Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 120748 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 348 AM EDT Thu Oct 12 2017 .SYNOPSIS...
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A weakening area of low pressure will slide east of the Mid-Atlantic coast through today. Meanwhile, strong high pressure centered across northern New England through tonight shifts into the Canadian Maritimes Friday into Saturday. A cold front moves through our area Sunday night into early Monday, then high pressure builds in Monday night through Wednesday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A weakening mid level short wave trough was located over the eastern Great Lakes early this morning. The feature will continue progressing eastward and it should pass overhead this afternoon. Showers in advance of the short wave are expected to continue affecting our region this morning. However, dry air building down from the north should cause the area of showers to erode from north to south as the day progresses. The dry air is associated with an area of high pressure that will remain centered over Quebec today. Low clouds are forecast to lift gradually today with some breaks of sunshine anticipated for this afternoon. We expect that maximum temperatures will be mainly in the 60s in northeastern Maryland, Delaware, New Jersey and eastern Pennsylvania. Readings should not get above the 50s in the elevated terrain. The circulation around the high will maintain and easterly wind in our region for today. Speeds are forecast to range from 10 to 20 MPH with gusts of 20 to 30 MPH. The strongest of the winds will be near the coast.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
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The center of the surface high is forecast to slide over Canada`s Maritime Provinces tonight. Moisture is expected to begin building northward and into our region as an inverted surface trough develops off the Middle Atlantic coast. As a result, clouds should begin to lower and there is a chance of rain showers for northeastern Maryland, Delaware and southern New Jersey. The wind is anticipated to be out of the east and northeast for tonight around 5 to 10 MPH inland and 10 to 15 MPH near the coast. Low temperatures will favor the 50s in our region, with readings falling into the 40s in the far north.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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Summary...Cool and potentially unsettled Friday into Saturday; significant warming over the weekend mainly during Sunday; strong cold front moves through Sunday night into early Monday followed by significant cooling early next week as high pressure builds in. Synoptic Overview...A ridge in the East will allow strong surface high pressure to shift into the Canadian Maritimes over the weekend. The associated onshore flow will eventually turn from the south and southwest, allowing for another surge of warmth with a developing warm sector during the course of the weekend. A weak disturbance though Friday into Saturday may result in periods of unsettled/wet weather. A sharpening upper-level trough over the weekend drives a strong cold front across our area Sunday night into early Monday. The upper-level trough swings through Tuesday into Wednesday, however surface high pressure should be building in. We used a model/continuity blend for Friday through Saturday night, then blended in mostly the 00z WPC Guidance. For Friday...Surface high pressure shifts more into the Canadian Maritimes. An onshore flow will continue though for our area and this will result in lots of cloud cover and cooler temperatures (although close to where we should be for this time of the year). The guidance shows a low-level jet from the east and southeast Friday below 850 mb. Within this region, areas of lift should result in some showers (perhaps even some drizzle in the morning where less lift is present) although the guidance does differ on the areal extent of the showers. Surface high pressure is forecast to be wedging down across our area, which many times tends to focus the showers farther south and west. Eventually this area of lift or weak surface trough starts to shift northward at night, which may allow for the showers to migrate north and eastward. As a result, we kept mostly chance PoPs for the idea of scattered showers around. There will be a breeze, however it is forecast to not be as strong as today (Thursday). For Saturday and Sunday...As an upper-level ridge builds from the Mid-Atlantic on south-southwestward during the weekend, surface high pressure will continue to shift farther away from the New England coast. This will eventually lead to a return flow developing. A fly in the ointment though on Saturday is the presence of a very weak surface low or trough near the Mid-Atlantic coast that works northward. This will keep the chance for some showers and therefore kept slight chance to chance PoPs Saturday into Saturday evening. Despite this, some warming is expected to begin on Saturday. A more