Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 190253 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 953 PM EST Wed Jan 18 2017 .SYNOPSIS... Low pressure over the western Atlantic waters will continue to drift out to sea tonight. Meanwhile, high pressure over the Midwest will build east and then move offshore at the end of the work week. Weak low pressure will impact the region this weekend, and then a stronger and more complex area of low pressure will impact the Mid- Atlantic and Northeast early in the new week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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IR satellite imagery and surface observations are indicating some breaks in the clouds are developing in eastern New Jersey, an indication the dry air is beginning to descend to the lowest levels. However, an additional contribution to the drying appears to be an increased northeasterly component to the winds this evening (advecting somewhat drier near-surface air into the area). Latest surface observations suggest this latter trend may be temporary, as winds are beginning to back to a more northwesterly direction west of the Delaware River. Where this is occurring, lower clouds are filling back in rather quickly. Nevertheless, given the increasingly transient nature to the thicker cloud cover in our eastern CWA, adjusted/lowered the sky grids a little bit through the night. Notably, this thinner cloud cover will act to increase nocturnal radiational cooling, which will likely aid in the development of patchy fog, especially in the Pine Barrens. Current grids handle this well and did not change at this time. Temps/dew points are running about 2-4 degrees higher than forecast this evening, as guidance is underestimating the effect of low cloud cover. Raised hourly temps/dews through the night and increased minimum temperatures by about 1-3 degrees across the region. As such, not quite as concerned about the chances for freezing fog, though this cannot be ruled out entirely near Mount Pocono and High Point, NJ.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... Patchy fog that does develop could linger into mid-morning, given maintenance of the low-level inversion with a building ridge aloft, and subsequent high pressure at the surface and light winds. The deeper moisture will continue moving north of the area, with some lingering clouds north of I-78 in the morning. Otherwise, a mostly sunny day develops, with some scattered clouds below the low-level inversion. Dry weather is expected, with no support for precipitation. As for high temperatures, generally 10 to 15 degrees above normal, from the low 40s in the Poconos to mid 50s in Delmarva. Northwest winds 5 to 10 mph. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... A prolonged period of warm and wet weather is on tap for the Long Term period. Broad area of high pressure along the Eastern Seaboard will move offshore Thursday night as weakening low pressure approaches from the west. Weak secondary low will form over the Mid-Atlantic, and the primary low will dissipate as is tracks from the Great Lakes into eastern Canada. This will send a quick shot of precip into the Mid-Atlantic and Northeast, but not expecting much more than 0.25" QPF or so. Best chances will be from midday Friday through Friday evening. Conditions dry out after midnight Friday night. One concern is timing of onset of precip for the Poconos and areas to the north of I-80. If precip develops before noon on Friday, surface temps may not yet have risen above freezing, and there could be a brief initial period of rain/freezing rain. Otherwise, with onshore flow, temperatures will be warm enough for precip to be all rain. Weak high pressure then builds across the region Friday night and Saturday. Patchy fog may develop Friday night and Saturday morning, as with weak flow, there will not be much of a chance for the moisture to scour out. Conditions will otherwise be dry and mild on Saturday with highs in the upper 40s to mid 50s. High pressure moves offshore Saturday night. Meanwhile, an upper trough will move into the West Coast sometime early in the weekend and will become a closed upper low over the Southern Plains and Gulf Coast states during the day Sunday. As this system organizes and develops, it will send waves of precip out ahead of it and into much of the East Coast. The first wave will develop over the TN Valley and lift towards the area on Sunday. Both the GFS and the ECMWF bring measurable precip into the region by Sunday afternoon, and then the bulk of the rain approaches Sunday night and Monday as the main system lifts into the Mid-Atlantic region. An area of concern: high pressure will nose its way into eastern Canada and northern New England. Depending on the placement of the high, winds could take on more of a NE/E flow as opposed to an E/SE flow. This could then usher a shallow area of cold air into mainly northern zones, and would result in a period of wintry weather sometime Sunday night and Monday morning. Latest track, based on both the GFS/ECMWF, keeps temperatures above freezing, so will keep precip as all rain throughout the CWA. There may be a brief break in the precip late Monday morning, but the main low will lift through the region Monday afternoon and evening, bringing another round of potentially moderate to locally heavy rainfall. With deep onshore flow, PWATs will build to around 1.5". Pressure gradient tightens up, and with strong low level jet passing through, can expect E winds to increase to 15-25 MPH with 25- 35 MPH gusts, mainly on Monday. Rainfall ends fairly quickly from SW to NE Monday night through Tuesday morning. Behind that departing system, a deep area of low pressure will be entrenched over the northern Great Lakes region, and several shortwaves will rotate around the low and into the local area. This may touch off some showers during the mid-week period. During this time, Arctic air remains bottled up to the north. Temperatures will average above normal, with highs nearly 10 degrees above normal. && .AVIATION /03Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. A light northeasterly surface wind helped to raise ceilings and break up the clouds a bit along/east of the Delaware River, but winds are beginning to back to a northwest direction. Expecting ceilings to return close to or even below the upper MVFR threshold overnight at KPHL, KPNE, KTTN, and KMIV. KACY will likely stay in VFR, while KRDG and KABE will likely be well into MVFR through the night. Rapid improvement in ceilings is expected after sunrise, with conditions becoming VFR area wide by late morning. Winds should be northwesterly generally in the 5-10 kt range. OUTLOOK... Thursday night...VFR. LGT/VRB winds less than 5 KT. High confidence. Friday through Friday night...Sub-VFR conditions possible in -RA. SE winds 5-10 KT on Friday become SW less than 5 KT Friday night. Moderate confidence. Fog possible Friday night. Saturday...Improving conditions Saturday morning. VFR. West winds 5 KT or less. Saturday night...LGT/VRB winds. Mainly VFR, but cannot rule out passing shower. Sunday...E winds 10-15 KT. IFR conditions possible in RA. Sunday night through Monday...IFR and lower conditions possible in RA. E winds 15-20 KT with 20-30 KT gusts. LLWS possible with 60-65 KT LLJ Monday afternoon.
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&& .MARINE...
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Barnegat, NJ, buoy indicating seas rising above 5 feet this evening. Latest wave guidance is about 1-2 feet below observations, and the trend through the night will be upward. Will issue a small craft advisory for hazardous seas through 6 pm Friday, as winds will be well below advisory criteria. OUTLOOK... Thursday night through Sunday morning...A weak pressure gradient will result in sub-SCA conditions during this time. VSBY restrictions possible in rain on Friday, and in fog Friday night and Saturday morning. Sunday afternoon through Monday night...Easterly flow increases to 15-20 KT with 25-30 KT gusts starting Sunday afternoon, and then gale force gusts of 35-40 KT likely Monday and Monday night. Moderate to heavy rain with low VSBY expected. Conditions improve late Monday night, and winds decrease to sub-SCA levels. However, seas on the ocean should remain above SCA criteria. Tuesday...Ocean seas remain above SCA criteria.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory for hazardous seas until 6 PM EST Thursday for ANZ450-451.
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&& $$ Synopsis...MPS Near Term...CMS Short Term...Franck Long Term...MPS Aviation...CMS/MPS Marine...CMS/Franck/MPS

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