112 FXUS61 KPHI 262047 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 347 PM EST Sat Dec 26 2020 .SYNOPSIS... High pressure will build northward into the Mid-Atlantic through Sunday, moving offshore Sunday night. Low pressure will move through the Great Lakes region Sunday night, dragging a mostly dry cold front across the region Monday night into Tuesday. High pressure will build in from the west and crest over the area on Wednesday, moving offshore Wednesday night. Another cold front will move into the region on Thursday. Low pressure will move along the boundary and into our area on Friday. High pressure will start to build in from the west as we head into the weekend. && .NEAR TERM /THROUGH SUNDAY/... The mid-level trough associated with the Christmas Eve/Christmas Day weather continues to gradually rotate out of the northeast quadrant of the country, which will allow for the establishment of a more zonal flow late tonight and early Sunday. At the surface, high pressure over the southeast U.S. will migrate slowly toward the coast, resulting in mainly clear skies and decreasing wind speeds during the evening and overnight hours. Even though the westerly winds will be weak (around 5 MPH), they should be strong enough to keep temperatures from dropping below levels experienced last night (mid teens north, low to mid 20s south, which is slightly below normal for this time of year). High pressure across the southeast will move offshore as it migrates northeast on Sunday. Under mainly clear skies and light southerly winds, temperatures will rebound into the mid 30s up north and into the low to mid 40s south. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... A low pressure system makes its way through the midwestern states Sunday night and up into Quebec and Ontario on Monday. A shortwave will rotate through the 500mb flow and cross the region Monday followed by a more robust shortwave Monday night. The system is lacking in moisture so do not anticipate that we will see much, if any, precipitation from this as it rolls through. Should anything fall during the day Monday, it looks to be confined to the higher elevations of the southern Poconos and northwestern New Jersey. A few showers may find their way into the Lehigh Valley but with marginal temperatures and plenty of warm air aloft, it may be in the form of rain or a mix of rain and snow. The cold front associated with the low to our north will cross the region Monday night into Tuesday. With a tightening gradient, it may be a bit windy through Monday night and Tuesday until the low pulls further away from the region. The northwest flow will dry the region out and we should see relatively clear skies for Tuesday through temperatures will remain cold with 850mb temps around -10 to -13 C. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... High pressure will build in from the west Tuesday night and crest over our forecast area on Wednesday. The high will start to move offshore Wednesday afternoon, quickly pulling out to seas Wednesday night. With the high over the region, Wednesday should be a fairly quiet day. Winds will be pretty light with the high overhead and skies should remain pretty clear. The flow turns more southerly through the day and this will start to increase the low level moisture and will usher in some warmer air. Highs should be pretty close to normal for late December. The big storm of the long term period is associated with a couple of low pressures that will impact our area. The first low will pass to our north but we will see the cold front arrive on Thursday but starts to slow down as it makes its way into our area. The second low is to our south. This low will travel along the cold frontal boundary and into our area late Thursday into Friday. With the southerly flow ahead of the system, we will continue to see moisture increasing ahead of the boundary and approaching southern low pressure system. This will once again be a multi-faceted system (much like the previous Xmas Eve/Xmas system) as several hazards come to light. The models show a good slug of rain moving over the region, on the order of 1-3". With saturated ground, river already running high, and not much drying likely to occur in the days leading up to the event, we will see increased runoff and flooding will once again be a concern. The pressure gradient will ramp up between the departing high and approaching systems and it will once again be another event with high winds. Still some uncertainty as to how high the winds could get but just another thing to watch, especially when combined with the saturated ground, trees might be much more likely to come down and it won't take as strong of a wind to do that. While the temperatures look to be very warm (highs likely into the 50s to lower 60s on Thursday), there is a small chance the precipitation moves in before the warm air fully arrives (mainly across the higher elevations). The precipitation looks to cut off fairly quickly on the back side and before the bulk of the colder air arrives. So we could see some snow on the back side as well but confidence is low right now. Similar to Xmas day, New Years Day will see the high occur early in the day with temperatures falling through the day. Temperatures will likely fall around 10 to 20 degrees over a 12 hour period. Winds will remain up on Friday but any moisture around will likely freeze Friday night as temperatures drop back down below freezing through much of the region. It may take a while for the approaching high to push into the region for the weekend but it should usher in some cooler (and more seasonable) weather for Saturday. && .AVIATION /21Z SATURDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR. Westerly winds initially 5-10 kts will decrease to 5 kts or less by 06Z. High confidence. Sunday...VFR. Southwesterly winds 5 kts or less will veer more to the south during the afternoon. High confidence. Outlook... Sunday night through Monday...mainly VFR conditions expected. Southwest winds around 5 kts or less overnight, increasing to 5 to 10 knots on Monday. High confidence. Monday night through Tuesday...Mainly VFR conditions expected. Northwest winds around 5 to 10 knots, increasing to 10 to 15 knots on Tuesday. Moderate confidence. Tuesday night through Wednesday night...Mainly VFR conditions expected. Northwest winds around 5 knots or less becoming southerly Wednesday afternoon. Moderate confidence. Thursday...MVFR or lower conditions in rain. Southerly winds around 10 to 20 knots with higher gusts possible. Low confidence. && .MARINE... Recent observations over the Delaware Bay indicate that wind speeds have diminished significantly enough to cancel the SCA for both the upper and lower Bay. Winds have also been slowly decreasing over the coastal waters, but seas are expected to remain above 5 feet through much of the overnight hours, so the SCA will remain in place into Sunday morning. Winds and seas are then expected to remain below SCA over both the Bay and the ocean waters through the day on Sunday. Outlook... Sunday night through Tuesday...Winds will increase Sunday night in the southwest flow and may near SCA levels by late Sunday night into early Monday. Winds will gusts around 25 to 30 knots through the day Monday. Gusts will drop off Monday afternoon before increasing again Monday night and into Tuesday. Winds should finally drop off for good later Tuesday. Seas will build late Sunday into Monday and reach 5 feet by Monday morning. Seas are expected to fall below 5 feet Monday night but may remain between 4 to 5 feet through Tuesday. A Small Craft Advisory is likely though there may be some periods with wind gusts below 25 knots. Tuesday night through Wednesday...Sub-SCA conditions are expected on the area waters. Wednesday night through Thursday...both winds and seas increase ahead of an approaching low pressure system. SCA conditions are likely with the potential for gale force gusts late Thursday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EST Sunday for ANZ450>455. && $$ Synopsis...Meola Near Term...Miketta Short Term...Meola Long Term...Meola Aviation...Meola/Miketta Marine...Meola/Miketta