Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 291441 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 941 AM EST THU JAN 29 2015 .SYNOPSIS... HIGH PRESSURE OVERHEAD THIS MORNING WILL MOVE OFFSHORE LATE IN THE AFTERNOON. LOW PRESSURE WILL MOVE ACROSS NEW YORK TONIGHT AND THEN ACROSS THE NEW ENGLAND WATERS FRIDAY NIGHT. IT WILL SEND AN ARCTIC FRONT ACROSS OUR AREA EARLY FRIDAY. HIGH PRESSURE WILL BUILD IN FOR MOST OF THE WEEKEND. A LOW PRESSURE SYSTEM IS EXPECTED TO MOVE JUST SOUTH OF THE AREA SUNDAY NIGHT THROUGH MONDAY NIGHT. HIGH PRESSURE WILL BUILD BACK IN FOR THE MIDDLE OF NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... NO BIG CHANGES WITH THIS ESTF UPDATE. THE MESOSCALE MODELS REMAIN PRETTY TIGHTLY CLUSTERED AS TO THE ONSET OF PRECIPITATION PRETTY CLOSE TO 00Z ALG THE DE VLY. THERE IS A SOUTHWARD DP/DT TREND WITH THE HRRR. WE HAVE NOT ARRIVED WITHIN THE HOURS OF CONCERN AND THE LATEST 12Z NAM REMAINS DRY IN THE SRN PART OF OUR CWA. WE WILL SEE IF THE TREND CONTINUES TO UP POPS WITH THE NEXT UPDATE. MORNING 12Z SOUNDINGS SHOWING PLENTY OF DRY AIR BELOW 700MB. THIS IS A GOOD THING BECAUSE PRECIPITATION WOULD EVAP COOL TO SNOW. BASED ON FCST SOUNDINGS (NO TEMPS ALF GET >2C) IN OUR CWA CONTINUES PREVIOUS SHIFT`S THINKING IN THE SRN PART OF OUR CWA OF EITHER SNOW OR SLEET AS A NON LIQUID PTYPE AND NOT FREEZING RAIN. THE 12Z SOUNDINGS MAXT MACROS GIVE AROUND 40F FOR MAX TEMPS, BUT WITH CLOUDS ARRIVING AND SNOW COVER, WE JUST DID A SLIGHT UPWARD NUDGE. MUCH CLOSER TO CONTINUITY THAN THE SOUNDING SUGGESTIONS. SURFACE HIGH PRESSURE WAS CENTERED BETWEEN THE EAST COAST AND THE APPALACHIANS. THERE HAS BEEN A FAIRLY LARGE TEMP SPREAD ACROSS THE AREA. TEMPS HAVE DROPPED INTO THE SINGLE DIGITS IN THE SHELTERED VALLEYS OF NE PA AND NW NJ WHERE THE HIGH IS DIRECTLY OVERHEAD AND WINDS WERE CALM. THERE IS ENOUGH OF A PRESSURE GRADIENT FARTHER SOUTH AND EAST FOR A LIGHT NW WIND TO KEEP TEMPS STEADY IN THE UPPER TEENS/LOWER 20S ACROSS THE DELMARVA, FAR SE PA AND S NJ. HOWEVER, THESE AREAS HAVE A CHANCE TO COOL SEVERAL MORE DEGREES THRU DAYBREAK AS THE HIGH BUILDS TOWARD THE COAST. THE HIGH WILL MOVE OFFSHORE IN THE AFTERNOON WHILE AN AREA OF LOW PRESSURE THAT IS CURRENTLY OVER THE MIDWEST TRACKS EASTWARD TOWARD THE MID-ATLANTIC STATES LATE IN THE DAY. AFTER A SUNNY START TO THE MORNING, HIGH AND MID CLOUDS AHEAD OF THIS SYSTEM WILL OVERSPREAD OUR AREA LATER THIS MORNING AND LOWER/THICKEN DURING THE AFTERNOON. THERE IS GOOD MODEL AGREEMENT REGARDING THE TIME OF ARRIVAL FOR THE PRECIP LATE THIS AFTERNOON IN OUR FAR WESTERN ZONES (MPO-RDG-MQS-ESN ROUGHLY BETWEEN 4 PM AND 6 PM). NOTE THAT WE DID SPEED UP THE ONSET AN HOUR OR TWO EARLIER AS MODELS OFTEN ARE TOO SLOW WITH THE LEADING WAA BAND. THERMAL PROFILES SUPPORT PTYPE STARTING OUT AS SNOW IN PA, SN/IP IN NE MD/FAR N DELMARVA AND RA/IP TOWARD QUEEN ANNE`S AND TALBOT. