FXUS61 KPHI 040804 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 304 AM EST Wed Dec 4 2024 .SYNOPSIS... High pressure centered over the Appalachians early this morning will continue to dominate our weather through the first part of the day before sliding off to the south and east late day as low pressure moves into the Great Lakes region. This strengthening low will track to our north tonight and Thursday, pushing a strong cold front across our area early Thursday. Cold and dry high pressure will build into the Ohio Valley Friday through Saturday before weakening into our area through Sunday. The next low pressure system looks to affect the area early next week. && .NEAR TERM /THROUGH TODAY/... It remains mainly clear but cold early this morning as high pressure continues to dominate. Lows by morning should range from the teens over portions of NE PA into NW NJ with low to mid 20s for most areas farther south. As we head into the day today, it will be sort of like a 'transition' day as high pressure will still maintain control of our weather through much of the day. Upper level flow will gradually back and briefly become zonal ahead of an advancing strong trough over the Great Lakes. Although the airmass will be moderating, highs will mainly be in the upper 30s to mid 40s across the area with increasing clouds throughout the day. As a whole, most of Wednesday will remain dry. The exception is across northeast PA or northern NJ late in the afternoon as some energy in advance of the trough streams into the north portions of the area. This may result in a passing snow shower or two, otherwise, the bulk of the precip holds off until Wednesday night. Finally worth noting, it will also become quite breezy in the afternoon with S/SW winds 10 to 15 gusting as high as 20 to 30 mph. && .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/... A strong storm system will impact the region Wednesday night through Thursday night, bringing some rain and snow showers, strong winds, and continued below normal temperatures. A Wind Advisory remains in effect for Thursday from 6 AM until 10 PM for strong westerly winds near 20-35 mph, with gusts around 40-55 mph. Greatest impacts are expected Thursday morning when strong winds and scattered snow showers, mainly north, could impact the morning commute with slippery road conditions. Synoptic Overview...A deep positively tilted trough approaches the Great Lakes tonight. The trough axis will dive quickly southeastward across the Mid Atlantic early Thursday while becoming negatively tilted as it shifts offshore. Height falls quickly spread across the area tonight into Thursday morning. At the surface, a strengthening low pressure system will pass just north of the Great Lakes today, reaching the Canadian Maritimes late Thursday. A strengthening pressure gradient will result beginning today, remaining in place through Thursday night. A strong cold front will sweep through the area Thursday morning, likely offshore by noon. The frontal passage will yield very strong cold advection in its wake, with 850 mb temperatures upstream around -10C to -15C. Post frontal surface pressure rises will be near 1 mb/hour. This is not a clipper system, to be sure. Tonight...As stronger forcing for ascent arrives overnight, precipitation, mainly in the form of scattered showers, should develop within the region, with the greatest chances (60-70%) residing mainly north and east of the Philly metro. Within the Philly metro and south, less forcing may result in little to no precipitation until the arrival of the front Thursday morning. Areas along and north of the I-78 corridor will likely see mostly snow with this activity, with a rain/snow mix farther south and mainly rain near the coast. QPF is light, largely less than 0.10". Any snowfall accumulation outside of the Poconos and higher elevations of northwest New Jersey will remain less than 1", a brief dusting at best. The higher elevations and southern Poconos could see about an inch or two of snow tonight. A southwest breeze will be strengthening overnight as the cold front approaches, and especially toward daybreak to around 15-20 mph, with gusts near 25-30 mph possible. The winds, mixed boundary layer, WAA, and cloud cover will keep temperatures relatively mild, perhaps even rising a few degrees overnight. Forecast low temperatures are mainly in the 30s. Thursday through Thursday night...The strong cold front will quickly approach and begin passing through the forecast area near or just after daybreak Thursday, and should be offshore by around noon. If moisture is sufficient, some snow showers or snow squalls could develop along or just ahead of the frontal boundary following the diminishing overnight precipitation. Moisture is expected to be limited though, so it will probably be a struggle to get anything of significance farther south. The limiting factor for any impacts from this activity will be surface temperatures, as most areas south of I- 78 will be above freezing with above freezing roadway temperatures. Nevertheless, a quick dusting a snowfall could result in grassy and elevated surfaces as far south as the coastal plain, and may cause some slippery