Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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386 FXUS61 KPHI 231337 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 937 AM EDT Thu Mar 23 2017 .SYNOPSIS... High pressure will build across the east coast today, then shift offshore tonight. A warm front will lift to our northwest Friday, then a backdoor cold front pushes through the area Saturday. This front is forecast to stall near the southern portions of the area through Sunday, but may return northward as a warm front Sunday night into Monday. A couple of low pressure systems are forecast move across the east coast through early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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No major changes with the 930 AM update. Sprawling 1036 MB high centered over the eastern Great Lakes will slowly build to the south and east today. By late afternoon, the center of the high will be just off the Eastern Seaboard. This high will continue to bring a continental Polar airmass into the region with high temperatures 10-15 degrees below normal. Highs will top off in the 30s in the Poconos, and in the low to mid 40s for the rest of the CWA.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... High pressure off the Eastern Seaboard will continue to drift offshore tonight, and a warm front lifts towards the Mid- Atlantic and Northeast late in the overnight. The main question will be how cold temperatures drop this evening, as skies will be clear, and with the center of the high near the region, winds will be light. This results in strong radiational cooling conditions prior to midnight. Temperatures should drop into the low-mid 20s for most of NJ/PA, especially for the Poconos, Lehigh Valley, northern NJ, and the Pine Barrens of NJ. It is possible that temperatures could be even colder. After midnight tonight, clouds will build into the region, and temperatures will then hold steady and slowly rise. Think precip will hold off until after the end of the tonight period, so will keep precip out of the forecast. If precip does develop, it will start out as a wintry mix of sleet/freezing rain, mainly over the Lehigh Valley/Poconos. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... A warm front will lift to our northwest during the morning hours on Friday, while a couple of short wave/vorticity impulses slide across the area as well. This is expected to help create an area of precipitation that is forecast to move across the area during the morning into the very early afternoon hours. Timing of the precipitation will be critical, because depending on how early this precipitation begins, there could be a period of a wintry mix of freezing rain/sleet/snow across portions of eastern Pennsylvania and northern New Jersey. With the uncertainty of the timing, and the fact it is expected in the 3rd period, we will hold off on an advisory at this time. The rest of the area should remain all rain with warmer temperatures. Friday night is expected to remain dry as the precipitation associated with the warm front moves away from the area. A backdoor frontal boundary is forecast to approach the area from the north overnight, but will likely not reach the area until the daytime Saturday. Saturday begins an extended period of possible unsettled weather across the area. A backdoor cold front will sink through the area during the day Saturday, then likely stall just to our south through Sunday. There will be a chance of showers across the area Saturday through Sunday, but areas across the northern half of the area have the best chance. The frontal boundary is then forecast to lift back northward as a warm front overnight Sunday into Monday as an area of low pressure may develop along the boundary and move across the area. Another couple of short wave/vorticity impulses are forecast to move across the area as well, and will enhance precipitation potential across the area. Sunday night into early Monday morning has the greatest chance of seeing more widespread and heaviest precipitation potential. Unsettled weather continues into early next week as a couple of low pressures affect the east coast, which may eventually bring a cold frontal passage across the east coast by mid week. There will continue to be a chance of showers through Wednesday as several short waves/vorticity impulses slide across the area, before the possible frontal passage Tuesday night. && .AVIATION /14Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions are expected through the TAF period. High clouds will move in from the west after 09Z Friday. Precip should hold off until after 12Z Friday, but there is a very small chance for sleet/freezing rain at KABE and KRDG between 10Z-12Z Friday. NW winds 5-10 KT, backing to the W after 18Z. Winds become LGT/VRB after 00Z Friday. OUTLOOK... Friday...A period of MVFR or slightly lower conditions possible with a period of light rain; mostly during the morning into early afternoon. If precipitation begins early enough, a wintry mix is possible, especially for northern areas. Southwest winds may gust 20- 25 knots. Friday night...Conditions improving to VFR. Saturday-Monday...MVFR or IFR conditions with periods of rain possible.
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&& .MARINE...
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Winds and seas should stay below SCA criteria today and tonight. OUTLOOK... Friday-Friday night...Small Craft Advisory conditions likely to return to the waters. Saturday-Saturday night...Conditions expected to fall below advisory levels. Sunday-Monday...A return to Small Craft Advisory levels expected. Winds may fall below advisory level Sunday night into Monday, but seas are expected to remain above advisory levels.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...None.
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&& $$ Synopsis...Robertson Near Term...Johnson/MPS Short Term...MPS Long Term...Robertson Aviation...Johnson/Robertson/MPS Marine...Johnson/Robertson/MPS

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