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... LOW PRESSURE WILL MOVE THROUGH THE EASTERN GREAT LAKES THIS EVENING. THE INITIAL SHIELD OF PRECIP THAT IS EXPECTED TO BE ENTERING OUR FAR WESTERN ZONES BY THE START OF THE PERIOD WILL SPREAD EASTWARD DURING THE EARLY AND MID EVENING AS A LEADING SHORTWAVE TROUGH ALOFT SWINGS THRU. PTYPE FROM PHILLY AND POINTS NORTHWARD WILL BE ALL SNOW. A WARM NOSE ALOFT IS FORECAST TO CAUSE SNOW TO MIX WITH SLEET IN THE NORTHERN DELMARVA AND THE SOUTHERN MOST LOCATIONS IN NJ. WARMER SFC TEMPS WILL LIKELY RESULT IN MAINLY RAIN ACROSS SOUTHERN DE AND ADJACENT MD ZONES. POPS AND SNOWFALL AMOUNTS ARE HIGHEST ALONG AND NORTH OF THE I-78 CORRIDOR, WHERE SYNOPTIC LIFT WILL BE GREATEST AND LESS TRANSITORY CLOSER TO THE SURFACE LOW. FORECAST SNOWFALL AMOUNTS WITH THIS EVENT ARE AROUND 1-2 FOR THESE AREAS. THERE IS CERTAINLY A POSSIBILITY FOR LOCALLY HIGHER AMOUNTS UP TO 3 INCHES MAINLY ACROSS THE HIGHER ELEVATIONS IN NORTHEAST PA AND NORTHWEST NJ BUT NOT EXPECTING IT TO BE WIDESPREAD ENOUGH TO WARRANT A WINTER WX ADVISORY. THE MAJORITY OF THE SNOW IS EXPECTED TO MOVE OUT OF THE AREA BY MIDNIGHT. HOWEVER, SOME LIGHT SNOW MAY LINGER OVERNIGHT IN NORTHEAST PA AND NORTHERN NJ. WE ARE NOT ANTICIPATING TEMPS TO FALL MUCH DURING THE OVERNIGHT WITH CLOUD COVER BLANKETING THE AREA AND A SOUTHWEST WIND AHEAD OF A COLD FRONT. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... FRIDAY...THE ARCTIC FRONT AND LOW PRESSURE NORTH OF THE REGION WILL BE MOVING AWAY. SCT SNOWS ACROSS THE NORTHERN AREAS JUST AFTER 12Z WILL REMAIN INTO THE MORNING BEFORE DIMINISHING. COLD AND WINDY CONDITIONS DEVELOPING WITH TEMPS NOT CHANGING MUCH...REMAINING IN THE LOW 30S NORTH AND MID 30S SOUTH. TEMPS MAY BEGIN TO FALL DURING THE AFTERNOON AS THE COLD AIR ADVECTION INCREASES. WINDS GUSTING TO 25 TO 35 MPH AT TIMES. WIND CHILLS IN THE SINGLE DIGITS OVER THE SRN POCONOS...TEENS ACROSS THE NRN THIRD OF THE AREA AND LOW 20S ELSEWHERE. FRI NIGHT THRU SUN MORNING...HIGH PRESSURE REMAINS ACROSS THE AREA. A DRY FCST BUT BITTER COLD TEMPS CONTINUE SAT WITH SOME MODERATION SUNDAY. HIGHS SAT MOSTLY TEENS (NORTH) AND LOW 20S (SOUTH) WIND CHILLS MOSTLY SINGLE DIGITS EARLY WITH SUB ZERO FAR NORTH. A WIND CHILL FLAG MAY BE NEEDED. WIND CHILLS IN THE TEENS ACROSS THE DELMARVA AND SRN NJ. SUN AFTERNOON THRU MONDAY...ANOTHER LOW PRESSURE SYSTEM WILL AFFECT MUCH OF THE AREA. AFTER MORE DISORGANIZED SOLUTIONS FOR THE SYSTEM WITH THE 12Z WED MODELS...THE 00Z THU OP MODELS HAVE AGAIN SWUNG BACK TO WETTER SOLUTIONS FOR OUR AREA. GFS...MOVES LOW PRESSURE FROM THE CAROLINAS UP OFF THE DELMARVA THEN JUST EAST OF 40/70 MONDAY. A DECENT SWATH OF MODERATE QPF (MOSTLY SNOW) TO MUCH OF THE