518 FXUS61 KPHI 180318 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1018 PM EST Thu Nov 17 2022 .SYNOPSIS... High pressure to the southwest continues to currently nose in but cold front out west approaches. Cold front/shortwave looks to pass through later tomorrow. Another cold front looks to pass through Sunday morning. High pressure to follow and dominate to start the week. Watching for possible low pressure development towards the end of next week. && .NEAR TERM /THROUGH FRIDAY/... The cold pattern continues as an expansive upper-level trough amplifies more across the eastern U.S. A strong shortwave trough will continue to lift into the Canadian Maritimes through this evening. Strong westerly flow in the wake of this feature along with cold air advection is resulting in lake effect streamers extending well east of Lakes Erie and Ontario. Expect generally clear skies aside from perhaps some passing mid or high level clouds later on. A tight pressure gradient remains in place between low pressure near the Canadian Maritimes and strong high pressure building across the Plains and Gulf Coast states. With the mainly clear skies, dry airmass and light winds, it will be a fairly cold night, with overnight temperatures dropping into the 20s for much of the region. As we go through Friday, strong shortwave energy is forecast to arrive during the afternoon. The model forecast soundings show steep low-level lapse rates and deeper moisture present especially after 18z. This combined with the arrival of the shortwave may result in some afternoon snow showers/flurries (perhaps some rain showers farther south). The greater chance for this may be along and north of the I-78 corridor, however even down to I-95 could see a brief snow/rain shower. Despite the boundary layer warming into the low to mid 40s in much of the area, it is cold aloft and therefore if any showers become more robust some graupel/ice pellets cannot be ruled out. As of now, not anticipating actual snow squalls but given the steepness of the low-level lapse rates we may have to watch this especially for mainly parts of the I-80 corridor. For now, increased the PoPs to 20-30 percent from about I-95 north and west toward the later afternoon hours. It will be another brisk day with west or west-southwest winds increasing and turning gusty, although the winds should be a little lower than what is being observed this afternoon. Clouds will also increase some in the afternoon with heating and the approach of the strong shortwave (greater cloud cover should be north and west of I-95 for much of the day). High temperatures in the 40s (mid/upper 30s across parts of the northwest zones), and an added breeze will make it feel colder. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... The period begins tomorrow night with a cold front either finishing up passing through the region or located just offshore. Latest guidance mainly indicates no chance of PoPs persisting into the first few hours of the period tomorrow and have not included any chance of PoPs for tomorrow night with the exception of the more northwestern areas of Carbon and Monroe in PA. However, there is some indication among non-global guidance that a quick non-accumulating and isolated snow, rain, or mix shower is not out of the question for the first 3 to 6 hours of the period for some places across the region. After the first 3 to 6 hours, the rest of the Friday night into Saturday morning period should be quiet and dry. Skies should gradually clear with westerly winds persisting. Expecting overnight lows to be in the mid to upper 20s in the more southeastern areas and upper teens to mid 20s in the more northwestern areas. High pressure conditions will be present Saturday with surface high pressure centered to our south and southeast. Winds will be out of the southwest with mainly clear to partly cloudy skies. Highs in the low to mid 40s for the more southeastern areas and upper 30s in the more northwestern areas can be expected. Another cold front looks to pass through sometime during the early Sunday morning time frame. This front will not have any precipitation support with it but will reinforce more cold air across the region. Overnight lows should again be in the mid to upper 20s in the more southeastern areas and upper teens to mid 20s in the more northwestern areas; possibly being just a couple degrees higher than the previous overnight lows. With cold frontal passage, highs on Sunday should be 3 to 6 degrees colder Sunday than seen on Saturday. High pressure to our southwest will be approaching the region with time. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... The overall story of the long range period today is that there is high confidence in the beginning of the period and low confidence towards the end. The upper level pattern looks to flatten out and become zonal by Monday with not much to discuss feature wise. A ridge looks to build over the western CONUS Wednesday to Thursday and a trough may develop to the east of this ridge during the same time frame. Will be keeping an eye on this trough as it may lead to the development of the next surface low pressure system that could later impact the region. The ensembles today express very low confidence and a large spread in the timing, strength, and placement of this trough so it remains to be seen what output is in the coming days. At the surface level, high pressure dominates Monday, Tuesday, and Wednesday with no chance of PoPs included in the forecast during this time frame. Below normal temperatures can be expected Monday but more seasonable to just slightly below normal temperatures can be expected Tuesday and Wednesday. Given guidance today but also the large uncertainty present, have included slight chance PoPs for Thursday to indicate the next low pressure system impacting the region. However, again it must be expressed that there is very low confidence and a large spread in the timing, strength, and placement of a surface low pressure and associated trough among guidance. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR with mainly clear skies. Westerly winds diminishing to 10 knots or less. High confidence. Friday...VFR. A few snow or rain showers possible later in the afternoon especially for the RDG to ABE to TTN areas. West-southwest winds increase to 10-15 knots with gusts to 20-25 knots. Moderate confidence. Outlook... Friday night through Sunday...VFR conditions. High confidence. Sunday night through Tuesday...VFR conditions. High confidence. && .MARINE... A Small Craft Advisory remains in effect through Friday. Gusty westerly winds, gusting up to 25 kt or so tonight, will tend to pick up slightly on Friday. It is possible that the winds drop below 25 knots Friday on Delaware Bay, however we will maintain the advisory for now. Seas on the ocean zones should be mainly 3-4 feet. Outlook... Saturday...No headlines expected. Sunday...SCA conditions very likely. Gale Warnings possible. Monday through Tuesday...No headlines expected at this time. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST Friday for ANZ430-431- 450>455. && $$ SYNOPSIS...Wunderlin NEAR TERM...AAD/Gorse SHORT TERM...Wunderlin LONG TERM...Wunderlin AVIATION...AAD/Gorse/Wunderlin MARINE...AAD/Gorse/Wunderlin