445  
FXUS61 KPHI 251805  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
105 PM EST SUN JAN 25 2015  
   
SYNOPSIS
 
 
A STRONG COLD FRONT WILL CONTINUE TO PUSH SOUTHEAST THROUGH OUR  
REGION TODAY, REACHING A LATE DAY POSITION FROM THE DELMARVA WEST  
INTO LOW PRESSURE OVER THE LOWER OHIO VALLEY. THAT LOW WILL REACH  
THE NORTH CAROLINA COAST MONDAY MORNING THEN TURN NORTH NORTHEAST,  
INTENSIFYING VERY RAPIDLY AS IT NEARS CAPE COD TUESDAY. HIGH  
PRESSURE FOLLOWS BY LATE WEDNESDAY, THEN ANOTHER LOW WILL  
REDEVELOP ON THE NEXT COLD FRONTAL PASSAGE OFF THE MID ATLANTIC  
COAST LATE THURSDAY AND FRIDAY. HIGH PRESSURE FOLLOWS SATURDAY.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
WITH THE 12:30 PM UPDATE, WE HAVE INCREASED TEMPERATURES FROM PHL  
SOUTH AHEAD OF A COLD FRONT ALONG WITH CLOUD COVER FOR THE  
REMAINDER OF THE AFTERNOON. THIS CLOUD COVER SHOULD KEEP THE  
TEMPERATURES IN CHECK FROM WARMING TO MUCH MORE AS THE DAY GOES  
ON. THE LATEST RAP AND HRRR HOLD OFF ANY PRECIPITATION TILL THIS  
EVENING, THIS FORECAST UPDATE TAKES OUT AMY MENTION OF  
PRECIPITATION TILL THIS EVENING.  
 
OTHERWISE, AS THE LOW PRESSURE FROM YESTERDAY PULLS FARTHER TO  
OUR NORTHEAST AN ARCTIC-TYPE COLD FRONT PUSHES THROUGH OUR REGION  
FROM LATE MORNING AND THROUGH THIS AFTERNOON. WATER VAPOR IMAGERY  
THIS MORNING SHOWS ONE TROUGH AXIS TO OUR NORTHEAST WHILE ANOTHER  
SHORTWAVE AXIS PUSHES THROUGH THE GREAT LAKES...THIS IS DRIVING  
THE ARCTIC FRONT TODAY. WAY BACK ACROSS THE NORTHERN PLAINS IS THE  
ENERGY THAT WILL BE THE DRIVING FORCE FOR THE CLIPPER SYSTEM LATE  
TONIGHT AND THEN THE MUCH LARGER COASTAL NOR'EASTER EXPECTED ON  
MONDAY- TUESDAY.  
 
OVERALL A MAINLY DRY AND TRANQUIL DAY IS EXPECTED ACROSS THE  
REGION. THE AFOREMENTIONED FRONT WILL SLIP THROUGH THE REGION BY  
THIS AFTERNOON USHERING IN A COOLER AIRMASS. THE MORNING STRATOCU  
SHOULD LIFT AND MIX OUT A LITTLE AS THE DAY WEARS ON. DECENT  
DOWNSLOPING COMPONENT SHOULD ALLOW HIGHS TO REACH AROUND 40F THIS  
AFTERNOON, SLIGHTLY WARMER SOUTH AND EAST OF PHILLY, AHEAD OF THE  
FRONTAL PASSAGE. BEHIND THE FRONT WEAK MID-LEVEL WARM AIR  
ADVECTION OCCURS TO OUR SOUTHWEST AS MORE MOISTURE AND CLOUDS  
ADVECT IN BEGINNING LATER THIS EVENING.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/
 
 
BROAD SCALE SURFACE LOW PRESSURE, RIDING ALONG THE SAGGING COLD  
FRONT LATER THIS EVENING, WILL PASS TO OUR SOUTH TONIGHT. HIGH  
PRESSURE TO OUR NORTH WITH WEAK MID-LEVEL RIDGING WILL ALLOW FOR THE  
MID-LEVEL SHORTWAVE DRIVING THE SURFACE LOW TO DEEPEN AND TAKE MORE  
OF A NEGATIVE TILT TONIGHT. STRENGTHENING WAA, IN RESPONSE TO THIS  
PROCESS, WILL OCCUR ACROSS OUR REGION AS A LIGHT SNOW SHOULD BREAK  
OUT FROM WEST-EAST. ONSET TIMING IS STILL A BIT OF A QUESTION BUT A  
MAJORITY OF THE HI-RES GUIDANCE IS SHOWING THE INCREASING CHANCES  
DURING THE LATE EVENING. PTYPE SHOULD NOT BE MUCH OF AN ISSUE EXCEPT  
ACROSS OUR EXTREME SOUTHERN ZONES AS LOW-LEVEL TEMPERATURES STRUGGLE  
TO TRANSITION COLDER (BELOW 0C) JUST AHEAD OF THE APPROACHING  
LOW...WAA SHOULD KEEP A RAIN/SNOW MIX SOUTH OF DOVER WHILE NORTHWARD  
IS ALL SNOW.  
 
