276 FXUS61 KPHI 072040 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 340 PM EST Wed Nov 7 2018 .SYNOPSIS... High pressure gradually builds over our area later Thursday, then shifts into New England Thursday night and Friday. Low pressure tracks near the eastern Great Lakes Friday while another low develops near the Mid-Atlantic coast. Both of these lows then track northeastward and away from our area Friday night. High pressure builds in during Sunday before shifting offshore Monday. The next storm system arrives Monday night and Tuesday, then high pressure builds well to our southwest during Wednesday. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... A west to northwest flow is expected during the overnight hours as surface high pressure builds in from the west. However, any gusts associated with this flow are expected to dissipate after sunset resulting in wind speeds under 10 MPH. Skies are expected to clear north of the I-95 corridor during the overnight hours, but clouds will linger further south. Temperatures are expected to dip into the mid to upper 30s in the north, and into the mid 40s south, which is just about normal for this time of year. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... Benign weather is expected to continue through the day on Thursday as high pressure slides by just to our north. Light northwest winds will gradually become north by late in the day, and clouds may increase across the south as moisture associated with the next system moves in this direction, but no precipitation is expected. High temperatures will range from around 50 in the north to the upper 50s in the south, near normal for this time of year. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... Summary...Unsettled Friday with a strong cold front; Much colder and drier for the weekend; Another storm system later Monday night and Tuesday with the continuation of chilly air. Synoptic Overview...As an upper-level trough amplifies across the Midwest and Plains Thursday night into Friday, southwesterly flow aloft is across the East. The trough sharpens as it shifts eastward into the weekend, driving a strong cold front off the East Coast Friday night. The overall pattern looks to repeat itself later in the weekend and early next week, as the next trough amplifies eastward with yet another cold front moves across the East. Both the Friday and Tuesday systems look to develop a secondary surface low near the Mid-Atlantic coast while the primarily low tracks to our west and north. This pattern will usher in much colder air for the weekend and next week. For Thursday night...As a significant amount of energy dives across the Midwest and Northern Plains, surface high pressure slides eastward across the eastern Great Lakes and into northern New England by daybreak Friday. This surface high then looks to wedge its way southwestward into the Mid-Atlantic region. This will set the stage for a coastal front to become better defined with time with a weak surface low developing as we get close to daybreak Friday. The onset of some warm air advection atop a shallow onshore flow regime with veering winds with height will get an isentropic lift setup going. This should result in some light rain developing from the southwest late, although how far north and how much reaches the ground will depend on how quickly the airmass moistens. The farther north one goes it looks like the dry low-level air hangs on longer. Otherwise, clouds thicken and lower through the night and this will tend to put a lid on temperatures falling especially the second half of the night for the southern half of the region. For Friday...As an upper-level trough sharpens quite a bit across the Great Lakes and even closes off, a deepening surface low is forecast to track across the eastern Great Lakes region. This low looks to occlude with a secondary storm center developing near the northern Mid-Atlantic coast early Friday then tracking north- northeastward. The track of this secondary low will be key in where the heavier rain sets up, however the bulk of the guidance is generally placing this across eastern Pennsylvania and northern New Jersey. The combination of some colder air lingering along with the potential for evaporative cooling may result in some snow or ice pellets mixing in at the onset Friday morning across mainly the Pocono region. The timing of the precipitation this far north may be delayed though due to the drier air, allowing temperatures to warm enough for just a chilly plain rain. Given plenty of large scale ascent coupled with an easterly low- level jet ahead of the secondary surface low, the rain will be heavy at times across much of the region Friday afternoon and evening. The ground is wet due to recent heavy rain especially from the I-95 corridor westward, therefore some flooding may occur. For now, we will continue with a mention in the Hazardous Weather Outlook. As we go through Friday night, the rain should end fairly quickly as the entire system lifts away from the area and drying