Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 091503 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1003 AM EST Fri Dec 9 2016 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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930 AM ESTF: few changes except to boost gusts 5 MPH as model guidance suggests 25-30 mph gusts this afternoon. rcd a report from Mt Poconos at 942 AM of 0.2" snow fall between 8am and 930 am form the brief 2 mi snow shower band that passed through there. Otherwise, its a day of strong northwesterly flow resulting in breezy conditions and below normal temperatures. Highs, mostly 30s except 40-43F along and southeast of I95, which will be 5 to 8 degrees lower than normal. Higher elevations in the Southern Poconos are not likely to rise out of the 20s. Snow showers, a result of the strong northwesterly flow/cold air advection/lake effect, have begun to slide into the southern Poconos, so far though nothing more than flurries has been reported in our area. Scattered snow showers (flurries) will occur across the Poconos, NW NJ, and possibly as far south and east as the Lehigh Valley. 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 potentially bigger impact event). Tonight...Surface high over the Ohio Valley tries to build west. As a result, the pressure gradient relaxes resulting in the winds dropping off. However, this doesn`t mean that we will have a milder night temperature wise. If anything, we should be a bit colder tonight (generally in the 20s, teens in the Poconos and NW NJ). Please see climate section on PHL first temp of the season below 30F. Am probably adding flurries and measurable snow showers to the Poconos tonight in the midday review/update.
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&& .SHORT TERM /SATURDAY/...
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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 could continue to be isolated lake snow showers/flurries developing which could make their way down to I-80 (even a dusting is possible). We will keep flurries/sprinkles for the middle part of the area as well as the short wave passes just to our north. West to northwest winds should gust 20 mph, especially afternoon.
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&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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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.
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&& .AVIATION /14Z FRIDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of today...VFR sct-bkn aoa 4000 ft. flurries vcnty KABE and KRDG mid afternoon. west wind gusts increasing to 22-30 kt this afternoon. tonight...VFR becoming clear with west to northwest wind gusts under 20 kt. The exception is mvfr cigs and ocnl flurries in the Poconos. Saturday...VFR sct-bkn aoa 4000 ft. Isolated snow showers or flurries are possible across the northern half of the area during the day, which may temporarily lower conditions, especially I-80 region northward. Gusty west to northwest winds 15-20 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.
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&& .MARINE...
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SCA continues south and central with max gusts today into the evening of 28 to 32 kt. Hoping to not have to issue another GLW for the entrance to De Bay. Meanwhile, for the waters north of Atlantic city (little Egg Inlet to Sandy Hook), gusts occasionally around 35 kt today, especially a couple of miles out; and this evening there is expected to be a northwest flow enhancement of wind from Sandy Hook and 44065 southeastward with gusts of 35 kt to possibly 40 kt. Winds will only slow decrease late at night due to large over water lapse rates and the cool boundary layer heat sink. May need to extend sca a bit into Saturday. Gale verification: 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. We had many locations along the water with 30 to 100 min period of mid 30s gale gusts, 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.
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&& .CLIMATE...
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Note: The low temp expected at PHL Saturday morning should be the coldest of the season so far at PHL (25-29F), the first 20s of the season. Last winter, it didn`t drop into the 20s until January 4th 2016!
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 1 AM EST Saturday for ANZ452>455. Gale Warning until 6 PM EST this evening for ANZ450-451. Small Craft Advisory until 10 PM EST this evening for ANZ430- 431. && $$ Synopsis...Robertson 1003 Near Term...Drag 1003 Short Term...Drag 1003 Long Term...Robertson Aviation...Drag/Robertson 1003 Marine...Drag/Robertson 1003 Climate...1003

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