRONG COLD FRONT APPROACHES THE
AREA IN THE AFTERNOON AND PUSHES THROUGH AT NIGHT. MEANWHILE THE
UPPER LEVEL TROUGH WILL PIVOT ACROSS THE GREAT LAKES AND MID
ATLANTIC THROUGH THE DAY BEFORE PUSHING OFFSHORE OVERNIGHT
TONIGHT INTO TUESDAY MORNING. LOCALLY DAMAGING WIND GUSTS WILL
BE THE MAIN SEVERE WEATHER THREAT, BUT AN ISOLATED TORNADO OR
TWO CANNOT BE RULED OUT. HEAVY RAIN FROM THESE STORMS WILL ALSO
BRING THE RISK OF FLASH FLOODING ACROSS THE REGION WITH THE
HIGHEST THREAT FOR THIS BEING IN THE URBAN CORRIDOR FROM AROUND
WILMINGTON NORTH AND EAST THROUGH PHILLY AND TRENTON.
AHEAD OF THE COLD FRONT, MOSTLY CLOUDY SKIES HAVE GIVEN WAY TO
PARTLY/MOSTLY SUNNY SKIES. TEMPERATURES WILL WARM INTO THE LOW
TO MID 70S, THOUGH MANY LOCATIONS ARE RUNNING A FEW DEGREES
WARMER THAN INITIALLY FORECAST. AS A RESULT, WE COULD SEE
OVERALL INSTABILITY CREEP UP THIS AFTERNOON, POSSIBLY EXCEEDING
1000 J/KG OF MUCAPE IN SPOTS, WHICH WOULD HELP MORE STORMS
POTENTIALLY REACH SEVERE CRITERIA. REGARDLESS, THERE WILL BE
VERY STRONG DYNAMICS AND SHEAR IN PLACE, THUS MUCH OF THE REGION
REMAINS IN THE SLIGHT RISK FOR SEVERE WEATHER FROM THE STORM
PREDICTION CENTER. DEEP LAYER SHEAR (0-6 KM) WILL RANGE IN THE
40-50 KT RANGE, SUPPORTING THE POTENTIAL FOR SEVERE
THUNDERSTORMS WITH DAMAGING WIND GUSTS. IT IS ALSO WORTH NOTING
THAT THE 0-1 KM SHEAR AND HELICITY LOOK TO BE QUITE HIGH, IN
ADDITION TO 0-3 KM BULK SHEAR AROUND 30-35 KTS WITH VEERING
HODOGRAPHS. AS A RESULT, AN ISOLATED TORNADO OR TWO WILL BE
POSSIBLE.
THE BEST CHANCE FOR SEVERE THUNDERSTORMS WILL COME DURING THE
AFTERNOON THROUGH EARLY EVENING TIMEFRAME. BETTER DYNAMICS
ARRIVE ACROSS THE REGION TO INITIATE CONVECTION SOMETIME FROM
3-5 PM EDT, MAINLY ACROSS EASTERN PA AND WESTERN DELMARVA. A FEW
EARLIER SHOWERS AND PERHAPS AN ISOLATED THUNDERSTORM MAY ARRIVE
IN THE MORNING/EARLY AFTERNOON, BUT THESE ARE NOT EXPECTED TO
BE SEVERE. AS THE STRONGER CONVECTION INITIATES AFTER 2 PM, SOME
THUNDERSTORMS COULD START OFF MORE DISCRETE IN NATURE,
MAXIMIZING ANY SEVERE POTENTIAL THERE MAY BE. 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 WILL BEGIN TO INCREASE.
THE HEAVY RAIN AND FLASH FLOODING THREAT WILL BE HIGHEST
THROUGH THE MID TO LATE 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.
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/
A BRIEF COOL DOWN AHEAD FOR TUESDAY THROUGH WEDNESDAY AS A
COLDER AND DRIER AIRMASS PUSHES INTO THE AREA. TEMPERATURES
CLOSER TO CLIMATOLOGICAL NORMALS DURING THIS PERIOD ALONG WITH
FAIR WEATHER CONDITIONS.
UPPER TROUGHING WILL PUSH OFFSHORE ON TUESDAY, THEN RIDGING
WILL RETURN INTO WEDNESDAY. AT THE SURFACE, COLD AND DRY
CANADIAN HIGH PRESSURE WILL BRIEFLY BUILD INTO THE AREA TUESDAY
THROUGH TUESDAY NIGHT BEFORE DEPARTING INTO WEDNESDAY. A WARM
FRONT WILL RETURN NORTH THROUGH THE AREA WEDNESDAY NIGHT.