works in from the west and southwest. The onset of stronger cold air advection and a tightening pressure gradient should result in some increase in a west to northwest wind overnight Friday. For Saturday and Sunday...Deepening low pressure moving north of New England Saturday will combine with high pressure building into the Ohio Valley. Cold air advection combined with a tight pressure gradient and steepening low-level lapse rates will result in a gusty northwesterly wind Saturday. The forecast soundings generally indicate around 30 knots of wind is available to mix down to the surface, therefore the wind and wind gusts were increased during the day Saturday. High pressure edges closer Saturday night and while a tightened pressure gradient is present the winds overall are expected to diminish through Saturday night, then high pressure builds over our area on Sunday with even less wind with time. The flow is progressive therefore the surface high starts moving offshore Sunday night. As for some of the details, the passage of the strong trough aloft Saturday may result in more cloudiness than currently forecast, and some lake effect snow/rain showers may make it into portions of the Poconos before drier air and increasing subsidence takes hold. For Monday and Tuesday...As the next sharpening upper-level trough approaches the Ohio Valley Monday, surface high pressure quickly shifts offshore. This will once again result in an onshore flow developing across our region, which will strengthen Monday night and especially for a time Tuesday. Ample moisture advection and large scale forcing is forecast to accompany this system, with once again the potential for secondary surface low development near the Mid- Atlantic coast. The potential exists for another round of heavy rain, and if the precipitation arrives faster Monday night some snow or mixed precipitation can occur mostly in the Poconos before enough warming takes over. As the sharp trough arrives later Tuesday, cold air advection with the potential for some wrap-around moisture or precipitation lingering behind the cold front may result in a rain/snow mix or even some snow especially across the western areas. This is much less certain as it will depend on the development of the secondary surface low and the extent of the leftover moisture. It looks to start turning blustery Tuesday night as the winds increase. For Wednesday...An upper-level trough is favored in the East with cold cyclonic flow. There should be some lake effect response in the west-northwest flow and perhaps some of this could make a run at our northwestern zones. Otherwise, chilly with a gusty northwesterly wind is anticipated. && .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR conditions are expected to continue with light northwest winds in the 5 to 10 knot range. Mid to high level clouds overnight should have no impact on aviation operations. Thursday...VFR conditions will continue, with northwest winds becoming north by late in the day in the 10 to 15 knot range. OUTLOOK... Thursday night...VFR with increasing and gradually lowering ceilings. North to northeast winds less than 10 knots. Friday...MVFR to IFR conditions developing by the afternoon as rain overspreads the area and continues through the evening. The conditions improve to VFR as the rain ends by daybreak Saturday. Northeast to east winds mostly 10-15 knots, becoming westerly late. Saturday and Sunday...VFR. West-northwest winds 15-20 knots with gusts to around 30 knots Saturday, diminishing some at night and Sunday. Monday...Mainly VFR with increasing clouds at night. Light and variable winds becoming east-southeast 5-10 knots. && .MARINE... Tonight and Thursday...Conditions are expected to remain below advisory levels through the period. OUTLOOK... Thursday night...Northeasterly winds increase and Small Craft Advisory conditions are probable from south to north toward Friday morning. Friday and Saturday...Small Craft Advisory conditions are expected. Onshore winds should gust to around 30 knots on Friday, then turn offshore later Friday night through Saturday. Some low-end northwesterly gale force gusts (to 35 knots) are possible on Saturday. Sunday...Northwest winds may gust to near 25 knots in the morning, however a diminishing trend is anticipated as high pressure builds in. Monday...Onshore flow develops and increases especially at night, however as of now the conditions are forecast to be below Small Craft Advisory criteria. && .TIDES/COASTAL FLOODING... The gauge at Burlington just reached the minor flood level during the Wednesday afternoon high tide cycle. Minor flooding may occur again during the high tide cycle on both Thursday afternoon and Friday afternoon as water remains trapped in the upper portions of the tidal Delaware River, and as an onshore flow increases Thursday night into Friday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gorse Near Term...Miketta Short Term...Miketta Long Term...Gorse Aviation...Gorse/Miketta Marine...Gorse/Miketta Tides/Coastal Flooding...Miketta