000 FXUS61 KPHI 061145 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 645 AM EST Mon Feb 6 2023 .SYNOPSIS... High pressure builds in Tuesday before a fast moving trough crosses the northeast Tuesday night. A low pressure system is expected to progress from the southern Great Plains to the Great Lakes Region during the later half of the week, bringing a chance for precipitation to our region. Right on the heels of that system, another low is expected to lift out of the mid Mississippi Valley to the Mid Atlantic by Saturday. && .NEAR TERM /THROUGH TUESDAY/... The fog threat over southern New Jersey and DelMarVa continues to be difficult. Rapid refresh guidance has finally picked up on it and looks to scour out the fog generally in the 1 to 2 hours as winds will start to ramp up out of the north to northwest. Previous forecast remains fairly well on track with no changes to products this morning. Have a great start to your work week! Previous discussion...As the low pressure system just offshore has been pushing to the east there has been a ribbon on clearing skies through much of the forecast area. With clearing skies and winds decoupling the mild temperatures have fallen quite quickly into the low 30s with some spots below freezing. This has caused patchy dense fog to form across much of DelMarVa and southern NJ. The fog is showing up quite clearly on the Night Fog GOES product along with the Nighttime Microphysics RGB product as well. Given how quickly the onset occurred and the satellite imagery we have issued a Dense Fog Advisory for the areas impacted along with a Marine Dense Fog Advisory for the Delaware Bay and adjacent Atlantic Coastal Waters. The microclimate forecasting has been incredible difficult this evening as MIV dropped 7 degrees in an hour to 30 degrees while neighboring sites in Georgetown and Atlantic City at that time were still both in the low to mid 40s. There is no guidance that is currently capturing temperatures especially in the area where prevalent fog developed so we've opted for much of a persistence forecast over the next couple of hours. Eventually with daybreak we'll start to see some diurnal heating and mixing which will cause the fog to dissipate hopefully fairly quickly especially as the northerly winds pick up this morning. Low pressure will continue to exit to the east and moderate northerly winds will develop as the upper level trough digs through the region today. Using BufKit momentum transfer we should be looking at winds gusting around 25kts by midday. This will lead to strong cold air advection through most of the day as a ridge of high pressure will start building through Monday night. Expect with the ridge over the region expect temps to crash pretty quickly as soon as the winds decouple tonight. With the dry air being pushed in from the north the fog threat tonight will be limited relative to this morning. Lows should fall into the low to mid 20s with the exception being the urban corridor which should stay in the upper 20s. The ridge breaks down heading into Tuesday as an upper level trough digs through the Great Lakes and the flow will become southerly. Towards the late afternoon a narrow ribbon of energy associated with a cold front will start pushing through PA however it starts to wash out just before reaching the forecast area. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/... The main story through this period is the nearly vertically stacked trough that will be progressing across southern Canada and the northern tier of the U.S.. The associated cold front with this system should enter region Tuesday night before stalling. That being said, it won't be in our region for long as a warm front will lift through our region late Wednesday into Thursday morning. With the main area of lift associated with this trough staying well north of our region, most of the region should stay dry. However, there remains potential for a brief period of light rain, primarily north of the I-78 corridor ahead of and with the cold front. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Overview: Two systems we are watching through this period. First, a low passing to our W and NW Thursday into Friday is expected to bring precipitation (mostly rain) to our region. The next system is forecast to take a track closer to our region Friday and Saturday. Details: Wednesday night into Thursday...Guidance continues to come into better agreement with the overall track and timing of this system, though there was a trend with the 00Z models to faster timing (which bucks the slower trend we saw yesterday). The biggest change to the forecast is that there is an increasing concern for a cold air damming set up for areas west of the fall line. If the precipitation moves in before the day time, there