Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 191020 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 520 AM EST Mon Feb 19 2018 .SYNOPSIS... A strong warm front will lift through our area tonight as low pressure heads from the Ohio Valley into the Quebec by midweek. The associated strong cold front will ease southeast through our area Wednesday night. Thereafter, strong high pressure builds to our north Thursday and to the Maritimes by Saturday while a warm front forms to our southwest. Low pressure heads into the northeast USA next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... High pressure that controlled the weather overnight has pushed offshore and will center itself south of the Canadian Maritimes today. This will set up a return flow across the east coast today, with a warm front located well to our south. The front will be lifting northward through the day, but it will not make it into the region during the daytime hours. Moisture will be on the increase across the area through the day, so clouds will increase through the morning and into the afternoon. A couple of short wave/vorticity impulses will be moving across the area later this afternoon. The lift from these impulses, combined with the enhanced moisture across the area lifting north of the warm front will lead to a period of light rain this afternoon, especially for portions of northeastern Pennsylvania and northern New Jersey. It is possible that portions of southern New Jersey, as well as southern Delaware and Maryland could remain dry. But we will keep a chance of rain in the forecast as there could be a few showers. While temperatures are below freezing this morning for most areas, by the time the precipitation arrives, temperatures will be above freezing, so no wintry precipitation is expected. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... The short wave and lift that will help create the rain this afternoon will be lifting out of the area during this evening. Therefore the rain is expected to tapper off and lift to our north during the evening hours. The warm front to our south will continue lifting to the north overnight, but it is not expected to lift all the way through by daybreak Wednesday. There will be an inversion developing across the area, and moisture is expected to get trapped in the low levels north of the warm front. This will likely lead to areas of fog and low stratus overnight tonight into early Tuesday morning. Where ever the warm front does lift through, the fog may begin to dissipate; this would most likely be southern New Jersey and southern Delaware and Maryland. It is possible that some patchy dense fog may develop, but winds may be elevated enough in many locations to prevent widespread dense fog from developing. It is also possible that some drizzle may develop as well, especially where the fog becomes thickest. Very late in the night, toward the early morning hours Tuesday, as a bubble of enhanced area of Theta-E lifts across coastal areas of Delaware and New Jersey, there is indication by the models that some light showers may develop. So we`ve added some POPS late in the overnight/early morning hours for the coastal areas. && .LONG TERM /TUESDAY THROUGH SUNDAY/... **Record warmth likely Tuesday and everywhere on Wednesday** Hazards: Possible ice Thursday, and then again Friday into Saturday near and north of I-80. 500 anomalously warm strong ridge along the east coast prevails with a positive tilt trough back to the western USA, ejecting short waves northeastward. One short wave dents the top of the ridge Thursday. Subsequently another 1 or 2 disturbances ride into the northeast states by the weekend at the same time a blocking pattern becomes evident in Greenland with -NAO development. Temperatures: As we head toward a top 10 warmest February on record, multiple records are anticipated this coming week. The climate section has the record temperatures for Tuesday and Wednesday, and also the record rainfall for ACY which may be rewritten this weekend. Calendar day average temperatures Tuesday will be 20-25F above normal, 25-30F above normal Wednesday, then substantial differences develop between the warmer GFS and the colder ECMWF. The GFS continues 15 above normal Thursday, near 8 above Friday, 15 above Saturday and Sunday. The ECMWF is much cooler with only about 10 above Thursday, 5 to 7 above Friday, 10 to 15 above Saturday and less than 10F above Sunday. With blocking developing this weekend, i am favoring the colder EC solution and this forecast in my opinion for Thu-weekend is not cold enough across the board. Forecast basis: Unless otherwise noted used a 50 50 blend of the 00z/19 GFS/NAM MOS Tuesday-Wednesday (except mostly warmer GFS temps). Thereafter the 00z/19 GFS MEX MOS Wednesday night- Thursday and the 06z/19 WPC 12 hr max/min pop, 6hr td/wind/sky with all the temps blended colder using the GGEM/ECMWF 2m temps. The dailies... Tuesday...Record warmth likely (forecasting record equaling or exceeding at 5 stations including ACY, PHL, ILG GED MPO). The NAM in southwest flow tends to hold onto too much low lvl moisture, thereby forecasting too cool. My primary concern with temps is over the remaining rapidly melting snow cover of ne PA and NNJ which should for the most part be depleted. Morning fog/low clouds should give way to increasing afternoon sunshine. Southwest wind gusts 20 mph during the afternoon. Confidence: Average, the limit is stratus capping potential warmth. Wednesday...After any predawn reforming of stratus/spotty fog, a mostly sunny record warm day is expected with southwest wind gusts 20-25 MPH. A couple of locations may approach all time February records with 13C at 850 MB. Showers are now confined to mainly ne PA late in the day. Confidence: Well above average. Records should be exceeded at all stations and while this forecast may be 2 or 3 degrees on the warm side, have taken into acct the typical cool bias within a day of cfp on sw flow. A 564 1000-500 thickness. In some locations, the record could be exceeded by 4 to 7 degrees. Also, the numbers posted this morning are within 3 degrees of all time Feb records at ILG TTN GED RDG MPO. So no guarantee of getting that close but the forecast is the best estimate. If we are correct on GED`s 77, that would equal their all time Feb record set February 25, just last year. Wednesday night...a cold frontal passage but probably too late to prevent record warm daily mins for Wednesday as well. There could be a few showers with the front, mainly I78 north. All the record warm mins are in the Climate section. Confidence: Above Average. Thursday...