Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 191943 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 343 PM EDT Thu May 19 2022 .SYNOPSIS...
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Weak low pressure approaches late tonight and passes through on Friday. Bermuda high pressure sets up for the weekend. A cold front passes through Sunday night, and remains nearly stationary over the Mid-Atlantic into the new week. High pressure passes to the north as the week progresses. A cold front approaches late next week.
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&& .NEAR TERM /THROUGH FRIDAY/...
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The remnant MCV which passed across the region this and associated morning is now offshore. A shortwave trough axis across southern New England will also move away from the area into this evening allowing for some transient subsidence this evening and into the overnight period. A weak frontal boundary will push southeastward into the area this evening. This will result in a continued scattering out and eventually clearing of clouds from this afternoon, however a couple showers can`t be ruled out in the vicinity of the front through the early evening hours. Expect westerly winds around 10-15 mph through early evening as well. Temperatures are expected to drop off fairly quickly this evening and low temperatures should range from the low 50s north of I-80 to the mid 50s to low 60s elsewhere. Winds will become light and variable. Areas of fog are expected to develop overnight, particularly across coastal areas of New Jersey and into interior portions of northern and northeastern New Jersey. Confidence is low on how dense the fog may become, but a Dense Fog Advisory may need to be considered in a future update if confidence on dense fog increases tonight for those areas. Another shortwave trough and an associated MCV complex currently moving east across the central Mississippi and lower Ohio Valleys are expected to progress toward the region overnight. The approaching wave will lift a more pronounced warm front north through the area during the morning hours Friday. Temperatures, dewpoints, and thus instability will rise as the front lifts through the area as the day progresses. Meanwhile, the broad synoptic ridging will begin quickly building throughout the day and will continue building through Friday night. The latest CAM guidance suite indicates a wide variety of outcomes related to how the remnant MCV progresses across the region from the mid-morning and into the afternoon on Friday. The strengthening ridge axis across the East Coast and western Atlantic introduces a complex and low predictability scenario. It seems that the strengthening ridge axis may be enough to weaken/dry out the MCV or even push it north of the local forecast area (into northeastern Pennsylvania and Upstate New York). However, if the MCV slows down overnight and passes across the region after daytime heating has allowed instability to build, we could see a few thunderstorms become strong to locally severe. In any case, the probability of convection has undoubtedly increased enough to warrant a wholesale update and increase to the PoP and weather forecast for the daytime period. Aside from the convection potential on Friday, skies should start out partly cloudy with scattered clouds expected much of the day. The cloud cover will be more widespread if the MCV holds together or restrengthens across the region. Any lingering fog should mix out fairly quickly by late morning. Southerly winds will increase to around 10-15 mph. Expect highs about 10 degrees above normal in the mid to upper 80s in most areas.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
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Weak low pressure passes north of the region Friday evening. Any showers or thunderstorms should be over prior to sunset. Meanwhile, Bermuda high pressure sets up off the Mid-Atlantic coast with strong mid-level ridging along the Eastern Seaboard and developing surface ridging as well. Warm air and moisture advection will be underway Friday night. Surface dew points climb into the mid and upper 60s through the night. With sea surface temperatures still in the upper 50s to around 60, can expect advection fog to form over the ocean and to spread into coastal areas Friday night through Saturday morning. Any fog on land should burn off with heating of the day shortly after sunrise on Saturday. A hot and humid air mass will be over the area this weekend, but the hottest day will be Saturday. With abundant sunshine and 850 mb temperatures upwards of +20C, high temperatures away from the coasts will climb into the mid and upper 90s. Surface dew points will start out in the mid and upper 60s, but should mix out into the low to mid 60s by Saturday afternoon. There is not much wind aloft, and mixing does not look to be all that impressive, so not expecting dew points to crash. Regardless, the Heat Index will generally be in the mid to upper 90s, and around 100 along the Urban corridor and into portions of northeast New Jersey. For Delmarva and extreme southeast New Jersey, Heat Index values have to be over 105 for a Heat Advisory. It does not look as if the Heat Index will be quite that high in those areas, so any Heat Advisories will be limited to the Urban corridor and portions of northern New Jersey. Along the coasts, highs will top off in the upper 70s to low 80s. A warm and humid night is on tap for Saturday night. Some mid- level shortwave energy approaches from the west in the afternoon and evening, but will ride around the apex of the high. Any convection should stay well north and west of the local area during that time. Coastal fog redevelops Saturday night as moisture advection continues and surface dew points rebound into the mid and upper 60s. A cold front begins to approach on Sunday. Clouds will spread into the region ahead of the front, and the hottest air of the air mass will push offshore. As a result, high temperatures will be several degrees cooler compared to Saturday, generally in the upper 80s to low 90s inland and in the 70s along the coast. On Sunday, the cloud cover will help keep dew points elevated in the afternoon. As a result, although surface temperatures will be cooler compared to Saturday, the Heat Index will be high once again. Max Heat Index values will be in the low to mid 90s throughout, and in the mid to upper 90s along the Urban corridor. A more localized Heat Advisory may be needed for Sunday. Surface high pressure sags a bit to the south on Sunday afternoon as that cold front approaches, but mid-level ridging remains strong along the coast. Mid and upper level energy rides around the apex of the mid-level high north of the area, so there is not much support for widespread convection with the approach and passage of the cold front. Timing does not look good, as the front does not pass through until late Sunday night. Will carry chance PoPs to low-end likely PoPs for areas north and west, but will only carry a chance for thunder.
