Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 220730 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 330 AM EDT THU SEP 22 2016 .SYNOPSIS...
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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.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... Early this morning...cirrus bands, mostly thin with radiational cooling shallow fog expected by 6 am in parts of e PA and nw NJ. Today...Considerable sunshine with remaining bands of thicker cirrus thinning midday. Max temps 8-13 degrees above normal...greatest positive departure in the northwest portion of our area vcnty KABE and KMPO. light wind becomes east this afternoon around 10 kt with scattered gusts near 15, especially coasts. Forecast a max temp of 86F in PHL and confidence is very high that the max will fall in the range of 85-87F. KABE and KSMQ should be warmest with max temps around 87F, possibly even 88. Forecast basis started with a 50 50 blend of the 00z/22 GFS/NAM MOS. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... Clear or mostly clear with radiational cooling and a few patches of fog possible late at night, the usual countryside suspects of ne PA and nw NJ. Forecast basis started with a 50 50 blend of the 00z/22 GFS/NAM MOS. I did lower that blend by 3-5F to fcst 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/...
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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.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Early this morning...VFR bands of cirrus with small chance of MVFR fog KABE/KMIV but not in the TAF due to low confidence. light north wind or calm. Today...VFR bands of cirrus thinning. 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.
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&& .MARINE...
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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. Water temperatures continue 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 kt. Swim only in the presence of a lifeguard. Friday...A generally low risk is forecast. 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 4 to 5 foot east-southeast swell from Tropical Cyclone Karl arrives along with a gusty northeast wind. This will however greatly depend on the strength of Karl as the system has been struggling so far.
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&& .CLIMATE...
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We`ll re-review the forecast monthly outcome at 5 am.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory for hazardous seas from noon today to 6 AM EDT Friday for ANZ454-455. && $$ Synopsis...Gorse Near Term...Drag Short Term...Drag Long Term...Gorse Aviation...Drag/Gorse Marine...Drag/Gorse Climate...Drag

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