Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 170100 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 800 PM EST Fri Feb 16 2018 .SYNOPSIS... High pressure builds into the area tonight, then offshore on Saturday. An area of low pressure will approach the area from the south later Saturday into Saturday night. High pressure briefly builds across the area again Sunday, then offshore Sunday night. A warm front is expected to lift across into the area later Monday into early Tuesday, followed by a cold front Wednesday into Wednesday night. This front will sag to our south Thursday and Thursday night as high pressure builds to our north. && .NEAR TERM /THROUGH SATURDAY/... A cold front extended across southern New Jersey and the upper Delmarva at mid afternoon. The boundary will continue to push to the southeast and off the coast. The showers associated with the cold front will come to an end from northwest to southeast in our region through early evening. A northwest wind around 10 to 15 MPH behind the front will gust near 20 MPH into this evening, then wind speeds will begin to diminish for the overnight period. The northwest flow will bring dry air, a clearing sky and a drop in temperatures to our region. Tonight`s lows are forecast to range from around 20 in the Poconos and in far northern New Jersey to the lower 30s in southern Delaware. The northwest wind should dry most roads and walkways before temperatures fall below freezing. However, larger puddles will remain and there could be some patchy ice in spots. && .SHORT TERM /SATURDAY NIGHT/...
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High pressure is forecast to be centered in eastern Pennsylvania early on Saturday morning. The high is forecast to move eastward passing off Cape Cod around midday. Dry weather is anticipated for the morning with an increase in high clouds ahead of our next weather system. Precipitation is expected to spread into our region from the southwest during the mid to late afternoon hours. Temperatures should favor the upper 30s and the lower 40s in our region at the onset. As a result, the precipitation will begin as rain at most locations. As we lose daylight on Saturday evening and as precipitation rates increase, the precipitation should change to all snow except in our far southern counties. The precipitation rates are expected to be enhanced by some short wave energy that is being ejected out of the southwestern states. We are anticipating a relatively brief but robust precipitation event for late Saturday into Saturday night. The bulk of the precipitation is forecast to fall over an 8 hour period. The surface low is expected to move rapidly from around Cape Hatteras on Saturday evening to a point about 250 miles southeast of Cape Cod near daybreak on Sunday. Snowfall totals are expected to range from 2 to 5 inches in southeastern Pennsylvania, the Lehigh Valley, the Poconos, and northern and central New Jersey. Because of the potential for mesoscale banding, expect some locations within the watch area will see 6 inches or more. However, it is still far too uncertain to pin down where the banding will take place. Thus, have held on to the winter storm watch. An advisory may be needed for another tier or two of counties to the southeast of the current watch area as well, but in those areas there is considerable uncertainty as to how early and how long we will see a change over to snow. A fairly tight snowfall gradient is forecast to extend across the upper Delmarva and southern New Jersey. The event should be mostly rain in Sussex County, Delaware and in Cape May County, New Jersey. The precipitation is anticipated to end quickly late on Saturday night. A mid level short wave trough that was located over British Columbia this afternoon will race to the east and it should pass over our region at that time, kicking the last of the snow and rain out to sea. A light and variable wind on Saturday morning should settle into the southeast on Saturday afternoon. The wind is forecast to become variable again on Saturday evening before shifting to the northwest around 5 to 10 MPH late on Saturday night. Low temperatures on Saturday night are anticipated to be in the 20s and lower 30s.
