092 FXUS61 KPHI 070803 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 403 AM EDT Thu Apr 7 2022 .SYNOPSIS... An occluded area of low pressure will draw a cold front into our area later today, with a new surface low forming along it and moving over the Mid-Atlantic late this afternoon and evening. The upper- level low will remain over the Northeast through Saturday, leading to continued unsettled weather. High pressure will build into the region Sunday and Monday before sliding offshore into the middle part of next week as a stronger storm system organizes across the central portions of the country. && .NEAR TERM /THROUGH TONIGHT/... Increasingly unsettled today into tonight as a closed low, initially centered near the western Great Lakes early this morning, is forecast to gradually slide south and east through today and tonight. As the extensive closed low/trough to our west slowly shifts eastward through today, surface low pressure is forecast to remain in place across the central Great Lakes region. An occluded front will extend east and then southward from the low and this front will be arriving in our area by later this afternoon. The guidance continues to show weak low pressure developing over our area this afternoon at the triple point intersection. Onshore low-level flow will be maintained across our region which will continue to supply quite a bit of low-level moisture. As a result, extensive low clouds are expected to remain in place across nearly the entire region through the day. Some drizzle and/or fog will be around early this morning before showers start overtaking the region. The forecast soundings show a sharp low-level inversion holding right into this evening given the maintenance of warm air advection at the top of the inversion. This is also being enhanced by a strengthening low- level southerly jet. The combination of the incoming trough, front and low-level jet will result in increasing ascent through the day. One round of some showers this morning (with possibly some thunder), especially from about I-95 westward, may weaken some as it shifts eastward, followed by much more organized activity this afternoon. Model forecast soundings show elevated instability, with this mostly decreasing with a northern extent. This should be enough for some thunder activity, and there has been some lightning occurring in parts of northern and western Virginia very early this morning. Overall, the instability looks to remain elevated across nearly our entire area and therefore any thunderstorms should remain elevated. If more of a warm sector can lift northward, especially across portions of Delmarva, then there will be a window of opportunity this afternoon and early this evening for some surface-based instability. Given the shear profiles in place, will have to watch for any surface-based convection as a strong to severe thunderstorm cannot be ruled out across parts of Delmarva (SPC has a Marginal Risk in place from about southern Delaware southward). This will all depend on the extent of the instability and if it can become surface- based. As of now, the main severe weather potential looks to remain to our south. Temperatures may struggle today given the onshore flow and low clouds, however some low-level warm air advection may offset this to some extent especially from near Philadelphia south and eastward (remaining cooler at the coast though due to the wind off the colder ocean). Rainfall amounts are expected to be highest into this evening north and west of I-95 with 1.0-1.75 inches (lower amounts south and east). There can be locally higher amounts anywhere though with any stronger convective elements. Since the heaviest amounts are anticipated to be where less occurred with the recent system, we are not anticipating much in the way of any flooding impacts. Showers and some thunderstorms continue this evening before shifting offshore through the mid to late evening as the triple point low pressure tracks towards southern New England. As this occurs, the low-level flow will turn from the north and northwest and introduce some drying. As a result, some clearing or at least the erosion of the low clouds is expected to take place overnight. && .SHORT TERM /FRIDAY THROUGH SATURDAY/... The new surface low that formed along the triple point will continue to lift over New England Friday as a drier and cooler airmass works into the region. While the first portion of the day looks dry, scattered showers will develop into the afternoon as the deep cutoff upper level low shifts eastward into the Northeast. These will likely form once again Saturday afternoon as several weak shortwaves and vorticity maxima shift through the main trough axis. Given the steep low-level lapse rates, there is a good chance that we could see more graupel and small hail with these showers both days as just enough MLCAPE should lift moisture above the freezing level. Friday will be the warmer day behind the occluded front before the colder air really works into the region with highs in the upper 50s to low 60s south of the Fall Line. Saturday will be a few degrees colder as the continental polar airmass works into the region and main trough axis nudges east directly over our region. This results in highs in the low to mid 50s. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... We look to finally catch a break as the pattern turns more spring- like with above average temperatures working into the region as we head into next week. The weather looks quite a bit quieter, but I am hesitant to write anything off at this point with quite a bit of variability already showing up by Monday between the global guidance. High pressure will remain the main story through early next week as it works over the Mid-Atlantic and shifts offshore to our south and east into Monday. Things begin to diverge from there with the GFS bringing a much stronger shortwave into the Great Lakes, eroding the mid-level ridge over the East Coast and shunting the surface high towards Bermuda. The Canadian and EC are much more reserved in amplitude and timing of this system. At any rate, a decaying cold front will attempt to work across the Great Lakes and towards our region, but how far it makes it remains to be seen. The EC deepens the trough to our west and cancels out all impact of this shortwave. Kept mentionable PoPs Tuesday to our northwest for now but could see them working into the Poconos perhaps. Highs Monday should make it into the low 60s. A strong cyclone develops over the Central Plains Monday into Tuesday. Whatever comes to be with the fizzling front on Monday night, it will lift north as a warm front Tuesday into Wednesday as the surface low deepens to our west and moves into the Great Lakes. The GFS is notable much more progressive than the Canadian and EC so timing of the cold front is still uncertain into the Friday timeframe. Trended highs on the warm side with the overall ridging pattern over the eastern conus, resulting in widespread low to mid 70s Tuesday, Wednesday, and Thursday. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...IFR/LIFR ceilings. Showers will be on the increase from west to east, with even some thunder possible. MVFR/IFR visibilities at times due to fog/showers. A period of low-level wind shear is anticipated. East or east-southeast surface winds 8-14 knots with local gusts to around 20 knots at times. Low confidence regarding timing and coverage of thunder, therefore it is not included in the TAFs. Tonight...IFR/LIFR in the evening with showers and potentially some thunder, then conditions improve to MVFR and VFR overnight. Winds northeast to north mostly 5-10 knots, becoming northwest. Moderate confidence. Outlook... Friday...Generally VFR with scattered showers and associated brief periods of MVFR or lower restrictions. Southwest winds from 5 to 10 knots with gusts from 15 to 20 knots. Moderate confidence. Saturday...Mostly VFR with additional scattered showers and sub-VFR restrictions once again. Potential for graupel with these showers. West-southwest winds from 5 to 10 knots with gusts from 15 to 20 knots. Moderate confidence. Sunday...VFR with only a small chance for a brief afternoon shower at RDG and ABE with sub-VFR restrictions. Winds from the west- northwest from 10 to 15 knots with gusts to 20 knots. Moderate confidence. Monday...VFR. Westerly winds from 10 to 15 knots. High confidence. && .MARINE... Some fog this morning will reduce the visibility, however there is low confidence if it will become widespread dense enough for a Dense Fog Advisory. Increasing onshore flow today will result in wind gusts of 25-30 knots for a time. Seas will also remain above 5 feet on the ocean waters. The winds will diminish from south to north later this afternoon and this evening and also become north to northwest. Given a strong low-level inversion forecast to be in place, the strong winds above the surface should not all mix down. As a result, a Small Craft Advisory continues through tonight for the ocean zones and during the daytime period for Delaware Bay. Outlook... Friday and Saturday...SCA conditions likely with seas hanging around 5 feet and a few wind gusts approaching 25 knots out of the southwest each afternoon. Sunday and Monday...Sub-advisory conditions expected. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ450>455. Small Craft Advisory until 6 PM EDT this evening for ANZ430- 431. && $$ Synopsis...Davis Near Term...Gorse Short Term...Davis Long Term...Davis Aviation...Davis/Gorse Marine...Davis/Gorse