136 FXUS61 KPHI 100513 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 113 AM EDT Wed Oct 10 2018 .SYNOPSIS... High pressure offshore will remain dominant through Wednesday. A strong cold front will arrive in our area later Thursday, which will likely interact with the remnants of Hurricane Michael as it accelerates northeastward and off the Mid-Atlantic coast later Thursday night into Friday morning. High pressure then builds in for Saturday before shifting offshore Sunday. The next cold front should arrive early next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 100 am update: The process has been slow, but patchy fog is developing across the area, especially in the usual spots. Surface observations and webcams suggest locally dense (and shallow) fog is occurring. Though this fog is quite patchy currently, the dense nature of the patchy fog and the expectation that conditions will gradually worsen through daybreak necessitates issuance of a Special Weather Statement. Updated temperatures (a little too high), sky cover (a little too optimistic), and dew points (a little too low) through daybreak. Previous discussion... Earlier showers have almost completely dissipated, and do not expect any additional showers to develop overnight. With a thin layer of humid air in place in the boundary layer, patchy or areas of fog will be possible across the region overnight. In some areas, the layer of nearly saturated air will be thin, limiting the widespread low clouds that we have seen the last several nights. Lows again will be very mild with mid/upper 60s and low 70s in some areas. Winds will be light. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TODAY/... Slow improvement to the low clouds and morning fog across the area before partly sunny skies return for the late morning and afternoon (much like Tuesday). There will be a small chc for showers across the Delmarva and se PA with moisture pooling and a few weak vort maxs approaching the region. High temps Wed. will be much like today with upper 70s across the north and low 80s elsewhere. The high humidity levels will continue Wed. Winds will be mostly srly at 5 to 10 mph, but 10 to 15 mph during the afternoon. && .LONG TERM /TONIGHT THROUGH TUESDAY/... Wednesday night through Friday... The main story for this period will be potential impacts from a cold front and its interaction with Hurricane Michael as it moves up the coast. To start the period Wednesday evening, weakening upper level ridge will be centered over the area with a deep trough over the central CONUS and Michael located near the Gulf coast. Also, surface high pressure will be moving off the coast while a strong cold front will be over the midwest. Heading through Wednesday night, deep layer moisture will increase over the area as the cold front approaches and also as moisture starts streaming up the coast well ahead of Michael. This will bring increasing chances for showers and thunderstorms which should be mainly confined to eastern PA where we do raise POPs to likely in places by Thursday morning. Thursday looks to be an active day as we expect numerous showers with some embedded storms due to the combined effects of moisture streaming north from Michael ahead of the cold front as well as forcing from an upper disturbance moving through in the SW flow ahead of the trough. PWATs look to exceed 2.25 inches, so about as high as anything we've seen so far this year. Also, some indication from the forecast profiles we may have training or backbuilding cells for a time. So this all said, I see a favorable set up once again for very heavy rainfall with an associated flood/flash flood threat across the area. Through the morning, best chances for this very heavy rainfall and associated flooding will be over eastern PA and perhaps the Delmarva with the threat spreading east across NJ through the afternoon. By late day, a weakening Michael will be inland over the SE CONUS still well to our south while the cold front just begins to encroach on our N/W zones. Thursday night into early Friday looks to be the trickiest part of this forecast. During this time Michael will be moving northeast up the coast and likely pass near just south of the Chesapeake Bay entrance before passing near or just south of our coastal waters. In fact latest track indicated by the NAM and GFS (which are in pretty good agreement track wise)looks to have trended just a hair farther north. Thus will put our southern zones very close to or just within the shield of very heavy rainfall associated with Michael itself as it passes offshore while transitioning to post-tropical due to the interaction with the cold front. The upshot in terms of sensible weather is that heavy showers will continue into Thursday evening with the cold front as it moves through the I-95 corridor and points east/south with this rain/showers being enhanced and likely continuing into the overnight / early Friday along the coast as Michael passes by. Meanwhile, areas