Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 221616 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ Issued by National Weather Service Baltimore MD/Washington DC 1216 PM EDT Thu Sep 22 2016 .SYNOPSIS... High pressure over our area will gradually weaken as it shifts offshore into Friday. A cold front will move across our region later Friday into early Saturday, then high pressure builds in during the weekend and early next week. A warm front lifts to our north Tuesday, while a cold front remains well to our west Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Today...Mostly sunny and very nice except variable cloudiness and possibly a few sprinkles far southeast delaware. Max temps 8-13 degrees above normal...greatest positive departure in the northwest portion of our area vcnty KABE and KMPO. light north to northeast wind becomes east this afternoon around 10 kt with scattered gusts near 15, especially coasts. No major changes to the fcst with the midday update. Quiet wx patn. Just adjusted temps up a little given most places are slightly warmer than yesterday as of noon and should be more sun most places. Forecast basis started with a 50 50 blend of the 00z/22 GFS/NAM MOS.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... Clear or mostly clear with radiational cooling and patches of fog possible late at night...but not the usual suspects of ne PA and nw NJ. Instead southern NJ, the Delmarva and possibly se PA. Forecast basis started with a 50 50 blend of the 00z/22 GFS/NAM MOS. I did lower that blend by 3-5F to forecast mins in the countryside lower than guidance but within a couple of degrees of the coolest GFS 2m temps (09z) which has widespread 48F Northampton/ Warren and Sussex counties in ne PA and NW NJ. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Summary...A taste of Fall later Saturday into early next week before perhaps some moderation occurs. Not much chance for rainfall through the middle of next week. The synoptic setup is comprised of amplifying flow Friday and especially the first half of next week. This starts as a strong trough migrates across the Rockies Friday and Saturday with downstream ridging, while a trough amplifies across eastern Canada and New England. This pattern change to a much more amplified one will offer a much cooler airmass into our region, however the details are less certain especially next week. Overall though the evolving pattern locally looks to be mostly dry, especially as a significant trough closes off well to our west. We used a model blend approach Friday into Sunday, then blended the 00z WPC Guidance into continuity thereafter. Some adjustments were then made following additional collaboration with our neighboring offices. For Friday...An upper-level low near the eastern Carolinas should open up and and shift offshore. The pattern then starts to amplify as a trough digs across the Northeast. As this occurs, weak low pressure tracks from the eastern Great Lakes and then across New England, with an associated cold front dropping south-southeastward. This cold front is forecast to settle across our area later in the day and at night. There is some convergence and lift associated with the front, although on the weaker side and the moisture return looks fairly limited. There still could be isolated showers with the front mainly across our northern zones since they are closest to the energy sliding across New England. The forecast soundings from the GFS and NAM could support isolated thunder with the front. We added slight chance POPs across the northern areas in the afternoon and evening. Otherwise, the front should come through with a band of clouds. A much cooler and drier airmass is to follow this front, however this may lag a bit. For Saturday and Sunday...A strong upper-level trough slides across the Northeast Saturday with some additional amplification possible Sunday. This will drive a cold front to our south to start Saturday as surface high pressure, situated just north of the Great Lakes to start the day, builds southeastward. Decent cold air advection is forecast to occur under a north-northeast surface wind. While the airmass should be rather dry, there could be stratocumulus initially Saturday with the onset of the cold air advection particularly over the warmer ocean waters. There should be a zone of overrunning from near the Ohio Valley westward as the aforementioned cold front is draped back that way, however any precipitation induced by this should remain there instead of tracking east with the southbound cold front. Given high pressure building down, we kept a dry forecast going over the weekend. It may turn a bit breezy for a time over the weekend especially along the coast Saturday ahead of the building surface high. There should be enough subsidence and drying to promote less clouds at night, therefore both nights should be cool to chilly (upper 30s in the Poconos). For Monday through Wednesday...A much more amplified pattern is forecast with a trough in New England and another strong trough moving out of the West and across the Plains. In between, a ridge builds and should arrive in our area later Monday and Tuesday. This will drive surface high pressure over our area Monday before shifting offshore into Tuesday. Some quick return flow may occur late Monday as the high slips to the east. Given some warm air advection, a warm front may lift to our north Tuesday although lift looks limited. A pronounced amplified pattern then unfolds as the guidance overall shows a closed low evolving in the Plains. The location however of where this closed low develops will determine the placement of the downstream ridge. This should tend to slow down or even halt the next cold front that originally looked to arrive on Tuesday. As of now given the closed low forming well to our west with downstream ridging, this front is held well to our west through Wednesday. As a result, little in the way of precipitation is forecast through this time frame. && .AVIATION /16Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR. Light north to northeast wind becoming east northeast around 10 kt this afternoon with scattered gusts around 15 kt. Tonight...VFR but may degrade to areas of ifr or mvfr fog after 06z, vcnty KMIV/KACY and KILG where a little more shallow moisture available. Nearly calm wind. OUTLOOK... Friday and Saturday...VFR. A cold front moves across the area later in the day Friday into early Saturday with some clouds. An isolated shower or thunderstorm cannot be ruled out with the front, mainly north of PHL. Light southwesterly winds, becoming northwest Friday night, then north-northeast into Saturday and increasing to 10 to 15 knots. Sunday and Monday...VFR overall. Northerly winds near 10 knots Sunday, then becoming light east-southeast on Monday. && .MARINE... A Small Craft Advisory for hazardous is in effect from Noon today to 6 am Friday. Have pulled back a bit on the extensiveness and duration of SCA conditions and converted to Haz seas. Forecast seas are a little less than previous guidance. The 18z GWES prob for >6 ft is southeast of our area, and pulling eastward faster early Friday. We dont have 44009 data to measure seas so we rely on BTHD1. Elsewhere for the Atlantic waters a 2 to 4 foot easterly swell of 11 seconds occasionally 6 seconds through tonight. De Bay a few gusts 20 kt today, especially this morning with colder 18c BL air riding over the SST of DE Bay which are in the 22 to 25C range. Water temperatures continue significantly above normal. OUTLOOK... A cold front will move through later Friday into early Saturday. A much cooler airmass will arrive in its wake, and a cold air advection surge looks to take place Friday night and Saturday morning. It is at this time overall where a fairly short period of gusts to 25 knots can occur. This may also build the seas to 5 feet for a time before the winds settle some Sunday and especially into Monday. Otherwise, the conditions are anticipated to be below Small Craft Advisory criteria. RIP CURRENTS... There is a moderate risk for the formation of dangerous rip currents along the NJ shore and Delaware Beaches today, mostly driven by a 2-3 foot east-southeast swell of 11 seconds and additional onshore wind wave created by an east northeast wind gusting 15 to 20 kt. Swim only in the presence of a lifeguard. Friday...Statistically a low enhanced risk due the tendency for more of an offshore wind. However, experience tells us that a 3 ft 8 second swell causes increased rescues and threat to life. Tomorrow should see swell increasing to 3 ft and 11 seconds by days end. Weekend...There is a chance of a moderate risk for the formation of dangerous rip currents on at least one of the weekend days, as a 3 to 4 foot east-southeast swell from Tropical Cyclone Karl arrives along with a gusty northeast wind. Karl`s lack of development may result in a lower swell which would help reduce the potential risk for the formation of dangerous rip currents. && .CLIMATE... September continues well on its way to a top 10 warmest September through most of our forecast area, and...for the 3rd consecutive month! So while there may be a 2 or at most, 3 day string of below normal temperatures between Sunday and Tuesday, that is not likely to be enough to prevent a third consecutive top ten warmest month for much of the NWS Mount Holly forecast area. In this case a probable second consecutive top 5 warmest month in the period of record for PHL and ABE and possibly ACY too. We`ve run the actual numbers through the 21st, our forecast from today through the 29th and then the GFS2m max/min as seen on the FTPRHA for the 30th. While there is considerable run to run and operational model variability on outcomes Tuesday through Friday...it all averages out as follows at several long term climate sites representing both urban and countryside in our forecast area. Philadelphia: Projects a near 74 degree average or about 5 degrees above the monthly normal of 69.1. This will probably be a #4 or #5 warmest September on record for Philadelphia. Philadelphia September average temperature rankings 75.4 -1881 74.5 -2015 74.1 -1931 74.1 -1930 73.8 -2016 and 2005 tie #4 72.9 -2010 72.9 -1921 72.4 -1900 Philly ranked #7 warmest July followed by a warmest ever August (in the POR dating back to 1874). Atlantic City: where there can be greater variability due to the sea breeze cooling during the afternoon and the radiative cooling at night, is still projecting near a 71.5 degree monthly average temperature, or 4+ degrees above the monthly normal of 67.2. Odds are locking into a top 4 to 8 warmest September in the period of record dating back to 1874. Atlantic City recorded a #7 warmest July and warmest ever August. 73.3 - 1961 72.8 - 1881 72.3 - 1931 and 1930 71.7 - 1921 71.6 - 2015 71.5 - 1933 71.3 - 2016 and 2005 tie #7 Allentown: projects to a monthly average of near 69.7 degrees, or almost 6 degrees above the monthly normal of 63.9 and a highly probable 3rd to 5th warmest September on record. Allentown ranked 8th warmest July and #2 warmest August. 70.8 - 1961 70.3 - 1980 69.7 - 2016 and 2015 69.4 - 1931 Allentown and Philadelphia have so far recorded only 1 day below normal through the first 21 days of September, TTN only 2 days below normal and RDG 3 days below normal. Rainfall: The rains of earlier this week were welcome. Still only ACY and GED of our long term climate sites are above the monthly normal. Multiple weather forecast models indicate little or no rain here for at least the next 7 days. The only good news, is that evaporative rates will be a little smaller due to the climatology of lower temperatures and shortening daylight hours. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory for hazardous seas until 6 AM EDT Friday for ANZ454-455.
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&& $$ Synopsis...Gorse Near Term...Drag/Nierenberg/RCM Short Term...Drag Long Term...Gorse Aviation...Drag/Gorse Marine...Drag/Gorse Climate...627

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