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.
THE HIGH PRESSURE WILL START SHIFTING EAST TUESDAY NIGHT, WHICH
WILL SWITCH SURFACE WINDS TO THE NORTHEAST TO EAST. WINDS
REMAIN ELEVATED NEAR 5-10 MPH MUCH OF THE NIGHT ON THE FRINGE OF
THE HIGH, THOUGH THE TYPICAL COLD SPOTS COULD GO CALM AND
RADIATE BETTER. MID LEVEL MOISTURE WILL INCREASE AHEAD OF THE
NEXT SYSTEM AS WELL, SO RADIATIONAL COOLING WILL NOT BE OPTIMAL.
THIS IS NOTEWORTHY BECAUSE THE FROST/FREEZE PROGRAM BEGINS
APRIL 1 (TUESDAY) FOR OUR DELMARVA COUNTIES. THE DRY AIRMASS AND
PERSISTENT LIGHT BREEZE OVERNIGHT WILL LIKELY NOT SUPPORT ANY
FROST DEVELOPMENT DESPITE LOW TEMPERATURES IN THE MID TO UPPER
30S. FARTHER NORTH INTO NJ AND PA, LOW TEMPERATURES WILL BE IN
THE UPPER 20S TO MID 30S.
FOR WEDNESDAY, THE HIGH WILL CONTINUE TO DEPART THE REGION.
HOWEVER, THE MODIFIED CANADIAN AIRMASS WILL BE ADVECTING IN OFF
THE COLD OCEAN WITH A SOUTHEAST BREEZE INCREASING TO 10-15 MPH
WITH GUSTS UP TO 25 MPH. THIS PATTERN WON'T BRING ANY SURFACE
"WARM" ADVECTION TO OUR AREA DURING THE DAY DESPITE UPPER LEVEL
WARM ADVECTION BEGINNING, SO TEMPERATURES WILL ACTUALLY END UP
BEING A FEW DEGREES COOLER THAN TUESDAY IN MOST AREAS.
INCREASING CLOUDS WON'T HELP EITHER. LOW LEVEL WARM ADVECTION
WON'T REALLY BEGIN UNTIL LATE AFTERNOON OR EVENING, WHEN THE
WARM FRONT WILL FINALLY START LIFTING NORTH THROUGH THE AREA AS
WINDS SHIFT MORE SOUTHERLY.
HIGHS WEDNESDAY ARE MAINLY IN THE LOW TO MID 50S. CLOSER TO 60
DEGREES FOR DELMARVA AND THE HIGHER ELEVATIONS LIKELY REMAINING
STUCK IN THE 40S. TEMPERATURES WON'T FALL MUCH WEDNESDAY EVENING
(EVENING LOWS MAINLY IN THE 40S), AND WILL START RISING INTO
THE 50S OVERNIGHT IN MOST AREAS. A FEW SHOWERS POSSIBLE
WEDNESDAY NIGHT AS THE WARM ADVECTION RAMPS UP, BUT THIS WILL BE
ISOLATED TO SCATTERED IN NATURE AND INSIGNIFICANT WITH REGARDS
TO ANY MEASURABLE RAINFALL.
LONG TERM /THURSDAY THROUGH SUNDAY/
EAST COAST RIDGING WILL BE THE MAIN SYNOPTIC PATTERN FROM LATE
WEEK THROUGH THE WEEKEND. WE WILL CLOSE OUT THE WEEK THURSDAY
AND FRIDAY WITH ABOVE NORMAL TEMPERATURES, THEN RETURN TO MORE
MILD CONDITIONS WITH TEMPERATURE CLOSER TO NORMAL OVER THE
WEEKEND.
LOW PRESSURE WILL PASS NORTH OF THE AREA ON THURSDAY. AS THE
LOW DEPARTS THURSDAY NIGHT, THE WARM SECTOR WILL BE ORPHANED, SO
TO SPEAK, WITH THE FRONTAL BOUNDARY LINGERING TO OUR NORTH INTO
FRIDAY. THE BOUNDARY WILL PUSH SOUTHWARD FRIDAY NIGHT AS UPPER
AND SURFACE RIDGING RETREAT SOUTHWARD A BIT. THE BOUNDARY WILL
THEN BE SOUTH OF OUR AREA THROUGH THE WEEKEND. SEVERAL WEAK
TROUGHS WILL RIDE ALONG THIS BOUNDARY FROM LATE WEEK AND THROUGH
THE WEEKEND, WHICH WILL TRANSLATE TO A GENERALLY UNSETTLED
PATTERN FOR THE REGION. SEVERAL ROUNDS OF SHOWERS LIKELY.
