Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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379 FXUS61 KPHI 191912 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 212 PM EST Sun Feb 19 2017 .SYNOPSIS...
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A cold front will move south across our region later tonight. High pressure will build over the Mid Atlantic during Monday into Tuesday before shifting offshore. A warm front arrives early Wednesday, followed by another warm front on Friday. As a surface low lifts across the Great Lakes region, a cold front will sweep across our area on Saturday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Yet another spring-like day across the entire area, with even some new record high temperatures occurring. An upper-level trough in eastern Canada is forecast to amplify southward some especially across New England. This will push a cold front down from the north, also known as a backdoor front, later tonight. As this occurs, cold air advection will strengthen some later tonight however this is more notable across the northern zones. This will allow temperatures to drop much more later tonight. As surface high pressure begins to build in from the west and northwest overnight, a subsidence inversion is forecast to strengthen with some moisture pooling beneath it. This moist layer looks rather shallow, however some guidance indicates some low clouds developing toward daybreak especially for portions of northeastern Pennsylvania into northwestern New Jersey. Areas farther to the south, the moist layer looks delayed and therefore no low cloud development is expected. A north-northwest wind will be light tonight despite some cold air advection on the increase, as surface high pressure draws closer. Low temperatures were mostly a blend of MOS and continuity. The hourly temperature and dew point grids are being adjusted this afternoon based on the latest obs, then the LAMP/LAV guidance was blended with continuity through early this evening. A forecast challenge through this evening could be just how quickly the boundary layer cools.
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&& .SHORT TERM /MONDAY/...
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A strong upper-level trough/closed low is forecast to exit New England through about early afternoon on Monday. This will allow surface high pressure to slide across our area, although it remains centered well to our north. This will provide a northerly wind across the entire region, although this should be on the light side given a loose pressure gradient. Some cold air advection is forecast to continue through much of the day, with the coldest air aloft found over our northern zones. This all translates into a cooler day, however highs will still be several degrees above where we should be for this time of year. A strong subsidence inversion to start the morning may trap in some lower clouds across mainly portions of northeastern Pennsylvania and northwestern New Jersey, otherwise this should weaken as the boundary layer warms enough. Otherwise, plenty of sunshine should become dominant as the forecast soundings indicate the column overall dries out through the day. High temperatures are mostly a continuity and MOS blend. The winds may turn a bit more northeasterly along the coast to assist with cooling off the chilly ocean waters.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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In the wake of the back door cold front, temperatures Tuesday will be about 10 to 15 degrees lower than today. By the later half of Tuesday, the surface high will be shifting off shore as a pre frontal trough approaches from the west. This will set up southerly low level return flow by Tuesday afternoon. As a result, expect an increasing chance for rain showers across the region. The next warm front is expected by late Tuesday night/Wednesday morning. Stayed close to a blend of guidance at this time, but as confidence increases for an early morning warm front arrival time, may need to go above guidance for Wednesday highs as guidance continues to underestimate warm air advection events. For Thursday and Friday additional warm air advection is expected, with Thursday possibly being the warmest day of the week (assuming that the previously mentioned warm front doesn`t slide back south into our region as a cold front early Thursday). However, warming on Friday could be tempered by overcast conditions and an area of rain expanding into our region thanks to a closed surface low lifting over the Great Lakes Region. The associated cold front with this low should sweep through the region early Saturday, though there is some uncertainty with the timing. As it does so, it should bring an abrupt end to the rain. Even with the forecast strong cold air advection, temperatures over the weekend may still be slightly above normal.
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&& .AVIATION /19Z SUNDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of this afternoon...VFR with some lingering high level clouds across the area. Northwest winds around 10 knots with some localized gusts up to 20 knots possible. Tonight...VFR. However, some guidance shows few to scattered stratocumulus around 2500 feet developing towards daybreak mainly to the north and west of PHL. Winds will remain out of the north to northwest at 10 knots or less. Monday...Some clouds near 2500 feet possible early mainly north and west of PHL, otherwise VFR. Light north-northwest winds increase to 10-15 knots between 15-18Z. Outlook... Monday night...VFR. Tuesday...Ceilings could lower to MVFR with rain showers continuing into Tuesday night. Wednesday and Thursday...Mostly VFR conditions are expected.
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&& .MARINE...
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High pressure will gradually build in from the west and northwest later tonight and Monday. This will result in a northerly wind, however an increase in cold air advection overnight and Monday morning should result in some increase in the winds especially across the northern coastal waters. It appears that any gusts to 25 knots mainly across the northern ocean zones look to be short in duration, therefore we opted to hold off on a Small Craft Advisory. Otherwise, the conditions are expected to remain below advisory criteria through the day Monday. Outlook... Monday night...winds may gust near or above 20 kt at times, but should stay just below 25 kt. Tuesday through Thursday...winds and seas should stay below SCA criteria.
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&& .CLIMATE...
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Several places have either tied or set a new record high temperature for today, as of 3 PM. Preliminary Record Event Reports (RER) are being issued for the sites breaking their record highs, and the final RER`s will be issued late this afternoon. Here are the record highs for today: PHL 68-1948 ILG 67-1997 ABE 63-1997 TTN 68-1948 GED 74-1976 ACY 73-1961 RDG 67-1997 MPO 58-1981
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gorse/Johnson Near Term...Gorse Short Term...Gorse Long Term...Johnson Aviation...Gorse/Johnson/Meola Marine...Gorse/Johnson Climate...

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