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Area Forecast Discussion
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000
FXUS61 KPHI 210216
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
916 PM EST SAT DEC 20 2014

.SYNOPSIS...
HIGH PRESSURE WILL SLOWLY BUILD SOUTHWESTWARD INTO THE REGION
FROM ATLANTIC CANADA THROUGH MONDAY. LOW PRESSURE WILL ORGANIZE
OFF THE CAROLINAS MONDAY NIGHT AND MOVE NORTHEASTWARD OFFSHORE ON
TUESDAY. MEANWHILE...ANOTHER AREA OF LOW PRESSURE WILL DEVELOP
OVER THE OHIO VALLEY AND MOVE NORTHWARD INTO QUEBEC...LEADING TO A
STRONG COLD FRONTAL PASSAGE ON THURSDAY NIGHT. HIGH PRESSURE WILL
BUILD IN ON FRIDAY AND A WEAKER COLD FRONT MAY APPROACH THE REGION
NEXT WEEKEND.

&&

.NEAR TERM /THROUGH SUNDAY/...
WEAK SURFACE HIGH PRESSURE WILL REMAIN ACROSS THE AREA TONIGHT.
PLENTY OF MOISTURE REMAINS TRAPPED BELOW A LOW LEVEL INVERSION,
ESPECIALLY PHILLY NORTH. THE LOW CLOUDS HAVE BROKEN UP SOUTH OF
PHILLY, BUT SKIES WILL FILL UP AGAIN AS A MID-LEVEL DECK ADVECTS
IN OVERNIGHT. THESE CLOUDS ARE ASSOCIATED WITH A MID-LEVEL SHORT
WAVE.

THE HIGH RESOLUTION MODELS KEEP THE CWA PRECIP-FREE(MEASURABLE)
THROUGH THE OVERNIGHT AS DOES THE LOWER RES MODELS. WE'LL KEEP THE
GRIDS AS IS, BUT CAN'T RULE OUT A FLURRY OR TWO UP ACROSS THE
NORTHERN THIRD OF THE CWA.

ANOTHER SEASONABLY COLD NIGHT IS EXPECTED WITH LOWS IN THE LOW 20S
NORTH AND MID OR UPPER 20S SOUTH. WINDS WILL BE LIGHT FROM THE
NORTH.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH 6 PM SUNDAY/...
AFTER A WEAK SHORTWAVE CROSSES THE AREA SUN MORNING...UPPER RIDGING 
WILL TAKE PLACE. THIS WILL HOPEFULLY ALLOW MORE SUNSHINE ACROSS THE 
AREA. WE HAVE WRITTEN A PARTLY TO MOSTLY SUNNY FCST FOR NOW. WE HELD 
ONTO SOME EXTRA CLOUD COVER ACROSS THE SRN POCONOS HOWEVER. HIGH 
TEMPERATURES SUNDAY WILL RISE INTO THE LOW 40S ACROSS SRN NJ AND THE 
DELMARVA...WHILE READINGS HOLD IN THE MID/UPPER 30S ACROSS THE 
NORTH/WEST AREAS. WINDS WILL REMAIN LIGHT...MOSTLY FROM THE NORTH.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
HIGHLIGHTS...

* FREEZING RAIN POSSIBLE MONDAY NIGHT OVER THE NORTHWEST. 
* INCREASING POTENTIAL FOR HEAVY RAIN CHRISTMAS EVE WITH
  TEMPERATURES WELL ABOVE NORMAL.
* BRISK WESTERLY WIND CHRISTMAS DAY W/FLURRIES POSSIBLE.      

OVERVIEW...

VIGOROUS MID-LEVEL DISTURBANCE AND ACCOMPANYING 160 KNOT UPPER-LEVEL 
JET MAX COMING ASHORE OVER THE PACIFIC NORTHWEST LATE THIS WEEKEND 
WILL LEAD TO A DEEP TROUGH OVER THE MISSISSIPPI VALLEY BY MID-WEEK.
INITIAL PIECE OF ENERGY AHEAD OF THIS TROUGH IS EJECTED NORTHEAST 
AND WILL LEAD TO THE DEVELOPMENT OF AN AREA OF LOW-PRESSURE OFF THE 
CAROLINAS ON MONDAY. THIS WEAK FEATURE SHOULD TRACK OFFSHORE WELL 
SOUTHEAST OF THE REGION ON TUESDAY PER TODAYS 12Z UKMET AND GFS...
FEEL THE NAM AND ECMWF ARE TOO FAR NORTH, SLOW, AND DEEP W/THIS 
FEATURE...THUS THEY ALSO CRANK OUT TOO MUCH QPF. NEVERTHELESS...
QPF COMBINED WITH MARGINAL TEMPERATURE PROFILES OVER THE NORTHWEST
COULD SUPPORT SOME LIGHT FREEZING RAIN MONDAY NIGHT. MID-LEVEL FLOW 
THEN BECOMES INCREASINGLY MERIDIONAL...PUMPING ANOMALOUSLY WARM 
AND MOIST AIR UP THE EAST COAST...SETTING THE STAGE FOR HEAVY RAIN 
ON CHRISTMAS EVE DAY. THE TROUGH LOOKS TO BECOME NEGATIVELY TILTED 
AS IT CROSSES THE REGION...LEADING TO A STRONG FRONTAL PASSAGE LATE 
WEDNESDAY INTO EARLY THURSDAY...WITH SOME FLURRIES POSSIBLE ON THE 
BACK-SIDE OF THE STORM SYSTEM. 

