751
FXUS61 KPHI 202048
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
348 PM EST WED NOV 20 2024
SYNOPSIS
AS LOW PRESSURE TRACKS INTO THE GREAT LAKES REGION, AN ASSOCIATED
STRONG COLD FRONT MOVES ACROSS OUR AREA LATER TONIGHT AND THURSDAY
WITH SOME MUCH NEEDED RAIN AND HIGHER ELEVATION SNOW. A NEW LOW
DEVELOPS OFF THE COAST AND THEN SHIFTS WESTWARD AND MEANDERS IN OUR
REGION DURING THURSDAY AND FRIDAY KEEP OUR WEATHER UNSETTLED. THE
LOW THEN GRADUALLY MOVES AWAY THROUGH THE WEEKEND. WEAK HIGH
PRESSURE BRIEFLY ARRIVES FOR LATER SUNDAY AND MONDAY, FOLLOWED BY A
COLD FRONT MONDAY NIGHT INTO TUESDAY.
NEAR TERM /THROUGH THURSDAY/
345 PM...AS OF MID AFTERNOON, STILL QUITE A BIT OF LOW STRATUS
OVER THE AREA WITH THE NEXT SYSTEM, A BROAD AND OCCLUDING LOW,
LOCATED OVER THE GREAT LAKES. THE TRIPLE POINT IS LOCATED NEAR
OHIO / WESTERN PA WITH A WARM FRONT RUNNING TO THE EAST TOWARDS
DELMARVA. EXPECT RAIN/SHOWERS ASSOCIATED WITH THIS SYSTEM TO
MOVE EAST AND FILL IN A BIT MORE AS IT NEARS AND THEN MOVES IN
OVER OUR AREA WEST TO EAST THIS EVENING.
AS THE INITIAL LOW BEGINS TO LIFT NORTH OF OUR REGION, A NEW SURFACE
LOW LOOKS TO DEVELOP AT THE TRIPLE POINT OF THE OCCLUDED, WARM, AND
TRAILING COLD FRONTS, MORE OR LESS RIGHT OVER OUR REGION. AS A
RESULT, AREAS OF RAINFALL ACROSS DELMARVA AND SOUTHERN NEW JERSEY
MAY BECOME A BIT MORE CONVECTIVE IN NATURE IN THE DEVELOPING WARM
SECTOR AND A RUMBLE OF THUNDER CAN'T BE COMPLETELY RULED OUT. AREAS
FURTHER NORTH LOOK TO REMAIN WITHIN THE STRATIFORM REGION OF THE
SYSTEM ON THE NORTH AND WEST SIDES OF THE DEVELOPING LOW. THE
DEVELOPMENT OF THIS LOW AND PASSAGE OF THE ASSOCIATED FRONTS AT THE
SURFACE WILL RESULT IN A RAPID WIND SHIFT OCCURING ACROSS THE
REGION, FROM SOUTHEAST OUT AHEAD TO NORTHWEST BEHIND, WITH WINDS
BECOMING GUSTY TO AT LEAST 20-30 MPH AS THE PRESSURE GRADIENT
TIGHTENS AS A RESULT OF THE DEVELOPING LOW. IN FACT WE EXPECT A
BRIEF PERIOD OF A FEW HOURS WHERE GUSTS OF 40 TO 50 MPH ARE LIKELY
OVER MUCH OF DELMARVA LATER THIS EVENING INTO THE OVERNIGHT. FOR
THIS REASON, WIND ADVISORY HAS BEEN ISSUED RUNNING FROM 10PM - 4AM.
OVERALL, RAINFALL AMOUNTS STILL REMAIN LARGELY UNCHANGED WITH 0.5
INCHES TO 1+ INCHES EXPECTED ACROSS THE AREA TONIGHT.
