697 FXUS61 KPHI 011420 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1020 AM EDT Wed Apr 1 2020 .SYNOPSIS... Low pressure off the Southeast U.S. coast will move northeast into the western Atlantic, then will meander southeast of Nantucket Island through Friday. Meanwhile, surface high pressure builds in from the west. Low pressure departs over the weekend as high pressure builds along the Eastern Seaboard. Low pressure approaches for the start of the new work week. && .NEAR TERM /THROUGH TONIGHT/... For the mid morning update: The only significant change was to decrease cloud cover forecast in the Delaware Valley and Northern NJ where dry air has helped erode the earlier low clouds. Not sure this will continue all day however; as mentioned by the previous shift, cold air aloft should promote cloud development as low level temperatures increase into this afternoon. Previous discussion: An upper level trough axis will pivot across the area then shift offshore today as ridging very gradually starts to build over the Midwest. Meanwhile, an area of low pressure will shift further offshore of the mid-Atlantic today, developing into a powerful hurricane force low as it does so but taking its precipitation shield well away from us. The air aloft is quite cool with the upper trough overhead, so expect there will be a lot of diurnally driven cloudiness today, though should be some breaks of Sun also. Cannot rule out a spotty pop up shower, but with winds gradually shifting from northeasterly to northerly and northwesterly, the profiles will be drying out and expect it to be a dry day. Highs mainly in the low to mid 50s. Some wind gusts of 20 to 25 mph are possible especially to the east thanks to the offshore low, potentially a little stronger right at the coast. These winds should diminish later in the day. && .SHORT TERM /THURSDAY THROUGH 6 AM THURSDAY/... An uneventful night is expected. Skies will finally turn mostly clear overnight as low pressure moves further offshore and diurnally driven clouds dissipate early. With mainly clear skies and 850mb temperatures dipping to near -5C, it will be a chilly night. The pressure gradient will be at its weakest early in the night, but should start to restrengthen during the latter part of the night which will lead to a steady northwest breeze developing. This will preclude ideal radiational cooling, but most areas will still fall into the 30s for lows. Because of the warm winter, we are starting our frost/freeze program a little earlier than normal, with areas mainly south of I-78 starting as of today, April 1. Forecast lows leave open the possibility of some frost, but currently believe the winds should be sufficient to preclude its development. && .LONG TERM /THURSDAY THROUGH TUESDAY/... For the late-week period, the area finds itself between surface high pressure building in from the west and low pressure several hundred miles east of Nantucket Island. The low will retrograde back towards the mainland late Thursday through Friday, and warp-around precip will rotate towards northern and coastal portions of New Jersey. Not expecting much in the way of QPF during this time, generally a few hundredths of an inch or so total. Temperatures will be near to maybe a couple of degrees below normal, topping off in the mid to upper 50s throughout. Surface high pressure builds over the area for the weekend, but some strong shortwave energy associated with a deep closed low offshore will pass through the region on Saturday, and this may touch off some light rain showers. Will cap PoPs at slight chance. High pressure moves offshore Saturday night through Sunday morning, and then a weak cold front passes through Sunday afternoon. Again, some showers are possible, but will cap PoPs at slight chance for now. A broad 500 mb ridge develops over the central U.S. for the start of the new week, and WAA will be in place for Monday and Tuesday. Temperatures warm well into the 60s, possibly touching 70 in some spots, during this time. Developing low pressure approaches on Tuesday. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through this evening... Mainly VFR. However, localized MVFR conditions are possible especially at KACY and KMIV. Winds gradually shifting from northeast to north- northwest through the day. Wind speeds around 10 kt with gusts to 20 kt possible, a little stronger in coastal areas including ACY. Winds will gradually diminish during the later afternoon and evening hours. Moderate confidence. Tonight... VFR. Northwest wind 5 to 10 kt, with some gusts to 20 kt possible during the latter half of the night. High confidence. Outlook... Thursday through Thursday night...Mostly VFR conditions expected. Northwest wind 15 to 20 kt with gusts up to 25 kt. Moderate confidence. Friday through Friday night...Mostly VFR conditions, however, MVFR conditions possible as rain moves in from the east. N winds 10-15 kt, diminishing to less than 10 kt Friday night. Moderate confidence. Saturday...Mostly VFR conditions expected with light east winds. Moderate confidence. Sunday...Starting with VFR conditions, though ceilings could lower to MVFR through the day. Southerly and southwesterly winds of 5 to 10 kt. Moderate confidence. && .MARINE... Today...A Gale Warning is in effect for southern portions of the Atlantic coastal waters until 6PM today due to northeast winds gusting up to 35 kt, especially this morning. It is a bit questionable as to whether winds will get quite that strong in most areas, but will maintain the warning for now. Will likely be able to cancel the warning early and replace with an SCA this afternoon. For the northern Atlantic coastal waters, SCA conditions are expected with winds gusting up to 30 kt and seas 4 to 7 ft. For all Atlantic coastal waters, winds will gradually shift from northeasterly to northerly today along with a gradual decrease in speeds this afternoon. On the Delaware Bay, SCA conditions are expected this morning due to northeast winds gusting to 25 kt. This afternoon, conditions will subside to sub-SCA levels as winds gradually shift to northerly then northwesterly and decrease in speed. Tonight...SCA conditions expected on the Atlantic coastal waters with seas 4 to 6 ft and increasing northwest winds, with gusts 25 to 30 kt likely during the latter half of the night. On the Delaware Bay, initially sub-SCA conditions expected but SCA conditions will develop over the second half of the night as northwest winds gust to 25 kt. Outlook... Thursday through Thursday night...SCA conditions on all waters, although a brief period of gales is possible. Friday through Sunday...SCA conditions are expected, primarily on the coastal waters, mainly due to elevated seas. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ450>452. Gale Warning until 6 PM EDT this evening for ANZ453>455. Small Craft Advisory until noon EDT today for ANZ430-431. Small Craft Advisory from 1 AM Thursday to 6 AM EDT Friday for ANZ430-431. && $$ Synopsis...MPS Near Term...Johnson/O'Brien Short Term...O'Brien Long Term...MPS Aviation...Johnson/MPS/O'Brien Marine...MPS/O'Brien