Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 192054 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 354 PM EST Thu Jan 19 2017 .SYNOPSIS... High pressure over the Mid-Atlantic will move offshore tonight through Friday morning. Weakening low pressure will lift northeast through the region late Friday. Weak high pressure returns for Saturday. A strong and complex area of low pressure will impact the Northeast and Mid-Atlantic from Sunday through Tuesday. A series of frontal boundaries will impact the area late next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Considerable cloudiness developed today below the low-level inversion. With the loss of daytime heating and a continued building of the mid-level ridge across the area, expect the clouds to diminish this evening with mostly clear skies developing. Then a cirrus shield will begin overspreading the region, around midnight in Delmarva, and reaching northwest NJ by sunrise. These clouds will work their way over the aforementioned ridge, in advance of the next storm system to impact the region Friday. In spite of the cloudiness, we should radiate efficiently in the normally colder spots north of I-78, as well as in the Pinelands, as high pressure centers over the region, maintaining light and variable winds. In the aforementioned locations, low temperatures will be in the mid to upper 20s, with low to mid 30s elsewhere. We also expect additional patchy fog, mainly north of I-78 and in the Pinelands, particularly where it occurred Thursday morning, given a similar air mass. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Low pressure moving through the Ohio Valley on Friday begins to undergo redevelopment offshore of the NC/VA border during the afternoon. As the mid-level ridge moves east of the area in the morning, an overrunning regime will setup across the region, with modest isentropic ascent along the 300K surface. Prior to that, with high level cloudiness having overspread the region, there is a sharp gradient in the remaining column moisture, suggesting the day will start out with sunshine, followed by overcast skies across the region by late morning. There is good model agreement in terms of mass fields and PoPs for precipitation overspreading the region from west to east between mid-morning and noon. Initially, we expect 2-meter temperatures to be cold enough (lower 30s) for a brief period of light freezing rain across Carbon and Monroe counties, ending around noontime. The more substantial precip should hold off until early afternoon across this area, which will limit freezing rain accumulations. At this time, our ice glaze map maintains a chance for a Trace to one-hundredth of an inch for portions of Carbon and Monroe Counties. This is less than previously forecast, per collaboration with our surrounding offices and WPC WWD. There is still some potential for additional freezing rain in the early evening if the column wet- bulbs more than expected, but that is a low probability, as even the high resolution models and ensembles have trended warmer. In terms of rainfall amounts, generally two to three- tenths of an inch across the region. High temperatures will still average above normal, generally mid 30s to upper in the Poconos and northwest NJ, with 40s elsewhere. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Weakening low pressure continues to lift NE through the region Friday evening. Precip will taper off over SE PA, NE MD, DE, and S NJ by midnight, and then precip gradually tapers off over N NJ prior to daybreak. Latest trend is for temps to remain above freezing, at least during the precip, so will not have freezing rain in the forecast, and will keep precip as plain rain. Latest NAM/GFS/ECMWF have the precip working through the region from 00-06Z, so early in the period will carry likely PoPs for N NJ and the Poconos, and generally chance PoPs elsewhere. Weak high pressure builds in from the west after midnight Friday night and into Saturday morning. With abundant low level moisture in place, and light to nearly calm winds, can expect areas of fog to develop, and depending on how much rain falls through Friday evening, fog could be locally dense. Dry conditions on Saturday as high pressure builds across the region and moves offshore late. Storm develops over the Gulf Coast on Sunday and begins to lift to the north and east Sunday night. Although models in general agreement, there are some key differences between the GFS and the ECMWF that have shown up with the morning model cycle. High pressure over NE Canada will begin to nose its way southward towards northern New England. Where this high sets up will have a profound impact on the forecast. Latest GFS has the high a bit farther south than the ECMWF, as a result, suppresses the approaching more than the ECMWF does. The GFS holds off on the heaviest precip until late Monday/Monday night, whereas the ECMWF has bands of heavy precip sliding along the coast starting on Sunday. As of now, feel best way to approach this is by planning on having periods of moderate to heavy rain from Sunday night through Monday night. Another aspect to consider: If that high noses a bit farther south, then much colder temperatures would filter into the region, and there is the potential for freezing rain sometime during the period. For now, will have a few hours of freezing rain in the forecast for Carbon and Monroe counties Monday morning, as this follows with the diurnal temperature curve. With a tight easterly gradient developing between the approaching low and the aforementioned high, there is the potential for Wind Advisory level winds for much of eastern NJ and into DE, generally to the south and east of I-95, with sustained winds of 25-35 MPH with gusts up to 50 MPH. The rest of the forecast area can expect east winds 15-25 MPH with gusts up to 40 MPH. Once the low lifts through the region Monday night, precip will come to an end fairly quickly. Unsettled weather on tap for the mid to late week period as several weak boundaries impact the region. Colder air looks to make a return by the end of next week. Until then, temperatures look to remain at above normal levels. && .AVIATION /21Z THURSDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Occasional MVFR ceilings early will lift for a time, then possibly scattered IFR ceilings toward sunrise. There may also be some patchy fog as well. Northwest winds becoming light and variable. Friday...Scattered MVFR ceilings in the morning lowering to IFR in the afternoon. With rain arriving at the TAF sites from late morning into the afternoon, we expect some visibility restrictions below 3SM. Winds will be east at 5 to 10 knots. OUTLOOK... Fri night...Sub-VFR conditions possible in -RA. Moderate confidence. Fog possible Fri night. Light winds. Sat/Sat night...Improving conditions Saturday morning, otherwise VFR. High confidence. Sun...E winds 10-15 KT. Conditions deteriorating from S to N during the day with IFR conditions possible by afternoon. Moderate confidence. Sun night thru Monday night...IFR and lower conds possible in RA. E winds 15-20 KT with 20-30 KT gusts at terminals north and west of I- 95, and 20-30 KT with 30-50 KT south and east of I-95 possible. Moderate confidence. Tuesday...Mainly VFR, but cannot rule out passing showers. Low confidence. && .MARINE... SCA for hazardous seas has been extended through this evening as ocean seas remain at 5-6 feet due to the long period swell. Guidance has been well underdone. Otherwise, we expect sub-SCA criteria for the waters late tonight into Friday. OUTLOOK... Fri through Sun morning...No marine headlines anticipated during this time. Seas will genly be around 2 ft with wind 10 kts or less. Sun aftn thru Mon night...Easterly flow increases to 15-20 KT with 25-30 KT gusts starting Sun aftn, and then gale force gusts of 35-40 KT likely Monday and Monday night. Moderate to heavy rain with low VSBY expected. Storm force winds possible, especially on Monday. Conditions begin to improve late Monday night, and winds decrease to SCA levels. However, seas on the ocean should remain above SCA criteria. Mon night thru Wed...wind decreases below headline criteria, but ocean seas will remain above SCA criteria. It is possible that some areas, especially across southern waters, may drop below SCA seas on Wed. && .TIDES/COASTAL FLOODING... Due to the persistent and increasing easterly flow around a coastal low Sunday-Monday, there could be several tidal cycles of coastal flooding, but this will also be dependent on the track of the low and will become more evident as we approach Sunday night and Monday. Latest guidance indicates the potential for widespread minor coastal flooding, but that will come into better focus this weekend. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory for hazardous seas until 1 AM EST Friday for ANZ450>455. && $$ Synopsis...MPS Near Term...Franck Short Term...Franck Long Term...MPS Aviation...Franck/MPS Marine...Franck/MPS Tides/Coastal Flooding... is the U.S. government's official web portal to all federal, state and local government web resources and services.