travel during the morning rush hour. An additional inch or two of snowfall is forecast for the southern Poconos, and a Winter Weather Advisory may need to be considered in a future update for this area given event totals of 1-3". However, any impacts from the snow could be more short fused in nature, and may be covered by Snow Squall Warnings instead. Temperatures will likely reach their daytime maximum in the mid 30s to low 40s in the morning, then gradually fall into the afternoon. Beyond the shower potential with the front, the main story will the the windy conditions expected in its wake. Hard pressed to find any deterministic guidance showing anything less than widespread 35-45 kts of wind within the 925 to 850 mb layers during the post-frontal regime. BUFKIT profiles indicate we'll be mixing up to around the 800-850 mb layers post-frontal during the daytime, so it's reasonable to assume those winds speeds should translate to peak gusts at the surface given extremely strong cold advection, shortwave vort max pivoting through aloft with FROPA, and surface pressure rises around 1 mb/hour. Long story short, we remain confident that our area will experience widespread 40-55 mph wind gusts for much of the daytime period Thursday. Expect westerly sustained winds near 20-35 mph. A Wind Advisory remains in effect for the entire area for Thursday. Some tree damage and isolated power outages are possible. Friday...The cold and dry high pressure will build into the Ohio Valley Friday and Friday night. The pressure gradient and cold advection will persist, though not nearly as strong as Thursday. Expect highs in the 30s and lows in the 20s. A breezy northwest wind will persist with wind gusts near 20-30 mph during the daytime. && .LONG TERM /SATURDAY THROUGH TUESDAY/... High pressure will dominate our weather through the weekend bringing fair conditions. Saturday will continue to be quite chilly, with highs in the 30s to low 40s, with temperatures warming back up to more seasonable levels by Sunday as the high moves off the coast. Monday and Tuesday...Long-term guidance suggests early next week will become more unsettled with an amplified trough shifting across the central US. That said, guidance remains in some disagreement with the evolution of the system. However it does look like the system will be warmer with less chances for any wintry precip. We continue to carry chance/likely PoPs for the area during this period. Temperatures by next Tuesday could reach into the upper 50s to low 60s. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Overnight (to 11z Wed)...VFR with mostly clear skies and light winds from the W/SW generally around 5 knots or less. High confidence. Wednesday...VFR with increasing clouds and lowering ceilings throughout the day. Southwest winds around 5-10 kt in the morning will increase between 15z-17z to around 10-15 kt with gusts 18-22 kt, more out of the south/south-southwest. High confidence in prevailing VFR, moderate confidence in timing of wind shift and increase. Wednesday night...Sub-VFR conditions likely developing overnight along with rain or snow showers, especially at RDG/ABE. Southwest winds 10-15 kts with gusts of 20-30 kts possible. LLWS possible. Moderate confidence overall. Outlook... Thursday through Thursday Night...MVFR to IFR conditions early, with improvement to VFR conditions by midday. Windy. West winds increasing to around 20-25 kts with gusts 35-40 kts. Winds lessen Thursday night. Friday...VFR. West-northwest winds near 15 kts with gusts 20-30 kts, diminishing in the evening. Saturday through Sunday...VFR with no significant weather expected. && .MARINE... Winds ramp up once again as we head into the day Wednesday with a Small Craft Advisory beginning for all waters at 1 PM. By late day expect southwest winds 20 to 25 gusting up to 30 knots with seas 5 to 6 feet. Outlook... Tonight through Thursday night...Gale Warning now in effect. Gale force winds arrive Wednesday night, peaking Thursday, then gradually diminishing Thursday night. Wind gusts 35 to 45 kts possible. The strong offshore winds could result in abnormally low water during the Thursday late afternoon to evening low tide, which could make navigation difficult in shallow waters. Friday...Small Craft Advisory conditions abating into Friday night. Saturday through Sunday...Conditions look to be below Small Craft Advisory levels with west to southwest winds generally 10 to 15 gusting up to 20 knots and seas 2 to 4 feet. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Wind Advisory from 6 AM to 10 PM EST Thursday for PAZ054-055- 060>062-070-071-101>106. NJ...Wind Advisory from 6 AM to 10 PM EST Thursday for NJZ001- 007>010-012>027. DE...Wind Advisory from 6 AM to 10 PM EST Thursday for DEZ001>004. MD...Wind Advisory from 6 AM to 10 PM EST Thursday for MDZ012-015- 019-020. MARINE...Small Craft Advisory from 1 PM this afternoon to 6 PM EST this evening for ANZ430-431-450>455. Gale Warning from 6 PM this evening to 6 AM EST Friday for ANZ430-431-450>455. && $$ SYNOPSIS...Fitzsimmons NEAR TERM...DeSilva/Fitzsimmons SHORT TERM...Staarmann LONG TERM...Fitzsimmons AVIATION...Fitzsimmons/Staarmann MARINE...Fitzsimmons/Staarmann