Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 241337 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 937 AM EDT Sat Oct 24 2020 .SYNOPSIS... A cold front extended southwestward from Quebec, across western Pennsylvania and West Virginia to the lower Mississippi River Valley early this morning. The front will move to the east and it is forecast to pass through our region this afternoon and evening. High pressure is expected to build across New York and New England on Sunday. A warm front is anticipated to lift through our area on Monday, followed by a cold front from the northwest late on Monday night. Weak high pressure should influence our weather from Tuesday into Wednesday. Another cold front is expected to move slowly through our region late in the week as low pressure passes to our south. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 930 am update: Quite an interesting past 12 hours forecasting- wise. Fog generally failed to develop overnight as a low-stratus deck developed during the evening and winds remained just strong enough at the surface (probably aided in part by a passing perturbation in the midlevels during the overnight period). However, around sunrise, breaks in the stratus deck developed on the eastern edge of the cloud shield. In these areas, patchy fog developed and continues at this time, especially near the Delaware River, Delaware Bay, and in adjacent portions of southeast Pennsylvania and northern/central New Jersey. Meanwhile, as suspected for the past couple of days, models are underplaying shower activity along the advancing cold front (now beginning to influence the western CWA). Coverage remains sparse enough for now to maintain slight-chance PoPs, but will continue to monitor. Expect low clouds to continue until the advancing showers/front move through before relatively rapid improvement as winds become more westerly/northwesterly. Previous discussion follows... Once more, we are dealing with a murky morning across the region. Fog has been much less prevalent tonight versus prior nights, but low stratus has been abundant and most of the area is cloaked in the low cloud deck. Light but steady southwesterly flow will continue to develop this morning and will help to gradually erode the low clouds. Skies won`t go clear, but some breaks are expected by later this morning and into the afternoon. Once low clouds begin to lift and erode, the next forecast challenge will be a cold frontal passage this afternoon and evening. Seasonally strong low pressure tracks well to our north into Quebec today, and its trailing cold front will sweep through later on in the day. A respectable thermal gradient with this front, as will be evidenced by much cooler temperatures tonight and Sunday. However, with its parent low tracking so far away and with weak ridging present over the East Coast, there will not be much forcing for ascent this afternoon. As has been the case for several days, have maintained mostly slgt chc PoPs for most of the area for the possibility of some spotty light showers along the front, but a mainly dry day is expected. The expected timing of the frontal passage has slowed slightly over the past couple of days. Because of this, we will remain in the warm sector for most of today, and another warm day is likely. Temperatures will be somewhat dependent on the degree of clearing this morning and early afternoon. They could also begin to slide backwards a bit later this afternoon behind the front, especially to the west. Generally raised the max values slightly over the previous forecast but did not go too far from consensus. This brings most areas into the low to mid 70s today. If we do clear out a little more and sooner than expected, some values in the upper 70s to near 80 will be possible especially over southern NJ and Delmarva. Either way, a warm day for late October, with highs running about 10 degrees above average. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... For tonight, the cold front settles to our south. A mainly dry night is expected. There could be a lingering spotty shower in southeastern areas during the early part of the night along the front. In addition, an upper level disturbance will approach from the west-southwest during the second half of the night and will start to interact with the frontal boundary. The front may make it far enough south to keep the entire area dry, but at worst the approach of this disturbance would mean a renewed chance for some light showers later tonight, again mainly on Delmarva. The low temperature forecast tonight will be tricky with multiple factors in play. A colder air mass will be advecting in behind the front, but a steady 5 to 10 mph northerly breeze will keep values from falling off too much at least initially. However, as building high pressure to the north begins to encroach further, winds may let up during the second half of the night especially to the northwest. This should support lows falling into the mid to upper 30s over the Lehigh Valley, northern NJ, and the Poconos. Further south and east, winds are less likely to go calm, and there is also the chance of more cloudiness associated with the approaching disturbance mentioned above. So values along and southeast of I-95 will be mainly in the 40s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... A fairly progress weather pattern is expected during the period from Sunday through Friday. Surface high pressure in the Saint Lawrence River Valley on Sunday will try to push down into our region. However, the return flow aloft is expected to result in a mostly cloudy day along with a chance of rain in northeastern Maryland, Delaware, southeastern Pennsylvania and southern New Jersey. Increasing cloudiness is anticipated for the Lehigh Valley, the Poconos and northern New Jersey. The air mass centered to our north will be quite chilly. Highs on Sunday are forecast to be mainly in the 50s. Mostly cloudy conditions with a chance of rain will continue for Sunday night and Monday as a warm front lifts toward and through our region. Some improvement is expected across our southern counties on Monday afternoon as the front progresses farther to their north and that area gets more solidly into the warm sector. A cold front is expected to pass through our region late on Monday night. The boundary should be slow moving so the chance of showers will continue on Tuesday. It appears as though Wednesday will be the driest day of the week as high pressure drifts across our area. Clouds and the potential for rain are forecast to return late in the week. A mid level low is expected to be over west Texas on Wednesday, The feature will likely progress to the east northeast and it should pass off the Middle Atlantic coast on either Friday or Friday night. It may become an open wave by that time. Another cold front is anticipated to drop into our region on Thursday. Surface low pressure associated with the mid level feature is expected to pass to our south in the Thursday night into Friday time frame. Temperatures are forecast to be seasonable from Monday through Thursday, with readings falling below normal on Friday. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...IFR to low MVFR CIGs and light/variable winds will continue this morning in advance of a cold front moving through the area. Patchy fog is possible, especially near the Delaware River, through 16z or so. Once the front passes (generally 16z to 18z), quick improvement to higher MVFR and then VFR is expected with winds becoming northwest around 10 kt. Low confidence with several TAF amendments possible until frontal passage; moderate confidence thereafter. Tonight... Mainly VFR, though CIGs will begin to lower late tonight near and south of MIV and ACY. Winds becoming north then north- northeast at 5 to 10 kt, with some higher gusts possible near the coast. Moderate confidence. Outlook... Sunday...VFR ceilings with a chance of rain. Lowering conditions at night. North to northeast wind around 10 knots. Medium confidence. Monday...Generally IFR/MVFR in the morning with some improvement possible in the afternoon. A chance of rain. East wind 5 to 10 knots, becoming south to southwest. Low to medium confidence. Tuesday...VFR/MVFR with a chance of showers. Northwest to north wind 5 to 10 knots. Medium confidence. Wednesday...Mainly VFR. Northwest wind 5 to 10 knots, becoming southwest. Medium to high confidence. && .MARINE... A Small Craft Advisory (SCA) remains in effect on the Atlantic coastal waters due to continued 5 to 7 ft seas associated with Hurricane Epsilon well offshore. On Delaware Bay, sub-SCA conditions will continue through today and tonight. Southwesterly winds of 10 to 15 kt are expected for most of today, becoming westerly then northwesterly this evening. Overnight, winds will veer from northwest to north or northeast with some 20 kt gusts possible. Outlook... Sunday and Sunday night...A Small Craft Advisory is in effect on our ocean waters for wave heights of 5 to 6 feet. Monday...Wave heights on our ocean waters may remain around 5 to 6 feet, especially in the morning. Monday night through Wednesday...No marine headlines are anticipated. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Monday for ANZ450>455. && $$ Synopsis...Iovino Near Term...CMS/O`Brien Short Term...O`Brien Long Term...Iovino Aviation...CMS/Iovino/O`Brien Marine...Iovino/O`Brien

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