528 FXUS61 KPHI 102330 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 630 PM EST Tue Nov 10 2020 .SYNOPSIS... An area of low pressure will move across the Great Lakes into Canada tonight as high pressure moves further offshore. A cold front associated with this area of low pressure will move toward the region Wednesday before completely pushing offshore Thursday afternoon. High pressure will briefly build across the region into the weekend, quickly moving off to the east as another area of low pressure moves across the Great Lakes. A warm front accompanying this low will push northward across the region Sunday before another cold front crosses the area Monday. && .NEAR TERM /THROUGH WEDNESDAY/... While temperatures will cool tonight, the trend will be for a more gradual, less strikingly robust drop than what we have been seeing the past several evenings. Clouds will be on the increase at nearly all levels ahead of a cold front well to our west across the Mid- Mississippi Valley. This will lead to a warmer night as well with lows in the upper 50s to low 60s. With dew points nearing 60F, and less cloud cover today, am leaning more on the foggy side of things with the expectation that more appreciable radiational cooling will take place tonight ahead of the cloud cover to our south, which is still only building into the Carolinas. Thus, be prepared for morning fog and potentially longer commutes. Things begin to change tomorrow as we stay partly to mostly cloudy. Fog will be slower to burn off than past days as well. Another mild day at least, though cooler than today with highs making it into the upper 60s to near 70s across much of southeast Pennsylvania and northern New Jersey, and into the low 70s on the Coastal Plain. Temperatures could waver a degree or two if skies clear enough in the late morning after residual fog lifts. The large-scale pattern remains much the same as the longwave trough across the western U.S. stays mostly put, with the more notable change being a flattening and slight shift eastward in the ridge axis over the eastern U.S. that has led to the incredible dry stretch of weather as of late. A shortwave trough currently ejecting out of this longwave trough will continue to move across the Midwest and Great Lakes tonight into tomorrow morning before moving into Ontario. At the surface, an area of low pressure will, perhaps more colloquially termed a Colorado Low, will develop along the pre- existing frontal boundary draped across the mid-section of the CONUS. As this low deepens into Ontario, reinvigoration of the cold front will continue to propel it eastward into the Ohio and Tennessee Valleys closer to the Mid-Atlantic. Tropical Storm Eta's positioning with respect the surface high over the western Atlantic will be most formidable for funneling prolific moisture into the region, which can be summarized by the rise in PWATs to near 2 inches by tomorrow evening. Expect a precip shield to blossom over the Mid-Atlantic given a strengthening vort max to our southwest across the Carolinas Wednesday afternoon and evening. The initial rain shield looks to push across central Pennsylvania into our region in the early afternoon, with additional rain developing from the southwest, overtaking much of the CWA by 4-6 pm. This sets the stage for a wet night, so be alert for slippery driving conditions with wet leaves in the roadways. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... Wed night thru Thu night...Unsettled conditions with low pressure passing well north of the area and its associated front moving W to E across the area later Wed. A subtle weak wave moves along the front Thu prolonging the arrival of the drier and cooler air behind the system. The mild and humid airmass in place Wed will yield decent QPF across the area with 1.5 to 2.0 inches for the NE PA and nrn NJ areas and 2.0 to 2.5 inches for srn NJ, metro Philadelphia and Delmarva. Probably not enough to produce widespread flooding, but can;t completely rule out some localized flooding concerns for the period. Temperatures some 5 to 10 degrees above normal Thu then trending close to normal Thu night. Friday...Fair weather expected, can't completely rule out a scattered shower early, so we'll just keep pops in the slight chc range for now. Low pressure pulls away offshore while high pressure begins to build from the central part of the U.S. High temps a few degrees above normal with maxs in the upper 50s/low 60s most areas and some mid 60s for Delmarva. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Fri night/Saturday...High pressure will be across the region with fair weather expected thru the period. Increasing clouds late Sat. as the next system develops to the SW. Seasonable temperatures overall, maybe a degree or two below normal, with highs Sat. mostly in 50s for the forecast area and some upper 40s for the higher elevations NW. Sat night thru Monday...Unsettled conditions with an upper trough moving towards the region and the last of the remnant moisture associated with TS Eta moving up across the East Coast. Pops are in the chc range Sat night then increase to low likelies for Sunday as the best dynamics arrive for the Middle Atlantic. Beyond that the upper energy is more scattered so mostly chc pops for Sun night and Monday. The precipitation will be rain for most areas most of the time but a few snow flakes are possible up across the higher elevations of the Poconos late Sat night/Sun morning. Temperatures will be close to normal Sat night, but then turn above normal for the rest of the (Sun-Mon) period. Monday night/Tue... Fair weather behind the departing deep low across the Canadian Maritime Provinces and high pressure across the Central Plains. Colder air will be arriving with temperatures around 5 degrees below normal. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Mainly VFR until around 06Z, with conditions lowering to MVFR/IFR after 06Z in stratus and fog. Southerly wind 6 knots or less. High confidence in the overall trend but low confidence in the specific timing. Wednesday...Mainly MVFR/IFR conditions. Rain arriving from the west after 18Z. The rain will become moderate to heavy late in the period. Southerly wind 5 to 10 knots. Medium to high confidence. .Outlook... Wed night thru Thu night...Lower CIGS/VSBYS with showers. Fri thru Saturday...Mostly VFR. Morning fog possible. Sat night/Sunday...Restrictions possible. Showers. && .MARINE... Tonight through Wednesday...Sub-advisory conditions are expected with southerly winds from 10 to 15 knots and gusts to 15 knots. Seas from 1 to 3 feet building to near 4 feet by Wednesday night. .Outlook... Wed night thru Thu night...SCA conditions possible. Showers. Fri/Sat...sub-SCA. Fair weather. Sat night thru Sunday...sub-SCA. Showers possible. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Davis Near Term...Davis Short Term...O'Hara Long Term...O'Hara Aviation...Iovino/O'Hara Marine...Davis/O'Hara