Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 131010 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 510 AM EST Mon Nov 13 2017 .SYNOPSIS... Low pressure will move off the Mid-Atlantic coast today. High pressure builds into the Eastern Seaboard on Tuesday and lifts to the north and east and offshore late Wednesday. Low pressure passes north of the area Wednesday night and Thursday, followed briefly by high pressure on Friday. A complex area of low pressure, along with a strong cold front, will move across the area over the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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As of 5 AM, the winter weather advisory has been cancelled. Temperatures are holding steady or even locally rising a little, and dew points are also creeping up. Overall, a chilly light rain falling, however some snow may still occur especially into parts of the Poconos to far northwestern New Jersey but any accumulation would be light. An upper-level trough will move across our region today, however the flow is progressive and therefore this feature is expected to shift offshore late in the day, however it will induce surface low development east of our coasts. There is a fair amount of lift associated with it, with focused positive vorticity advection mostly across the southern and eastern areas. This is where nearly all the guidance is showing widespread measurable precipitation through about midday. Based on this and radar trends, increased the PoPs to 100 percent for a time. This is expected to be in the form of a chilly rain. The forecast challenge continues to be portions of the northwestern zones, particularly where a Winter Weather Advisory is in place for early this morning. There is a decent amount of dry air initially in place and this would normally result in evaporational cooling. However, the cloud cover is keeping temperatures up and the light intensity of the precipitation should allow the surface dew points to increase. This is already occurring for some places early this morning. This trend, if it continues, will result in little in the way of icing/mixed precipitation potential. The soundings also indicate no deep warm layer aloft, therefore perhaps some mixed snow and sleet especially at the onset due to some cooling effects. This would be light however. Any precipitation that reaches the Poconos may just be in the form of light snow. Otherwise, the precipitation ends from west to east by early to mid afternoon then lots of cloudiness for the area through much of the day. The clouds should thin some from the west during the afternoon. The eastern areas should hang onto the cloudiness the longest. With the idea of more clouds longer, a blend of the MOS results in cooler high temperatures for today.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... As the upper-level trough shifts farther to our east, the flow aloft is forecast to turn more zonal tonight. High pressure at the surface gradually builds eastward through the overnight, and with drier air and subsidence overspreading our area the clouds will clear out at least for awhile. There should be at least some high cloudiness streaming across parts of the region overnight within the more zonal flow aloft. It will be another chilly night, however not as cold as a few nights ago since the airmass is not nearly as cold or dry. Low temperatures are mostly an even blend of MOS and continuity. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Sprawling high pressure will expand from eastern Canada, down through the Northeast and Mid-Atlantic, and into the Lower Mississippi Valley on Tuesday, and this high lifts to the north and east through Wednesday, and finally moves offshore Wednesday night. Fair weather expected with high temperatures moderating through the 50s. Weak low pressure tracks across Canada Wednesday night through Thursday. This will drag a warm front through the Northeast and Mid- Atlantic Thursday morning, followed by a cold front late Thursday. Scattered showers possible, mainly north and west of I-95, late Wednesday night. Highs on Thursday top off in the mid and upper 50s across most of NJ, into southeast PA and the Delmarva, and in the upper 40s to low 50s across NW NJ and eastern PA. High pressure then briefly builds across the region on Friday. During this time, low pressure works its way across southern Canada and into the Great Lakes and is gearing up to impact the region over the weekend. Global models are in decent agreement with the big picture in terms of bringing the warm front through the region sometime Saturday, followed by a cold front sometime Saturday night or Sunday. The 00Z GFS is faster than the 00Z ECMWF and the 00Z CMC- GDPS, in which it brings the warm front through Saturday morning, followed by the cold front Saturday afternoon. The ECMWF and the CMC have a slower track, and does not lift the warm front through the region until sometime Saturday afternoon, and the cold front until late Saturday night or Sunday morning. Model guidance has been fairly consistent with likely PoPs on Saturday, so will follow suit. Several strong shortwaves will pass through the region during this time as well. Depending on timing and placement of those shortwaves, this could set up a period of heavy rain sometime Saturday afternoon, in addition to the potential for a rumble of thunder while the region is in the warm sector. When the cold front passes through, this ushers a much colder airmass into the region for Sunday. Low pressure remains over eastern Canada, and with this colder airmass spreading into the Northeast, there may be some snow showers across the Poconos Saturday night and Sunday morning. Also possible for some Lake Effect streamers to possibly graze the Poconos on Sunday as well. Highs fall from the mid to upper 50s over most of eastern PA and NJ and even the low 60s over the Delmarva on Saturday to the 40s on Sunday. && .AVIATION /10Z MONDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through today...MVFR ceilings at most terminals. Some IFR ceilings should develop especially at ACY this morning. An area of mainly light rain will move across the area, ending from west to east by early afternoon. This will lower the visibility to MVFR at times. Light and variable or light north-northeast winds, becoming north 5-10 knots. Tonight...VFR. Northerly winds mainly 5 knots or less. Outlook... Tuesday through Wednesday...VFR. Light north winds on Tuesday, becoming southeast late Wednesday. Wednesday night through Thursday...Sub-VFR conditions possible in -SHRA. Thursday night through Friday...VFR. NW winds possibly gusting to 20 kt Thursday night.
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&& .MARINE... The winds and seas are expected to stay below Small Craft Advisory criteria through tonight. However, a northerly wind will increase through the day with a bit of a northerly surge tonight for a time. The potential for 25-knot gusts looks marginal and mostly short in duration, therefore will hold off on an advisory. Low pressure develops offshore through today, then moves out to sea tonight and strengthens some. This will bring a round of rain to the area today. Outlook... Tuesday through Wednesday...N winds 10-15 kt with gusts to 20 kt. Seas below 5 feet. Thursday...W winds 10-20 kt with gusts to 30 kt. Brief period of gales possible Thursday night on the ocean. Friday...NW winds 5 to 10 kt. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...None.
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&& $$ Synopsis...MPS Near Term...Gorse Short Term...Gorse Long Term...MPS Aviation...Gorse/MPS Marine...Gorse/MPS

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