pronounced south to southwest flow occurs Sunday as an expansive warm sector takes hold. Therefore after some possible low clouds and/or fog to start Sunday, afternoon temperatures should surge into the lower 80s for much of the area. This occurs well ahead of a sharpening upper-level trough in the Midwest and Plains, which drives surface low pressure up across the Great Lakes Sunday with a trailing cold front. Some showers may approach the Poconos Sunday afternoon, however the main showers should hold off until Sunday night. Given the arrival time of the strong cold front, a band or broken band of showers (perhaps embedded thunder) may tend to weaken with an eastern extent Sunday night. The upper-level trough may be sharp enough to keep more organized showers occurring longer though, however the overall instability is less certain at this time. For Monday through Wednesday...A strong cold front should be offshore as we start Monday with any associated showers also offshore. Based on the timing of the front being offshore Monday, it will be much cooler with a northwest wind in its wake. High pressure builds in from the southwest Monday night into Wednesday with cool temperatures, although more toward where we should be for this time of the year.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Variable conditions are expected for this morning with rain showers. Ceilings are anticipated to favor the MVFR range but they will go to VFR and IFR at times. The rain showers are forecast to drop to the south of our TAF sites for this afternoon and this evening with conditions expected to improve to VFR. The rain showers may begin to spread back to the north tonight. The wind will favor the east today at speeds in the 10 to 18 knot range. The wind is forecast to gust into the 20s. Wind speeds are expected to diminish to 6 to 12 knots for tonight and they should be out of the east and northeast. OUTLOOK... Friday...MVFR ceilings which may improve to VFR at times during the day, then possibly local IFR ceilings developing at night. Some showers should be around. East-northeast winds near 10 knots, then lighter at night. Saturday...MVFR or IFR ceilings in the morning, then possibly improving to VFR. Local fog and/or low clouds may redevelop at night. Sunday...Early low clouds and/or fog possible, otherwise mainly VFR. South to southwest winds increase to 10-15 knots with gusts up to 20 knots possible, then diminish some at night. Some showers possible at night with a cold front. Monday...VFR overall. Northwest winds around 10 knots with local gusts up to 20 knots possible in the afternoon.
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&& .MARINE...
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The circulation around high pressure to our north will maintain an easterly flow along the coasts of New Jersey and Delaware for today. Gale force gusts are anticipated on our ocean waters into this evening. As a result, the Gale Warning remains in effect. A Small Craft Advisory is in place for Delaware Bay. Wave heights on our ocean waters are anticipated to build to 9 or10 feet. OUTLOOK... Friday and Saturday...Small Craft Advisory level winds are anticipated to diminish later Friday, however seas on the ocean should remain at or above 5 feet through much of Saturday. Sunday and Monday...The conditions should be below Small Craft Advisory criteria overall, however southwesterly winds Sunday may gust to around 20 knots for a time which may build the seas to near 5 feet on the ocean.
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&& .TIDES/COASTAL FLOODING...
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The strengthening onshore flow is forecast to result in a surge of 1.5 to 2 feet above the astronomical tide today. As a result, we continue to expect minor coastal flooding around this afternoon`s high tide in the coastal counties of New Jersey and Delaware. The same is true for the counties along Delaware Bay and along the far lower Delaware River. It appears as though this will be a one tide cycle event. The onshore flow is forecast to begin weakening tonight. Also, the astronomical tides associated with the overnight high tide are lower than those during the day.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...Coastal Flood Advisory from noon today to 6 PM EDT this evening for NJZ012>014-020>027. Coastal Flood Advisory from 3 PM this afternoon to 7 PM EDT this evening for NJZ016. DE...Coastal Flood Advisory from noon today to 6 PM EDT this evening for DEZ002>004. Coastal Flood Advisory from 3 PM this afternoon to 7 PM EDT this evening for DEZ001. MD...None. MARINE...Gale Warning until 10 PM EDT this evening for ANZ452>455. Gale Warning until 6 PM EDT this evening for ANZ450-451. Small Craft Advisory until 6 AM EDT Friday for ANZ430-431.
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&& $$ Synopsis...Gorse Near Term...Iovino Short Term...Iovino Long Term...Gorse Aviation...Gorse/Iovino Marine...Gorse/Iovino Tides/Coastal Flooding...Iovino

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