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&& .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
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Cold front slowly works its way through the region Sunday night. Not much in the way of mid-level troughiness. In fact, the mid- level ridge remains over the area into Monday morning. Although scattered showers are possible, not expecting much in the way of convection, especially considering how warm and humid it will be ahead of the front. Cold front finally pushes offshore on Monday, but will become nearly stationary south of the area and over the Mid-Atlantic into the new week. Meanwhile, surface high pressure builds in from the north. A fairly unsettled pattern sets up for most of next week, as several weak waves of low pressure develop on that stationary front. However, if the high is able to sag far enough southward, that would help keep precip mainly focused on southern areas. Either way, it is not looking like a washout for most of next week, but chances are enough to keep at least chance PoPs in the forecast for most of next week. Highs will be around 15 degrees cooler Monday compared to Sunday, and then temperatures will be on the cooler side of normal for the rest of the week.
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&& .AVIATION /19Z THURSDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through 00Z...Lingering MVFR ceilings will continue to scatter out and lift. Westerly winds around 10 kts with gusts up to 20 kts possible. High confidence. Tonight...VFR/SKC early, but some fog may develop after 06Z, especially at ACY, MIV, TTN, and ABE. Winds light and variable. Low confidence on timing and any associated restrictions with the fog. Friday...Once any morning fog dissipates, prevailing VFR conditions are expected. However, a period of showers or thunderstorms may move into the region after between 15-21Z. Confidence on the occurrence of the showers or storms is low, so PROB30 groups were introduced at some terminals to highlight this potential. Southerly winds increasing to 10-15 kts with gusts up to 20 kts. Moderate confidence overall. Outlook... Friday night...VFR overall. Fog may develop at KACY and possibly KMIV with sub-VFR VSBYs. S wind 5 to 10 kt. Moderate confidence. Saturday through Saturday night...VFR. Reduced VSBY in fog at KACY and possibly KMIV. S to SW winds 5 to 10 kt. High confidence. Sunday through Sunday night...VFR on Sunday, and then scattered SHRA/TSRA will result in sub-VFR conditions in the evening and at night. SW winds 5 to 10 kt, becoming NW late Sunday night. Moderate confidence. Monday through Monday night...Mainly VFR. NW winds 5 to 10 kt. Moderate confidence. Tuesday...VFR. E winds 5 to 10 kt. Moderate confidence.
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&& .MARINE...
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South to southwesterly winds will prevail tonight around 5-10 kts. Areas of fog are expected to develop overnight, some of which could be locally dense reducing visibility to 1-3 NM. The winds will increase to around 10-15 kts from the southeast during the daytime Friday. Seas 2-3 feet. A period of showers or thunderstorms is possible Friday morning or afternoon. Outlook... Friday night through Tuesday...Conditions overall will remain below SCA criteria. S-SW winds generally 10 to 15 kt with 3 to 4 ft seas. The SW gradient will result in 15 to 20 kt winds Sunday afternoon and evening, and seas may build close to 5 feet as a cold front approaches. Winds shift to the NW behind the departing front on Monday, and then an E wind develops for Tuesday. As a warm and humid airmass overspreads the colder waters starting Friday night, reduced VSBYs in areas of fog are likely through Sunday.
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&& .CLIMATE... A hot and humid air mass is forecast to overspread the region this weekend. The hottest day will be Saturday. Here is a list of the high temperature records for Saturday and the record high temperatures for the month of May. Locations 5/21 Record High Temps May Record High Temps --------- ---------------------- --------------------- Philadelphia, PA 95 in 1934 97 in 1991 Reading, PA 96 in 1996 96 in 1996/ 1962 Allentown, PA 92 in 1934 97 in 1962 Mount Pocono, PA 87 in 1911 94 in 1911 Trenton, NJ 94 in 1934 99 in 1986/ 1911 Atlantic City (airport), NJ 93 in 1996 99 in 1969 Atlantic City (marina), NJ 85 in 1934 95 in 1925/ 1895 Wilmington, DE 95 in 1996 98 in 1895 Georgetown, DE 94 in 1996 98 in 1991 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...MPS Near Term...Staarmann Short Term...MPS Long Term...MPS Aviation...MPS/Staarmann Marine...MPS/Staarmann Climate...WFO PHI

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