Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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448 FXUS61 KPHI 091953 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 253 PM EST Fri Dec 9 2016 .SYNOPSIS... Strong low pressure will continue to slowly drift to the south of Greenland through the weekend while strong high pressure advances toward the mid Atlantic coast, arriving here early Sunday. A warm front is expected to move north into our area Sunday night, before low pressure passes to our north on Monday. This low sends a cold front across the mid Atlantic states later Monday. Another frontal boundary is expected to move across the area Tuesday night or Wednesday, and a coastal low may develop along this boundary Wednesday. A strong west to northwest flow is expected to develop by the end of the week as high pressure tries to build in from the west. && .NEAR TERM /THROUGH TONIGHT/... The 330 PM forecast through Saturday was basically posted at 1230 PM. Remainder of this afternoon...chilly blustery northwest winds gusting 25-35 mPH til sunset then decreasing gusts on the land except high terrain ne PA and NJ where gusts 30 to 40 mph may linger past sunset. Temps leveled in the 30s with the instability SC and virga (upper 20s KMPO). Few passing flurries may be seen here and there but nothing ominous as of this 230 PM writing. Still bears monitoring for a streamer breaking free of the mountains and dropping a quick 1/2 inch somewhere in e PA (Berks into the Pocs). Tonight...Considerable cloudiness from vcnty reading into the Poconos and far nw NJ with periods of cloudiness near I-95 where I`ll think of it as Partly cloudy at times, otherwise clearing. some cirrus toward dawn too. Fcst temps were mostly the warmer NAM values in a still gusty northwest flow to 20 or 25 mph in PHL and adjacent the waters. So min temps maybe a degree or three below normal. Scattered flurries or even a snow shower possible e PA and far northwest NJ. Any additional accumulations should be near or below one half inch in the Poconos (note: the storm total snow graphic on our website is now for the Sunday night event since that looks to be a much more extensive and larger impact via snow and ice. We did not say major or heavy, just larger and more extensive and will probably require travel slow downs). Please see climate section on PHL first temp of the season below 30F...probably a saturday morning low of 28 or 29F and that is forecast with above average confidence. && .SHORT TERM /SATURDAY/... There will be fairly steep lapse rates combined with some enhanced moisture across the far northern tier of the area. With the west- northwest flow remaining across the area, there should be scattered lake and moist lapse rate enhanced snow showers/flurries developing which could make their way down to I-80 (even a dusting is possible). West to northwest winds should gust 20-25 mph, especially afternoon. Forecast basis: 50 50 blend of 12z/9 GFS/NAM MOS. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... High pressure briefly affects the area Saturday night, providing dry conditions. Saturday will remain cold and windy, although winds are not expected to be as high as Friday. The high builds offshore Sunday ahead of the next storm system. As this happens, it is possible that some showers could develop during the day across the area as a short wave passes just to our north and spreads an area of moisture across the area north of the advancing warm front to our south. If any precipitation develops during the day, temperatures should be cold enough for the northern half of the area to see snow, or at least a rain/snow mix. However, the best chance of precipitation looks to be Sunday night into Monday. A warm front is forecast to lift across the area late Sunday night and into Monday as an area of low pressure is forecast to move north of the area Monday. Conditions are expected to be cold enough overnight across the northern half of the area for snow to fall for a period of time. However, as the warm front lifts northward into the area, temperatures are expected to begin warming. This should help precipitation begin to transition into a wintry mix for the northern half of the area. It is possible that a period of sleet and freezing rain could occur across the northern areas as a chance over to rain occurs from south to north. The most likely area to recieve accumulating snowfall is expected to be the northern third of the area, although the middle third could get some light snow before changing over to rain. This change over would limit any accumulations. The southern third is expected to stay rain through the event. As the low continues to lift northward during the day, a cold front is expected to move across the area late in the day and overnight. Precipitation chances should diminish behind the cold front later in the day and overnight. Any precipitation overnight should change to snow for the northern half while the