(max temps for the day at 1201AM!) Cloudy and much colder with a gusty north-northeast wind developing and a period of cold rain likely. It`s possible sleet or freezing rain will occur along the northern fringe from ne PA through far northwest NJ but not enough confidence to grid-fcst at this time. Confidence: Above Average. Thursday night...a period of clearing is possible as a subtle ripple of low pressure along the front that brought the rain Thursday zips off the coast and allows the front to sag well south of our area. Confidence: Average. Friday-Saturday-Sunday...Provocative in multiple ways. Once cold air gets in, its hard to dislodge with high pressure to the north and northeast. We will be at the top of the ridge with short waves not forcing much lowering of surface pressure but sending periods of precipitation east north east into our area. It looks like there will have to be some icing occuring in ne PA and nw NJ, especially high terrain n of I80 Friday morning Its possible this could turn into a subtle ice storm depending on the duration of the icing. Have lowered guidance temps from the 00z/19 values and suspect am not cold enough in ne Pa and nw NJ for most of this 3 day period. Confidence: Average. Also, I am not starting a hydro section today, but there is potential for a couple of inches of rain Friday-Sunday, in pieces. That could be pushing a few small streams to near bankfull. See and follow WPC D4-7 guidance for both qpf and winter the next couple of days. MMEFS will soon extend into the weekend for other review. && .AVIATION /10Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR conditions with light and variable winds will start the day off as high pressure moves out to sea. Any steady wind direction will be from the east to southeast this morning. Winds will increase out of the south-southeast through today around 5-10 knots. Clouds will increase through the day, and lower to MVFR and possibly IFR by this afternoon. As a warm front lifts toward the region, rainfall is expected to move into the area by this afternoon, and could affect all TAF sites. The most likely sites to be affected for the longest period of time by rain will be ABE and RDG. Tonight...Conditions expected to continue to lower to IFR overnight as a warm front lifts into the region. The front is not expected to make it all the way through the area through daybreak however. North of the warm front, IFR conditions with low clouds, fog, and possibly drizzle are expected. South of the warm front, the fog and low clouds may lift. Winds will be mostly south to southeast north of the warm front, then turn south to southwest south of the warm front with speeds generally around 5 knots or less. OUTLOOK... Tuesday morning...Leftover IFR conditions expected in low clouds and fog. Southwest wind. Confidence: Average. Tuesday afternoon and evening...Mainly VFR. Southwest wind gusty 20 kt. Confidence: Above Average. Tuesday night and Wednesday morning...Patchy low clouds and fog with some IFR conditions possible. Southwest wind. Confidence: Average. Wednesday afternoon...Mainly VFR. Gusty southwest wind 20 kt. Confidence: Well above Average. Wednesday night...VFR with a chance of showers vcnty KRDG/KABE/KTTN and wind shift from southwest to northwest-north near or after midnight. Confidence: Well above average. Thursday...VFR with possible MVFR conds in a period two of rain. a Gusty north to northeast wind developing of 15-20 kt. Confidence: Above average. Thursday night...VFR. Northeast wind. Confidence: Above Average. Friday...VFR to start but deteriorating to MVFR or IFR conditions in rain. Northeast wind to start becoming east or southeast at night. Confidence: Above Average. && .MARINE... Conditions will remain below Small Craft Advisory levels through tonight. Winds will remain 10-15 knots as high pressure pushes to the east, and a warm front lifts toward the area overnight. Seas will build some overnight, but may only reach 3 to 4 feet. Areas of fog and drizzle are likely to develop this evening and overnight as warm, moist air moves across the waters. There may even be some showers later today and into tonight as well. OUTLOOK... Tuesday through Wednesday...Wind speeds and wave heights are forecast to remain below the Small Craft Advisory criteria. A 3 to 4 ft southerly 5 second wind wave group will be predominant in the Atlc coastal waters. Patchy fog may develop over the coastal waters. Confidence: Well above Average except less certainty on fog. Thursday through Friday...An SCA, especially for seas may be needed for the Atlantic waters due to persistent northeast flow. Confidence: Average. && .CLIMATE... Record high temperatures are possible on Tuesday and Wednesday. Tuesday, 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 Wednesday, 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 A record warm minimum temperature may be set for Atlantic City on Tuesday. The current record is 44 in 1949. The following are the record warm minimum temperatures for Wednesday, all which should be exceeded. ABE 46-1981 ACY 49-1954 PHL 49-2002 ILG 47-2002 RDG 48-1930 TTN 48-2002 The all time February max temps that may be approached at ILG, TTN, GED RDG MPO are ACY 77 2/25/30 PHL 79 2/25/30 ILG 78 2/24/85 ABE 77 2/24/17 TTN 76 2/25/30 GED 77 2/25/17 RDG 77 2/24/17 MPO 70 2/25/30 Our expectation is that ACY will exceed the previous all time record rainfall for February, by the end of the weekend. The record is 6.50 inches in 2010. #2 is 1958 with 5.98 inches. And...adding only half an inch to PHL and ILG will put both locations in the top 9 ranking for Feb rainfall. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Drag Near Term...Robertson Short Term...Robertson Long Term...Drag Aviation...Drag/Robertson Marine...Drag/Robertson Climate...519 is the U.S. government's official web portal to all federal, state and local government web resources and services.