Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 230912 CCA AFDPHI Area Forecast Discussion...CORRECTED National Weather Service Mount Holly NJ 512 AM EDT Fri Mar 23 2018 .SYNOPSIS... Low pressure will linger today in the vicinity of the Canadian Maritimes. Strong high pressure builds to our north over the weekend, then extends southward over our area early next week. Meanwhile, a weak low pressure system slides well to our south Saturday night into Sunday. A cold front is then forecast to arrive toward later next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The mid and upper level low over Lake Huron early this morning will quickly dig southeast over our region through the day. This could result in some rain and snow showers, primarily along and north of the I-78 corridor. However, it is looking less likely today than at this time yesterday. First, aside from a very shallow low level layer (around 850 mb), I expect large dew point depressions through much of the column (based on model and upstream RAOB soundings). Secondly, from water vapor satellite imagery, the low appears to be propagating more SSE than SE, which could put the vorticity max south of our area. Additionally, as quickly as the low is propagating, any lift associated with this low could come ahead of instability developing across our area. That being said, the GFS has been consistent in showing this potential for the last few runs, and some of the near term, higher resolution models depict this potential as well, including the HRRR. Therefore, kept PoPs close to the previous forecast. If showers do develop, any snow accumulations should be less than one inch given the very dry air. As for temperatures, I went with a blend of the NAM and GFS MOS guidance. The fresh snowpack yesterday appeared to have only a small impact on temperatures as much of the region got into the upper 40s and lower 50s, close to what MOS guidance was depicting yesterday. Temperatures today may be somewhat tempered by mid level clouds associated with the low, but expect most of the region to get into the 40s, which is still 5 to 10 degrees below normal. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... As the mid and upper level low propagates off shore, should see clouds clear out. This, combined with relatively light winds, will set the stage for efficient radiative cooling. Therefore, expect temperatures to be 5 to 10 degrees below normal, with lows generally in the 20s across the region. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Summary...Weak low pressure slides well to our south over the weekend with chilly air in place, then warming is forecast to arrive as next week progresses. Synoptic Overview...A highly amplified pattern over the weekend and to start next week, with a closed low in the western Atlantic while a ridge builds into the East. An upper-level trough is forecast to become established from central Canada to the southern Plains next week, and a cutoff low in the western Atlantic may slow the eastward movement of the Plains trough. This should result in a ridge aloft into the East, which probably narrows with time and also surface high pressure that gradually weakens. A cold front is forecast to gradually approach from the west late Thursday. For Saturday and Sunday...A potent upper-level trough, at least the western portion of it, slides across the Northeast and Mid-Atlantic region Saturday night and Sunday. This along with strong high pressure that builds across portions of eastern Canada will steer a weakening surface low well to our south Saturday night into Sunday. While no precipitation is anticipated with the southern system, potent short wave energy moving across the area with some enhanced low/mid level moisture and low/mid level lapse rates steepening during Sunday, may lead to some rain/snow showers. This does not look all that widespread if it were to occur, therefore kept PoPs on the low side across portions of the area. Otherwise, it will be chilly and breezy at times especially Sunday as strong high pressure well to our north has more influence and strengthens a northeast wind. Therefore, much more of a breeze and even cooler conditions along the coast as opposed to farther inland. For Monday and Tuesday...High pressure builds southwestward across much of the East Coast, while a potential storm is located well offshore. This will maintain a northeasterly flow which should weaken during Tuesday. Given some ridging aloft and stronger high pressure building southwestward at the surface, dry conditions are anticipated across the area. Temperatures remain on the chilly side, although some warming is expected on Tuesday as the northeast flow wanes. It will likely still be cooler though at the coast. For