Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 172344 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 644 PM EST Wed Jan 17 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 THURSDAY MORNING/...
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630 PM ESTF: Lowered min temps tonight nw NJ and parts of e PA for some expected radiational cooling where lows may dip to 5 above over the typically cold sheltered areas when radiational cooling develops later tonight over a nice new fresh snowpack. Will post an updated snowfall PNS later tonight and expect another tomorrow. The snow analysis posted this afternoon on our social media sites will have to suffice. Remainder little change. From the 4 PM fcst discussion below. Expecting a return to tranquil weather overnight. The mid and upper level low progressing east should move off the Carolinas coast late tonight. The track of this low should be far enough south that we won`t see any additional precipitation, except for some very light snow through early evening across southern Delaware. Otherwise, expect clearing skies. With the light northwesterly flow, should see temperatures continue to fall, with lows in the single digits and teens across the area. The strongest winds and lowest temperatures should not be coincident with each other which will limit the low wind chill threat. Still, wind chill values below zero are possible across the southern Poconos (cold, but still above advisory level, and a far cry better than a few weeks ago).
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... 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 /THURSDAY NIGHT THROUGH WEDNESDAY/...
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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.
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&& .AVIATION /00Z 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 are expected with cigs abv 9000 ft along and e of ILG PHL TTN clearing east during the night. Northwesterly winds near or below 10kt are expected to continue overnight. High confidence. Tomorrow...VFR conditions with few, if any clouds. Northwesterly winds 10 to 15 kt with gusts up to 20 kt. High confidence. 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 tonight 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. OUTLOOK... Thursday night...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...
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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.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST Thursday for ANZ450>455. Small Craft Advisory until 10 AM EST Thursday for ANZ430-431. && $$ Synopsis...AMC Near Term...Drag/Johnson 644 Short Term...Johnson Long Term...AMC Aviation...AMC/Drag/Johnson 644 Marine...AMC/Drag/Johnson 644 Equipment...644

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