DECENT CONVERGENCE ACROSS OUR CENTRAL ZONES LATE TONIGHT, BOTH  
THERMALLY AND DYNAMICALLY. GUIDANCE IS PAINTING A NOSE OF A TENTH OF  
LIQUID FROM A PHL/ABE LINE WEST SO THIS IS WHERE WE SHOULD SEE  
SLIGHTLY HIGHER SNOW AMOUNTS...ON THE ORDER OF 1-2" IN AND AROUND  
PHILLY, 2-3" FARTHER WEST TOWARDS RDG...MESOSCALE BANDING POTENTIAL  
ALSO EXISTS ALBEIT NOT NEARLY AS ROBUST AS SATURDAY MORNING.  
 
EVEN THOUGH THIS SNOW WILL AFFECT THE MONDAY MORNING COMMUTE WE DID  
NOT WANT TO ADD TO ANY CONFUSION WITH MULTIPLE WINTER WEATHER  
HEADLINES DEALING WITH THE SAME EVENT...JUST TWO DIFFERENT PIECES OF  
ENERGY. GIVEN WE ARE EXPECTING A MUCH MORE IMPACTFUL STORM BEGINNING  
LATER ON MONDAY...SEE LONG TERM DISCO...WE DECIDED TO FORGO AN  
ADVISORY BUT MAKE MENTION OF THE EARLY MORNING SNOWFALL IN THE  
HWO/WSW PRODUCTS.  
 

 
   
LONG TERM /MONDAY THROUGH SATURDAY/
 
 
**MAJOR DISRUPTIVE SNOWSTORM POTENTIAL LATE MONDAY INTO TUESDAY  
MORNING PHILLY AREA NEWD TO NEW ENGLAND...WINTER STORM WATCH IN  
PLACE FOR MOST OF THE FORECAST AREA**  
 
**BLIZZARD WATCH HAS BEEN ISSUED FOR MONMOUTH, OCEAN, AND  
MIDDLESEX COUNTIES**  
 
500 MB: A STRONG SHORT WAVE MONDAY MORNING OVER THE CENTRAL APPALACHIANS  
INTENSIFIES INTO A CLOSED LOW SOUTH OF LONG ISLAND TUESDAY. RIDGING  
IN THE WAKE OF ITS MARITIMES DEPARTURE FOLLOWS TO THE EAST COAST  
WEDNESDAY. A SOUTHEASTWARD MOVING SHORT WAVE REACHES THE MID  
ATLANTIC COAST FRIDAY WITH A TEMPORARILY FLATTENED WESTERLY FLOW  
NEXT WEEKEND.  
 
TEMPERATURES (ENERGY USE): BELOW NORMAL MONDAY THROUGH THURSDAY,  
POSSIBLY 5 TO 10 DEGREES BELOW MON-WED; NEAR NORMAL FRI, CHILLING  
AGAIN SATURDAY.  
 
FORECAST BASIS: UNLESS OTHERWISE NOTED WITHIN THE DAILIES. THIS  
FORECAST IS A 50 50 BLEND OF THE 00Z/25 MAV/MET FOR MONDAY-TUESDAY.  
THE 00Z/25 MEX MOS WAS APPLIED TUESDAY NIGHT AND WEDNESDAY. THE 05Z/25  
WPC D4-8 ELEMENTS OF DEWPOINTS/WIND/SKY/POP/MAX-MIN TEMPS WERE NOT USED  
FOR THE LONGER RANGE DUE TO FOCUS ON THE POTENTIALLY VERY HIGH IMPACT  
STORM FOR MONDAY NIGHT.  
 
THEREFORE...THERE WAS NO UPDATE OF THE FORECAST BEYOND WEDNESDAY  
IN THE EARLY ISSUANCE TODAY.  
 
THE DAILIES...  
MONDAY-TUESDAY...WSA IN DIFFERING SEGMENTS TO BE REFINED WHEN  
WATCHES CONVERT TO WARNINGS AND OR ADVISORIES.  
 
MODEL DISAGREEMENT FOR THE 00Z/25 CYCLE WITH THE NAM THE MAIN OUTLIER  
RIGHT NOW. THE UKMET IS LARGE BUT A FASTER DEPARTURE THAN THE ECMWF.  
 
THE 00Z/06ZNAM WAS ACCEPTABLE THROUGH MIDDAY MONDAY AND THEREAFTER  
DID NOT RELY ON THE NAM FOR ITS QPF...INSTEAD THIS FORECAST IS  
BASED HEAVILY ON NCEP QPF/SNOWFALL AS WELL AS THE 00Z/25 ECMWF  
AND GFS BLEND.  
 
