270
FXUS61 KPHI 081041
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
641 AM EDT THU MAY 8 2025
SYNOPSIS
WEAK HIGH PRESSURE WILL BE ACROSS THE NORTHERN MIDDLE ATLANTIC
REGION EARLY TODAY. AFTER THAT, A UPPER LEVEL TROUGH AND A
SURFACE FRONT ARRIVE FROM THE WEST FOR LATE TODAY AND TONIGHT.
LOW PRESSURE DEVELOP ALONG THE FRONT AND MOVES ACROSS THE AREA
FRIDAY. HIGH PRESSURE BUILDS IN OVER THE WEEKEND. MORE LOW
PRESSURE APPROACHED THE AREA EARLY NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
AN UPPER LEVEL TROUGH WILL DIG INTO THE REGION THURSDAY,
PUSHING A COLD FRONT TOWARDS THE REGION THIS AFTERNOON. THE
UPPER LEVEL TROUGH WILL THEN BECOME CUT OFF FROM THE MAIN POLAR
JET STREAM AND BECOME A CLOSED LOW ACROSS SOUTHERN ONTARIO
THURSDAY EVENING AND INTO THE OVERNIGHT HOURS.
THURSDAY MORNING WILL BEGIN MOSTLY DRY ACROSS THE REGION WITH MOSTLY
ZONAL FLOW ALOFT. AS WE WORK INTO THE AFTERNOON, THE UPPER LEVEL
TROUGH WILL BEGIN TO DIG ACROSS SOUTHERN NEW ENGLAND AND THE MID
ATLANTIC, PUSHING A COLD FRONT SOUTH AND EAST INTO THE REGION. LIGHT
SOUTH TO SOUTHEAST FLOW AHEAD OF THE FRONT WILL ALLOW FOR SOME
LIMITED INSTABILITY AND MOISTURE TO ADVECT INTO THE REGION,
SUPPORTING THE DEVELOPMENT OF SCATTERED SHOWERS AND THUNDERSTORMS
ALONG THE FRONTAL BOUNDARY. SEVERE PARAMETERS DO NOT LOOK OVERLY
FAVORABLE, THOUGH MODEST LOW-LEVEL LAPSE RATES (AROUND 8.0C/KM) MAY
HELP CONVECTION INITIATE RATHER EASILY. THERE REMAINS A HIGHER THAN
USUAL LEVEL OF UNCERTAINTY HOW QUICKLY THE FRONT WILL PUSH SOUTH AND
EAST INTO THE REGION, BUT THE GENERAL CONSENSUS IS THAT THE BEST
CHANCE FOR SHOWERS AND THUNDERSTORMS THROUGH THE AFTERNOON WILL BE
NORTH AND WEST OF THE I-95 CORRIDOR. HIGHS WILL BE IN THE 70S FOR
MOST AREAS (60S IN THE FAR NORTHWEST).
TRANSITIONING INTO THE EVENING AND OVERNIGHT HOURS, OUR UPPER LEVEL
TROUGH WILL BEGIN TO BECOME CUT OFF FROM THE MAIN POLAR JET STREAM
AND TRANSITION INTO A CLOSED LOW. A RATHER ROBUST SHORTWAVE PULSE
ALONG THE SOUTHERN FLANK OF THIS CUT-OFF LOW WILL DIG ACROSS THE
OHIO RIVER VALLEY, PROVIDING BAROCLINIC FORCING ACROSS THE GREATER
DELAWARE VALLEY. SHOWERS WITH EMBEDDED THUNDERSTORMS WILL BECOME
MORE NUMEROUS THROUGHOUT THE EVENING AND INTO THE OVERNIGHT HOURS AS
LIMITED INSTABILITY PERSIST. RAIN MAY BE LOCALLY HEAVY AT TIMES,
WITH PWAT VALUES INCREASING TO AROUND 1 TO 1.5 INCHES. THE HEAVIEST
RAINFALL WILL LIKELY START OFF NEAR AND AROUND WHERE THE FRONTAL
BOUNDARY SETS UP FOR THE EVENING, BUT GUIDANCE SUGGESTS THE BROAD
SCALE ASCENT WILL MAKE THESE SHOWERS AND STORMS OVERSPREAD THE
REGION BY EARLY FRIDAY MORNING. LOWS ON THURSDAY NIGHT WILL RANGE
FROM THE 40S IN THE NORTHWEST TO THE 50S FOR MOST OTHER LOCATIONS.
FOR THURSDAY AND THURSDAY NIGHT, GENERAL RAINFALL AMOUNTS LOOK TO BE
AROUND 0.5 TO 1.5 INCHES ALONG THE I-95 CORRIDOR AND POINTS NORTH
AND WEST. AREAS SOUTH AND EAST LOOK TO HAVE 0.25 TO 1.0 INCH OF
RAIN.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/
FRIDAY, THE STORM SYSTEM THAT BEGINS LATER THURSDAY CONTINUES ACROSS
THE REGION FRIDAY AND FRIDAY NIGHT. CATEGORICAL POPS FRIDAY DECREASE
FROM SW TO NE THRU THE DAY LEAVING CHANCE POPS (N/E) FOR THE
OVERNIGHT FRI PERIOD. SCATTERED TSTMS ARE EXPECTED AS WELL. HEAVY
RAINS WHICH BEGIN LATER THURSDAY CONTINUE FRIDAY WITH EVENTUAL STORM
TOTALS REACHING 1 TO 2 INCHES ACROSS THE AREA. TEMPS FRIDAY WILL BE
COLD WITH READINGS ONLY TOPPING OUT IN THE LOW/MID 60S WITH ONLY 50S
ACROSS THE NORTH/WEST AREAS.
