Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 281323 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 923 AM EDT Wed Jun 28 2017 .SYNOPSIS... High pressure over our region today will shift offshore this evening, then remain there through Friday. A weak cold front is forecast to arrive later Sunday, however this boundary may then stall across our region early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... No major changes with the 930 AM forecast update. Agree with the previous shift that there may be meager instability and enough moisture to support light showers around and north of the I80 corridor this afternoon. However, synoptic scale subsidence makes it too unlikely to include in the forecast at this time. Today...Sunny or mostly sunny and comfortably cool for summer with few or sct sc 16z-21z aoa 5000 ft, mainly northwest of I-95. west northwest wind gusting 15-20 mph this morning becoming more westerly this afternoon and diminishing slightly. Dewpoints in the 40s while max temps 2 to 7 degrees below normal. One of the nicest days we`ll see for quite a while. Forecast basis: a 50 50 blend of the 00z/28 GFS/NAM MOS. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... Tonight...Mostly clear with some cirrus after midnight, especially northwest of I-95. Lowered the 50 50 blended 00z/28 mos gfs/nam temps a degree or two from that guidance due to light wind. These temps 1 to 4 degrees below normal. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Summary...Increasing heat and humidity Friday into Sunday, then the humidity should lower some early next week for much of the area. The details though will depend on the timing and location of a weak cold front that may end up stalling across our region. Synoptic Overview...A more zonal flow aloft Thursday will give way to some amplification across the Northeast. This change will be due to a strong short wave carving out a trough in the Midwest and Great Lakes Friday and Saturday, which then gradually shifts eastward later in the weekend and early next week. There may be several stronger short waves within this trough, which will impact the sharpness and timing eastward. At the surface, high pressure remains anchored offshore which will result in a hot and humid southwest flow for a time. The main feature is a weak cold front that will settle into our area later Sunday, however it may then stall in our vicinity through early next week. The presence of the incoming front and trough nearby will result in some convection. We used a model/continuity blend for Thursday through Friday night, then blended in the 00z WPC Guidance thereafter. Some adjustments were then made following additional collaboration with our neighboring offices. For Thursday and Friday...High pressure anchored offshore will drive an increasing southwesterly wind across our area. The flow aloft is mainly zonal, with the main short wave energy tracking to our north Thursday. There is increasing low-level warm air advection forecast during Thursday, which will boost temperatures well into the 80s. The southwesterly flow will also start to transport increasing low- level moisture our way especially as a 40-50 knot low-level jet moves through Thursday night. This moisture increase should be gradual during the day Thursday resulting in a not so humid feel overall. This will change however Thursday night and Friday as dew points are forecast to increase into the 60s. As the low-level warm air advection continues in addition to perhaps some subsidence on the northwest side of offshore high pressure, daytime highs on Friday will edge into the lower 90s for several areas. This combined with higher dew points will result in heat indices into the mid 90s during peak heating. There will be a southwesterly breeze, and as mixing deepens the dew points may locally lower some during peak heating which in this case would keep the heat indices a bit lower. Thursday looks to be a dry day for much of the region, although some upstream convection may get into our northwestern zones later in the day and in the evening. A lead short wave crossing the northern areas Friday afternoon may allow for some convection. This looks to be focused near the higher terrain areas of our northwestern zones. We will continue to carry slight chance to low chance PoPs especially Friday afternoon and evening. For Saturday and Sunday...Low pressure is forecast to track from the Great Lakes Saturday morning to just east of James Bay Canada by later Sunday. This will pull a cold front slowly eastward, and it currently is not forecast to arrive into our area until later Sunday. The synoptic setup would suggest though that a lee-side trough will be in place, with this potentially being located near the I-95 corridor both days. There will be a hot and humid airmass in place, especially Saturday where the humidity should peak. The main upper-level trough is forecast to hang back over the Great Lakes for Saturday, then more eastward progress occurs Sunday. This will settle a weak cold front into our area later Sunday. The bulk of the convection Saturday may reside to our