Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 130738 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 338 AM EDT Fri Oct 13 2017 .SYNOPSIS...
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High pressure, initially centered near northern New England however it extends into the Mid-Atlantic region, shifts to near and south of the Canadian Maritimes through Saturday. Meanwhile, a weak system from the south moves over our area later tonight and Saturday. A strong cold front moves across our region Sunday night, followed by a weak cold front late Tuesday. High pressure builds in Monday night and Tuesday and remains right over our area during Wednesday into Thursday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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High pressure was centered over Canada`s Maritime Provinces early this morning. The high will drift southeastward today. Meanwhile, an inverted surface trough is forecast to develop off the Middle Atlantic coast. The surface pattern will maintain an onshore flow in our region for today. The wind should be from the east and northeast around 10 to 15 MPH near the coast and 5 to 10 MPH inland. A deck of stratus covered northeastern Maryland, Delaware and southern New Jersey around 3:30 AM. A return flow of increasingly moist air is expected to cause the clouds to continue spreading to the north and northwest. Spotty light rain is anticipated in our region today, mainly in southern New Jersey and southeastern Pennsylvania, and on the upper Delmarva. Maximum temperatures are forecast to be in the 60s. Readings should not get above the middle and upper 50s in the elevated terrain.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
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The center of the high is expected to continue drifting out to sea tonight as the inverted trough remains along the Middle Atlantic coast. Moist air will remain in place in our region. As a result, we are anticipating a mostly cloudy sky along with a low or slight chance of light rain. Patchy fog and drizzle may develop as the surface flow remains off the ocean. A light easterly wind is expected. Low temperatures are forecast to range from the middle 50s to the lower 60s.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/...
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Summary...Potentially unsettled at times Saturday; much warmer Sunday; strong cold front moves through Sunday night; significant cooling early next week as high pressure arrives, followed by some warming mid to late next week. Synoptic Overview...A ridge centered across the southern states to start the weekend gets pushed south and east Sunday as an upper- level trough tracks from the Northern Plains to the Great Lakes and eventually into the Northeast. This trough settles in the Northeast and Mid-Atlantic early next week before gradually lifting out during mid to late next week. At the surface, a strong cold front moves through Sunday night which looks to be followed by a weak/dry cold front late Tuesday. Overall, high pressure looks to dominate much of next week with cool temperatures (actually closer to where we should be for this time of the year) before some moderation takes place during the mid to late week timeframe. We used a model/continuity blend for Saturday through Sunday night, then blended in mostly the 00z WPC Guidance. For Saturday and Sunday...A split weekend looks to occur with the second half turning brighter and much warmer. As an upper-level ridge centered across the southern states Saturday gets pushed south and east through Sunday, high pressure becomes more established offshore allowing for a strengthening return flow. The guidance overall continues to bring a weak disturbance northward across our area Saturday, although there are some differences regarding the amount of rain/showers that occurs. We will still have an onshore flow along with some increase in the surface dew points. Given the majority of the moisture is locked in within the lowest levels of the atmosphere, Saturday may start out with areas of either light rain or drizzle with some fog. Some improvement should take place in the afternoon from south to north but some showers are still possible for much of the area. There should be some breaks of sunshine in the afternoon to help boost the temperatures. We leaned closer to the warmer GFS as the NAM may be locking the stratus in to long. A more pronounced south to southwest flow develops Sunday as an expansive warm sector takes hold. Therefore after some possible low clouds and/or fog with light rain/drizzle to start Sunday, afternoon temperatures should surge into the upper 70s and lower 80s. This occurs 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. The cold front should arrive into our western areas early in the evening then progress eastward Sunday night. A band or broken band of showers (perhaps embedded thunder) may weaken with an eastern extent Sunday night as the main forcing lifts to our north. The overall instability is less certain at this time, thus lower confidence in thunder this far east. As a result, kept PoPs no higher than the chance range and did not add in thunder. A wind shift to the northwest occurs with the passage of the cold front and the surface dew points will start to lower later Sunday night from west to east as drier air advects in. For Monday and Tuesday...A strong cold front is forecast to be offshore as we start Monday with any associated showers near the coast ending early. 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 and Tuesday with cool temperatures, although more toward where we should be for this time of the year. A strong upper-level trough though moving across New England Tuesday will push a secondary weak cold front through our area. This front looks to be moisture starved here therefore we are carrying a dry frontal passage. For Wednesday and Thursday...As a gradually building ridge replaces the trough in the Northeast, surface high pressure over our area Wednesday will start to shift east during Thursday. This will result in rising heights aloft, translating to some moderation in the temperature department during this timeframe.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. An area of stratus over the upper Delmarva and southern New Jersey will continue to expand to the north and northwest. As a result, we are anticipating mainly MVFR conditions at our eight TAF sites for today. Patchy light rain may affect KACY, KMIV, KILG, KPHL and KPNE. Conditions may briefly improve to VFR at KACY, KMIV, KILG, KPHL, KPNE and KTTN for a time this evening. However, lowering conditions are anticipated for late tonight with patchy drizzle and fog possible along with IFR ceiling and visibility values. An east to northeast wind around 6 to 12 knots is expected for today. A light east to northeast wind should continue into tonight. OUTLOOK... Saturday...MVFR or IFR ceilings especially early along with local fog. Some possible morning light rain or drizzle will give way to a chance for some showers. Areas of low clouds and/or fog should develop or expand at night. Northeast to east winds 5 knots or less. Sunday...Any low clouds and/or fog with drizzle in the morning give way to mainly VFR conditions. A cold front arriving at night should result in some showers, however the coverage is less certain. South to southwest winds increasing to 10-15 knots with possible gusts to 20 knots, then becoming northwest behind the front at night and diminishing some. Monday and Tuesday...VFR. Northwest winds 10-15 knots with gusts up to 20 knots Monday, then diminishing at night and Tuesday.
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&& .MARINE...
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The circulation around high pressure to our northeast and a developing inverted surface trough to our south will maintain an east to northeast flow along the coasts of New Jersey and Delaware for today and tonight. Wind speeds should be 15 to 20 knots today and 10 to 15 knots tonight with some gusts. We will discontinue the Small Craft Advisory for upper Delaware Bay. We will leave the advisory in place until 11:00 AM for the lower part of Delaware Bay, mainly for waves in excess of 5 feet near the mouth of the bay. The Small Craft Advisory will remain in effect for today and tonight on our ocean waters, mostly for seas. However, wind gusts in excess of 25 knots remain possible this morning. OUTLOOK... Saturday...The winds are expected to be below Small Craft Advisory criteria, however seas on the ocean should remain 4-6 feet for awhile. The seas are anticipated to lower later in the day and at night, therefore only extended the Small Craft Advisory through the daytime Saturday. Sunday...The conditions should be below Small Craft Advisory criteria overall, however southwesterly winds may gust to around 20 knots for a time which may build the seas to near 5 feet on the ocean. A wind shift to the northwest occurs at night as a cold front moves through. Monday and Tuesday...Northwest winds should gust to 20 knots Monday, then diminish Tuesday. Seas may start near 5 feet on the ocean Monday, but should favor lower. A Small Craft Advisory is not anticipated.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EDT Saturday for ANZ450>455. Small Craft Advisory until 11 AM EDT this morning for ANZ431.
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&& $$ Synopsis...Gorse Near Term...Iovino Short Term...Iovino Long Term...Gorse Aviation...Gorse/Iovino Marine...Gorse/Iovino

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