992
FXUS61 KPHI 210650
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
150 AM EST THU NOV 21 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 TODAY/
130 AM...FRONT HAS PASSED THE REGION. IT LOOKS LIKE GUSTS WERE
MOSTLY BELOW 40 KTS BUT WILL LET WIND ADVISORY CONTINUE FOR NOW.
OTHERWISE, THUNDERSTORMS ARE ABATING AND FROM THIS POINT, LOOKS
LIKE MAINLY LIGHTER BUT STEADIER STRATIFORM RAIN FOR MUCH OF THE
AREA.
955 PM...STRONG COLD FRONT IS NOW KNOCKING ON OUR DOORSTEPS IN
EASTERN PA. WEATHER STATIONS ACROSS CENTRAL PA WHERE THE FRONT
HAD JUST PASSED HAVE 30-40 MPH AT TIMES WITH STATIONS ACROSS MD
AND VA REPORTING UPWARDS OF 40-50 MPH GUSTS AT TIMES. THE WIND
ADVISORY REMAINS IN EFFECT ACROSS AREAS AROUND THE PA TURNPIKE
AND I-195 CORRIDORS WHERE THE STRONGEST WIND GUSTS ARE EXPECTED
TO BE.
PREVIOUS DISCUSSION...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 30-40 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, SOUTHEAST PA, AND SOUTHERN NJ
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 /TONIGHT 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 /07Z THURSDAY THROUGH MONDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
REST OF TONIGHT...MVFR OVERALL WITH INTERVALS OF IFR AND VFR
MIXED IN WITH CHANGING CONDITIONS WITH INTERVALS OF RAIN.
THUNDERSTORMS HAVE PASSED SO REMOVED FROM TAFS. GUSTY NW WINDS
CONTINUE WITH SOME GUSTS UPWARDS OF 30 KTS. MODERATE
CONFIDENCE.
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
SOUTHWESTERLY TO WESTERLY WINDS AT GALE FORCE OR NEARLY SO WILL
CONTINUE ON OCEAN WATERS THROUGH FRIDAY WITH DEVELOPING LOW
WHICH WILL THEN BECOME NEARLY STATIONARY JUST TO OUR NORTH. HAVE
EXTENDED AND EXPANDED GALE WARNING TO ALL ZONES THROUGH THE DAY
FRIDAY, BUT WILL LET BAY ZONES DROP LATER TODAY FOR THE TIME
BEING, DEPENDENT ON FUTURE TRENDS.
OUTLOOK...
SATURDAY AND 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:
9/1-11/20 DRIEST DRIEST 3 YEAR/
SITE 2024 PRECIP AUTUMN YEAR CALENDAR MONTHS MONTHS
ALLENTOWN (ABE) 1.96 3.81 1922 3.58 OCT-DEC 1928
A.C. AIRPORT (ACY) 1.01 3.34 2001 2.35 OCT-DEC 1946
A.C. MARINA (55N) 0.79 2.89 1941 2.52 AUG-OCT 1895
GEORGETOWN (GED) 1.17 2.67 2001 2.20 AUG-OCT 2024
MOUNT POCONO (MPO) 3.35 4.21 1931 3.36 OCT-DEC 1928
PHILADELPHIA (PHL) 1.66 2.37 1922 2.37 SEP-NOV 1922
READING (RDG) 1.96 2.89 1922 2.89 SEP-NOV 1922
TRENTON (TTN) 0.79 3.18 1922 2.66 JUN-AUG 1966
WILMINGTON (ILG) 1.49 3.17 1922 3.17 SEP-NOV 1922
PHI WATCHES/WARNINGS/ADVISORIES
PA...WIND ADVISORY UNTIL 4 AM EST EARLY THIS MORNING FOR PAZ060-070-
071-101>104-106.
WINTER STORM WATCH FROM THIS AFTERNOON THROUGH FRIDAY
AFTERNOON FOR PAZ054-055.
NJ...WIND ADVISORY UNTIL 4 AM EST EARLY THIS MORNING FOR NJZ013>027.
DE...WIND ADVISORY UNTIL 4 AM EST EARLY THIS MORNING FOR DEZ001>004.
MD...WIND ADVISORY UNTIL 4 AM EST EARLY THIS MORNING FOR MDZ012-015-
019-020.
MARINE...GALE WARNING UNTIL NOON EST TODAY FOR ANZ430-431.
GALE WARNING UNTIL 6 PM EST FRIDAY FOR ANZ450>455.
SYNOPSIS...GORSE/RCM
NEAR TERM...AKL/FITZSIMMONS/MJL
SHORT TERM...FITZSIMMONS/RCM
LONG TERM...GORSE
AVIATION...GORSE/MJL/ROBERTSON
MARINE...AKL/FITZSIMMONS/GORSE
HYDROLOGY...PHI
CLIMATE...PHI
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