Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 200234 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 934 PM EST Sun Feb 19 2017 .SYNOPSIS... A cold front will move south through our region early Monday. High pressure will build over the Mid Atlantic Monday afternoon through Tuesday before shifting offshore. A warm frontal passage occurs early Wednesday. It will be followed by a cold front dropping down into Pennsylvania and New Jersey early Friday which should return north as a warm front early Saturday. Low pressure is probably going to move from the Great Lakes region into southeast Canada Saturday and sweep a cold front off the east coast this weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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930 pm update: Made a few more modifications to the temperature forecast based on latest couple of hours of obs. Trouble spots were about as expected: the Pine Barrens/Millville, Somerset/Sussex Airports, and portions of the Lehigh Valley -- where nocturnal radiational cooling has been quite pronounced. Millville has dropped 30+ degrees this evening, for example. Surface analysis at 02Z indicates the cold front in New England is progressing southward nicely -- now generally along a line from Buffalo, NY, to Manchester, NH. WV loop shows main vort max approaching Maine with pronounced subsidence/drying and a developing jet streak on the upstream side. IR satellite imagery showing low clouds are developing on the north side of the front, but the question remains how far south these clouds get. So far...see little reason to change sky cover forecast much from previous forecast. Previous discussions below... 630 pm: Vort max over northern New England and adjacent southeast Canada will continue to dig southeastward overnight, with 23Z surface analysis showing associated cold front moving south through northern New England at this time. Strong diabatic heating and downsloping effects more than compensated for weak near-surface cold air advection today, allowing for temperatures to soar to record or near-record territory in much of the Mid Atlantic south of this front. Main forecast concern this evening is timing the temperature drop with decreasing winds and mostly clear skies. Suspect spots notoriously prone to radiational cooling (such as the Pine Barrens) may see plummeting temperatures this evening before a brief period of thickening upper-level clouds occurs as the vort max makes its closest approach late this evening and overnight. Already starting to see evidence of this at Millville. Made a few adjustments to the temperature grids through the evening hours, and suspect more modifications will be needed in the next couple of hours once the details become clearer. Did not make much change to morning lows, but did lower them a degree or two in a couple spots based on the favorable radiational cooling conditions expected this evening. Other main concern is sky cover later tonight as a low-level subsidence inversion becomes established as a transient/high- amplitude ridge moves into the East. Boundary layer moisture may be sufficient to develop some low-level clouds, especially in the southern Poconos. This may also wreak havoc with temperatures, as the cold air advection behind the front will fight against the emission of radiation back to the surface from any low clouds that develop. Latest high-resolution guidance does not appear particularly aggressive with this low cloud development, so made no changes to the forecast at this time. But it will be something to watch during the overnight hours. 330 pm: Yet another spring-like day across the entire area, with even some new record high temperatures occurring. An upper-level trough in eastern Canada is forecast to amplify southward some especially across New England. This will push a cold front down from the north, also known as a backdoor front, later tonight. As this occurs, cold air advection will strengthen somewhat later tonight; however, this is more notable across the northern zones. This will allow temperatures to drop much more later tonight. As surface high pressure begins to build in from the west and northwest overnight, a subsidence inversion is forecast to strengthen with some moisture pooling beneath it. This moist layer looks rather shallow; however, some guidance indicates some low clouds developing toward daybreak especially for portions of northeastern Pennsylvania into northwestern New Jersey. Areas farther to the south, the moist layer looks delayed and therefore no low cloud development is expected. A north- northwest wind will be light tonight despite some cold air advection on the increase, as surface high pressure draws closer. Low temperatures were mostly a blend of MOS and continuity. The hourly temperature and dew point grids are being adjusted this afternoon based on the latest obs, then the LAMP/LAV guidance was blended with continuity through early this evening. A forecast challenge through this evening could be just how quickly the boundary layer cools.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... A strong upper-level trough/closed low is forecast to exit New England through about early afternoon on Monday. This will allow surface high pressure to slide across our area, although it remains centered well to our north. This will provide a northerly wind across the entire region, although this should be on the light side given a loose pressure gradient. Some cold air advection is forecast to continue through much of the day, with the coldest air aloft found over our northern zones. This all translates into a cooler day, however highs will still be several degrees above where we should be for this time of year. A strong subsidence inversion to start the morning may trap in some lower clouds across mainly portions of northeastern Pennsylvania and northwestern New Jersey, otherwise this should weaken as the boundary layer warms enough. Otherwise, plenty of sunshine should become dominant as the forecast soundings indicate the column overall dries out through the day. High temperatures are mostly a continuity and MOS blend. The winds may turn a bit more northeasterly along the coast to assist with cooling off the chilly ocean waters. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... 500 MB: A strong ridge in the Great Lakes Monday night slides east. A weak short wave cuts eastward into the ridge across New England Wednesday. In the wake of the short wave, a ridge dominates over the mid Atlantic States Thursday into Saturday before a strong short wave moves into the Great Lakes over the weekend. Temperatures: As our forecast area proceeds to a 1st or 2nd warmest February on record and a top 10 warmest winter in the period of record dating back to the late 19th century, the coming week of Tuesday through Sunday should average 12 to 17 degrees above normal. The coolest day is expected to be Tuesday...only several degrees above normal, but thereafter, some model guidance points to a three day period of temperatures 15 to 25 degrees above normal between Thursday and Saturday. BUT... a wrinkle has developed. After near record warmth on Thursday and max temperatures 25 to 30 degrees above normal, a cold front will probably interrupt the excessive warmth one day with a cooler east-southeasterly flow on Friday. Forecast basis: Unless otherwise noted, a 50 50 blend of the 12z/19 GFS/NAM MOS guidance Monday night-Tuesday night, thereafter the 12z/18 15z/18 WPC guidance Wednesday - Sunday, raising the fcst temps by 3-4 degrees due to the recent cool bias in the guidance, lack of snow cover and expected westerly isobaric gradient. The dailies including any possible significant insight... Monday night...Fair.. some high cloudiness that may slightly limit otherwise ideal radiational cooling. nearly calm wind. Tuesday...WAA increasing high clouds limiting max temperature potential. Chance showers may invade ne PA late in the day in the leading portion of the instability burst. Wind southeast to south. Max gust 15 MPH. Confidence: average on max temps. Tuesday night...Chance of light showers during the evening ahead of a warm front. Low probability there could be a touch of freezing rain highest terrain above 1500 feet north of I-80. This ice risk isn`t in the HWO or zones since confidence is below average and guidance favors above freezing min temps during any rain. Confidence: average or below average regarding the occurrence of any rain. Wednesday...Becoming mostly sunny and warmer. Near record warmth (vulnerable records). Forecast temps may end up a degree or warmer than now predicted. This fcst is above all available guidance and reflects the recent cool bias in max temps the past several days... the warm regime with a 550 1000-500mb thickness. cooler coastal seabreezes likely. West wind. Confidence: above average. Wednesday night...Fair (thin high clouds). patchy fog possible in a few countryside locations. Thursday...mixed clouds and sun with near record warmth. Some cirrus as per the GFS. Max temps may end up 2f warmer than the now I95 predicted 70 to 75F. However cooler coastal sea breezes embedded within the west southwest wind gradient. Confidence: above average. Friday...early morning stratus/fog possible along a cool front that has settled into our area. maybe a shower north of the boundary during the afternoon or maybe the boundary doesn`t make it down into our forecast area? otherwise considerable clouds. Confidence: below average on the scenario. Note: considerable instability is showing up in the GFS and ECMWF. Friday night...a good chance of showers ahead of the cold front moving east toward our area and/or the quasi-stationary front moving north as warm front from I-78. Shower timing and temperature uncertainty as well as wind uncertainty, though probably southeast turning south to southwest, depending on latitude in our area. Note: considerable instability is showing up in the GFS and ECMWF. Confidence: average. Saturday...Maintained continuity. I think we need a 90 pop here...as it should rain ahead of the cold front and there may be a tstm. Dewpoints probably close to 60 in a sliver ahead of the cold front. Operational EC and GGEM as well as the 12z/19 GEFS are slower and at this time, did not want to raise hopes for the GFS blustery dry westerly flow on Saturday. The UKMET is kind of unsettling and if idea of a low way back in Ohio is correct... we will need to rethink progressive cold frontal passage for Saturday morning. Confidence: average. Sunday...Becoming mostly sunny and cooler but still above normal temps as the sfc low moves northeast into Canada taking the primary chunk of colder air northeast with it, making it difficult to import too much of the cold air here from the midwest. Breezy with west winds gusting 20 to 25 mph. Confidence: average. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. For the 00Z TAFs...VFR conditions expected through the period; however, there is a chance of some CIGs near MVFR around daybreak north/west of KPHL -- including KABE/KRDG. Confidence too low to include in the TAF at this time, but this will be monitored closely. Any low clouds will dissipate by mid morning. Winds generally northwest around or below 10 kts, with an occasional gust to 20 kts possible tomorrow afternoon. Outlook... Monday night...VFR with some cirrus. Light mostly north through east wind or calm. Confidence: Much above average. Tuesday...Cirrus ceilings may briefly lower to MVFR during the late evening in scattered rain showers. South wind max gust around 15 kt during the afternoon becoming southwest at night. Confidence: average. Wednesday...VFR. This cirrus afternoon and night. west wind. Confidence: Above average. Thursday...Patchy fog possible early with mvfr vsby. Otherwise, VFR occasional cigs. West southwest wind. Confidence: Above average. Friday...Patchy IFR or MVFR CIGS along a cold front that stalls and begins returning north at night. Chance of a shower at night. Wind east turning southeast to south. Confidence: Below average. && .MARINE...