west closer to the frontal zone, however some convection is anticipated tied to the lee- side trough. Given the higher heat and humidity on Saturday a heat advisory may be needed, especially for the urban corridor from Wilmington to Philadelphia/Camden to Trenton, as heat indices may approach 100 degrees during peak heating. The convective evolution during this time frame is less certain, as the timing of the front will be key and also how much can develop near or along the lee-side trough. There is some potential that upstream organized convection moves across much of our area Saturday night. Given less certainty, held PoPs no higher than the chance range. For Monday and Tuesday...The main part of an upper-level trough may lift into Northern New England during this time frame, therefore the flow is more parallel to a surface front in the vicinity. As a result, our sensible weather will be dependent on the location of this front as it stalls out. Some lingering low-level convergence combined with instability and some short waves aloft may result in some convection especially each afternoon and evening. The overall timing though and especially coverage is less certain. While it will still be rather warm, a bit of cooling is anticipated based on the front in the area and the dew points should be a little lower as well. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through today....VFR. few or sct clouds aoa 6000 ft. west northwest wind gust around 15 kts backing a bit this afternoon. Tonight...VFR. Broken cirrus probably arrives toward dawn Thursday. Light southwest wind. OUTLOOK... Thursday and Friday...VFR overall. A shower or thunderstorm is possible Thursday afternoon and evening mainly north and west of KABE, then this may spread south and east some through Friday. Southwest winds increase each day to 10-15 knots, with local gusts up to 20 knots each afternoon. Saturday and Sunday...Times of lower conditions possible due to some showers and thunderstorms, especially each afternoon and evening. && .MARINE... No headlines through tonight. Northwest wind gust 15-20 kt at times during the daylight hours becomes south to southwest late this afternoon and continues tonight. Local sea breezes should develop 15-18z. Gusts to 25 kt possible late this afternoon NNJ waters. OUTLOOK... Thursday and Friday...A low-level jet is forecast to move across the area Thursday night into Friday, however the forecast soundings show vertical mixing is not all that efficient due to a very warm airmass in place. However, stronger winds are not that far above the surface. As a result, wind gusts up to 30 knots are possible for a time especially on the ocean zones. This stronger southwesterly flow will also build the seas. A Small Craft Advisory therefore may be needed starting Thursday afternoon and continuing into Friday. The winds and seas should diminish Friday night. Saturday and Sunday...The winds and seas are forecast to be mostly below Small Craft Advisory criteria. RIP CURRENTS... This mornings observation from LBI indicated a water temp in the lower 60s and it might be colder than that on parts of the NJ coast from Ocean County down to Cape May as evaluated by the 0822z Rutgers IMCS satellite imagery. The forecast is for a low risk for the formation of dangerous rip currents today. Offshore winds this morning turn southerly this afternoon and increase considerably late in the day, especially Ocean and Monmouth counties. So a clearly defined low risk morning-midday may become low enhanced late this afternoon, especially as head to the late afternoon low tide. We ran a late day swell scenario of 1 ft 9 sec or 2 feet 5 seconds, with a south wind of 19 knots and still came up with low risk. Low risk does not mean NO risk and it is always advised for ultimate safety, swim in the presence of the lifeguards. They have the flotation devices that can more easily save a life. Where the surf zone waters are steeper, there may be fewer rip currents, but there, the danger of wave related injury increases. An ongoing DE 6+ year study shows the 10-20 year and 40-60 year age groups most vulnerable. The 10-20 year olds surf zone injuries are associated with body boarding and body surfing, while the 40-60 year old waders are knocked down by wave action, especially with back turned to the ocean. Males are statistically far more likely to be injured or lose their life in the surf zone but as June 15 reminds us...ANYONE is vulnerable. && .CLIMATE... Monthly avg temp for June PHL projecting 74.5 or 1.2 degrees above the average of 73.3 ABE projecting 70.8 or 1.7 degrees above the average of 69.1 Seven of our eight long term climate sites will average above normal probably from about 8 tenths of a degree for TTN/ILG to as much as 2 degrees for GED. Mount Pocono is our only below normal average and projecting 1-1.5 below). These projections are based on our 330 am forecast. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gorse Near Term...Drag/Johnson Short Term...Drag Long Term...Gorse Aviation...Drag/Gorse Marine...Drag/Gorse Climate...

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