Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 232011 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 411 PM EDT SAT JUL 23 2016 .SYNOPSIS...
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A very weak front will cross Delmarva this evening. High pressure will build over the area later tonight and through the day Sunday. A weak cold front will cross the region Monday. High pressure will return for the middle part of the week. Another front may affect the area Thursday and Thursday night.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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Surface low pressure was over the Canadian Maritimes this afternoon. A cold front extends southwestward from the low into downeast Maine and then westward along the I-90 corridor of the Northeast states. Meanwhile, a pre-frontal trough was analyzed over the mid-Atlantic region. The surface trough was positioned over the coastal plain in southern NJ, stretching to the west into far southern PA. Dewpoints were in the low 70s with a west-southwest wind south of the boundary. Meanwhile north of the boundary, gusty northwest winds have resulted in much drier air mixing down to the surface with dewpoints in the 50s and lower 60s north of Philadelphia. The surface trough will sharpen over the next few hours, but it is not expected to move much through sunset. The cold front to our north will eventually catch up with the pre-frontal trough later this evening. The front should then dissipate as it moves south of the region. Made only minor edits to the hourly PoP and Wx grids for the rest of the afternoon and tonight. Isolated to widely scattered showers and thunderstorms are anticipated along and south of the surface trough. There could be an uptick in coverage late this afternoon as additional lift from an upper shortwave trough passes nearby to our north. As mentioned in the previous discussion, added enhanced thunderstorm wording (gusty winds and hail) for far southern PA and NJ as well as eastern MD and DE through mid evening. The latest mesoanalysis shows a moderately unstable airmass along and southeast of the surface trough with MLCAPE values already 2000-2500 J/kg across the southern third of the CWA. High values of DCAPE off SPC mesoanalysis indicate a favorable thermodynamic environment for locally strong convective wind gusts via wet microbursts given how moist the boundary layer is and dry the column is above it. The threat of severe weather should start to wane after sunset. There could be an isolated storm or two lingering after midnight toward the lower Delmarva. The Excessive Heat Warning continues for the urban I-95 centers of the greater Philadelphia metro where heat indices are currently in the 97-103F range this afternoon. Same goes for the Heat Advisory farther east into central/ southern NJ where heat indices are currently in the 97-103F range and farther south into eastern MD and DE where it is the 100-109F range. Low temperatures range from the mid 60s in northeast PA and northwest NJ to mid 70s in the urban areas and the coastal plain.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
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The cold front will move south of the area by morning. The airmass will be only slightly cooler behind the front. In northeast PA and northwest NJ, where CAA is a bit more robust high temperatures will be about 3-5 degrees lower than today. Farther south, expect only a 1-3 degree difference between tomorrow and today. However, drier air will works its way into the region behind the cold front, so it shouldn`t be too humid outside of the southern DE and adjacent eastern MD (where dewpoints will still be around 70F). Forecast soundings show a subsidence inversion that should cap convection with us located underneath the ridge. The forecast was kept dry accordingly. Winds will be light and variable through the day.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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No huge changes foreseen in the summer-like pattern with upper heights remaining high across much of the U.S. The storm track will be across southern Canada with short waves and weak low pressure systems moving across the area. The weakening cold fronts associated with these features will cross the area thru the week. The best chc for showers and tstms will center around both Mon and Thu. We have kept pops in the chc range for these periods with mostly dry or slgt chc pops for other periods. The exact timing will depend on the individual waves which the models have difficult resolving by the end of the extended period. Pretty much all of the major models have precip somewhere across the area Monday. SPC has a marginal risk for SVR storms across much of area then. The above normal temperatures will continue thru much of the week. Monday will likely be the hottest day with readings in the mid/upper 90s and heat index values in the 100s. The temperatures and dew points will be lower for Tue and Wed, but still in the uncomfortable/marginally unsafe range with heat index values 95-100 over the urban areas.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Predominately VFR thru Sunday. However, isolated showers and storms from PHL southward could result in brief/localized restrictions to MVFR or IFR between about 20 and 00Z. Some patchy fog may develop across mainly the southern portions of the area later tonight, especially if any precipitation falls at any of the terminals. W-NW winds will continue to gust to 20 kt this afternoon before becoming light and variable tonight. Winds AOB 10 kt on Sunday. outlook... VFR much of the time. Scattered (mostly) late afternoon and evening showers and thunderstorms may limit cigs/vsbys at times through the period.
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&& .MARINE...
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Winds have backed out of the SW and even S in spots this afternoon. S-SWly winds will be strongest late this afternoon and early evening in our coastal waters off S NJ and DE. Winds could be sustained near 20 kt but the potential to mix down higher gusts is minimal with a hot airmass residing over the relatively cooler waters. While there could be a few gusts near 25 kt late in the day nearshore, do not expect conditions will warrant a SCA. Winds will be light tonight and Sunday with high pressure building in. Medium-period sly swells will persist today and tomorrow. Wave heights should subside in the 2-3 ft range through the remainder of the weekend. outlook... Mostly a period of sub-sca conditions expected. scattered showers and thunderstorms will create locally higher winds and seas through the period.
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&& .CLIMATE... Record high temperatures today through Thursday are below. Site 23rd 24th 25th 26th 27th 28th ---- ---- ---- ---- ---- ---- ---- PHL... 101-2011 98-2011 96-1899 101-1892 101-1940 100-1941 ABE... 99-1955 95-1999 95-1999 98-1940 98-1955 97-1949 ACY... 105-2011 100-2011 99-2010 96-2011 99-2005 98-1999 ILG... 100-2011 98-2011 96-1987 99-1894 100-1894 101-1894 TTN... 104-2011 98-1910 97-1999 99-1892 100-1894 101-1894 GED... 104-2011 99-2011 99-2010 97-2012 98-2005 99-1949 RDG... 100-2011 96-2010 96-1999 99-1940 98-1955 99-1941 MPO... 91-1955 91-1914 90-1999 89-1949 91-1955 93-1949 && && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Heat Advisory from 11 AM to 6 PM EDT Monday for PAZ060>062-101- 103-105. Excessive Heat Warning until 6 PM EDT Monday for PAZ070-071- 102-104-106. NJ...Heat Advisory from 11 AM to 6 PM EDT Monday for NJZ007>010- 012>014-016-020>027. Heat Advisory until 8 PM EDT this evening for NJZ012>014-016- 020>027. Excessive Heat Warning until 6 PM EDT Monday for NJZ015- 017>019. DE...Heat Advisory from 11 AM to 6 PM EDT Monday for DEZ002>004. Heat Advisory until 8 PM EDT this evening for DEZ002>004. Excessive Heat Warning until 6 PM EDT Monday for DEZ001. MD...Heat Advisory from 11 AM to 6 PM EDT Monday for MDZ008-012-015- 019-020. Heat Advisory until 8 PM EDT this evening for MDZ008-012-015- 019-020. MARINE...None.
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&& $$ Synopsis...O`Hara Near Term...Klein Short Term...Klein Long Term...O`Hara Aviation...Klein/O`Hara Marine...Klein/Robertson/Meola/O`Hara Climate...Staff

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