Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 182322 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 722 PM EDT Sun Apr 18 2021 .SYNOPSIS... A stationary front will linger offshore and to the south early this week. A cold front is expected to push through the region on Wednesday, followed by dry high pressure through late week. Low pressure and a more unsettled weather pattern could impact the region next weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Based on latest trends and the expectation that there is just too much dry air in place with condensation pressure deficits greater than 30 or 50 millibars, we trended even lower on the coverage of showers tonight. For now we have no more than 20-30% PoP roughly south of a line Skidaway Island to Midway to Ludowici. Another mild night, with lows close to 5F above climo. Previous discussion... Zonal flow will prevail in the mid-levels this evening, with a weak shortwave moving over the Appalachians towards daybreak Monday. At the surface, a stationary front will be offshore and stretching to our south. Likewise, models have the highest PWATs and POPs in these locations. Similar to 24 hours ago, the synoptic models tended to show higher QPF amounts inching into our far southern and coastal counties overnight, while the CAMs had much lower QPF amounts in these same locations and keep a majority of our area dry. Given the CAMs performed better yesterday into today and considering the pattern of drier conditions winning, we leaned more towards the CAMs with this package. Lows will generally be in the 50s for most locations and the lower 60s at the beaches. && .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/... A weak upper level short wave will be departing north of the area for the first part of Monday, followed by generally zonal to west- southwest upper flow. Another weak upper short wave is expected to move just southeast of the region on Tuesday. By Wednesday, a broad upper trough is shown by models to cover the entire eastern and southeastern portion of the country. The overall dry pattern is expected to continue, with significant rainfall not expected. The best chance for any rainfall still looks to be Tuesday, as better deep layer moisture associated with a weak upper level short wave impacts mainly the southeastern portion of our CWA. Have mostly slight chance PoPs, reaching low end chance PoPs over the extreme southeast portion of the area and Atlantic Waters. Any precipitation chances are expected to end by Tuesday evening. By Wednesday, as the broad upper trough moves into the area, there models show that the associated surface cold front will move through dry/no precipitation. High temperatures are expected to be near to slightly above normal. Mainly in the mid 70s to around 80. Slightly cooler in the mid to upper 70s for Tuesday given more clouds and slight chance for precipitation/showers. Lows around normal in the lower to mid 50s most areas through Tuesday night. With afternoon surface dewpoints relatively dry /in the 40s Monday, 50s Tuesday, and then 40s again on Wednesday/ afternoon conditions will feel very pleasant. Lake Winds: There are indications that winds will be strong enough for a Lake Wind Advisory on Lake Moultrie given deep mixing and a tight gradient ahead of and behind the next cold front during mid week. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Models are in good agreement for late week showing cool and dry high pressure prevailing. Unsettled weather is then expected over the weekend as low pressure impacts the region. Positioning and details are still a bit uncertain, but regardless, this system will bring healthy rain chances to the local area. Temperatures through the period will average below mid/late April climatology. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... VFR through 00Z Tuesday. Gusty W-NW winds Monday afternoon through the early evening. Extended Aviation Outlook: VFR conditions expected to prevail through the week. Winds could get a bit gusty Wednesday as the dry cold front moves through the area. && .MARINE... Tonight: A stationary front will be offshore and to our south, leading to "gentle" to "moderate" SW breezes much of the night. Land breeze circulations will allow for winds to veer more W closer to daybreak. Seas will average 2 or 3 feet. Monday and Tuesday: No highlights are expected with winds generally 15 knots or less and seas 2 to 3 feet. Wednesday and Wednesday Night: Winds and seas are expected to increase ahead of, and then behind the next cold front, which will likely push through the waters later half of Wednesday. Models indicate winds reaching marginal SCA levels, with seas possibly reaching 5 to 6 feet beyond 20 NM offshore. Thursday and Friday: Winds and seas expected to fall back below highlight levels as high pressure builds over the waters. && .FIRE WEATHER... Minimum relative humidity values Monday afternoon are expected to be 25-30% away from the immediate coast. Wind gusts will be near 20 mph at times, and we will need to consider Fire Danger Statement given the lack of rainfall the past several weeks. A combination of gusty winds, low relative humidity, and dry fuels could produce hazardous fire conditions Wednesday afternoon/early evening. Very low relative humidity is expected to persist into Thursday and Friday afternoons. Though, sustained winds may remain below 10 mph. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM... LONG TERM...ETM AVIATION... MARINE... FIRE WEATHER...

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