southern half would stay rain. High pressure may briefly affect the area Tuesday, but will quickly build offshore. Then a cold front is expected Tuesday night into Wednesday, which could bring another round of precipitation. The GFS and ECMWF have different timing with the front, as well as with a possible coastal low that could develop and move along this boundary. The GFS is slower, moving the front through Wednesday and the coastal low up the coast late on Wednesday. The ECMWF moves the front through Tuesday night, and moves the coastal low farther offshore and then out to sea. We will keep a chance of precipitation Tuesday night into Wednesday with the frontal passage and possible effects of the coastal low if it gets close enough. Even if the low remains offshore, we should get some precipitation from the front. Strong west to northwest flow is expected again by Thursday as high pressure tries to build in from the west. This is expected to usher in very chilly air along with the breezy conditions. There could again be a chance for isolated snow showers/flurries across much of the area Thursday. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of this afternoon...VFR sct-bkn aoa 4000 ft. Scattered flurries but should be inconsequential at any TAF site. West to northwest wind gusts 22-30 kt. Tonight...VFR becoming clear or sc clouds aoa 4000 ft with west to northwest wind gusts under 22 kt. The exception is mvfr cigs and ocnl flurries in the Poconos and possibly a cig much of the night near 4000 ft vcnty KRDG/KABE. Saturday...VFR sct-bkn aoa 4000 ft. Isolated or scattered snow showers/flurries E PA and northwest NJ, which may temporarily lower conditions, especially I-80 region northward. Gusty west to northwest winds around 20-22 knots during the day. OUTLOOK... Saturday night...Generally VFR. Isolated showers or flurries/sprinkles are possible across the northern half of the area during the day which may temporarily lower conditions. Gusty west to northwest winds 15-20 knots during the day. Sunday...VFR early, lowering to MVFR by the afternoon. Rain or snow possible late in the day. Sunday night-Monday...MVFR early, then IFR overnight into Monday. Rain or snow becoming likely. Accumulating snow possible for the northern third of the area, with a chance of freezing rain around daybreak. Rain/snow mix for central third of the area. Rain across the southern third. All precipitation likely to become all rain Monday. Winds could become gusty during the day Monday 20 to 25 knots. Monday night...Improving conditions overnight to VFR. Tuesday...VFR expected with west to northwest gusts around 15 to 20 knots. && .MARINE... SCA continues south and central with max gusts today into the evening of 28 to 32 kt. Have delayed the ending to sometime in the morning upper De Bay and ANZ455 (De Atlc waters), and through early afternoon remainder of the waters. GLW extended through 11 PM for the waters north of Atlantic city (little Egg Inlet to Sandy Hook), with gusts occasionally 35-39 kt into this evening, especially a couple of miles out. Wind gusts to 40 kt vcnty High Point NJ during mid aftn corroborates the modeled nw flow jet near 925 MB that should flow southeast through the NNJ waters this evening with wind gusts increasing a few knots from mid afternoon. Winds will be only very slow to decrease late at night and Saturday due to large over water lapse rates and the cool boundary layer temp heat sink. Gale verification for overnight and this morning: Brandywine and Cape May verified the 2 hour minimum/12 hr gale gust criteria for the southern zones and then 44065 (our closest overwater operational wind buoy) verified the far northern NJ portion of the warning this morning and gain during the past two early afternoon hours. We had many locations along the water with 30 to 100 min period of mid 30s gale gusts last night, centered near 03z/9. Outlook... Saturday night-Sunday...Conditions expected to remain below Small Craft Advisory levels, although winds could gust around 20 knots at times. Sunday night...Small Craft Advisory levels possible overnight. Monday-Monday night...Small Craft Advisory conditions likely, possibly reaching gale force for a period of time. Tuesday...Small Craft Advisory conditions remain possible. && .CLIMATE... Note: The low temp expected at PHL Saturday morning should be the coldest of the season so far at PHL (28-29F), the first 20s of the season. Last winter, it didn`t drop into the 20s until January 4, 2016. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 4 PM EST Saturday for ANZ431- 452>454. Gale Warning until midnight EST tonight for ANZ450-451. Small Craft Advisory until 11 AM EST Saturday for ANZ455. Small Craft Advisory until 4 AM EST Saturday for ANZ430. && $$ Synopsis...Robertson Near Term...Drag 253 Short Term...Drag 253 Long Term...Robertson Aviation...Drag/Robertson 253 Marine...Drag/Robertson 253 Climate...253

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