Area Forecast Discussion
Issued by NWS Columbia, SC

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000 FXUS62 KCAE 212027 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 427 PM EDT Sat Oct 21 2017 .SYNOPSIS... Fair weather will continue through early Sunday, with a slight chance of showers in the afternoon. A cold front will bring a chance of showers and thunderstorms Sunday night through early Tuesday, followed by cooler temperatures for mid week. Fair with a warming trend late week. Next weather system may approach by next weekend. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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A strong upper ridge will remain over the east coast, but will start to shift eastward tonight. The center of the surface high will also continue to shift eastward, and surface winds will therefore remain easterly. The air mass still remains dry this evening, but as the high moves east, mid-level flow will become more southeasterly and low-level moisture will increase going into Sunday morning. Scattered to broken low and mid-level clouds are expected to develop overnight, but fog is less likely due to the presence of a 15 to 20 kt low-level jet. With increasing moisture and cloud cover, overnight lows will be several degrees warmer than last night, in the mid 50s.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY NIGHT/... The upper and surface ridges will shift to our east offshore Sunday ahead of an approaching upper trough and surface front. Low level flow to gradually veer to ESE/SE and pick up some Atlantic moisture, with indications of showers possible by afternoon mainly S FA/CSRA. Upper trough to shift east into the central CONUS Sun nt into Mon with cut off low developing over the Lower Mississippi valley. Upper low to open and shift to the ENE Mon nt and Tue ahead of deepening upper trough. Surface low to develop along the Gulf coast and track NE into the Ohio Valley and southern Appalachians. Increasing moisture and dynamics along and ahead of the upper trough and surface front sets the stage for increasing chances of showers and thunderstorms. Some slight timing differences and uncertainties with the timing of the system, but latest model consensus has highest POPs generally in the late Monday through early Tuesday time period. Indications of moderate to strong wind fields and shear, but only weak instability, provides some severe threat but with limited confidence at this time. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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Models continue to indicate a significantly deepening upper trough over the E CONUS behind this system, with indications of cooler air coming in Wednesday. Dry air is expected to preclude any significant precipitation with the passage of the strong upper trough. Fair and cool mid week. Models indicating the upper trough quickly lifting to the east Thursday with ridging developing along the east coast by Friday. This should result in a quick warm up late week. Considerable uncertainty for next weekend, with significant model differences noted between the 12Z GFS and 00Z EC on the next system. GFS brings it in Saturday, with Gulf/Tropical moisture infusion, while the 00Z EC maintains an upper ridge over the region, keeping the approaching system well to our west.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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Expect mainly VFR conditions through the TAF period. High pressure aloft and at the surface continues to dominate with just a small moisture increase in a light easterly flow. There will be an increase in low-level moisture in an onshore flow. The moisture combined with nocturnal cooling may lead to stratus and fog. However, the models depict just weak isentropic lift and it is initially very dry. The GFS MOS and LAMP plus NAM MOS maintain mainly VFR conditions through the TAF period. Some of the guidance indicates a period of MVFR fog during the early morning hours. The SREF guidance has low probabilities of restrictions. Upper cloudiness and some mixing associated with a weak low-level jet should help limit fog. We maintained VFR conditions during the TAF period. EXTENDED AVIATION OUTLOOK...A frontal system may bring widespread restrictions in showers Sunday night into Tuesday, with thunderstorms possible Monday and Tuesday.
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&& .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$ SYNOPSIS...99 NEAR TERM...99 SHORT TERM...99 LONG TERM...99 AVIATION...99

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