HEADING INTO THURSDAY, THE LOW CONTINUES TO MEANDER NEAR OUR AREA,
AS IT WILL BE PIVOTING TO THE NORTH AND POTENTIALLY NORTHWEST AS IT
MOVES CYCLONICALLY AROUND A LARGE CLOSED UPPER LEVEL LOW. AS A
RESULT, CONTINUING RAINFALL IS FORECAST ACROSS MUCH OF THE NORTHERN
HALF OF THE REGION, PARTICULARLY NORTH OF THE I-78 CORRIDOR. AN
ADDITIONAL 0.25-0.75 INCHES OF RAINFALL IS FORECAST FOR THIS AREA.
DRIER AIR WILL BEGIN TO MOVE IN FOR AREAS FARTHER SOUTH (SE PA,
SOUTH JERSEY, DELMARVA) SO WE AREN'T EXPECTING A LOT MORE RAIN HERE
THOUGH THERE WILL BE SOME WRAP AROUND SHOWERS. COLD AIR ADVECTION
WILL ALSO BE RAMPING UP ACROSS THE REGION, AS GUSTY WEST-NORTHWEST
WINDS CONTINUE. HIGHS ARE FORECAST TO BE ONLY IN THE 40S TO LOW 50S.
BY LATER IN THE AFTERNOON, TEMPERATURES AT THE HIGHEST ELEVATIONS IN
THE SOUTHERN POCONOS LOOK TO BECOME COOL ENOUGH FOR ONGOING TO
PRECIPITATION TO CROSSOVER FROM RAIN TO A RAIN/SNOW MIX, AND
EVENTUALLY SNOW.
SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/
STRONG LOW PRESSURE WILL BE LOCATED NEAR NEW YORK CITY THURSDAY
EVENING, WITH STRONG AND GUSTY NORTHWEST WINDS FUNNELING COOLER AIR
SOUTHEASTWARD ACROSS THE REGION. THE UPPER LOW WILL REMAIN TO OUR
WEST IN THE UPPER OHIO VALLEY, AND AS THAT FEATURE HEADS EAST, THE
SURFACE LOW WILL ACTUALLY RETROGRADE SLIGHTLY, WITH IT BECOMING
"CAPTURED" OVER OUR NORTHERN AREAS EARLY FRIDAY. STRONG FORCING OVER
OUR NORTHERN ZONES RELATIVELY CLOSE TO THE SURFACE LOW AND NORTHEAST
OF THE UPPER LOW WILL RESULT IN CONTINUING PRECIPITATION THROUGH THE
NIGHT, WITH PRECIPITATION TAPERING OFF FARTHER SOUTH AND MOSTLY DRY
CONDITIONS IN THE DELMARVA. WITH THE COLD ADVECTION AT THE SURFACE
AND ALOFT, ODDS FAVOR A TRANSITION TO HEAVY WET SNOW ACROSS THE
HIGHER TERRAIN, ESPECIALLY ABOVE 1500 FEET ON THE POCONO PLATEAU AND
POSSIBLY A FEW HIGHER RIDGES ELSEWHERE IN EASTERN PA AND NORTHERN
NJ. WITH THE BEST ODDS OF HEAVY WET SNOW BEING ACROSS THE POCONOS, A
WINTER STORM WATCH REMAINS IN EFFECT THOUGH AGAIN, IT WILL BE MAINLY
THE HIGHER ELEVATIONS AROUND AND ABOVE 1500 FEET THAT WE ARE
THINKING FOR AMOUNTS OF 6+ INCHES. LOWER ELEVATIONS MAY SEE FAR LESS
SNOWFALL, IN FACT THE LOWEST VALLEYS EVEN UP THERE MAY FAIL TO GET
AN ENTIRE INCH OF ACCUMULATION WITH THIS ELEVATION-DEPENDENT SYSTEM.
AS THIS WILL BE A HEAVY WET SNOW WITH SIGNIFICANT WIND IN THE 20-30
MPH RANGE, A BIG POTENTIAL IS THERE FOR DOWNED TREES AND POWER
LINES. TRAVEL THURSDAY NIGHT IN PARTICULAR IS DISCOURAGED.