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930 pm update: No changes to the marine forecast tonight. High pressure will gradually build in from the west and northwest later tonight and Monday. This will result in a northerly wind, however an increase in cold air advection overnight and Monday morning should result in some increase in the winds especially across the northern coastal waters. It appears that any gusts to 25 knots mainly across the northern ocean zones look to be short in duration; therefore, we opted to hold off on a Small Craft Advisory. Otherwise, the conditions are expected to remain below advisory criteria through the day Monday. Outlook... Monday night...northerly winds may gust near or above 20 kt at times, but should stay just below 25 kt during the evening then diminish during the night and turn northeast to east. Confidence: above average. Tuesday through Thursday...winds and seas will remain below SCA criteria. Winds southeast Tuesday turning southwest Tuesday night and continuing west to southwest Wednesday and Thursday with local southerly afternoon sea breezes. Confidence: Above average. Friday...easterly becoming southerly. Confidence: below average with considerable uncertainty regarding direction and speed.
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&& .CLIMATE...
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New records for this date have been established at PHL ILG ABE TTN and RDG. Here are/were the previous record highs for Sunday: PHL 68-1948 now 70-2017 ILG 67-1997 now 71-2017 ABE 63-1997 now 68-2017 TTN 68-1948 now 69-2017 GED 74-1976 ACY 73-1961 RDG 67-1997 now 68-2017 MPO 58-1981 Wednesday 2/22 Thursday 2/23 ACY 68-1991 72-1985 PHL 68-1997/1974 75-1874 ILG 69-1997/1974 72-1985 ABE 68-1974 71-1985 TTN 66-1997 74-1874 GED 72-1997 no data RDG 70-1974 72/1932/1922 MPO 56-1997 60-1977 The following monthly and seasonal expectations were number crunched with our forecast at 9am this morning. We will tweet and Facebook this post tomorrow morning around 10 am with basically one final check of the numbers, which could run even warmer than what we now have posted. We did check our past 24 hr max/mins through 7AM, as well as the new max/min fcst fm our office issued at 330 AM and the FTPRHA guidance beyond. That also accounts for possible midnight mins tonight at PHL ILG ACY, and also possible midnight mins Saturday night the 25th. The only day in significant uncertainty over the next 7 days is Friday, when a cold front could settle south to the Delmarva and leave us in cooler southeasterly flow, thereby lowering the forecast average temperature by 7 degrees. Even so that would only lower the monthly average by half a degree and that might be made up by warmer than fcst temps on a couple of other days, especially on the 28th. So, the forecast numbers continue warming. There is guidance variability but its virtually certain we`re looking at a widespread top 2 warmest February on record in our forecast area and a top 10 warmest winter season... records dating back to the late 19th century. Confidence: well above average. Details below. February: PHL 43.3. #1 Normal 35.7 Record 42.2-1925 POR 1874 ABE 37.6 #2 Normal 30.7 Record 38.6-1998 POR 1922 ACY 42.2 #1 Normal 35.3 Record 41.6-1890 POR 1874 ILG 42.3 #1 tie Normal 35.1 Record 42.3-1903 POR 1895 Winter (DJF) PHL 40.1 #7 ABE 35.4 #5 ACY 39.6 #10 ILG 39.1 #6 tie Past two years of monthly average temperatures through February 2017, a summary of above normal months listed below: For ABE: 23 consecutive months of above normal temps! FOR PHL: 22 of the past 23 months have been above normal. For ACY: 19 of the past 23 months have been above normal. For ILG: 17 of the past 23 months have been above normal. (Jan Feb March 2015 was the last time we had significant and persistent below normal monthly temps.) Snow: February least on record: Atlantic City may end up tied for 5th with very little opportunity for snow on the horizon?
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Drag Near Term...CMS/Gorse Short Term...Gorse Long Term...Drag Aviation...CMS/Drag/Gorse/Meola Marine...CMS/Drag/Gorse Climate...CMS/Drag

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