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&& .LONG TERM /SUNDAY THROUGH FRIDAY/... High pressure will build across the region Sunday, then build offshore Sunday night. There could be some lingering clouds during the day and winds could gust around 15 to 20 mph early in the day. But otherwise, dry and tranquil conditions are expected Sunday through Sunday night. On Monday, the high continues to move out to sea, while a warm front is forecast to lift into the area. As this happens, a couple of short wave/vorticity impulses are expected to move across the area as well Monday and Monday night, which could help produce some light precipitation. Temperatures are expected to be above freezing, except at the beginning of Monday morning, so precipitation should be all rain unless it begins early enough Monday. Some patchy fog may develop as well overnight Monday, especially for portions of eastern Pennsylvania and northern/central New Jersey. The warm front is expected to have lifted north of the area by Tuesday morning. Tuesday into Tuesday night are expected to be dry unless a few isolated showers develop if any short wave vorticity impulses move across the area. Some patchy fog may develop as well overnight Tuesday, especially for potions of eastern Pennsylvania and northern/central New Jersey. The main thing of note for Tuesday will be the warm temperatures. Temperatures about 20-25+ degrees above normal are expected as a warm southwest, return flow is expected. Many places could exceed record highs, especially if temperatures are a couple of degrees warmer than forecast. Wednesday has the potential to be another record warm day as well, depending on how fast the cold front comes through. Another potential limiting factor for Tuesday and Wednesday would be cloud cover across the area. If we do have more cloud cover, this could limit warming. There is also a chance of showers Wednesday into Wednesday night as the cold front moves across the area. Thursday through Friday the cold front pushes to our south while high pressure builds to our north. Thursday should be mostly dry except across the far south where there could be some lingering lift/moisture behind the cold front that may combine to bring some light rain to the area. Friday has the better chance of rain as return flow develops as the high to our north builds offshore, and a warm front may lift across the area at the same time a couple of short waves/vorticity impulses do as well. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight: VFR conditions expected with skies gradually clearing. Northwesterly wind gusts near 20 KT may continue through 06Z, but then expect winds to taper off. High confidence. Saturday and Saturday night: Starting VFR, but expect conditions to go down to MVFR by 00Z across the area. Between 00Z and 09Z, expect widespread precipitation, including some heavy snow bands, in the area. IFR or lower conditions will be possible with the precipitation, especially under heavy snow bands. After 09Z, conditions should improve to VFR. Moderate confidence on the overall evolution, but low confidence on the location and development of heavy snow bands. OUTLOOK... Sunday-Sunday night...VFR. Winds may gust around 15-20 knots early. High confidence. Monday...VFR early, lowering to MVFR or IFR during the day with rain possible. Winds may gust around 15 to 20 knots. Moderate confidence. Monday night...MVFR/IFR conditions continue with rain possible in the evening, and low clouds/fog possible overnight. Moderate confidence. Tuesday...MVFR/IFR conditions possible early with light rain, and low clouds/fog. Conditions improving to VFR during the day. Southwest winds may gust around 20-25 knots. Moderate confidence. Tuesday night...VFR early, then possibly lowering to MVFR/IFR as low clouds/fog may develop overnight. Moderate confidence. Wednesday...MVFR/IFR conditions possible early with low clouds/fog. Conditions improving to VFR during the day. Southwest winds may gust around 20-25 knots. Moderate confidence.
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&& .MARINE... A cold front will pass off the coast and move out to sea this evening. High pressure is expected to follow for tonight and Saturday morning. Low pressure is anticipated to pass off the coast near Cape Hatteras on Saturday evening. A gusty northwest wind is expected in the wake of this evening`s cold front. As a result, a Small Craft Advisory remains in effect until 4:00 AM Saturday. Conditions should remain below the Small Craft Advisory criteria for Saturday and Saturday night. The area of low pressure on Saturday night is expected to remain well to the south and east of our coastal waters. OUTLOOK... Sunday-Monday...Sub Small Craft Advisory conditions expected. Monday night...Sub Small Craft Advisory conditions expected, although winds may gust around 20 knots. Tuesday-Wednesday...Winds may stay below advisory levels, but seas may increase to near 5 feet. && .CLIMATE... Some record high temperatures could be challenged on Tuesday, February 20th and Wednesday February 21st. These records are listed below. February 20: Atlantic City...70 in 1930 Philadelphia....70 in 1939 Wilmington......71 in 1930 Allentown.......68 in 1930 Trenton.........70 in 1930 Georgetown......68 in 2002 Mount Pocono....59 in 1930 Reading.........72 in 1930 February 21: Atlantic City...74 in 1930 Philadelphia....72 in 1930 Wilmington......70 in 1953 Allentown.......67 in 1953 Trenton.........70 in 1930 Georgetown......71 in 2014 Mount Pocono....60 in 1930 Reading.........71 in 1930 && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Winter Storm Watch from Saturday afternoon through late Saturday night for PAZ054-055-060>062-101>106. NJ...Winter Storm Watch from Saturday afternoon through late Saturday night for NJZ001-007>010-012-013-015. DE...None. MD...None. MARINE...Small Craft Advisory until 4 AM EST Saturday for ANZ430-431- 450>455.
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&& $$ Synopsis...Robertson Near Term...Iovino Short Term...Iovino/Johnson Long Term...Robertson Aviation...Gaines/Johnson/Robertson Marine...Iovino/Robertson Climate...

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