THERE ARE A FEW SIMULATIONS WHICH IMPLY SNOW COULD REACH
SIGNIFICANTLY FARTHER SOUTH ACROSS OUR REGION, EVEN DOWN TO THE I-95
CORRIDOR AND PHILLY METRO, PARTICULARLY THE CANADIAN MODELS. FOR THE
MOMENT WE'VE MOSTLY DISCOUNTED THAT GUIDANCE AS BEING OUTLIERS, BUT
WILL BE KEEPING IT IN MIND AS WE WATCH FURTHER PROGRESS WITH THIS
SYSTEM. HAVE ALLOWED FOR SOME MIXING ACROSS AREAS JUST NORTH AND
WEST OF THE I-95 CORRIDOR THURSDAY NIGHT INTO EARLY FRIDAY, BUT
LITTLE TO NO ACCUMULATION IS CURRENTLY EXPECTED OUTSIDE THE POCONOS.
EITHER WAY, BRISK AND COLD WILL BE THE THEM FOR THURSDAY NIGHT, WITH
LOWS IN THE 30S FOR MOST, UPPER 20S PERHAPS IN THE HIGHER TERRAIN OF
THE POCONOS.
FOR THE BULK OF FRIDAY, THE SURFACE LOW WILL REMAIN CAPTURED UNDER
THE UPPER LOW OVER OUR REGION, RESULTING IN CONTINUING SHOWERS.
ENOUGH INSOLATION LIKELY DEVELOPS TO ALLOW A TRANSITION FROM A
RAIN/SNOW MIX TO JUST PLAIN RAIN AT THE LOWER ELEVATIONS, WITH
SIGNIFICANTLY LESS ACCUMULATION IN THE HIGHER TERRAIN AS WELL, WITH
PRECIPITATION STARTING TO TAPER OFF TOWARDS THE END OF THE DAY AS WE
START TO SEE SOME MOVEMENT EASTWARD AND THE SURFACE LOW BEGINS TO
SLOWLY FILL. REGARDLESS, A CHILLY, RAW DAY WILL BE HAD BY MOST WITH
TEMPS GENERALLY NO HIGHER THAN THE 40S REGION-WIDE, WITH TEMPS NOT
STRAYING FAR FROM FREEZING IN THE POCONOS.
PRECIP SHOULD MOSTLY END DURING THE EVENING FRIDAY AS THE SURFACE
AND UPPER LOWS BEGIN MOVING FURTHER EAST, BUT THE BRISK CONDITIONS
CONTINUE. LOWS IN THE 30S FOR MOST, UPPER 20S POCONOS. WE EXPECT
STORM TOTAL LIQUID PRECIP AMOUNTS TO BE HIGHEST NORTH AND LOWEST
SOUTH. GENERALLY EXPECT UPWARDS OF 2 TO 3 INCHES QUANTITATIVE PRECIP
OVER NE PA INTO NW NJ (SOME OF THIS FALLING AS SNOW) WITH 1 TO 2
INCHES TOTAL FARTHER SOUTH OVER SE PA INTO ADJACENT SOUTH JERSEY
WITH A HALF INCH TO AN INCH OVER DELMARVA.
AS THE STORM PULLS FURTHER AWAY TO OUR NORTHEAST SATURDAY, A GUSTY
NORTHWEST WIND WILL CONTINUE AND CLOUDS WILL LINGER, WITH SOME
SPOTTY SHOWERS IN THE POCONOS, BUT OVERALL, SIGNIFICANTLY IMPROVED
COMPARED TO FRIDAY. EXPECT HIGHS MOSTLY IN THE UPPER 40S TO LOW
50S.
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
SUMMARY...TEMPERATURES SHOULD TURN MILDER MONDAY AHEAD OF A COLD
FRONT, THEN COOLING TAKES PLACE. SOME LOW SHOWER CHANCES LATE
MONDAY INTO TUESDAY WITH A COLD FRONT.
