604 FXUS61 KPHI 070207 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 907 PM EST Fri Jan 6 2023 .SYNOPSIS... Cool and dry high pressure will build to our west through Saturday before eventually shifting offshore on Sunday. A quick moving system will bring precipitation and perhaps some light snow accumulation to the region Sunday night through early Monday. High pressure will then prevail across the region with seasonable temperatures and quiet weather Tuesday through Thursday. A coastal system may impact the area starting next Friday. && .NEAR TERM /THROUGH SATURDAY/... A long wave trough will remain over eastern Canada and the northeastern states overnight and Saturday. A series of short waves will continue to round the trough. The next short wave is expected to move overhead on Saturday morning, with one more following late on Saturday. While we are anticipating a decrease in cloud cover overnight, the pattern should not allow for the sky over our region to clear entirely. Clouds will likely be on the increase again on Saturday, especially in the afternoon ahead of the late day short wave. Even with the cold advection, temperatures will remain slightly above normal overnight and Saturday. A northwest wind 5 to 10 MPH is forecast for tonight. Wind speeds should increase to around 10 MPH on Saturday with gusts in the 15 to 20 MPH range. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... Attention in the Short Term remains on the potential for some light accumulating snowfall across portions of the area Sunday night. Brief ridging Saturday night through early Sunday will give way to falling heights into Sunday evening as a trough approaches from the Ohio Valley. This will bring a broad and disorganized/weak system across the area Sunday night before moving offshore Monday morning. Guidance suggests this system will not intensify until it is well offshore from our coast. High pressure will then begin to build back in as the system departs on Monday. Saturday night should be seasonably cold with clearing skies and lessening winds as high pressure briefly settles over the region. Temperatures are forecast to fall well into the 20s across the area, coldest in the typical colder locations of interior southern new Jersey, and locations along and north of I-78. Temperatures Sunday should climb to near normal values for highs, mainly in the low 40s. Skies will start out mostly clear, but clouds will increase in coverage throughout the day as the Sunday night system approaches from upstream. Winds will be mostly light and variable Saturday night through Sunday. An initially cool and dry airmass in place across the area will be overtaken by weak warm advection into Sunday evening as heights begin to fall and broad upper diffluence spreads over the area. Light precipitation is expected to spread into the region during the late afternoon and evening hours, generally from southwest to northeast. Given the subtle and broad forcing mechanisms and marginal thermal profiles with this system, confidence remains fairly low on exactly how the precipitation types and amounts will evolve. That being said, current indications in the guidance are that there will be a period of snow across portions of the area, especially at the onset of precipitation before the warm advection begins switching the precip type over to mostly rain across much of the area. Precipitation is currently expected to start mainly as light snow near the Philly metro and mainly as light rain farther south across a line from near Kent Island to Dover to Cape May. However, if any banding or stronger intensity of precipitation occurs to the south, it is possible some snow mixes in early in the event farther to the south near the aforementioned line due to dynamic cooling. The thermal profiles will support a rain or snow precip type, and no sleet or freezing rain is expected. The heaviest precipitation should occur mostly before midnight, but light precipitation may linger in some areas overnight. By this time, the thermal profiles will support mainly rain in the Philly metro and south with rain and snow possible farther north. North of the Philly metro and I-95 corridor, the biggest question is how far north does the accumulating precipitation get. The antecedent airmass will be fairly dry, so as forcing decreases to the north, the QPF should as well. We currently have the higher QPF near the Philly metro and areas to the south generally ranging from a tenth to two tenths of an inch. We are currently forecasting less than an inch of snow for the entire forecast area for Sunday night. If more intense or banded precipitation develops near the Philly metro or areas to the north, snow duration and thus amounts may be locally higher than we currently have advertised. I would not be surprised to see at least a few areas come in with totals in the 1-2" range, with the most probable area for this occurring being across portions of southeastern Pennsylvania. Confidence is just too low to pinpoint exactly where that may be in the deterministic forecast at this time though. In any case, impacts from any snowfall with this system appear to be limited. Surface temperatures will be very marginal, and it is possible little if any snow that does fall will stick to the roads. Temperatures will continue to slowly rise above freezing overnight south of I-78. Precipitation will diminish in intensity and coverage by daybreak Monday and continue to move offshore. Skies should begin to clear out during the afternoon with temperatures rising into the 40s across much of the area and a northwest breeze. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Quiet and seasonable weather conditions are expected Monday night through Thursday. A trough will pass well to our south Tuesday night into early Wednesday, but this should bring mainly just clouds to our region. Otherwise, cool and dry high pressure will be the story with 3-4 days of seasonable temperatures. By next Friday, it appears the next trough will be approaching the East Coast. This could mean a coastal system for us, but consensus in the guidance is low on any details with this setup. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Overnight...VFR with decreasing cloud cover. Northwest wind 5 to 10 knots. High confidence. Saturday...VFR with increasing cloud cover. Northwest wind around 10 knots with gusts of 15 to 20 knots. High confidence. Outlook... Saturday night...VFR. Winds northwest around 5 kts or less. High confidence. Sunday...VFR with increasing coverage of clouds. Winds light and variable. High confidence. Sunday night...MVFR and IFR conditions likely with periods of rain and snow. Mainly rain and MIV/ACY. Winds 5 kts or less, but favoring a southerly direction. Moderate confidence overall. Monday...Lingering restrictions should gradually clear and the day progresses. Northwest winds around 5-10 kts. High confidence. Monday night through Wednesday...VFR. West to northwest winds around 5-10 kts, becoming 5 kts or less at night. High confidence. && .MARINE... Surface low pressure will move away to our northeast and high pressure is forecast to approach from the west and southwest. The pattern will maintain a west to northwest wind on the coastal waters of Delaware and New Jersey into Saturday. Sustained speeds are expected to be around 15 knots with gusts into the lower 20s. The wind gusts are anticipated to remain generally below the Small Craft Advisory criterion, although some localized gusts near 25 knots are possible. Waves on our ocean waters are expected to be 2 to 4 feet, with waves on Delaware Bay at 2 feet or less. Outlook... Saturday night through Wednesday...No marine headlines anticipated. West to northwest winds around 10-15 kts through the period, except for Sunday night when southerly winds are expected. Winds gusting up to 20 kts possible Saturday night and Monday. Seas 2-3 feet. Rain possibly mixed with snow Sunday night through Monday morning, otherwise fair weather. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ SYNOPSIS...Staarmann NEAR TERM...Iovino/RCM SHORT TERM...Staarmann LONG TERM...Staarmann AVIATION...Iovino/Staarmann/RCM MARINE...Iovino/Staarmann