510 FXUS61 KPHI 021127 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 627 AM EST Mon Jan 2 2023 .SYNOPSIS... High pressure will build to our south through today with temperatures remaining above normal. The high pressure will slide offshore tonight with southerly flow bringing increasing temperatures through the middle of the week. A frontal system will impact the region Tuesday through Wednesday bringing increasing chances for rain showers, fog, drizzle, and near record breaking warmth by Wednesday. Cooler and more seasonable conditions will return by the end of the week and into the weekend as colder high pressure builds to our west. && .NEAR TERM /THROUGH TONIGHT/... Some patchy fog is forming across portions of southeast New Jersey and Delmarva. Any fog that does form should quickly diminish shortly after sunrise. Otherwise, high pressure is centered over the Southeast and Mid- Atlantic and will gradually slide offshore tonight. Meanwhile, a zonal flow aloft will keep Arctic air bottled to the north, and a mild airmass will continue to spread into the Northeast and Mid-Atlantic. Some shortwave energy will approach from the west and will pass through the region this afternoon and evening. Hi-res models showing some light rain moving into southeast Pennsylvania late this afternoon. Will go ahead and add minimal PoPs, capped at slight chance, for southeast Pennsylvania. Any rain that falls will be light. Highs today will be almost 20 degrees above the seasonal normals and will top off in the mid to upper 50s for most of the area, and as high as the low 60s in southern New Jersey and southern Delmarva. With the high offshore, a light southerly flow sets up across the area tonight. Surface dew points will creep up during the overnight hours, climbing into the mid 40s. With this increase in moisture, patchy fog is likely to develop across the region. Whether fog becomes dense remains to be seen. Low pressure over the Midwest, and a warm front will extend out from this low and will lift towards the region late tonight. Combined with some mid-level shortwave energy, some rain may move into far northern and western portions of the forecast area prior to daybreak Tuesday. Will add some slight chance/low-end chance PoPs to the forecast for those areas. Low temperatures tonight will be in the low to mid 40s. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... The short term period Tuesday through Wednesday night will be characterized by unseasonable warmth and several periods of showers, fog, and drizzle. Near record breaking warmth is expected on Wednesday. High pressure is forecast to be offshore across the western Atlantic Tuesday morning. As low pressure approaches the central Great Lakes region early Tuesday, increasing low-level south to southwesterly warm advection is forecast to overspread our area. This is pronounced at the 925 mb level and will result in a northeastward developing warm front. The latest guidance has increased the support for widespread advection fog Tuesday morning as the warm advection ramps up. This fog may become locally dense in spots, particularly near coastal areas and along and north of I-78 where cooler surface air may persist longer and increase the intensity and duration of the fog. The chance for showers during the daytime Tuesday will be greatest northwest of I-95. The latest guidance has continued to show stronger isentropic lift ahead of a warm front and near and north/west of an axis of robust low-level warm air advection. This should result in a ribbon of showers or even a period of rain as the main forcing for ascent quickly lifts north and northeast from Tuesday morning through early afternoon. PoPs were increased northwest of I-95, with the highest PoPs closest to the Poconos, decreasing southeastward. Aside from the showers, the other story will be the increasing temperatures. Cloud cover will limit more robust diurnal heating, but 925 mb temperatures increasing to +14C to +18C will support highs in the upper 50s to low 60s across much of the area. Some guidance shows a pocket of weak cold air damming across mainly north of I-78, however given the robust low-level warm air advection and southerly flow, this should weaken even more with time Tuesday. Winds will increase from the south to southwest around 10-15 mph with some gusts near 25 mph possible. Temperatures are unlikely to fall much Tuesday night with southerly flow and warm air advection continuing. In fact, temperatures could rise a few degrees overnight. We are currently forecasting low temperatures in the low to mid 50s for most of the region. As surface dew points continue to climb overnight, low clouds and some fog/drizzle should develop, especially along coastal areas and in the higher terrain of eastern Pennsylvania and northwest New Jersey. Some showers will remain across the entire area overnight as well. As we go through Wednesday, the best forcing for widespread showers will arrive especially during the afternoon hours as the cold front gets closer to the area. The southwest flow will continue to advect warm and moist air into the region. We are expecting widespread temperatures in the mid 60s Wednesday afternoon along with dew points nearing 60 degrees. So it will be a warm and muggy January afternoon with showers. Any breaks in the clouds and showers could locally push temperatures toward 70 degrees across the urban corridor and interior portions of the coastal plain. Both high and low temperatures for the calendar day on Wednesday will be near record warmest values for all 9 of our climate stations. Details on these records can be found in the Climate section below. Rainfall for the Tuesday through Wednesday looks to be generally near or less than a half inch. Precipitation chances will decrease late Wednesday night, however the latest trend in the guidance has been generally slower with the progression of the system moving offshore. The cold front may not move offshore until Thursday morning, which has implications for Thursday's high temperature forecast. Given the uncertainty, temperatures for Thursday were increased a few degrees. In any case, the cold front will eventually push through the area bringing an end to the shower activity and warm, muggy air. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Summary...Mild to start then temperatures trending closer to average; mainly dry with the exception of a possible coastal or offshore storm. Synoptic Overview...An upper-level trough in the East is forecast to be in place, although it may end up lifting out during the weekend. This should trend temperatures much closer to average. As the main trough axis crosses our area later Thursday into Friday, associated energy should activate an offshore baroclinic zone leading to surface low development. This feature looks progressive though and tending to be on the weaker side, therefore impacts as of now look to be on the low side. For Thursday and Friday...The upper-level trough axis is forecast to be arriving along the East Coast by Friday afternoon. Some guidance is tighter with this feature with a fairly compact closed low. Strong shortwave energy ahead of this feature along with colder air aloft will assist in energizing an offshore baroclinic zone. This should result in surface low pressure development offshore. Overall this surface looks to be on the weaker side and also the entire system looks to be progressive, therefore impacts should be limited especially given a lack of blocking to our northeast. Given the uncertainty though with the details, will continue with a period of either slight chance or chance PoPs. Temperatures should be close to average, although may be colder if thicker cloud cover and precipitation actually occurs especially with a north to northeast low-level wind. For Saturday and Sunday...While one upper-level trough has lifted well to our northeast, another one may slide across the Northeast Saturday. At the surface, high pressure is forecast to build across our region Saturday before shifting offshore during Sunday. An upper- level trough tracking across the Plains and into the Great Lakes to Ohio Valley Sunday may send a developing warm front toward our area. It looks to be dry overall, however some warm air advection induced lift Sunday will send in some more clouds and perhaps eventually some showers. Temperatures are forecast to continue to be close to average. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today (12Z through 00Z)...Some fog is developing at KMIV and possibly KACY, but fog should dissipate by 13Z to 14Z. VFR otherwise. CIGs gradually lower through the day to around 3500 to 4000 feet by this evening. Some light rain with no VSBY restrictions possible at KRDG/KABE late this afternoon. Light SW winds. Moderate confidence. Tonight (00Z through 12Z)...VFR initially, but MVFR or lower CIGs/VSBYs possible after 03Z as low clouds and fog develop. Will include MVFR CIGs for now, but conditions may end up being much lower than that. Light S winds. Low confidence. Outlook... Tuesday...MVFR and IFR restrictions likely with a period of rain likely northwest of I-95. LIFR possible, especially Tuesday morning and Tuesday night. Areas of fog and drizzle in the morning. Fog and drizzle is anticipated to develop again Tuesday night along with increasing chances for showers. Winds south around 10-15 kts. LLWS possible. Low confidence on timing and coverage of any restrictions. Wednesday...MVFR to IFR restrictions likely with rain showers and areas of drizzle and fog also likely at times. South to southwest winds around 10-15 kts. Moderate confidence on occurrence of restrictions. Thursday through Friday...Mainly VFR, but sub-VFR conditions are possible late Thursday and Friday along with a chance of precipitation. Northerly winds around 10-15 kts. Low confidence. && .MARINE... Sub-Small Craft Advisory conditions today through tonight. SW winds 5 to 10 kt, becoming NW this afternoon, then becoming S tonight. Seas 2 to 3 feet. VSBY restrictions possible in fog this morning, but more widespread VSBY restrictions will develop in fog tonight. A Marine Dense Fog Advisory is now in effect starting at midnight tonight for all waters. Outlook... Tuesday through Wednesday...Small Craft Advisory conditions likely developing Tuesday and persisting into Wednesday night. Southerly winds increasing to 15-20 kts with gusts up to 30 kts possible and seas building to 4-6 feet. Periods of rain showers likely during this period, especially on Wednesday. Areas of dense fog and drizzle may develop with visibility 1 nautical mile or less both Tuesday morning and Tuesday night through Wednesday. The Marine Dense Fog Advisory is in effect until 1 PM Tuesday for Delaware Bay and the Atlantic coastal waters south of Atlantic City and through 4 PM Tuesday for the Atlantic coastal waters near and north of Atlantic City. A Small Craft Advisory is in effect from 1 PM Tuesday through Tuesday night. Thursday through Friday...Small Craft Advisory conditions possible. North to northeast winds around 15 kts with gusts up to 25 kts possible and seas 3-6 feet. Chance of rain Thursday night through Friday. && .CLIMATE... Near record breaking temperatures are forecast for Wednesday, January 4th. Record warmest high and low temperatures for January 4th are listed below: Warmest High Warmest Low Site Record/Year Record/Year Allentown (ABE) 66/1950 51/1950 AC Airport (ACY) 68/1950 52/1950 AC Marina (55N) 67/1998 52/2000 Georgetown (GED) 71/2000 59/1950 Mount Pocono (MPO) 59/1950 50/1950 Philadelphia (PHL) 68/1950 57/1950 Reading (RDG) 67/1950 57/1950 Trenton (TTN) 68/2000 57/1950 Wilmington (ILG) 69/1950 56/1950 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Dense Fog Advisory from midnight tonight to 1 PM EST Tuesday for ANZ430-431-453>455. Dense Fog Advisory from midnight tonight to 4 PM EST Tuesday for ANZ450>452. Small Craft Advisory from 1 PM Tuesday to 6 AM EST Wednesday for ANZ450>455. && $$ SYNOPSIS...Staarmann NEAR TERM...MPS SHORT TERM...Gorse/Staarmann LONG TERM...Gorse/Staarmann AVIATION...MPS/Staarmann MARINE...MPS/Staarmann CLIMATE...