SYNOPTIC OVERVIEW...A STRONG CLOSED LOW IS FORECAST TO GRADUALLY
MOVE ACROSS PORTIONS OF THE CANADIAN MARITIMES THROUGH SUNDAY. AS
THIS OCCURS, THE CYCLONIC FLOW ACROSS OUR REGION EASES INTO SUNDAY
WITH THE FLOW ALOFT BECOMING MORE ZONAL THROUGH EARLY NEXT WEEK. A
SHORTWAVE TROUGH HOWEVER MAY SLIDE ACROSS THE NORTHEAST TUESDAY. AT
THE SURFACE, STRONG LOW PRESSURE IS FORECAST TO SHIFT NORTHEASTWARD
ACROSS PORTIONS OF THE CANADIAN MARITIMES IN TANDEM WITH THE CLOSED
LOW THROUGH SUNDAY. WEAK HIGH PRESSURE BRIEFLY BUILDS IN LATER
SUNDAY INTO MONDAY, THEN LOW PRESSURE TRACKING TO OUR NORTH PULLS A
COLD FRONT ACROSS OUR AREA MONDAY NIGHT INTO TUESDAY. HIGH PRESSURE
THEN STARTS TO EXTEND EASTWARD TOWARD OUR AREA WEDNESDAY.
FOR SATURDAY NIGHT AND SUNDAY...A CLOSED LOW GRADUALLY SHIFTS ACROSS
PARTS OF THE CANADIAN MARITIMES AND THEREFORE THE CYCLONIC FLOW
EASES INTO SUNDAY WITH THE FLOW TURNING MORE ZONAL THEREAFTER.
STRONG SURFACE LOW PRESSURE WILL FOLLOW THE CLOSED LOW, HOWEVER A
TIGHTENED PRESSURE GRADIENT REMAINS ACROSS OUR AREA SATURDAY NIGHT
THROUGH MUCH OF SUNDAY AS HIGH PRESSURE APPROACHES FROM THE WEST AND
SOUTH. A NOTABLE BREEZE THEREFORE WILL CONTINUE, HOWEVER THIS SHOULD
START TO EASE SOME SUNDAY AND ESPECIALLY SUNDAY NIGHT. TEMPERATURES
MAY EDGE UPWARD A LITTLE SUNDAY GIVEN HEIGHTS ALOFT STARTING TO
RISE. OTHER THAN A SNOW OR RAIN SHOWER SATURDAY NIGHT INTO THE
POCONO REGION, DRIER AIR IS EXPECTED TO CONTINUE TO OVERSPREAD THE
AREA. SOME MORE SUNSHINE SHOULD ALSO OCCUR ESPECIALLY DURING SUNDAY
AS THE INFLUENCE OF THE CLOSED LOW WANES, THEN CLOUDS MAY START
TO INCREASE SOME AGAIN SUNDAY NIGHT AHEAD OF THE NEXT COLD FRONT.
FOR MONDAY THROUGH WEDNESDAY...THE FLOW IS FORECAST TO BE MORE ZONAL
WITH WEAK HIGH PRESSURE CRESTING BRIEFLY ACROSS OUR AREA MONDAY.
THIS WILL RESULT IN MUCH LESS WIND. A FAIRLY QUICK MOVING SYSTEM
CROSSING MUCH OF EASTERN CANADA MAY SHARPEN SOME ACROSS THE
NORTHEAST MONDAY NIGHT AND ESPECIALLY TUESDAY. THIS SHOULD DRIVE
SURFACE LOW PRESSURE TO OUR NORTH WITH A COLD FRONT CROSSING OUR
AREA MONDAY NIGHT INTO TUESDAY. AS OF NOW WITH MOISTURE POTENTIALLY
BEING MORE LIMITED, CONTINUED WITH SLIGHT CHANCE POPS (20 PERCENT)
WITH THIS SYSTEM. THE FRONT MAY THEN SETTLE TO OUR SOUTH TUESDAY
INTO WEDNESDAY. HIGH PRESSURE CENTERED ACROSS THE MIDWEST MAY THEN
START TO EXTEND TOWARD OUR AREA DURING WEDNESDAY.
