Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 260845 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 345 AM EST Sun Feb 26 2017 .SYNOPSIS...
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Cool high pressure with critical RH will build into the region today, then shift offshore tonight and early this week, as a warm and moist air mass gradually builds from the Atlantic and Gulf of Mexico. A cold front will move through Wednesday night into Thursday, followed by high pressure for the end of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Today: A fast moving zonal flow within a de-amplified pattern aloft will prevail, as cool and dry Canadian high pressure in the TN valley at the start of the day progresses to the coast of NC/SC by evening. This scenario will provide us with abundant bright sunshine and offshore winds this morning shifting onshore over the coastal corridor during this afternoon. We stayed relatively close to the low level thickness forecast scheme, which will support a brief change from the abnormally warm springlike weather of late. Today will actually only be the 8th day this month at KCHS and just the 7th time at KSAV, where we fail to achieve 70F. Tonight: High pressure will cover much of the E and SE parts of the nation, with a modifying clockwise return flow from off the Atlantic across the local district. Winds will quickly decouple away from the coast this evening, allowing for a rapid fall of temps the first half of the night. However, low level warm advection will slow the overnight fall of temps, as minimums on average will make it down to the upper 30s or lower 40s inland from US-17, closer to 50F on the barrier islands. Skies will begin the night clear, but some jet stream cirrus will arrive overnight, having little to no effect on temps.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY/...
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Surface high pressure will slide into the Atlantic Monday and persist through Wednesday. Southerly flow on the back side of the high will bring warm and moist air into the area. Aloft, a series of shortwaves will eject out of the southwest flow and pass over the forecast area late Monday into early Tuesday. This could spur some showers, however coverage does not look to be that impressive. Models actually seem to have trended drier, so have decreased precipitation chances. Slight chance/chance PoPs seem reasonable. Otherwise, a few diurnal showers/thunderstorms possible Tuesday and Wednesday afternoons. Another warming trend will get underway with temperatures expected to be well above late February/early March normals. Highs in the mid 70s Monday will warm to the low/mid 80s by Wednesday. Lows in the upper 50s/low 60s.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
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Models are in decent agreement that a cold front will approach and cross the forecast area late Wednesday night into early Thursday. Showers and maybe a few rumbles of thunder possible with the front. High pressure will return in its wake and remain the dominant feature through Saturday. Temperatures will be on a slight cooling trend through the period.
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&& .AVIATION /09Z SUNDAY THROUGH THURSDAY/...
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VFR. Extended Aviation Outlook: Flight restrictions possible in early morning fog/stratus Tuesday and Wednesday. A cold front will move through early Thursday with brief restrictions possible in clouds/showers.
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&& .MARINE...
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Today: Cool advection and continued isallobaric pressure rises this morning will allow for Small Craft Advisory conditions to persist across the Atlantic waters. However, there is quick improvement by mid to late morning (if not sooner) once cool advection slackens and the gradient around continental high pressure relaxes. Offshore winds as high as 15 or 20 kt and gusty this morning, will shift to onshore at considerably less speeds (no more than 10 or 12 kt) this afternoon, as continental high pressure slides to the SE coast and a "pure" but light sea breeze occurs. Seas will be highest this morning, up to 3-5 ft, before they subside to no greater than 2-3 ft by late day. Tonight: High pressure will expand over the western Atlantic, with it`s associated ridge axis to align itself to the north of the maritime area. E`erly winds will dominate, generally at or below 15 kt and seas will climb about a foot or so within the onshore fetch. Monday through Friday: East/southeast flow Monday will veer to the south by Tuesday as high pressure shifts into the Atlantic. Wind speeds will then increase Wednesday as the pressure gradient tightens ahead of an approaching cold front. Conditions look to remain below small craft advisory criteria at this time. The front will cross the waters early Thursday with high pressure to return in its wake. Sea fog: Warm southerly flow moving over the cooler shelf waters may result in patchy sea fog developing late Tuesday into Wednesday.
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&& .CHS WATCHES/WARNINGS/ADVISORIES...
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GA...None. SC...None. MARINE...Small Craft Advisory until 7 AM EST this morning for AMZ350- 352-354. Small Craft Advisory until 10 AM EST this morning for AMZ374.
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&& $$ NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE...

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