MONDAY: SEVERAL INCHES OF SNOW EXPECTED BUT AN ADVISORY NOT ISSUED  
SINCE WE DID NOT WISH TO DRAW ATTENTION AWAY FROM THE POTENTIALLY  
VERY HIGH IMPACT EVENT FOR MONDAY NIGHT. TOO WARM FOR MUCH ACCUMULATION  
FAR SNJ AND MUCH OF THE DELMARVA. THE ARCTIC FRONT AND ITS SLOWLY  
DEEPENING BOUNDARY LAYER COLD IS CRUCIAL FOR THE LIFT OF THE SELY  
850MB FLOW AND A GENERAL SNOW IN EASTERN PA/MUCH OF NJ. COMMUTES  
IMPACTED. HIGH CONFIDENCE.  
 
MONDAY NIGHT INTO TUESDAY MORNING...UNCERTAINTY ON AMOUNTS ETC ALL  
HINGING ON INTENSITY AND TRACK OF A COASTAL STORM. OVERALL, THIS  
LOOKS LIKE A MAJOR STORM FOR US AND POTENTIAL FOR BLIZZARD CONDITIONS  
IN NE NJ. OUR FORECAST AMOUNTS ARE PROBABLY CONSERVATIVE.  
 
BANDING IN THE COMMA HEAD WITH A BENT BACK FRONT ALOFT LOOKS TO BE  
A MAJOR PLAYER...GENERATING SNOWFALL RATES MONDAY NIGHT POSSIBLY  
IN EXCESS OF AN INCH AN HOUR ACROSS NJ AND PORTIONS OF E PA. IF  
THE 00Z/06Z NAM MASS FIELDS ALOFT ARE CORRECT THEN ALL THIS HEAVY SNOW  
WOULD MISS TO THE EAST.  
 
THOSE WITH TRAVEL PLANS IN E PA AND NJ ESPECIALLY FOR MONDAY NIGHT  
AND TUESDAY SHOULD BE AWARE THAT THOSE PLANS MAY NEED MAJOR  
ALTERATION/CANCELLATION. BE PREPARED WITH ALTERNATE PLANS. "IF"  
CONFIDENCE IS VERY HIGH, WE MAY CONVERT TO WARNINGS LATE TODAY.  
 
WATCHES DO NOT MEAN A DONE DEAL BUT DO PAY ATTENTION. A DRIER  
MORE POWDERY SNOW WILL BE EASIER TO ACCUMULATE IN THE COLDER  
AIRMASS THAN JUST WHAT OCCURRED EARLY SATURDAY. WIND WILL BECOME A  
FACTOR IN BLOWING/DRIFTING, MAINLY IN NJ/DEL.  
 
TUE NIGHT THRU WED NIGHT... HIGH PRESSURE WILL DOMINATE DURING THIS  
PERIOD WITH FAIR BUT COLD WEATHER EXPECTED.  
 
THU INTO FRI...THIS FORECAST WAS NOT UPDATED ON THIS MID SHIFT.  
MODELS ARE SHOWING ANOTHER CLIPPER TYPE SYSTEM APPROACHING FROM  
THE WEST AFTER THE MID WEEK PERIOD. TEMPERATURES WILL HAVE BEGUN  
TO MODERATE BY THE TIME THE PRECIP ARRIVES...SO SOME RAIN/SNOW  
LINE ISSUES WILL OCCUR. MOSTLY USED CHC POPS FOR NOW. TEMPS WILL  
STILL BE BELOW NORMAL...BUT NOT AS COLD AS WED.  
 

 
   
AVIATION /18Z SUNDAY THROUGH FRIDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
TODAY...VFR CIGS AOA 4000 FT. STRATOCU DECK WILL REMAIN IN PLACE  
MOST OF THE DAY UNDER WESTERLY WINDS WITH A FEW GUSTS POSSIBLE TO  
NEAR 20 KT.  
 
TONIGHT...MVFR/IFR IN AREAS OF SNOW. TIMING IS STILL A BIT SUSPECT  
BUT LIGHT SNOW SHOULD OVERSPREAD FROM THE WEST-EAST BY LATE TONIGHT.  
MINIMAL RAIN/SNOW MIXING EXPECTED VCNTY KMIV TOWARD 12Z MONDAY.  
EXPECT SOME LIGHT ACCUMULATIONS THROUGH EARLY MONDAY MORNING...AROUND  
1-2 INCHES PHL/ILG/TTN/PNE, MAYBE 2-3 INCHES RDG/ABE.  
 
