Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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722 FXUS61 KPHI 180533 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1233 AM EST Thu Jan 18 2018 .SYNOPSIS... Low pressure with its attendant frontal system will move off the East Coast tonight. High pressure will build across the Gulf coast through the end of the week, then offshore over the weekend, bringing fair weather to the mid- Atlantic region. Low pressure is forecast to develop over the central U.S. on Monday. This low will move northeast through the Great Lakes Monday night into Tuesday, pulling a cold front across the mid- Atlantic area on Tuesday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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Quiet weather on tap through the overnight. Skies continue to clear out, and winds for most of the area will diminish to less than 5 mph. The exception will be along the southeast NJ coast and into the Delmarva, where NW winds range from 10-15 mph with gusts up to 20 mph. For areas where winds are light, the combination of clear skies, light winds, and new snow on ground will allow for radiational cooling and temperatures will drop off dramatically. Will adjust hourly temperature grids going through the early morning hours. Will also drop overnight lows by a few degrees across the Poconos and Lehigh Valley.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... On the heels of the low, a mid level short wave ridge is expected to propagate over the region through the day tomorrow resulting in mostly sunny conditions. At the surface, the pressure gradient is expected to increase for a period tomorrow as the surface high builds in. As a result, could see some gusty conditions, but on land, not expecting gusts above 25 mph. Temperature wise, we will still have cold air advection with the northwesterly flow. As a result, expect highs to be from the mid 20s to near 40 across the region, or about 5 degrees below normal. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... The extended forecast will feature somewhat above normal temperatures (for a change) and generally fair weather at least through this weekend. A fairly strong frontal passage with associated low pressure and precipitation is expected sometime on Tuesday of next week. By Thursday night the low pressure aloft now over the southern Appalachians will be well offshore. A fast-moving shortwv trof will swing across New England but should have little effect on sensible weather over the mid-Atlantic region. Thereafter through the weekend zonal flow aloft will prevail across the north-central and northeast US. Meanwhile a large area of high pressure centered along the GlfMex coast will gradually shift east and off the southeast US coast by Sunday. Westerly flow around the northern periphery of this high will help maintain fair weather with a trend toward moderating temps, especially starting Saturday. A fairly deep trof aloft is forecast to move into the western US over the weekend and into the central GrtPlns by Monday. In response surface low pressure should develop over the Plains and move eastward into the GrtLks by Tuesday. The associated cold front should move through NJ and vicinity roughly in the Tuesday morning time frame, although the latest ECMWF looks a bit slower. Increasing SW low-level flow ahead of the low/front will result in increasing moisture starting Sunday night. At that time the forecast includes slight chance PoPs well north of PHL, with the possibility of some freezing rain or drizzle, depending on the degree of overnight surface cooling. Forecast PoPs increase from chance on Monday to likely Monday night with the approaching cold front. Depending on how quickly cold air moves in, there could be some changeover to snow in the Poconos late Monday night. Due to timing uncertainty, the forecast maintains some chance for precip through Tuesday, mainly in the morning. Forecast max temps for Tue are still above freezing (and above normal) but cold advection aloft could produce snow showers well N/W of PHL. The air mass behind the front is not terribly cold and forecast max temps for Wednesday look to be still slightly above normal. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Overnight...VFR conditions. After 09-10Z, wind speeds at 2000 feet will will increase to around 40 kt with light surface winds. Will add a LLWS group to the 06z TAFs. High confidence. Thursday...VFR/SKC. NW winds 10-15 KT with gusts up to 20 KT, except for KPHL/KACY, where gusts up to 25 KT are possible. OUTLOOK... Friday through Sunday...VFR conditions expected. West to southwest winds, generally less than 10 kt. High confidence. Monday...Mainly VFR conditions but occasional MVFR possible in scattered showers.
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&& .MARINE...
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Expect the highest winds, and most widespread Small Craft Advisory conditions to occur late through mid morning Thursday. Gusts near or above 25 kt are likely to continue through the rest of Thursday. Therefore, have continued the SCA as is for now. Small chance a short fuse Gale Warning may be needed for the De Waters and lower De Bay in the 08-14z/18 time frame. Sct gusts 35 kt. OUTLOOK... Thursday night...Will extend SCA on ocean to 1AM Friday for continued 25 KT gusts. Otherwise, conditions expected to drop below advisory levels. Friday-Sunday...Conditions expected to remain below advisory levels, but winds may periodically gust around 20 knots. Monday...Increasing south winds with gusts possibly approaching SCA levels late in the day.
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&& .EQUIPMENT... The NOAA All-hazards weather radio transmitter in Sudlersville has returned to service with the correction of earlier phone line issues. RDG temp has rts. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 1 AM EST Friday for ANZ450>455. Small Craft Advisory until 10 AM EST this morning for ANZ430- 431.
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&& $$ Synopsis...AMC Near Term...Drag/Johnson/MPS Short Term...Johnson Long Term...AMC Aviation...AMC/Drag/Johnson/MPS Marine...AMC/Drag/Johnson/MPS Equipment...

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