AVIATION /21Z WEDNESDAY THROUGH MONDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
REST OF TODAY...CONDITIONS VARY BETWEEN MVFR AND VFR DEPENDING
ON THE LOCATION EARLY THIS AFTERNOON. ALL SITES COULD BRIEFLY
RETURN TO VFR THIS AFTERNOON. LIGHT AND VARIABLE WINDS WILL
BECOME EAST TO SOUTHEAST AROUND 5 KNOTS. MODERATE CONFIDENCE.
TONIGHT...CONDITIONS ARE EXPECTED TO START OUR VFR EARLY THIS
EVENING, BEFORE ALL LOCATIONS LOWER BACK TO MVFR BY 02-04Z AS
RAIN MOVES INTO THE AREA, WITH A PERIOD OF IFR WITH THE HEAVIEST
RAIN OVERNIGHT BETWEEN 03Z-07Z. AS THE HEAVY RAIN MOVES NORTH
OF THE AREA, CONDITIONS WILL LIKELY RETURN TO MVFR FOR MOST
AREAS. WINDS WILL BEGIN OUT OF THE EAST TO SOUTHEAST AND BECOME
GUSTY 15-20 KNOTS THIS EVENING, BEFORE RATHER ABRUPTLY SHIFTING
TO THE NORTHWEST OVERNIGHT, WITH GUSTS 20-25 KNOTS. MODERATE
CONFIDENCE, OVERALL, LOW CONFIDENCE ON TIMING OF CATEGORY/WIND
CHANGES.
THURSDAY...MVFR, LOCALLY IFR, IN THE MORNING IMPROVING TO VFR
DURING THE AFTERNOON; ABE AND TTN WILL LIKELY KEEP THEIR LOWER
CONDITIONS THROUGH THE DAY. SCATTERED SHOWERS MAY LINGER INTO
THE DAY, ESPECIALLY AT ABE AND TTN. WINDS REMAIN GUSTY OUT OF
THE NORTHWEST 20-25 KNOTS. MODERATE CONFIDENCE.
OUTLOOK...
THURSDAY NIGHT AND FRIDAY...SUB-VFR, WITH POTENTIAL IFR, WITH
SHOWERS, WHICH MAY MIX WITH SNOW AT KRDG AND KABE. NO ACCUMULATIONS
CURRENTLY EXPECTED AT THE TERMINALS. WINDS WILL ALSO BE GUSTY
FROM THE NORTHWEST.
SATURDAY AND SUNDAY...VFR. WEST OR WEST-NORTHWEST WIND GUSTS UP
TO 25 KNOTS, DIMINISHING SUNDAY NIGHT.
MONDAY...VFR OVERALL.
MARINE
WINDS AND SEAS INCREASE THROUGH THIS EVENING. FOR ATLANTIC COASTAL
WATERS SOUTH OF GREAT EGG INLET AND ALONG THE DELAWARE BAY, WINDS
ARE EXPECTED TO BE 20-30 KNOTS WITH GUSTS UP TO 35 KNOTS. A GALE
WARNING IS IN EFFECT BEGINNING AT 11 PM FOR THESE AREAS AS A RESULT.
NORTH OF HERE, EXPECT GALES TO BEGIN OVERNIGHT. AN ABRUPT WIND SHIFT
IS ALSO EXPECTED LATE IN THE EVENING INTO THE OVERNIGHT WITH THE
PASSAGE OF A COLD FRONT.
GALES CONTINUE FOR THURSDAY INTO THURSDAY NIGHT FOR THE
AFORMENTIONED NORTHERN OCEAN ZONES WHILE FARTHER SOUTH WINDS
SHOULD DIMINISH BELOW GALES BY THURSDAY AFTERNOON.
OUTLOOK...