DETAILS...

MONDAY...
MID-LEVEL RIDGE CRESTS OVER THE REGION EARLY IN THE DAY...W/SURFACE
HIGH ANCHORED ALONG THE EAST COAST IN A COLD-AIR DAMMING SIGNATURE. 
PRECIPITATION WILL BE LARGELY DRIVEN BY INSENTROPIC ASCENT OVER THE 
COLDER LOW-LEVEL AIRMASS AND WILL BEGIN LATE IN THE DAY AS MOISTURE 
STREAMS IN ALOFT AND LOW-LEVELS GRADUALLY SATURATE. THERE MAY BE A 
PERIOD OF LIGHT FREEZING RAIN OVER THE NORTHWEST AS A COLD AIR 
IS REINFORCED W/NORTHERLY SURFACE WINDS AND PRECIP LEADS TO 
EVAPORATIONAL COOLING.

TUESDAY...
ANY LIGHT FREEZING RAIN SHOULD END EARLY IN THE MORNING WITH STRONG 
WARM AIR ADVECTION ALOFT. ALTHOUGH THE BEST FORCING REMAINS WELL TO 
THE WEST...BROAD ISENTROPIC ASCENT AND INCREASING MOISTURE SHOULD 
LEAD TO SCATTERED RAIN SHOWERS THRU THE DAY. QPF SHOULD BE GENERALLY 
LIGHT.

WEDNESDAY...
A VIGOROUS TROUGH APPROACHES FROM THE WEST W/STILL SOME SPREAD NOTED 
FROM THE MEAN IN BOTH THE ECENS AND GEFS 500 HPA HEIGHT FIELDS...
INDICATING SOME DISAGREEMENT WITH REGARD TO WHAT DEGREE IT GOES 
NEGATIVELY TILTED. NEVERTHELESS...A VERY DYNAMIC SYSTEM WITH SEVERAL 
INGREDIENTS COMING TOGETHER FOR UP TO 1-2 INCHES OF QPF...ESPECIALLY
OVER THE HIGHER TERRAIN. NOTING A STRONG MID-LEVEL VORT MAX AND THE 
LEFT-FRONT QUADRANT OF A 160 KNOT UPPER-LEVEL JET TRAVERSING THE 
APPALACHIANS. ALSO NOTING STRONG WARM AIR ADVECTION AND ANOMALOUSLY 
HIGH /2-3 STANDARD DEVIATION/ PRECIPITABLE WATER VALUES STREAMING
UP THE EASTERN SEABOARD. THUS THERE IS PLENTY OF MOISTURE AND 
ASCENT FOR HEAVY RAINFALL...W/THE MODELS KEYING IN ON WEDNESDAY 
AFTERNOON AND WEDNESDAY NIGHT FOR THE BULK OF THE PRECIP...AND 
THIS WILL NEED TO BE MONITORED FOR FLOODING POTENTIAL PARTICULARLY 
DUE TO THE HOLIDAY TRAVEL CHRISTMAS EVE. LATER SHIFTS WILL ALSO 
NEED TO FURTHER EVALUATE THE POTENTIAL FOR GUSTY SURFACE WINDS 
AND CONVECTION.

THURSDAY AND FRIDAY...
LOW-PRESSURE MOVES NORTHWARD INTO QUEBEC AND HIGH-PRESSURE BEGINS TO 
BUILD IN. TEMPERATURES WILL REMAIN ABOVE SEASONABLE LEVELS AND THERE 
COULD BE SNOW SHOWERS IN THE BLUSTERY NORTHWEST FLOW ON THURSDAY...
PARTICULARLY NORTHWEST.

SATURDAY...ANOTHER COLD FRONT MAY APPROACH THE REGION...BUT IT/S TOO 
EARLY TO SPECULATE...ESPECIALLY GIVEN THE UNCERTAINTY THAT THE STORM 
SYSTEM MOVING THROUGH THE NORTHEAST CONUS MID-WEEK COULD ADD TO THE 
FORECAST.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY AND SURROUNDING AREAS.