SATURDAY, THE LOW PRESSURE SYSTEM OFF TO THE NORTHEAST AND THE UPPER
LOW ACROSS NORTH NJ PULL AWAY AS HIGH PRESSURE BEGINS TO BUILD IN
FROM THE WEST. ANY LINGERING SHOWERS ACROSS THE NORTH/WEST AREAS
DURING THE EARLY MORNING WILL END AS DRIER AND COOLER AIR ARRIVE
ACROSS THE REGION. IT WILL BE RATHER WINDY SATURDAY WITH STRONG COLD
AIR ADVECTION OCCURRING THRU THE MORNING. WINDS WILL GUST BETWEEN 20
AND 25 MPH THROUGHOUT THE DAY. TEMPERATURES WILL BE CHILLY WITH
READINGS DURING THE EARLY MORNING IN THE 50S AND HIGHS ONLY EXPECTED
TO RISE TO THE UPPER 60S N/W AND LOW 70S ELSEWHERE. SKIES WILL HAVE
SOME CLOUDS EARLY, BUT THEN BECOME MOSTLY SUNNY BY AFTERNOON.
LONG TERM /SUNDAY THROUGH WEDNESDAY/
A MIXED BAG FOR THE LONG TERM WITH NICE WEATHER AT THE END OF THE
WEEKEND AND INTO MONDAY, THEN POORER CONDITIONS WITH A SLOW MOVING
UPPER LOW MOVING IN FROM THE SOUTH.
SUNDAY AND MONDAY BOTH LOOK FAIR AS THE SURFACE HIGH WILL RIDGE
ACROSS THE AREA DURING THE AFTERNOON/EVENING BEFORE MOVING OFFSHORE.
TEMPERATURES WILL HAVE RECOVERED FROM THE COOL TEMPS OF THE SHORT
TERM WITH READINGS MAKING IT BACK TO NORMAL LEVELS (OR PERHAPS A BIT
MILDER) FOR SUNDAY AND CONTINUING INTO MONDAY. NORMAL HIGHS FOR
EARLY MAY ARE MID 70S FOR PHILADELPHIA AND SURROUNDING AREAS, LOW
70S FOR ALLENTOWN AND READING AND MID 60S FOR MOUNT POCONO. LOWS
MOSTLY 50S WITH MID/UPPER 40S FAR NORTH/WEST.
A LOW PRESSURE SYSTEM AMBLES NORTHEAST TOWARDS THE MIDDLE ATLANTIC
LATER MONDAY AND THRU MIDWEEK. ONSHORE FLOW AHEAD OF THE LOW WILL
BRING CLOUDS MON NIGHT TO MOST AREAS AND HIGHER CHANCES FOR RAINS
FOLLOW FOR TUE/WED. WE WILL HAVE CHANCE POPS FOR TUE AND LIKELY POPS
IN THERE FOR WED. TEMPS WILL BE NEAR NORMAL TUE AND THEN ABOVE
NORMAL WED. A TREND TOWARDS WARMER TEMPS COULD EXTEND INTO THU AS
WELL.
AVIATION /12Z THURSDAY THROUGH MONDAY/
THURSDAY...VFR THROUGH 18Z-20Z, THEN MVFR IN SHRA LATE IN THE DAY.
VCTS AFTER 18Z; GREATEST CHANCE MAINLY FOR RDG/ABE. LGT/VRB WINDS,
BECOMING S 5 TO 10 KT LATE IN THE DAY. MODERATE CONFIDENCE OVERALL.
THURSDAY NIGHT...SUB-VFR CONDITIONS DEVELOP AFTER 02Z OR SO WITH
PERIODS OF RAIN SHOWERS AND ISOLATED TO SCATTERED THUNDERSTORMS.
RAIN BECOMES MORE WIDESPREAD OVERNIGHT. PERIOD OF IFR CEILINGS
POSSIBLE AFTER 06Z. LIGHT AND VARIABLE WINDS, MAINLY FROM THE E TO
NE.
OUTLOOK...
FRIDAY...SUB-VFR WITH SHOWERS AND A CHANCE OF TSTMS.
FRIDAY NIGHT... CONDITIONS IMPROVING BACK TO VFR FROM SW TO NE
OVERNIGHT.
SATURDAY... VFR. GUSTY W TO NW WINDS UP TO 25 KTS.
SUNDAY/MONDAY... VFR EXPECTED.
MARINE
MARINE CONDITIONS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT CRITERIA.
LIGHT ONSHORE FLOW DEVELOPS THURSDAY AND THURSDAY NIGHT WITH SE TO
ESE FLOW AROUND 10 KTS OR LESS. SEAS WILL REMAIN AROUND 2 TO 4 FEET.
SHOWERS AND THUNDERSTORMS DEVELOP OVER THE WATERS MAINLY AT NIGHT.
OUTLOOK...
FRIDAY/FRIDAY NIGHT... SUB-SCA WITH RAIN AND SCATTERED TSTMS.
SATURDAY... SCA PROBABLE. FAIR WEATHER.
SAT NIGHT THRU MONDAY... SUB-SCA WITH FAIR WEATHER.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.
SYNOPSIS...MJL
NEAR TERM...MJL
SHORT TERM...OHARA
LONG TERM...OHARA
AVIATION...MJL/OHARA
MARINE...MJL/OHARA
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