FORECAST AREA. EC...WEAKER LOW PRESSURE MOVES FROM THE CAROLINAS UP WELL EAST OF THE 40/70 MARK WITH SLOWER DEEPENING. STILL SOME SNOW TO THE AREA...BUT MUCH LIGHTER AND THE HIGHER TOTALS ARE ACROSS THE DELMARVA AND SRN NJ. CMC...MUCH CLOSER...STRONGER AND VERY WET. AREAS S/E OF I-95 WOULD CHANGE TO RAIN MON WITH THE CMC SOLUTION. THERE CAN BE A TENDENCY FOR A NORTHWARD TRACK BIAS WITH SYSTEMS WHEN A STRONG HIGH IS NORTH/NORTHWEST OF THE SYSTEM. THE GFS/CMC MODELS MAY BE DISPLAYING THIS...SO WE HAVE GONE WITH THE WPC NUMBERS FOR NOW AND OFFERED THE HIGH CHC/LOW LIKELY POPS FOR THESE PERIOD. NOT MUCH OF A CHANGE FROM PREVIOUS FCST. WITH THIS WRITTEN...AN INCREASING CHC FOR AN ACCUMULATING SNOW FOR SUN NIGHT MONDAY FOR THE SRN/ERN PARTS OF THE CWA. WE WILL MAKE MENTION OF THIS IN THE HWO AND ASK USERS TO CONTINUE TO FOLLOW THIS SYSTEM OVER THE NEXT FEW DAYS. MODELS HAVE YET TO LOCK ON TO A SOLUTION...BUT MAY BE BEGINNING TO SETTLE...WITH AT LEAST MORE AGREEMENT THAN THIS TIME LAST NIGHT. MON NIGHT THRU WED...MORE HIGH PRESSURE WITH COLD TEMPS TUE AND A BIT WARMER WED. A MOSTLY DRY FCST FOR THIS PERIOD. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR THIS MRNG AND FIRST PART OF THE AFTN. EXPECT A BAND OF SNOW TO REACH THE WRN TERMINALS LATE IN THE DAY (RDG AROUND 22Z AND ABE 23Z). VSBYS WILL LIKELY LOWER TO IFR QUICKLY AFTER ONSET OF SNOW. SNOW MOVES EWD TOWARD THE I-95 TERMINALS BETWEEN 00Z-02Z. THIS WILL BE A QUICK MOVING SYSTEM, SO ONLY EXPECTING A BRIEF, 3-6 HOUR, PERIOD OF SNOW. SLEET MAY MIX IN AT ILG/MIV/ACY BUT CONFIDENCE IN PRECIP MAKING IT TO ACY IS RELATIVELY LOW FOR THIS CLOSE TO THE EVENT. SNOW MAY LINGER OUT TOWARD ABE-RDG AFTER MIDNIGHT. WINDS WILL BE LIGHT THIS MORNING, BECOMING SLY THIS AFTN/EVE AND SWLY OVERNIGHT 5-10 KT. OUTLOOK... FRIDAY THRU SUN MORNING...VFR EXPECTED. GUSTY WINDS FRIDAY. SUN AFTERNOON THRU MONDAY...LOWERING CIGS. SNOW WITH MVFR/IFR POSSIBLE. && .MARINE... LIGHT WINDS TODAY WITH HIGH PRESSURE OVERHEAD. THE HIGH SHIFTS OFFSHORE TONIGHT AND SOUTHWEST WINDS INCREASE. SCA WAS ISSUED FOR THE COASTAL ZONES, WHICH STARTS AT 11 PM AND CONTINUES THRU THE OVERNIGHT. WAVES WILL BUILD TO NEAR 5 FT DURING THE OVERNIGHT. OUTLOOK... SAT THRU SUN...GALE WARNINGS ISSUED. WINDS AND SEAS SUBSIDE BACK TO SCA CONDITIONS SUNDAY. FREEZING SPRAY EXPECTED. SUN NIGHT...SUB-SCA CONDITIONS. MON THRU TUE...SCA CONDITIONS. WINDS/SEAS SUBSIDE TUE AFTERNOON. TUE NIGHT THRU WED...SCA SEAS POSSIBLE. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 6 AM EST FRIDAY FOR ANZ450>455. GALE WARNING FROM 6 AM FRIDAY TO 6 AM EST SATURDAY FOR ANZ430- 431-450>455. && $$ SYNOPSIS...O`HARA NEAR TERM...GIGI/KLEIN SHORT TERM...KLEIN LONG TERM...O`HARA AVIATION...KLEIN/O`HARA MARINE...KLEIN/O`HARA

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