Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 181929 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 229 PM EST Sat Feb 18 2017 .SYNOPSIS... A warm front will lift north of our area through today. A weak cold front is expected to settle through our area late tonight and early Sunday as low pressure tracks well to our north. Another cold front is forecast to push through the area early Monday, then high pressure moves in later Monday into Tuesday before shifting offshore Tuesday night. A weakening cold front moves across the area early Wednesday, then another frontal boundary approaches Thursday and stalls near the area through Friday. && .NEAR TERM /THROUGH TONIGHT/... A quick update was sent to raise the high temperatures for many areas, and adjust the hourly temperature grids to reflect an even faster temperature increase this afternoon. A spring-like afternoon in progress as low-level warm advection has increased as a warm front continues to lift north of our area. The 12z Sterling, VA raob showed +14C at the top of a strong low-level inversion (about 1500 feet). Some cooler temperatures are noted right along the coast though with a more southerly wind component off the chilly ocean water. Through tonight, our region is mostly between systems. One tracks well to our north as the parent trough slides from Hudson Bay toward the Canadian Maritimes. This will however push a weak cold front into our area later tonight. The second system is a closed low that will open up/weaken as it tracks eastward from the Tennessee Valley to the southern Mid Atlantic overnight. Is is mostly the southern system that is driving an increase in mostly high level cloudiness across our area this afternoon and especially tonight. There is a low-level jet around 40 knots forecast to develop close to our northern zones for a time tonight before shifting into coastal New England. This will aid in some moisture advection, however forcing with the incoming cold front is weak and moisture looks rather limited. As a result, perhaps some sprinkles across mostly our southern zones overnight. Given the expected cloud cover on the increase tonight in combination with a southwesterly wind, will result in milder temperatures. Low temperatures are mostly an even blend of MOS and continuity. && .SHORT TERM /SUNDAY/... Surface low pressure will move into the Canadian Maritimes Sunday, with a weakening upper-level trough sliding offshore of the southern Mid Atlantic region. A weak cold front associated with the northern surface low will settle across our area but then tend to stall or even wash out. There is a secondary cold front that is forecast to stay to our north during the day Sunday, and colder air is found behind it. The initial front has little change in temperature with it with just some weak cold air advection forecast in the afternoon, however the boundary layer remains warm. The low-level flow turns more from the west and northwest during the day which will add a downslope component for the coastal plain. As a result, another warm afternoon is expected although the far north should be a bit cooler given the weak cool air advection settling in. Some spots, mainly from Philadelphia on south and east, may be very close to their record high temperature for the date. An area of mainly mid level clouds associated with the southern system will exit to the east in the morning, with an increase in sunshine expected. High temperatures are a MOS blend, however these were boosted a bit especially for the coastal plain (I-95 south and east) given a downsloping component to the flow. It should be warmer at the coast given enough of an offshore flow. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... A back door front is forecast to push southward through the area early on Monday before high pressure builds across the area later Monday into Tuesday. Cooler conditions are expected Monday and Tuesday as compared to Sunday, but will remain above normal. A warm front may pass across the area Tuesday into Tuesday night as high pressure shifts offshore. Dry weather should continue on into Tuesday. A cold front is then expected to approach the area Tuesday night and pass through during the day Wednesday. Precipitation may start overnight Tuesday as a short wave/vorticity impulse slides across the area. If precipitation starts early enough, there could be a wintry mix across the far northern areas, mainly along and north of I-80 corridor. Guidance indicates the precipitation beginning to dissipate as it approaches the east coast as the front moves through the area. So we`ll keep a chance/slight chance for isolated showers across the area Tuesday night into Wednesday. Another front is forecast to approach the area Thursday, then stall near the area through Friday. There is a chance that some scattered showers could develop overnight Thursday into Friday as a couple of short wave/vorticity impulses move across the area. However, the best chance for precipitation looks like Saturday as a stronger frontal boundary moves into the area. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. This Afternoon...VFR with some increasing high level clouds. Southwesterly winds around 10 knots, with some local gusts up to 20 knots. Tonight...VFR with thickening clouds, and a ceiling lowering into mainly the 7000-10000 feet range. Southwest winds less than 10 knots, becoming westerly. Sunday...VFR. A ceiling between about 7000-10000 feet to start, which then thins out. West to northwest winds increasing to around 10 knots. OUTLOOK... Sunday night-Tuesday...Generally VFR expected. CIGS may approach MVFR at times Sunday night into Monday morning. Gusty winds 15-20 knots during the day. Tuesday night-Wednesday...Conditions lowering to MVFR or IFR overnight into Wednesday morning with a chance of showers. && .MARINE... The conditions are expected to remain below Small Craft Advisory criteria through Sunday. A southwesterly flow through tonight will gust to around 20 knots at times, then turn west and northwest late tonight and Sunday as a weakening cold front moves through. OUTLOOK... Sunday night-Monday...Generally sub Small Craft Advisory conditions expected, although winds may approach advisory levels across the northern New Jersey coastal waters overnight Sunday into Monday morning. Monday night-Wednesday...Sub Small Craft Advisory conditions expected although winds may gust up to 20 knots at times. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gorse/Robertson Near Term...Gorse Short Term...Gorse Long Term...Robertson Aviation...Gorse/Robertson Marine...Gorse/Robertson is the U.S. government's official web portal to all federal, state and local government web resources and services.