THERE HAS BEEN PLENTY OF LOW LEVEL MOISTURE TRAPPED BELOW THE 
INVERSION AGAIN TODAY. CIGS WERE BETWEEN 025-035 ACROSS THE AREA
THIS AFTERNOON. THIS EVENING WE'RE SEEING MORE 030-035. STILL,
MOSTLY IN THE NORTH QUADRANT. 

WE'LL KEEP THE LOW CLOUDS IN THE TERMINALS FROM KPHL NORTHWARD
THROUGH THE NIGHT. TO THE SOUTH, WE'VE SCATTERED THE LOW LEVEL
DECK OUT. A SHORT WAVE WILL BRING SOME ALTOCU TO JUST ABOUT
EVERYWHERE OVERNIGHT. 

WINDS WILL REMAIN LIGHT OVERNIGHT. NO PRECIPITATION HAS BEEN 
MENTIONED.

OUTLOOK...

SUNDAY NIGHT AND MONDAY MORNING...VFR.

MONDAY AFTERNOON...POTENTIAL FOR MVFR CIGS AS MARINE LAYER BECOMES 
ESTABLISHED AND STRATUS ADVECTS INLAND.

MONDAY NIGHT THROUGH TUESDAY NIGHT...THE COMBINATION OF 
STRENGTHENING ONSHORE FLOW AND IN-SITU CAD FROM LIGHT RAIN 
OVERSPREADING THE TERMINALS COULD YIELD AN EXTENDED PERIOD OF 
MVFR/IFR CONDITIONS (CIGS WOULD BE THE MORE LIKELY CONTRIBUTOR TO 
IFR THAN VSBYS) MONDAY NIGHT INTO TUESDAY.

WEDNESDAY...WINDS VEER MORE OUT OF THE SOUTH AS A WARM FRONT SLOWLY 
LIFTS NORTHWARD. RAIN IS EXPECTED TO BE THE MOST WIDESPREAD AND 
HEAVIEST DURING THIS PART OF THE FORECAST PERIOD. PREDOMINATELY MVFR 
AND IFR CONDITIONS. SOUTHERLY WINDS WILL BECOME BREEZY FOLLOWING 
WARM FROPA.

WEDNESDAY NIGHT...COLD FRONT IS FORECAST TO MOVE THRU SOMETIME AT 
NIGHT. LOW CLOUDS AND RAIN WILL END FROM WEST TO EAST IN WAKE OF 
FROPA. 

THURSDAY...WESTERLY WINDS COULD BECOME STRONG BEHIND THE FRONT 
THURSDAY WITH BUFKIT FORECAST SOUNDINGS FROM THE 12Z GFS SHOWING THE 
POTENTIAL FOR 30-40 KT GUSTS.

&&

.MARINE...
WEAK HIGH PRESSURE WILL REMAIN ACROSS THE WATERS TONIGHT AND SUNDAY. 
WINDS AND SEAS WILL REMAIN BELOW SCA FLAG CRITERIA. WINDS WILL 
MOSTLY BE NORTHERLY THROUGH THE PERIOD. 

OUTLOOK...
SUNDAY NIGHT THROUGH MONDAY NIGHT...WINDS AND SEAS BELOW SCA 
CRITERIA.

TUESDAY AND TUESDAY NIGHT...ONSHORE FLOW STRENGTHENS ON TUESDAY. 
WINDS 15-20 KT FORECAST ON TUESDAY. SEAS ARE FORECAST TO BUILD TO 
5-6 FEET TUESDAY AND TUESDAY NIGHT, WARRANTING THE NEED FOR A SCA.

WEDNESDAY AND WEDNESDAY NIGHT...SOUTHERLY WINDS STRENGTHEN AFTER 
WARM FROPA. DESPITE WINDS OF 40-50 KT FORECAST 1000 FT ABOVE THE 
SURFACE, THERMAL PROFILES NOT FAVORABLE FOR MIXING WITH THE SETUP OF 
WARM AIR MOVING ATOP THE COOLER WATERS. EXPECTING MORE OF A HIGH END 
SCA WITH 25-30 KT WINDS. WINDS FORECAST TO BECOME WESTERLY LATE 
WEDNESDAY NIGHT BEHIND A COLD FRONT BUT THE CORE OF THE COLD AIR 
WILL STILL REMAIN UPSTREAM OF THE WATERS. SEAS FORECAST TO INCREASE 
TO 6-8 FEET.

THURSDAY...GUSTY WESTERLY WINDS EXPECTED. GALES CERTAINLY A 
POSSIBILITY.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...FRANCK
NEAR TERM...O'HARA
SHORT TERM...O'HARA
LONG TERM...FRANCK
AVIATION...FRANCK/KLEIN/O'HARA
MARINE...KLEIN/O'HARA






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