Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 181401 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 901 AM EST Sat Feb 18 2017 .SYNOPSIS...
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A warm front will lift north of our area through today. A weak cold front is expected to settle through our area late tonight and early Sunday as low pressure tracks well to our north. Another cold front is forecast to push through the area early Monday, then high pressure moves in later Monday into Tuesday before shifting offshore Tuesday night. A weakening cold front moves across the area early Wednesday, then another frontal boundary approaches Thursday and stalls near the area through Friday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Surface low pressure is located this morning between the Great Lakes and Hudson Bay, while an upper-level low is centered over Arkansas. A warm front will continue to progress northeastward across our area through the day, with warmer air low-level overspreading the region. Speaking of warmer air, the 12z Sterling, VA raob shows a very strong low-level inversion due to radiational cooling last night and early this morning. At the top of this inversion (near 1500 feet), the temperature was measured at nearly +14C. Once this inversion is eroded, we are expecting our temperatures to jump quite a bit later this morning into the afternoon. Just some high level clouds around, which should begin to increase toward late afternoon ahead of two systems mentioned above. No major changes to the high temperatures at this time, which favored the warmer NAM MOS. The one exception is across the southern Poconos and far northwestern New Jersey where a snow pack remains (at least for now). While it will be a much warmer afternoon, we are not anticipating record highs. The hourly temperature and dew points were adjusted based on the latest obs, then the LAMP/LAV guidance was blended into continuity. We will monitor trends as high temperatures at least for some areas may need to be increased a bit. A more southerly wind component though along the coast will result in cooler temperatures given the colder water temperatures.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... Winds should shift from southwesterly to westerly overnight, resulting in weak downslope low level flow. That, combined with the moisture advection, will limit radiational cooling. Lows are forecast to be 15 to 25 degrees above normal, ranging from the mid 30s to upper 40s. A closed mid level low, currently over OK and AR is expected to cross VA and Delmarva late tonight. However, it is expected to fill and weaken today and tonight as it does so. Thus, we are not expecting the same widespread convection currently on the front side of this low. However, isolated rain showers will be possible generally south of Philly as the low crosses Delmarva late tonight. && .LONG TERM /SUNDAY THROUGH FRIDAY/...
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On Sunday, the cold front that affects the area overnight Saturday will push through the area. Any precipitation associated with this boundary will end before daybreak, and a dry forecast is expected Sunday through Sunday night. Sunday is forecast to be a warm day, and several places could get within a few degrees of record. However, no one is expected to break any records at this time. A back door front is forecast to push southward through the area early on Monday before high pressure builds across the area later Monday into Tuesday. Cooler conditions are expected Monday and Tuesday as compared to Sunday, but will remain above normal. A warm front may pass across the area Tuesday into Tuesday night as high pressure shifts offshore. Dry weather should continue on into Tuesday. A cold front is then expected to approach the area Tuesday night and pass through during the day Wednesday. Precipitation may start overnight Tuesday as a short wave/vorticity impulse slides across the area. If precipitation starts early enough, there could be a wintry mix across the far northern areas, mainly along and north of I-80 corridor. Guidance indicates the precipitation beginning to dissipate as it approaches the east coast as the front moves through the area. So we`ll keep a chance/slight chance for isolated showers across the area Tuesday night into Wednesday. Another front is forecast to approach the area Thursday, then stall near the area through Friday. There is a chance that some scattered showers could develop overnight Thursday into Friday as a couple of short wave/vorticity impulses move across the area. However, the best chance for precipitation looks like Saturday as a stronger frontal boundary moves into the area.
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&& .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of Today...VFR with just some high level clouds increasing mainly late in the day. Winds becoming southwesterly and increasing to around 10 knots. Tonight...VFR with thickening clouds, however a ceiling should only lower to around 10000 feet. Southwest winds less than 10 knots, becoming westerly. OUTLOOK... Sunday-Tuesday...Generally VFR expected. CIGS may approach MVFR at times Sunday night into Monday morning. Gusty winds 15-20 knots during the day. Tuesday night-Wednesday...Conditions lowering to MVFR or IFR overnight into Wednesday morning with a chance of showers.
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&& .MARINE...
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Winds and seas should stay below SCA criteria. Gusts above 20kt are possible late this afternoon and this evening, but winds are expected to remain below 25kt. OUTLOOK... Sunday-Monday...Generally sub Small Craft Advisory conditions expected, although winds may approach advisory levels across the northern New Jersey coastal waters overnight Sunday into Monday morning. Monday night-Wednesday...Sub Small Craft Advisory conditions expected although winds may gust up to 20 knots at times.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gorse/Robertson Near Term...Gorse/Johnson Short Term...Johnson Long Term...Robertson Aviation...Gorse/Robertson Marine...Johnson/Robertson

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