FRIDAY THROUGH FRIDAY NIGHT...POTENT LOW PRESSURE WILL CERTAINLY
RESULT IN HIGH END SMALL CRAFT ADVISORY CONDITIONS AND IN FACT MAY
RESULT IN LOW-END GALES.
SATURDAY SUNDAY...SMALL CRAFT ADVISORY CONDITIONS PROBABLE.
SOME LOW-END GALE FORCE GUSTS POSSIBLE AT TIMES THROUGH
SATURDAY NIGHT. WINDS DIMINISH SUNDAY NIGHT.
MONDAY...THE CONDITIONS ARE ANTICIPATED TO BE BELOW SMALL CRAFT
ADVISORY CRITERIA.
HYDROLOGY
SIGNIFICANT RAINFALL IS FORECAST ACROSS THE REGION FOR THE FIRST
TIME IN MONTHS, WITH WIDESPREAD TOTALS IN EXCESS OF 2 INCHES
EXPECTED ACROSS NORTHERN PARTS OF THE FORECAST AREA. WITH THE
GROUND RELATIVELY DRY AND HARD, WE COULD END UP WITH SOME MINOR
FLOODING ISSUES DUE TO EXCESSIVE RUNOFF, DESPITE HOW LOW WATER
LEVELS ARE PRESENTLY. THESE WOULD MAINLY BE FOR THE FLASHIER
SMALL STREAMS. IN ADDITION, ACCUMULATION OF LEAVES AROUND STORM
DRAINS MAY RESULT IN LOCALIZED ROADWAY ISSUES. THAT ALL HAVING
BEEN SAID, GIVEN THE EXCESSIVE DRYNESS ACROSS THE REGION
PRESENTLY, THERE ARE NO PLANS FOR A FLOOD WATCH AT THIS TIME.
CLIMATE
DRIEST AUTUMN (SEP-NOV) ON RECORD, AND ANY 3-CALENDAR MONTH
PERIOD ON RECORD, PLUS CURRENT STATUS:
9/1-11/19 DRIEST DRIEST 3 YEAR/
SITE 2024 PRECIP AUTUMN YEAR CALENDAR MONTHS MONTHS
ALLENTOWN (ABE) 1.61 3.81 1922 3.58 OCT-DEC 1928
A.C. AIRPORT (ACY) 0.99 3.34 2001 2.35 OCT-DEC 1946
A.C. MARINA (55N) 0.79 2.89 1941 2.52 AUG-OCT 1895
GEORGETOWN (GED) 0.85 2.67 2001 2.20 AUG-OCT 2024
MOUNT POCONO (MPO) 3.17 4.21 1931 3.36 OCT-DEC 1928
PHILADELPHIA (PHL) 1.09 2.37 1922 2.37 SEP-NOV 1922
READING (RDG) 1.42 2.89 1922 2.89 SEP-NOV 1922
TRENTON (TTN) 0.71 3.18 1922 2.66 JUN-AUG 1966
WILMINGTON (ILG) 0.86 3.17 1922 3.17 SEP-NOV 1922
PHI WATCHES/WARNINGS/ADVISORIES
PA...WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR PAZ054-055.
NJ...NONE.
DE...WIND ADVISORY FROM 10 PM THIS EVENING TO 4 AM EST THURSDAY FOR
DEZ002>004.
MD...WIND ADVISORY FROM 10 PM THIS EVENING TO 4 AM EST THURSDAY FOR
MDZ012-015-019-020.
MARINE...GALE WARNING FROM 11 PM THIS EVENING TO NOON EST THURSDAY FOR
ANZ430-431-453>455.
GALE WARNING FROM 1 AM THURSDAY TO 6 AM EST FRIDAY FOR
ANZ450>452.
SYNOPSIS...GORSE/RCM
NEAR TERM...AKL/FITZSIMMONS
SHORT TERM...FITZSIMMONS/RCM
LONG TERM...GORSE
AVIATION...GORSE/ROBERTSON
MARINE...AKL/FITZSIMMONS/GORSE
HYDROLOGY...
CLIMATE...
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