Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 071803 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 103 PM EST Wed Dec 7 2016 .SYNOPSIS... Low pressure off the mid Atlantic coast will move out to sea today while another area of low pressure drifts through southeast Canada. This low will continue to slowly drift eastward through the end of the week and move offshore of the Canadian maritimes by Friday and Saturday. With high pressure to our west, a strong west to northwest flow will remain through the end of the week. High pressure briefly affects the area Saturday night. An area of low pressure is forecast to move north of the area Sunday into Sunday night, bringing a cold front across the area. && .NEAR TERM /THROUGH TONIGHT/...
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1230 PM: Low clouds hanging on longer than modeled and possibly due to a lack of much nw flow dry air advection. the the drizzle/light rain is essentially done. nw flow with isolated gusts 18 kt. a bit of sun through multilayers of sun. Little change to the mid shift fcst temps. High temperatures will generally be in the 45-50F range with cooler spots in the higher elevations of NE PA and NW NJ (mid 30s to lower 40s) and warmer spots in S DE and E MD (low 50s). Tonight...we will presume the subsidence inversion dissipates and that so too it clears, before mid deck arrives after midnight from the west. light west to northwest wind. fcst elements are a 50 50 blend of the 12z/7 GFS/NAM MOS. its possible that there could be isolated frosty fog patches in the countrysidein light boundary layer flow radiational cooling sitn.
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&& .SHORT TERM /THURSDAY/... Considerable mid and high cloudiness during the morning becoming mostly sunny and breezy during the afternoon with westerly winds gusts expected to increase to 25 mph. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... On Thursday, an area of low pressure will slowly be moving across eastern Canada, before reaching the Canadian maritimes Friday into Saturday, while high pressure remains across the central part of the country. This will keep a steady west to northwest flow across the area. A broad trough aloft will remain across the east coast, with an elongated vorticity impulse moving across the area Thursday and a weaker impulse moving across the area Friday. There is not a lot of moisture across the area Thursday as it`s forecast to remain northwest of the area, but the strength of the vort max and the surface winds may help carry some flurries/sprinkles across the area during the day. On Friday, the short wave is weaker, but there is more enhanced low level moisture and steep low-mid level lapse rates during the day, so there could be even more widespread showers or flurries/sprinkles across the area. Especially across our northwestern areas. By Saturday, another short wave/vorticity impulse is forecast to move across the area as the northwest flow begins to weaken as the low lifts farther away and high pressure begins to approach from the west. There will continue to be steep low-mid level lapse rates during the daytime combined with some enhanced moisture, especially across the northern areas. Therefore there will continue to be a chance for some isolated showers/flurries across the northern half of the area. High pressure briefly affects the area Saturday night, providing dry conditions. Thursday through Saturday will be a cold and windy period, with Friday being the windiest, and Saturday being the coolest of the 3 day period. On Sunday night, an area of low pressure is forecast to move north of the area, pulling a cold front across the region. Another low pressure is forecast to develop along the boundary, although the GFS and ECMWF differ on where they develop the low. The GFS develops this secondary low north of the area, while the ECMWF develops it to our south. Sunday night looks like the most likely period for precipitation, but it could linger into Monday if the low does develop around or south of the area as the ECMWF indicates, so we`ll keep a chance of precipitation into Monday. Temperatures will be cold enough for portions of the area to experience wintry precipitation. The exact timing and placement of wintry precipitation is still to be determined, but as usual, the most likely areas for snow would be the northern half of the area. Dry conditions are currently expected for Monday night into Tuesday as high pressure is forecast to briefly build to our south and nose its way into our area. The GFS and ECMWF are showing the potential for a coastal low to develop on the old frontal boundary to our south by next Wednesday, which could bring some precipitation to the southern half of the area. With cold temperatures, it`s possible that a period of snow could develop for the southern portions of the area. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of this afternoon...mvfr cigs in the process of lifting to vfr cigs near 3000 ft. Wind generally northwest with gusts under 15 kt. Tonight...VFR. W-NW winds will be light (under 10 kt). Thursday...VFR multi layered cigs aoa 10000 ft during the morning with chance of an hour of cigs near 6000 ft during midday with isolated sprinkles. Then becoming VFR clear by late in the day. Westerly wind with gusts 20-28 kt during the afternoon. OUTLOOK... Thursday night-Saturday...MVFR CIGS may be possible each morning before lifting to VFR during the day. Scattered showers or flurries/sprinkles are possible during the daytime of each day which may temporarily lower conditions. Gusty west to northwest winds 15- 25 knots, strongest winds Thursday and Friday. Sunday...VFR early, lowering to MVFR then IFR by the afternoon and overnight. Rain or snow possible late in the day and overnight.
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&& .MARINE...
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SCA seas may need an extension. Will make a decision by 2 or 3PM. Seas are still running above predicted values in response to last evenings gale. Pls see MWW or the CWF. Seas subside this evening. Thursday...anticipating the need for a westerly flow cold air advection small craft advisory for many of the waters Thursday afternoon. OUTLOOK... Thursday night-Saturday...Small Craft Advisory levels winds expected through the periods with west to northwest winds gusting 25-30 knots. Saturday night-Sunday...Winds expected to drop below Small Craft Advisory levels, but pick up again late Sunday.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory for hazardous seas until 10 PM EST this evening for ANZ452>455. Small Craft Advisory for hazardous seas until 6 PM EST this evening for ANZ450-451. && $$ Synopsis...Robertson Near Term...Drag 103 Short Term...Drag 103 Long Term...Robertson Aviation...Drag/Robertson 103 Marine...Drag/Robertson 103

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