471 FXUS61 KPHI 190118 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 918 PM EDT Mon Oct 18 2021 .SYNOPSIS... Our region will remain in west to northwest flow through Wednesday as high pressure remains centered across the Southeast with low pressure over the Canadian maritimes. A weak area of low pressure will track through the Great Lakes on Thursday, causing a cold front to move through the region Thursday night. A couple of upper level disturbances may bring some reinforcing colder air by next weekend. && .NEAR TERM /THROUGH TUESDAY/... For the rest of tonight, the loss of diurnal heating combined with the upper low moving slightly farther away will result in clearing skies the second half of the night with diminishing winds. Temperatures will be on the cool side with lows mostly in the low to mid 40s. However portions of the Lehigh Valley northward into the Poconos and NW NJ should see temps dip into the upper 30s. Winds, however, should stay up just enough due to the pressure gradient to keep temps from really bottoming out so no frost/freeze headlines are needed. For Tuesday, low pressure continues to pull away as high pressure settles into the SE CONUS. This will bring mainly sunny skies but it will still be a bit breezy due to the pressure gradient persisting. However it won't be quite as windy as today. Temperatures will also be a bit warmer with highs mostly in the middle to upper 60s...pretty close to average. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... Very quiet weather heading through the midweek period. Strong high pressure will remain centered to our south, slowly shifting east with time. Dry weather is expected. We get some warm advection on Wednesday as ridging over the Great Lakes region shifts east. Associated height rises and a shift to more westerly flow with plenty of sunshine and dry air will bump temperatures back up into the lower 70s. It will be a beautiful day. Otherwise, overnight lows will mostly favor the lower 50s. This is above average, mainly due to winds remaining a bit elevated at night as a decent pressure gradient remains in place between the high to the south and slow- moving low pressure over Atlantic Canada. && .LONG TERM /THURSDAY THROUGH MONDAY/... Overview... A relatively benign pattern continues through the weekend, though we will deal with the usual ups and downs of autumn. At upper levels, the main feature to watch will be a developing trough over the Great Lakes region. After a midweek warm-up, this trough is likely to bring a period of cooler weather by the end of this week and the weekend, but there remains uncertainty on how robust this trough will be. The overall appearance of the guidance for the late week and weekend is not as cold as it was, say, 24 hours ago, due to the trough being held back to the west a little more and keeping our flow more zonal. It does still look like we will trend cooler into the weekend, but how much of a cooldown remains in question with models still exhibiting considerable run-to-run variation. So some additional changes to the temperature forecast are very possible. Otherwise, our recent run of drier than normal weather looks to continue, as while there may be a couple of chances for showers, it does not look like we will have any widespread soaking rain events this period. Dailies... Thursday-Thursday night... As surface high pressure shifts offshore of the Southeast, fast-moving low pressure will track into the Great Lakes. This combination will allow steady southwest flow to develop, advecting additional warmer air into the region. Thursday looks like the warmest day of the week, with highs returning to the mid-70s. A cold front associated with the low pressure will start to approach by late afternoon or more likely the evening. Due to the unfavorable diurnal timing, meager dynamics, and very limited moisture, this front is likely to produce little if any rainfall. There will be just a slgt chc heading through the evening and overnight, with somewhat better odds across the northern zones. Friday-Friday night... Most indications are for a dry day behind the cold frontal passage. A few degrees of cooling are likely behind the front, but the deeper troughing and associated colder air hangs back to the west, so it will still be fairly mild for the season. Highs in the upper 60s and lower 70s are currently forecast. Some guidance has also suggested a wave of low pressure riding along the offshore front may bring some rain at least to the southern portion of the area overnight. This does not look like a big deal and it may miss entirely, but have maintained some slgt chc to chc PoPs for the possibility, greatest to the south. Saturday-Monday... As mentioned, the details of the forecast here are quite uncertain. Troughing will become more established over the Great Lakes, with a reservoir of colder air building up over the Lakes and southern Canada. That troughing should make at least some progress south and east with time, but models are wavering on how deep the trough will become. It is likely we will see a continued cooling trend. The latest consensus guidance suggests only a trend towards seasonable values, but there is still some potential for colder outcomes, which could result in frost/freeze concerns if they materialize. Confidence regarding precipitation chances is a little higher. While some spotty showers here or there cannot be ruled out due to a couple of shortwaves in the flow, especially on Saturday, there are no heavy precipitation events expected, and much of the time should be dry. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR conditions expected with skies clearing and winds diminishing. W/NW winds diminishing to around 5-8 knots. Tuesday...VFR with WNW winds around 10 knots with gusts of 15 to 25 knots by late morning into the afternoon. Outlook... Tuesday night-Wednesday night... VFR. Westerly winds 5 to 10 kt, with some gusts near 20 kt Wednesday afternoon, then becoming light and variable Wednesday night. High confidence. Thursday-Thursday night... VFR. Slight chance of a shower in the afternoon or evening mainly north and west of PHL. Southwest wind 5 to 10 kt. High confidence. Friday-Friday night... Mainly VFR, with a chance for showers during the evening and overnight. Westerly wind 5 to 10 kt becoming light and variable at night. Moderate confidence. Saturday-Saturday night... Mainly VFR, but showers are possible which may bring restrictions. Northwest wind 5 to 10 kt. Moderate confidence. && .MARINE... We've extended the Small Craft Advisory of our ocean waters until 6 AM Tuesday. Generally expect winds gusting up to 30 knots however a few gusts to Gale force will be possible through early this evening. Winds over Delaware Bay should diminish below SCA levels around midnight. For Tuesday, winds should be below SCA levels through the first half of the day before starting to increase again through the afternoon...potentially to marginal SCA levels by the evening. Outlook... Tuesday night... SCA conditions may continue mainly for the waters of northern and central New Jersey as westerly winds gust near 25 kt. Elsewhere, winds should be a little lighter. Seas 2 to 3 ft. Wednesday-Wednesday night... Sub-SCA conditions expected. West wind 10 to 15 kt with gusts to 20 kt, becoming southwest overnight. Seas around 2 ft. Thursday-Thursday night... A period of SCA conditions is possible for late Thursday and Thursday night as southwest winds gust near 25 kt and seas build to 4 to 5 ft. Friday-Saturday... No marine headlines are currently anticipated. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ450>455. Small Craft Advisory until midnight EDT tonight for ANZ430-431. && $$ Synopsis...O'Brien Near Term...Fitzsimmons/Kruzdlo Short Term...O'Brien Long Term...O'Brien Aviation...Fitzsimmons/O'Brien Marine...Fitzsimmons/O'Brien