FXUS61 KPHI 251320 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 920 AM EDT Thu Apr 25 2024 .SYNOPSIS... High pressure arrives from the Great Lakes today before shifting to our northeast and east on Friday. A warm front should lift north of our area later Saturday, then a cold front gradually approaches later Monday before moving across our area later Tuesday. && .NEAR TERM /THROUGH TONIGHT/... Weak shortwave passing by this morning likely keeps some clouds around from Philly on southward for a good chunk of the day, and in fact there could be a stray shower, most likely over the Delmarva but a small chance even in southern NJ. Looks like any showers would end before noon, and we should gradually start to dry out and clear out more late in the day. While the cold advection has lagged, still expect today to be notably cooler than yesterday, with highs mostly in the 50s. High pressure builds to the north tonight with the gradient slacking off enough. With drier air in place by then along with clear skies, expect radiational cooling to maximize. Thus, have leaned hard on the colder guidance and issued a Freeze Watch for a large chunk of the region, mainly for our Pennsylvania and New Jersey zones outside of urban Philadelphia. Areas further south and west look more marginal for a freeze, but still likely need Frost Advisories for these areas. Lows overall in the 30s, with near or below 30 in the Freeze Watch area and Poconos but closer to mid 30s in the urban centers and Delmarva. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... An upper-level trough is forecast to shift to our east to start Friday, allowing high pressure to build across New England and the Mid Atlantic. After a cold start Friday morning, surface flow shifts south- southeast by the afternoon to allow some warming to begin. With mostly clear skies, high temps in the afternoon should reach low 60s inland. Onshore flow, however, will help keep the coastal communities and adjacent inland locations in the mid to upper 50s during the afternoon. Calm winds and clear skies to start the nighttime hours will aid in cooling, but increasing clouds overnight will help stave off runaway radiational cooling. We will still see temperatures dip into the mid 30s to low 40s with patchy frost possible in the most sheltered areas. High pressure shifts offshore Saturday with an approaching warm front, expected to arrive around the evening timeframe. Winds will become more southerly with return flow of our offshore high aiding in the warm air advection we can expect as the warm front pushes through. That said, the increased cloud coverage will prevent us from warming up too much, with afternoon highs expected to reach the upper 50 to low 60s, right around or just warmer than on Friday. While a few showers cannot be ruled out with this warm front probabilities and coverage remain rather minimal with the only mentionable POPs north and west of I-78. Warmer overnight with the warm front passing through and cloud coverage preventing much radiational cooling. Lows will be in the mid to upper 40s. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... High pressure shifts to our south, allowing southwest flow to really crank up the warm air advection across the region. Sunday and Monday will look to bring some of the warmest temperatures we have seen thus far this season with mid to upper 70s on Sunday and low to mid 80s by Monday afternoon! Mostly dry across the region during this timeframe as well, though a few isolated showers or a rumble of thunder cannot be ruled out mainly across the Poconos where the aforementioned warm front may linger nearby. The stacked low shifting across the upper Midwest will slowly move into central Canada Monday into Tuesday, dragging along a cold front across the Ohio River Valley and eventually through the Mid Atlantic. This is where our next best chance for precipitation will come from and will be highly dependent on the timing of this low and its associated cold front. At the moment, some showers will be possible Monday night as the front gradually approaches the region, but the best chance for showers and thunderstorms will come Tuesday as the cold front, washing out at this point, finally arrives. Temperatures remain warm again Tuesday with upper 70s to low 80s. Not much cooler behind this weak cold front on Wednesday, however, with a surface high ridging in from the southeastern US to keep things on the mild side in the 70s. && .AVIATION /13Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas... Through today...VFR. Northeasterly winds generally 5 to 10 knots before diminishing late day. High confidence. Tonight...VFR. Winds becoming more easterly but slacking off to 5 kts or less overnight. High confidence. Outlook... Friday...VFR. Saturday...A period of near MVFR ceilings possible, most likely Saturday night as a warm front pushes through. Otherwise, mainly VFR. Sunday and Monday...VFR conditions anticipated. && .MARINE... Seas will remain elevated through today before slowly starting to come down tonight. For this reason, the Small Craft Advisory was extended to 22z today for our northern ocean zone off the coast of Monmouth County with it running until 10z Friday for the remaining ocean zones. Northeast winds will mostly be sub SCA. Outlook... Friday through Monday...The conditions are anticipated to be below Small Craft Advisory criteria. && .FIRE WEATHER... RH's across much of the region will get quite low today across our Pennsylvania and New Jersey zones, and we've had little rain now for a couple of weeks, allowing fine fuels to dry. Minimum relative humidity values are forecast to drop into the 20-30% range. Northeast to east winds will be strongest this morning, diminishing into the afternoon when the lowest RH values are anticipated. Thus, there will be no special statements issued for danger of fire spread today. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Freeze Watch from late tonight through Friday morning for PAZ060>062-101>106. NJ...Freeze Watch from late tonight through Friday morning for NJZ001-007>010-012-013-015>022-027. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ450. Small Craft Advisory until 6 AM EDT Friday for ANZ451>455. && $$ SYNOPSIS...Fitzsimmons/RCM NEAR TERM...RCM SHORT TERM...MJL LONG TERM...MJL AVIATION...MJL/RCM MARINE...MJL/RCM FIRE WEATHER...WFO PHI