is a potential for freezing rain in the southern Poconos and far northwestern New Jersey. The overall pattern hasn't changed much: cyclogensis in the ArkLaTX region is expected to occur once a southern stream mid and upper level trough crosses over to the lee side of the Rockies. The resulting low pressure system lifts northeastward along the front towards the central Great Lakes region. A warm front should first lift through the region on Thursday morning, resulting in an initial round of precipitation (though as mentioned above, this could be complicated by a cold air damming set up). The warm air advection behind this warm front will allow temperatures to increase into the 50s and even lower 60s for some areas by Thursday afternoon. Dry slot should advect in by late Thursday or Thursday night, bringing and end (albeit temporary) to the rain chances. Friday and Saturday...On the heels of the Thursday system, another surface low is expected to develop in response to a mid and upper level trough digging SE over the plains. The track of the surface low looks to be from the mid Mississippi Valley on Friday to over our region on Saturday. This track would mean that only the southern Poconos would be solidly in the cold sector of this low and our region never quite gets in the prime location for the warm conveyor belt for precipitation on the back side of the low. Thus, if this track and timing holds, expect a period of mostly rain on Saturday, with rain/snow possible in the southern Poconos, but then a quick end to the precipitation late Saturday or Saturday night. However, still plenty of time for other trends both in track and timing to develop, so have stayed close to a blend of guidance. Sunday...A surface high will building in from the southwest along with a mid level ridge building in from the west, means that any cool down behind the Saturday system will likely be short lived and we should start the week with tranquil conditions. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Generally VFR expected however as skies cleared this evening, areas of dense fog developed over southern NJ leading to periods of LIFR over MIV/ACY. Fog is expected to clear either by daybreak or shortly after as north to northwesterly winds will pick up through the morning and becoming fairly gusty this afternoon. Expect winds gusting to 20-25kts out of the north until sunset and then winds will start to decouple and weaken again heading into Monday night. Outlook... Tuesday and Wednesday...Mostly VFR. E wind becoming S 5 to 15 kt gusting to 20 kt on Tuesday becoming NW Tuesday night into Wednesday. Moderate confidence. Thursday...MVFR or even IFR conditions possible as rain and lower ceilings move in. S and SW winds 10-20 kts with gusts up to 25 kts. Low confidence. Thursday night and Friday...A period of VFR conditions is possible as rain moves out before lower ceilings ahead of the next system move in late Friday. SW winds becoming W 10 to 20 kt with gusts to 25 kt. By Friday night, becoming NW 5 to 15 kt. Low confidence. && .MARINE... The winds and seas will diminish overnight before increasing out of the north/northwest this morning at around 15 to 20 gusting up to 25 or 30 knots. Seas should be 3-4 feet overnight before increasing once again to 4-5 feet this afternoon. As the winds have gone mostly calm, fog has developed over much of the coastal locations near the Delaware Bay and along the coastal communities of Delaware and southern New Jersey. With the same satellite presentation over the waters as inland we've issued a Marine Dense Fog Advisory through the early morning before the winds start to ramp up. After the SCA comes down this evening, winds and seas should remain below SCA through Tuesday with generally light onshore flow in the morning becoming southerly through the day. Outlook... Wednesday...Seas will gradually diminish below SCA criteria during the day on Wednesday. Thursday...S winds and seas could build to SCA criteria by Thursday afternoon or Thursday night. Friday...There should be a lull in SCA conditions, though gusts near 20 kt possible, especially Friday night. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...Dense Fog Advisory until 8 AM EST this morning for NJZ021>025. DE...Dense Fog Advisory until 8 AM EST this morning for DEZ002>004. MD...Dense Fog Advisory until 8 AM EST this morning for MDZ015-019- 020. MARINE...Dense Fog Advisory until 8 AM EST this morning for ANZ430-431- 452>455. Small Craft Advisory from 10 AM this morning to 7 PM EST this evening for ANZ430-431-454-455. Small Craft Advisory from 10 AM this morning to 10 PM EST this evening for ANZ450>453. && $$ SYNOPSIS...Johnson NEAR TERM...Deal SHORT TERM...Johnson/MJL LONG TERM...Johnson/MJL AVIATION...Deal/Johnson MARINE...Deal/Johnson