Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 090313 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1013 PM EST Thu Dec 8 2016 .SYNOPSIS... Colder high pressure will extend over the area through the first half of the weekend. A weak trough of low pressure is expected to develop over the Atlantic coastal waters Saturday night and Sunday. By next week, a series of cold fronts are expected, with the first one arriving by Monday night, then potentially a stronger cold front by mid week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Tonight: A deep mid and upper level cyclone moving through eastern Canada, and it`s associated and trailing short wave will trek through the northeast quadrant of the country. At the surface, the leading edge of the arctic air is overspreading much of the nation east of the Rockies, including the local forecast district. Expect variable amounts of mid and upper clouds associated with a robust coupled upper jet, and patches of stratocumulus. There is plenty of cold advection with the 850 mb 0C isotherm to make it as far south as near I-16 in Georgia by daybreak. That allows for temps to decline to generally the mid or upper 30s around 7-8 am Friday. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... Overview...This period will be marked by much colder temperatures and little or no chance of precipitation. Friday...The area will be just in the wake of a strong cold front with polar high pressure building from the Northwest. Even with mostly sunny skies, strong cold advection will hold high temperatures to around 50 north to the lower 50s south. Winds will not be more than 5-10 mph, thus the wind chill effect will be minimal. Friday night...Expect some of the coldest temperatures so far this season as high pressure continues to settle over the area. The pressure gradient weakens allowing winds to drop to calm/near calm under mostly clear skies. Expect temperatures to reach a solid freeze in most areas away from the immediate coast. Still going for mid 20s well inland upper 20s to lower 30s elsewhere. Saturday...High pressure moves to just north of the region with light northeast winds. Given models not showing much warm advection, expect highs will struggle to reach back into the lower to mid 50s. Saturday night...Not quite as cold as Friday night, but still freezing temperatures likely from I-95 west and mid to upper 30s closer to the coast. The one factor that could keep temperatures from getting this cold, especially closer to the coast, will be the potential for a developing coastal trough of low pressure over the near shore waters as low and mid level flow veers to east-southeast. Some models actually trying to produce some light QPF, but have kept slight chance pops for the coastal waters, possibly reaching extreme coastal areas of South Carolina counties toward day break. Sunday...Although models differ on the strength and position of the developing coastal trough, they seem to agree that it will weaken and move northward through the day. Surface high continues moving northeast into the Atlantic ahead of a developing storm system over the central U.S. by late in the day. Have kept slight chance/low end chance pops mainly over the water with again slight chance scrapping the immediate SC coast, mainly Charleston county. The presence of the coastal trough offshore most of the day and a departing high to the north will hold a weak wedge with low level northeast winds and likely mostly cloudy skies. Thus, although temperatures will be warmer, they will still likely stay just below normal in the upper 50s to lower 60s. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... A zonal flow will prevail over much of the United States early week through mid week, setting up a period of quick moving systems and associated fronts shifting across the Southeast. Expect the first of two fronts to push through the area on Monday with potentially some showers over parts of the area. Tuesday will be relatively quiet and dry while a light southerly wind develops ahead of the next approaching front. On Wednesday, a more significant cold front will sweep through the area with showers. Dry and cooler high pressure will then extend across the region on Thursday. Overall high temps should range in the upper 60s to lower 70s Monday, then low/mid 60s Tuesday and Wednesday. By Thursday, high temps should only peak in the upper 40s to lower 50s. Overnight lows will generally range in the mid/upper 40s away from the coast Monday and Tuesday nights. Wednesday night lows should range in the mid/upper 30s inland to low/mid 40s near the coast. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... VFR. Extended Aviation Outlook: Mainly VFR. && .MARINE...
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Tonight: A humongous region of arctic high pressure will continue to build from western Canada and the Great Plains. Cold advection continuing to surge in, steady isallobaric pressure rises and geostrophic winds of 25 or 30 kt will produce northerly winds as high as 20-25 kt over AMZ350 and AMZ374, where we have SCA`s in effect. While a few gusts will reach near 25 kt on the rest of the Atlantic waters, the coverage and frequency is too limited to hoist advisories elsewhere. Seas will build as high as 6 or 7 ft on the outer Georgia waters, to 4 or 5 ft 10-20 nm out, and 2-3 ft closer in toward shore. In Charleston Harbor winds will flirt with advisory conditions, but will remain just shy through the overnight. Friday...Marginal small craft conditions expected to end by afternoon as cold high pressure continues building from the northwest. Saturday...No highlights as high pressure builds just north of the waters. North-northeast winds of generally 15 knots or less and seas 4 feet or less. Sunday...A weak coastal trough of low pressure is expected to slowly move up the coast and then dissipate by late day. Other than the potential for scattered showers, no highlights expected as winds veer to east-southeast. By sunday night, models are showing winds to increase from the south, but not thinking they will reach small craft levels. Monday...Southwest winds of 15 to 20 knots possible ahead of the next cold front, expected to move through by late afternoon/evening. Not much moisture again with this front, with slight chance for showers. Tuesday...High pressure returns north of the area with north- northeast winds of mainly 15 knots or less and seas 2 to 4 feet, highest offshore.
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&& .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory until 2 PM EST Friday for AMZ374. Small Craft Advisory until 11 AM EST Friday for AMZ350. && $$ NEAR TERM... SHORT TERM... LONG TERM...DPB AVIATION... MARINE...

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