Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 170339 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1039 PM EST Sat Dec 16 2017 .SYNOPSIS... A cold front will move southeast across our region tonight, then it will return northeast of the region as a warm front late Sunday night. Another cold front will then move through the Mid- Atlantic states Tuesday night. High pressure follows Wednesday night. Thereafter, to end the week, an area of low pressure will track northeast from the Great Lakes and advance a warm front into our region. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... As of 900 PM, a cold front was draped west to east across about the middle of our region. This front will continue to settle south-southeastward through the night. Strong northwesterly flow above the surface continues to pull plenty of cloud cover across much of our area, although far southern New Jersey, Delaware and northeast Maryland have pretty much cleared out. These clouds may be stubborn for much of the night as an inversion develops in the wake of the cold front. Some drier air may entrain though and assist in eroding at least the southern portion of the cloud field overnight. We increased the clouds some especially across the northern areas. The presence of the clouds is keeping temperatures from dropping as fast, and farther south there is just enough of a southwest wind ahead of the front keeping the temperatures from dropping faster. As a result, temperatures needed some adjusting. Low temperatures especially up north might be to low if the cloud cover hangs on all night. The earlier area of light snow across central New York to just northwest of the Poconos has dissipated, although radar shows some weak returns moving toward the Poconos. We carried a mention of flurries through the rest of the evening across the far northwest zones. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... Weak high pressure will be across the region on Sunday, with the cold front just to our south. This front will begin to lift north as a warm front, and cloudiness will increase during the day. For now, precip is expected to hold off until later in the evening. (see the long term section for more details on this system). Max temps will be a few degrees below normal with light winds. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... 500 MB: A warm ridge centered over the southern Appalachians will weaken Wednesday with the passage of a substantial short wave through se Canada. Thereafter...warmer that normal heights prevail over the se USA with a resurgence of the ridge over the se coast next weekend. Cooler than normal heights are near Hudson Bay, resulting in a fairly strong wsw jet from the southern Plains to the mid and north Atlantic coast. Temperatures: The first 15 days have averaged below normal, ranging from 3.5F below normal at KMPO to near 1 degree below normal elsewhere. (Monthly melted w.e. pcpn has been below normal but snowfall, at least in our area of the I95 corridor is already well above the monthly normal at both PHL and NYC!) In any case calendar day average temps are modeled near normal around 5F above Monday, around 10 above Tuesday, maybe as much as 5 above Wednesday, near normal Thursday then probably warming again next Thursday and Friday to at least several degrees above normal (the EC suggests 15F above normal average temps next Saturday-we used the cooler WPC/MEX blend). Forecast basis: Unless otherwise noted Sunday night-Monday night is a 50 50 blend of the 12z/16 GFS-NAM MOS, Tuesday the 12z/16 GFS MEXMOS and next Wednesday-Saturday (D4-8) is the 15z/16 WPC 12 hr elements of the max-min temps/pops and 6 hrly td/wind/sky. Sunday night...our grids have a 25 to 40 pct chance for a period(s) of light snow or mixed freezing-frozen pcpn in E PA and the n2/3rds of NJ in weak waa. There is considerable uncertainty regarding the extent and timing of any light pcpn so snow and ice amounts are not officially posted in storm total grids (less than 55% chance). Also, the forecast wording is also therefore fraught with uncertainty. Near 1/2" snow is possible near and north of I80 and spotty trace to .03 radial freezing rain icing is possible in the I78-I276 region. Subfreezing ground temps will need to be considered for any possible advisory. Otherwise mostly cloudy and milder. Light south to southwest wind. PWAT 0.55" Confidence: average. Monday and Monday night...Variable cloudiness or P/S and milder. PWAT dries out slightly from nw to se to 0.45". West wind. Confidence: average Tuesday and Tuesday night...a very very nice mid December day- warmup...southwest wind may gust 20-25 MPH during the afternoon, then shifts northwest by midnight. Above normal temps by 10 to 14 degrees. A CFP during the evening may generate a few rain showers-sprinkles far north (end as snow showers or flurries Poconos?) but PWAT is further drying out from nw to se so Confidence: average or below average on whether it precipitates. Wednesday...High pressure building in from the west. P/S cooler with a nw wind gust 20-25 mph during the morning diminishing mid afternoon. Thursday...Variable, mostly high clouds. Seasonable colder. Light wind. Saturday...conservative and much below average confidence on what may happen. Pretty much WPC grids. && .AVIATION /04Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR, with a ceiling mainly between 4000-8000 feet at most terminals. Southwest winds 5 knots or less, becoming west and then northerly overnight (locally light and variable) as a dry cold front moves through. Sunday...VFR overall. Some cloud bases around 2500 feet may develop especially north and west of KPHL. Northeast winds around 5 knots or light and variable. Outlook... Sunday night: Brief Sub-VFR possible with patchy light rain, mixed precipitation possible at KABE, KTTN and KRDG. South to southwest winds under 10 knots. Confidence: Average or below. Monday and Monday night: Mainly VFR. Westerly sustained winds generally under 10 knots. Confidence: Above average. Tuesday through Wednesday: VFR. An isolated shower cannot be ruled out Tuesday evening north. Southwest wind gusts around 15-20 knots then shifting to northwest and increasing to around 20-27 knots Wednesday morning. Confidence: Above average. Thursday...VFR. Light wind. Confidence: Above average. && .MARINE...
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The cold front has moved south of the northern and central New Jersey shore. As a result, winds and seas have diminished. Therefore, the small craft advisory has been cancelled. As the front continues south overnight, winds will veer from southwest to north- northwest, then to the northeast on Sunday (expect southeast on DE Bay), but winds are not expected to return to Small Craft Advisory levels late tonight and Sunday. Outlook... Sunday night-Thursday...No headlines anticipated except for Wednesday morning when a NW flow SCA of 25-30 kt wind gusts is anticipated. Confidence: Above average.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...None.
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&& $$ Synopsis...Drag Near Term...Gorse Short Term...Franck Long Term...Drag Aviation...Drag/Gorse Marine...Drag/Franck/Gorse/Johnson

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