Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 170854 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 354 AM EST Sat Feb 17 2018 .SYNOPSIS...
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High pressure overhead this morning shifts offshore this afternoon. Low pressure rapidly intensifies off the mid Atlantic coast this evening then races out to sea by Sunday morning. High pressure briefly builds across the area again on Sunday, then offshore Sunday night. A strong warm front lifts northward across our area later Monday into early Tuesday, followed by a cold front late Wednesday. High pressure builds to our north next Thursday with a complex frontal system developing to our south and west at the end of next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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This section updates around 4 am. The cold front is now well offshore. Skies have mostly cleared thanks to the dry air advection in northwesterly flow. 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.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
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This section updates around 4 am. 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/...
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**Record warmth possible Tue and expected Wed** 500 MB: a very strong ridge develops along the east coast during mid week, then slowly weakens Friday and next weekend as a positive tilt trough develops across the United States. Temperatures: February through the first 16 days is averaging 3 to 6 degrees above normal and this weeks record warmth will likely make this February a top 10 warmest in our Mount Holly area history. I still need to confirm the month around 6 am when we`ll sample Philadelphia for the month in our climate section. In the mean time...the warming trend begins in earnest on Monday with calendar day averages 3 to 7 degrees above normal, then 20 to 25 degrees above normal Tuesday and maybe 25 to 28 degrees above normal Wednesday, cooling to between 15 and 20 above normal Thursday and still about 10 degrees above normal next Friday and Saturday. Forecast basis: Except as noted generally a 50 50 blend of the 00z/17 GFS/NAM MOS was applied for Sunday-Monday, the GFS MEXMOS for Monday night-Tuesday and then the 06z/17 WPC D4-8 12 hr elements of max/min temp/pop and 6 hrly sky/wind/td were used Tuesday night- Friday. The dailies... Sunday...A nice day. Seasonable. Gusty northwest winds in the morning to 20 mph quick diminish by midday as the high moves overhead. Confidence: Well above average. Sunday night. Frosty with light wind and generally clear sky atop the melting snow and remaining moisture from the Saturday night event. Confidence: Well above average. Monday...A p/sunny start quickly becomes overcast with a period of rain during the afternoon or evening in eastern PA but lesser chances elsewhere. South wind. Still sort of cool due to skycover and little in the way of mixing. Confidence: Well above average. Monday night...after rain ends, areas of dense fog possible late at night. Confidence: average. Tuesday...Stratus probably limits potential warmth. It becomes partly sunny during the afternoon. Record max temps possible, especially Georgetown DE. Confidence: average. Wednesday...Partly sunny and very warm! Widespread records likely. Mid 70s. Potential for equaling record warm Feb max temp. See climate section at 6 am for the records. Chance of showers late day or evening with the cold frontal passage. Confidence: Above average. Thursday and Friday...Considerable cloudiness. chance of showers. Confidence: Below average on both rain and max temps because of model differences. The primary scenario for Thu/Fri as outlined ydy at 330 PM by our previous long term forecaster: 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.
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&& .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. This section updates around 4 AM. Through Saturday...VFR through early/mid afternoon as clouds lower, then MVFR/IFR conditions develop after about 20z from southwest to northeast as snow and rain arrive. Snow is expected at the terminals, except MIV and ACY where it will mix with rain before changing to all rain. Winds becoming southeasterly less than 10 knots. Saturday night...Widespread precipitation including some moderate to heavy snow at times. IFR or lower conditions, especially with heavier snowfall rates. Some rain may mix in up to the PHL metro. Snowfall rates of up to 1-inch per hour possible and this is when accumulations would be the most efficient. Snow/rain ends quickly after 06z from southwest to northeast with conditions improving to VFR by daybreak. High confidence regarding precipitation occurring, but low confidence on a wintry mix into the I-95 terminals. Light and variable winds overall, becoming west-northwest overnight less than 10 knots. OUTLOOK... Sunday-Sunday night...VFR. Northwest winds may gust around 15-20 knots Sunday morning-midday. Confidence: Well above average. Monday...VFR early, lowering to MVFR or IFR during the afternoon or evening with rain. South to southwest wind. Confidence: above average. Monday night...MVFR/IFR conditions continue with rain possible in the evening, and low clouds/dense fog possible overnight. Confidence: Above average. Tuesday...MVFR/IFR conditions possible through midday in low clouds/fog. Conditions improving to VFR during the afternoon. Southwest winds may gust around 20-25 knots in the afternoon. Confidence: average. Tuesday night...VFR early, then possibly lowering to MVFR/IFR as low clouds/fog may develop overnight. Confidence: average. Wednesday...MVFR/IFR conditions possible early with low clouds/fog. Conditions improving to VFR during the day. chance of showers late in the day. Southwest winds may gust around 20-25 knots. Confidence:Above average.
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&& .MARINE...
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This section updates around 4 am. The Small Craft Advisory for Delaware Bay has been cancelled as winds continue to diminish. High pressure is expected to follow for overnight and Saturday morning. Low pressure is anticipated to pass off the coast near Cape Hatteras on Saturday evening. A gusty northwest to north wind is occuring in the wake of a cold front. As a result, a Small Craft Advisory remains in effect until 4:00 AM Saturday for the Atlantic coastal waters. 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..may need a brief SCA for nw winds gusty 20-25 kt early in the day then sub advisory nw winds in the aftn. Confidence: average. Monday...Sub Small Craft Advisory south winds. Confidence: Well above average. Monday night...Sub Small Craft Advisory conditions expected, although winds may gust around 20 knots. Confidence: Above average. Tuesday-Wednesday...Winds should stay below advisory levels, but seas may increase to near 5 feet. Confidence: Average.
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&& .CLIMATE...
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Record high temperatures could be challenged on Tuesday, February 20th and probably will be equaled or exceeded 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 More records will post by 6 am. Atlantic City rainfall already ranks 11th wettest in February history with 6.50" in 2010 the wettest. By sunrise Sunday, Atlantic City should rank about 8th wettest in its historical database.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Winter Weather Advisory from 4 PM this afternoon to 4 AM EST Sunday for PAZ054-055-060>062-070-071-101>106. NJ...Winter Weather Advisory from 4 PM this afternoon to 4 AM EST Sunday for NJZ001-007>010-012-013-015>019. DE...Winter Weather Advisory from 4 PM this afternoon to 4 AM EST Sunday for DEZ001. MD...Winter Weather Advisory from 4 PM this afternoon to 4 AM EST Sunday for MDZ008. MARINE...None.
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&& $$ Synopsis...Drag 353 Near Term...Iovino Short Term...Iovino Long Term...Drag 353 Aviation...Drag/Gorse 353 Marine...Drag/Gorse 353 Climate...353

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