near and north/west of the I-95 corridor will see rain diminish by the overnight with the passage of the front. By late morning Friday, post-tropical Michael will be moving east of our coastal waters with any heavy rain along the coast ending. By this time, expect total rainfall from the combined effects of the cold front and Michael to be a widespread general 1-2 inches with locally higher amounts possible in areas that see the heaviest showers and also higher amounts possible over over our southern zones from Sussex Co. Delaware east along the Atlantic coast of NJ closer to the track of Michael. Finally, it should also be noted, a period of strong gusty winds will be possible through the first half of Friday in the NW flow behind the departing system. These NW winds could gust 25-35 mph as the cooler, drier airmass surges in. Temperatures Friday will only be in the 60s with 50s in the far north. Friday night through Tuesday... Cooler, drier air continues to advect in for Friday night and Saturday on a NW flow while a broad surface high moves in. This will bring much cooler fall temperatures to the area with highs Saturday mainly in the 50s to low 60s. As the upper trough axis moves through this may bring some variable cloud cover at times Saturday but don't expect any precipitation. A chilly but quiet night will follow for Saturday night with lows dipping into the 40s for most areas and even some 30s in NW NJ and the southern Poconos. Heading into the latter part of the weekend into early next week, progressive pattern continues with the next system looking to approach during this time though there are model differences regarding the timing and evolution of this system. At this point, Sunday looks to most likely stay dry with precip chances increasing early next week. Temperatures look to stay near or below average for this time of year. && .AVIATION /05Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of tonight...Highly variable conditions expected at the terminals, with CIGs/VSBYs oscillating between VFR and LIFR as shallow fog and/or scattered low CIGs develop and dissipate over the next few hours. Conditions should generally worsen for longer durations near daybreak. Nearly calm winds. Overall confidence is moderate, but very low regarding the timing of category changes. Wednesday...Gradual improvement to sustained VFR is expected by late morning, though timing this transition is a challenge. Current indications are this process should occur between 13Z and 16Z, though models have not been stellar with similar scenarios in recent days. Winds becoming south around 5 to 10 kts. Low confidence. Wednesday night...Conditions are expected to be VFR during the evening but will gradually deteriorate overnight. Showers are likely late, with rapid changes in CIG/VSBY in their proximity. Winds light southerly. Moderate confidence. Outlook... Thursday and Friday...MVFR/IFR conditions to start Thursday may improve briefly to VFR ceilings before widespread showers and embedded storms develop ahead of a cold front with associated restrictions. A period of even steadier/heavier rain will be possible Thursday night into Friday morning for KACY/MIV associated with Michael as it tracks off the coast. If this occurs expect at least IFR/MVFR to continue here or lower. The conditions should improve to widespread VFR during Friday. South- southwest winds around 10 knots (perhaps somewhat gusty later Thursday into Friday), become west and northwest later Thursday night into Friday behind the cold front and potentially gusty at times. Low confidence. Saturday through Sunday...Mainly VFR. High confidence. && .MARINE... Few changes are expected on the waters tonight and Wednesday. Winds will begin to increase later Wednesday afternoon with winds gusting up to 20 knots late, but conditions will remain sub-SCA through the period. There will be some patchy fog tonight and perhaps a little drizzle. A isolated shower is not out of the question, but limited impacts expected. Outlook... Wednesday night...The conditions are anticipated to be below Small Craft Advisory criteria, although winds and seas will be starting to increase. Thursday and Friday...Small Craft Advisory conditions or higher are expected with initially southerly winds Thursday, then northwesterly by Friday. Rain/Showers are expected with even some thunderstorms possible. The details are still not completely certain but Michael has trended just a bit farther north meaning the potential for gale force winds exists for Thursday night into Friday morning, especially for the southern waters. SCA conditions may linger behind the system through Friday night. Saturday through Sunday...The conditions should be below Small Craft Advisory criteria as high pressure moves in. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Fitzsimmons Near Term...CMS/Johnson/Miketta/O'Hara Short Term...O'Hara Long Term...Fitzsimmons Aviation...CMS/Fitzsimmons Marine...Fitzsimmons/Miketta/O'Hara