Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 211858 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 258 PM EDT Tue Mar 21 2017 .SYNOPSIS...
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A cold front will slide through the area tonight. A large area of high pressure then builds in from the northwest and stays over our region through Thursday before shifting off shore. A warm front is forecast to lift through our region on Friday. Low pressure is expected to approach from the west over the weekend.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Mostly quiet conditions much of tonight before a strong cold front crosses the area. The front should cross the northern areas 3 - 5 a.m. and reach the southern parts of the forecast areas 5 - 7 a.m. No precipitation and little in the way of cloudiness is expected. Temperatures will drop into the 20s up across the north and dip into the low/mid 30s over south NJ and se PA. The front will not reach Delmarva before morning, so readings there will only drop into the mid/upper 30s. Winds will be light before the front and then gust to 20-30 mph from the NW behind it.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
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Strong high pressure will build towards the area Wednesday. A strong and gusty NW wind with dry air will be across the area through the day. Skies will be clear and temperatures will be below normal. Highs will only be in the low/mid 40s over Delmarva and the 30s elsewhere. Wind chill values will will only be in the 20s in many areas for the afternoon. Winds will gust 30-40 mph at times.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
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Long term discussion will be issued shortly. Previous long term discussion: Cold front will be south of the Mid-Atlantic region by Wednesday morning, and then strong CAA will be underway with well below normal temperatures for the mid-week period. Low pressure near the Canadian Maritimes will intensify, and although there should not be many direct impacts from this low, a tight NW pressure gradient will form between that and high pressure building into the Great Lakes. This will tap into cold Canadian air, resulting in highs in the 20s in the Poconos, 30s for most of PA/NJ, and in the low 40s for MD/DE. With NW winds 15-20 MPH with gusts up to 30 MPH, wind chills will range from the single digits up north to the 20s for most of the CWA. Lows Wednesday night will be quite cold for this time of the year, ranging from the single digits in the Poconos to the teens for much of NJ/PA, and around 20 for the Delmarva. Temperatures moderate a bit on Thursday as heights rise as the low over the Canadian Maritimes moves offshore, and high pressure over the Great Lakes builds east. Although still below normal, highs will be in the 30s and 40s. By Friday, high pressure moves off the Mid-Atlantic coast, and return flow sets up as a warm front lifts towards the region. Some overrunning precip will develop ahead of that warm front, and a brief period of freezing rain is possible for the Lehigh Valley/Pocono Mountains early Friday morning. Rain then develops for most of the area by Friday afternoon as that warm front continues to lift north through the region. Temperatures return back closer to normal, topping off in the 40s and 50s. On Saturday, high pressure off the Mid-Atlantic coast drifts out to sea. Meanwhile, low pressure organizes over the Southern Plains and Midwest. This will put the Northeast and Mid-Atlantic in the warm sector, and temperatures will soar well into the 60s, and possibly the low 70s across MD/DE. Although some sites may come close, high temperature records look to be safe. Thereafter, low pressure over the Midwest tracks east through the Ohio Valley and then towards the Appalachians Sunday and Monday. Based on the latest forecast, there may be enough cold air at the surface initially for a period of freezing rain Sunday night/Monday morning. Otherwise, temperatures currently look to be warm enough to support all rain, and can expect precip for the start of the new week.
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&& .AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Clearing has continued to progress across the terminals this afternoon. Skies will only feature some high level clouds this evening and much of the overnight. A few low clouds with a sharp cold front which will cross the area towards dawn. I have only put few-sct coverage for any low clouds overnight. Winds will be light W/NW into the overnight, then winds will sharply increase after fropa. The timing of the front is roughly 09z West and 11Z east. Winds will become NW at 15 to 20 knots with gusts 25-30 knots. These winds will continue into Wed with mostly SKC. Outlook... Thursday...Mostly VFR conditions are expected. Friday...MVFR or lower conditions are possible with precipitation generally along and northwest of the Delaware Valley (including PHL, ILG, PNE, TTN, ABE, and RDG). For ABE, RDG, and TTN, there may be a brief period of a wintry mix Friday morning. Friday night through Saturday...mostly VFR conditions are expected. Saturday night and Sunday...MVFR or lower conditions are possible with rain across the region.
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&& .MARINE...
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Nice conditions on the waters this afternoon will continue through much of the overnight. A sharp cold front will cross the waters well after midnight and cause winds to shift to NW and increase. Gale warnings are in effect for the period after this frontal passage as winds will probably gust 35 to 40 knots at times. We expanded the Gale to cover Delaware Bay and the Delaware coastal waters. Cold air and decent flow aloft should have no problem mixing down. No precipitation is expected tonight or Wednesday. Outlook... Wednesday night...winds and seas will diminish through the overnight hours. Thursday...Once wind gusts drop below 25 kt early in the day, sub-SCA conditions are expected. Friday...winds may approach 25 kt leading to SCA conditions Saturday...sub-SCA conditions expected. Sunday...there is a chance wind gusts could build above 25 kt late in the day.
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&& .FIRE WEATHER...
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Relative humidity levels will drop behind the front Wednesday. Gusty winds will cause near Red Flag conditions during the afternoon. After calling the fire weather partners, it seems that soil moisture is still rather high in many areas. The Delmarva is the only exception where conditions may be rather marginal for RFW. We will probably issue an SPS overnight to highlight these dry windy conditions.
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&& .CLIMATE...
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More record events possible this week. One or 2 of the following are vulnerable record equaling lows Thursday morning March 23, primarily ABE. Others are listed for reference ACY-13 1875 PHL-14 1885, 1875 ILG-14 1934 ABE-13 1934 TTN-13 1934 GED-16 1959 RDG-14 1906 MPO- minus 8 1912
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Gale Warning from 6 AM to 11 PM EDT Wednesday for ANZ430-431- 450>455.
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&& $$ Synopsis...Johnson Near Term...O`Hara Short Term...O`Hara Long Term...Johnson Aviation...Johnson/O`Hara Marine...Johnson/O`Hara Fire Weather... Climate...

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