425 FXUS61 KPHI 221424 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1024 AM EDT Sun Oct 22 2023 .SYNOPSIS... Coastal surface low pressure strengthens while moving northeastward away from our region today. Simultaneously, surface high pressure approaches from the west and looks to dominate over the region for next week. && .NEAR TERM /THROUGH TONIGHT/... Overall, few changes to the near term forecast. Latest analysis places strong low pressure up near Nova Scotia, continuing to head northeastward. A much weaker wave of low pressure accompanying a reinforcing cold front is now offshore to the east of Delmarva, and continuing to head southeastward and weakening as it progresses. Aloft, a strong closed low is up near Nova Scotia with a secondary shortwave crossing the southern Mid-Atlantic. Broad troughing dominates the eastern US with ridging over the western US. Today, the weakening wave of low pressure now offshore, will be the main chance of any precip, as we still have a few lingering showers. These are mainly in Delaware but are rapidly weakening. Guidance still supports some chance POPs in this area for the remainder of this morning but by early this afternoon conditions should be dry everywhere. With the cold front passing through this morning, we have seen cold advection and wind reinvigorated somewhat, but with the pressure gradient a touch weaker, conditions so far are not quite as windy as yesterday. Maximum winds today are expected to be mainly in the 20-30 mph range vs 30-40 from yesterday. The cold advection will hold temps lower, with most areas failing to reach 60 despite a bit more sun. Temps likely get stuck in the 40s in the Poconos, where some upslope moisture may bring a stray shower or sprinkle. Elsewhere, do expect some more stratocumulus this afternoon, but it should be concentrated from Philly north, with more sun this afternoon in the Delmarva (especially compared to early this morning). Tonight, high pressure continues slowly building in from the west, but gradient stays a bit elevated with lingering clouds, so don't expect a huge temp drop nor a big drop-off in winds just yet... likely staying around 10 mph with gusts up to 15 mph overnight with temps held close to 40, mid-upper 30s in the Poconos. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... Upper ridging builds on Monday as the trough departs to the east while surface high pressure builds across much of the Northeast and Mid-Atlantic. Strong subsidence and dry air will result in a tranquil day with temperatures just a few ticks below normal in the low 60s. The pressure gradient weakens as well as the high builds closer overhead, so wind will be much less of a factor than it was over the weekend. Monday night looks like our first decent shot at potentially more widespread frost/freeze headlines for the Poconos and the Pine Barrens with surface high pressure directly overhead, much less wind than Sunday night, and dry air in place, but a couple complications are in play. One being a weak shortwave traversing the top of the building ridge which may increase cloud coverage overnight, mostly for areas north of I-78, and not allow for otherwise efficient radiating. Across the Pine Barrens though, even NBM 95th percentile lows are in the mid 30s and still cold enough for frost development, so likelihood is increasing for that part of the area; NBM probabilities at a 70-75% chance of temperatures below 36F. Will have to watch to see what the cloud coverage does over the next few days as the guidance is not entirely in agreement on how extensive it will be, which will significantly impact how low temps get in the Poconos/Lehigh Valley. What is looking more likely at this point is a flipped situation where the Pine Barrens see colder temps with the most efficient radiational cooling conditions while areas to the north remain more mild (relatively speaking) under increased cloud coverage. Current forecast lows are mid 30s in the Poconos/Lehigh Valley/Pine Barrens and low 40s in the urban areas/Delmarva. Tuesday will be warmer than Monday as temperatures recover a bit thanks to return flow as the surface high begins to shift offshore and brings weak southerly flow across the region. Not much of a moisture increase though as flow aloft still remains more westerly, though warm advection will drive 850 mb temps up to 10-12C as the air mass begins to moderate. It will be another dry day with afternoon highs closer to climo in the mid 60s with upper 50s in the Poconos and higher elevations. Lows Tuesday night will be warmer than Monday night and no frost/freeze potential is expected. Despite high pressure still in control and mostly clear skies expected overnight, wind will remain slightly more elevated and warm advection continues with flow aloft becoming more southwesterly, so temps should only bottom out in the low to mid 40s. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... The long term period looks pretty uneventful as the upper ridge builds further across the eastern seaboard. Thicknesses will increase within the ridge as well indicative of a warming trend through mid-week with flow turning southwesterly aloft. Ensembles paint expansive surface high pressure across the Mid- Atlantic into the Northeast through Wednesday, keeping the region precipitation- free. Quiet weather is expected through much of the week, though guidance becomes notably more spread on how the end of the week evolves. An upper low will eject out of the Southwest sometime late Wednesday into Thursday and lift across the central US, though models are exhibiting quite the spread with timing and progression with the GFS being much more progressive than the ECMWF/GEM. It seems that the associated surface low and front will wash out as it pushes north and east with little to no impact across the region as to rejoins the main flow across New England. Model consensus has continued with the drier trend and ensemble means bring no measurable precipitation into our area. Temperatures look to be a few degrees above normal for the latter half of the week, and it looks like we'll close out the week much warmer than we started it. We will likely remain on the dry side of things through at least Friday night, though the ridge will begin to break down towards the end of the week as another upper wave traverses the Great Lakes. The next storm system looks to take shape sometime over the weekend, but a high amount of model spread keeps the forecast quite uncertain at this time. Latest ensemble QPF has trended drier for this system as well with only a slight chance for some showers mainly across the higher elevations of the Poconos, Lehigh Valley, and northern NJ, but confidence remains low. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR. Winds west-northwest around 15 kts with gusts to 25 kts. High confidence. Tonight...VFR. Winds west-northwest around 10 kts with gusts to 20 kts, mainly in the evening. High confidence. Outlook... Monday...VFR. Northwesterly wind around 10 knots with gusts to 20 knots. High confidence. Tuesday...VFR. Southwesterly 5-10 knots. High confidence. Wednesday...VFR. Southwesterly wind around 10 knots. High confidence. Thursday-Friday...VFR. Southwesterly wind 5-10 knots. High confidence. && .MARINE... Gradient has weakened enough such that further gales no longer look likely today, so replaced with Small Craft Advisory for all zones through tonight. Gradient will remain elevated through that time for gusts of 20-30 kts on all waters, and seas will be up to 7 feet today, dropping gradually overnight. Outlook... Monday...Lingering SCA conditions possible in the early morning but subsiding to sub-advisory for the remainder of the day. Northwest wind 15-20 knots early and becoming 10-15 knots by afternoon. Seas 3- 4 feet. Monday Night-Friday...No marine headlines expected. Southwesterly wind around 10 knots. Seas 2-3 feet. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Monday for ANZ430-431- 450>455. && $$ SYNOPSIS...Brudy/RCM NEAR TERM...AKL/RCM SHORT TERM...Brudy LONG TERM...Brudy AVIATION...Brudy/RCM MARINE...Brudy/RCM