Wednesday and Thursday...An upper-level ridge along the East Coast Wednesday is forecast to narrow and weaken with time as a trough amplifies across the Midwest and Plains. The eastward progression of the trough may be slowed due to a cutoff low in the western Atlantic. This will have an impact on the timing of an incoming cold front. As of now, looks like the frontal zone slows Wednesday and especially Thursday as the trough sharpens some more. There should be some waves of low pressure developing along the front as additional short wave energy swings through the base of the amplifying trough and interacts with the baroclinic zone. Given a more southwesterly flow ahead of the main trough aloft and surface cold front, warm air advection should start to boost the temperatures during this time frame. We even have temperatures around 60 degrees forecast for parts of the area Thursday afternoon. The degree of warming will depend on cloud cover and the timing of the cold front and any showers with it. For now given the warming, kept the precipitation type as rain for much of the region along with low PoPs as the front may end up being slower. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Mostly VFR conditions expected. There is a slightly chance of rain/snow showers along and north of a KRDG to KPNE line. However, the chance is too low to include in the TAFs at this time, and even if showers develop near these TAF sites, it is unlikely that conditions will lower below VFR. Northwesterly wind will continue around 10KT, gusts could approach 20 KT between 15 and 21Z, primarily for KPHL, KILG, and KACY. High confidence on the flight category, moderate confidence that the entire period will be dry. Tonight...VFR conditions with only high clouds (at or above 15000 ft AGL). Winds will remain northwesterly but wind speeds should drop below 10 KT. High confidence on all aspects of the forecast in this period. Outlook... Saturday...VFR, with a ceiling between about 3000-5000 feet possible late at night especially for ACY and MIV. Northwest winds around 10 knots, becoming north-northeast at night. Sunday...Mostly VFR. Isolated snow/rain showers possible during the day. Northeast winds 10-18 knots with gusts up to 25 knots, with the highest winds closer to the coast. Monday and Tuesday...VFR overall. Northeast winds around 10 knots with gusts up to 20 knots Monday especially closer to the coast, then becoming light east or southeast during Tuesday. && .MARINE... Winds and seas on the coastal waters have dropped below small craft advisory criteria. Therefore, we have cancelled the remaining SCA. For today and tonight, winds and seas are likely to stay below SCA criteria on all the waters. Gusts near or above 20 KT are expected late this evening and overnight. There is a small chance of gusts at or above 25 KT in that same period on the coastal waters, but chance is too low to issue another SCA at this time. Outlook... Saturday...The conditions are anticipated to be below Small Craft Advisory criteria. Sunday and Monday...Small Craft Advisory conditions are anticipated due to gusty northeast winds (around 30 knots) and building seas. The winds should start diminishing during Monday, however seas look to remain elevated. Tuesday...Winds are expected to be below Small Craft Advisory criteria, however seas on the ocean may remain elevated especially due to a storm well offshore. && .CLIMATE...
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It has been a snowy March this year, and the four climate sites with snowfall data are now in their top 5 snowiest March`s on record. Snowiest March`s on Record... Philadelphia - Currently tied for second. 1) 17.7" in 1941 2) 15.2" in 2018 2) 15.2" in 1914 4) 13.4" in 1958 5) 12.4" in 1993 Allentown - Currently at fourth. 1) 30.5" in 1958 2) 21.6" in 1993 3) 21.3" in 1960 4) 20.7" in 2018 5) 18.3" in 2017 Wilmington - Currently at second. 1) 20.3" in 1958 2) 14.2" in 2018 3) 13.9" in 1993 4) 13.4" in 1960 5) 13.3" in 1914 Atlantic City - Currently at fifth. 1) 17.6" in 1969 2) 15.6" in 2014 3) 13.4" in 1960 4) 12.7" in 1956 5) 9.6" in 2018 1-Day Snowfall Records in March... Atlantic City, 5.7 inches on 3/21/18 is the 7th highest. Wilmington, 6.7 inches on 3/21/18 is the 6th highest (2-day total of 8.1 inches is tied for the 7th highest). Allentown, 13.2 inches on 3/21/18 is the 4th highest behind 16.7 inches on 3/13/93, 16.5 inches on 3/20/58 and 13.8 inches on 3/3/60.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gorse Near Term...Johnson Short Term...Johnson Long Term...Gorse Aviation...Gorse/Johnson Marine...Gorse/Johnson Climate...Drag/Gorse is the U.S. government's official web portal to all federal, state and local government web resources and services.