INSTABILITY WILL BE SUFFICIENT FOR THUNDERSTORMS BY THURSDAY
NIGHT, BUT SEVERE CONVECTION IS NOT ANTICIPATED GIVE THE
SYNOPTIC SETUP, MAINLY JUST SHOWERS WITH EMBEDDED THUNDER. THE
USUAL GARDEN VARIETY SPRING CONVECTIVE ACTIVITY. BEYOND THURSDAY
NIGHT, THUNDERSTORMS ARE UNLIKELY, BUT SHOWERS WILL REMAIN
POSSIBLE EACH DAY, ESPECIALLY OVER THE WEEKEND WHEN FORCING IS
MAXIMIZED. LONG STORY SHORT, ACTIVE AND UNSETTLED SHOWERY
WEATHER, BUT NOTHING PARTICULARLY SIGNIFICANT OR IMPACTFUL TO
SPEAK OF.
HIGH TEMPERATURES THURSDAY AND FRIDAY MAINLY FROM 70 TO 80
DEGREES, WARMEST THURSDAY WHEN THE WARM ADVECTION IS STRONGEST.
QUITE MILD THURSDAY NIGHT WITH LOWS IN THE MID 50S TO MID 60S.
TURNING COOLER INTO THE WEEKEND ONCE THE FRONT IS SOUTH OF US.
HIGHS SATURDAY AND SUNDAY IN THE 50S TO MID 60S, AND LOWS MAINLY
IN THE 40S.
AVIATION /18Z 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.
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 KNOTS.
OUTLOOK...
TUESDAY THROUGH WEDNESDAY...VFR. GUSTY WINDS, OTHERWISE NO
SIGNIFICANT WEATHER.
WEDNESDAY NIGHT THROUGH FRIDAY...CHANCES FOR SHOWERS THROUGH
THE PERIOD, ALONG WITH SOME PERIODS OF RESTRICTIONS LIKELY.
GUSTY SOUTH TO SOUTHWEST WINDS ON THURSDAY, WITH POTENTIAL FOR
THUNDERSTORMS THURSDAY NIGHT.
MARINE
SMALL CRAFT ADVISORY CONDITIONS CONTINUING THROUGH TONIGHT DUE
TO ELEVATED WINDS AND SEAS. SW WINDS GENERALLY AROUND 20 GUSTING
TO AROUND 25-30 KNOTS WITH SEAS 5 TO 7 FEET. WINDS SHIFT TO
NORTHWEST OVERNIGHT TO NIGHT. THE OTHER HAZARD EARLY THIS
MORNING WILL BE REDUCED VISIBILITY OVER OUR NORTHERN OCEAN ZONES
WHERE A MARINE DENSE FOG ADVISORY REMAINS IN EFFECT FOR OUR
ZONES OFF THE COAST OF OCEAN AND MONMOUTH COUNTIES. THIS IS IN
EFFECT UNTIL 9 AM. FINALLY, EXPECT SOME HEAVY SHOWERS AND STORMS
OVER THE WATERS THIS EVENING INTO TONIGHT AND THIS COULD
PRODUCE LOCALIZED WIND GUSTS OVER 40 KNOTS.
OUTLOOK...
TUESDAY...ADVISORY CONDITIONS CONTINUING THROUGH MIDDAY WITH
NORTHWEST WIND GUSTS 20-25 KTS AND SEAS REMAINING NEAR 4-6 FEET.
CONDITIONS IMPROVING BY LATE IN THE DAY. THE SMALL CRAFT
ADVISORY WAS EXTENDED TO COVER THIS PERIOD.
TUESDAY NIGHT THROUGH WEDNESDAY...NO MARINE HAZARDS EXPECTED.
WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...ADVISORY CONDITIONS
LIKELY. WIND GUSTS UP TO 30 KTS AND SEAS BUILDING 4-6 FEET.
SCATTERED SHOWERS WITH THUNDERSTORMS POSSIBLE THURSDAY NIGHT.
FRIDAY...NO MARINE HAZARDS EXPECTED. CHANCES FOR SHOWERS.
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 4 PM EDT TUESDAY FOR ANZ450>455.
SYNOPSIS...STAARMANN
NEAR TERM...AKL/FITZSIMMONS/MJL
SHORT TERM...STAARMANN
LONG TERM...STAARMANN
AVIATION...FITZSIMMONS/MJL/STAARMANN
MARINE...FITZSIMMONS/JOHNSON/MJL/STAARMANN
TIDES/COASTAL FLOODING...
CLIMATE...
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