OUTLOOK...  
MON AND MON NIGHT...IFR/LIFR SOUTH AND MVFR OR INTERMITTENT IFR  
NORTH IN SNOW OR PERIODS OF SNOW. N-NE WINDS GUSTING 20-30 KT AT  
TIMES WITH 35 KT GUSTS POSSIBLE VCNTY KACY. VERY HIGH CONFIDENCE.  
PLOWABLE AMOUNTS AND POTENTIAL FOR AIRPORT CLOSURES AT NIGHT INTO  
EARLY TUESDAY DEPENDENT ON SNOW AMOUNTS AND RATE OF FALL AS WELL  
AS DRIFTING.  
 
TUE...IFR PROBABLE EARLY IN COMMA HEAD BENT BACK BANDING OF THE BIG  
NOREASTER THEN PROBABLY BECOMING VFR BY LATE IN THE DAY. NORTHWEST  
WINDS GUSTING 20-30KT, EXCEPT POSSIBLY STRONGER VCNTY KACY.  
AVERAGE CONFIDENCE.  
 
TUESDAY NIGHT-WED: MOSTLY VFR. N-NW WINDS. HIGH CONFIDENCE:  
 
THURSDAY: CONDITIONS MAY DEGRADE IN A PERIOD OF PCPN DURING THE  
AFTERNOON OR NIGHT.  
 

 
   
MARINE
 
 
REST OF TODAY...WE REMOVED THE SCA FROM THE OCEAN FRONT AS WINDS AND  
SEAS HAVE FALLEN BELOW THRESHOLDS.  
 
TONIGHT...SUB-SCA EXPECTED. LOW PRESSURE WILL MOVE BY TO OUR SOUTH  
LATE AS WINDS VEER TOWARDS THE NORTH-NORTHEAST. SEAS BEGIN TO BUILD  
ACROSS THE SOUTHERN WATERS LATE AS DO THE WINDS. GALE WARNINGS/STORM  
WATCHES IN PLACE STARTING MONDAY AFTERNOON.  
 
OUTLOOK...  
MONDAY INTO TUESDAY...MOSTLY GALE CONDITIONS ON THE WATERS BUT POCKETS  
OF STORM FORCE GUSTS. HAVE FORECAST WHERE THE STORM FORCE 50 KT GUSTS  
OVER THE NJ WATER WHERE THEY ARE MOST LIKELY TO OCCUR, BUT WITH THE  
UNDERSTANDING THAT ISOLATED STORM FORCE GUSTS MAY OCCUR IN THE  
DELAWARE WATERS AS WELL. THE HEADLINES ARE THE MOST LIKELY WORST  
CASE SCENARIO.  
 
TUESDAY AFTERNOON THROUGH THURSDAY...MAINLY SCA CONDITIONS WITH  
AREAS OF FREEZING SPRAY EXPECTED.  
 

 
   
TIDES/COASTAL FLOODING
 
 
ANOTHER NORTHEASTER IS EXPECTED TO AFFECT THE COASTAL WATERS OF  
DELAWARE AND NEW JERSEY FROM MONDAY NIGHT INTO TUESDAY. MINOR TO  
POSSIBLY MODERATE TIDAL FLOODING SHOULD OCCUR AROUND THE TIMES OF  
HIGH TIDE, MAINLY THE MIDNIGHT TUESDAY MORNING HIGH TIDE CYCLE.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...WINTER STORM WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY  
MORNING FOR PAZ054-055-060>062-070-071-101>106.  
NJ...WINTER STORM WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY  
MORNING FOR NJZ001-007>010-015>019-027.  
WINTER STORM WATCH FROM MONDAY EVENING THROUGH TUESDAY MORNING  
FOR NJZ021>025.  
BLIZZARD WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY MORNING  
FOR NJZ012>014-020-026.  
DE...WINTER STORM WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY  
MORNING FOR DEZ001.  
WINTER STORM WATCH FROM MONDAY EVENING THROUGH TUESDAY MORNING  
FOR DEZ002>004.  
MD...WINTER STORM WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY  
MORNING FOR MDZ008.  
WINTER STORM WATCH FROM MONDAY EVENING THROUGH TUESDAY MORNING  
FOR MDZ012-015-019-020.  
MARINE...STORM WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY MORNING FOR  
ANZ450>453.  
GALE WARNING FROM 11 AM MONDAY TO 11 AM EST TUESDAY FOR ANZ431-  
454-455.  
GALE WARNING FROM 5 PM MONDAY TO 11 AM EST TUESDAY FOR ANZ430.  
 

 
 

 
SYNOPSIS...DRAG/KLINE  
NEAR TERM...GAINES/HEAVENER/KLINE  
SHORT TERM...HEAVENER  
LONG TERM...DRAG/KLINE  
AVIATION...DRAG/HEAVENER/KLINE  
MARINE...DRAG/HEAVENER/KLINE  
TIDES/COASTAL FLOODING...  
 
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