Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 250556 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 156 AM EDT Mon May 25 2020 .SYNOPSIS... A weak cold front will push into the area later tonight and Monday, and high pressure will build over the region from the north. A coastal trough should develop around mid week, and low pressure could track over or near the Southeast coast mid to late week. A cold front could approach the region next weekend. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... As of 150 AM: A backdoor cold front was pushing across the Santee River basin. Surface based observations along and north of the front were observing low ceilings with light fog. Based on the latest run of the HRRR, it appears that a period of fog will slide across the SC Lowcountry between 07-11Z and SE GA between 10-13Z. Previous Discussion: One last convective cluster will work west across northern Jenkins County over the next hours, then dry weather will prevail. Adjusted pops based on short term radar trends. Expect low stratus and possible some fog to fill in along/ahead of the backdoor front early Monday. The fog is not expected to have much impact, but some areas of reduced visibilities could occur. Dense fog is not expected at this time. Warm and humid conditions will persist with lows ranging from the upper 60s/near 70 inland, lower 70s at the coast, with mid 70s at the beaches and Downtown Charleston. && .SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/... Monday: High pressure will build into the region from the north and will push a weakening cold front toward the south. At least scattered showers and thunderstorms could develop near this boundary, with higher PoPs across northern counties during the morning followed by high PoPs shifting into southern/western sections during the afternoon. Forecast instability suggests only a low chance for a brief/isolated pulse severe thunderstorm or two. Monday night: Due to diurnal stabilization, isolated/scattered showers and perhaps isolated thunderstorms near the stalling cold front across southern/western counties should diminish in coverage through at least the first half of the night. Then, guidance depicts a band of deeper moisture to spreading from the south in at least southern counties later on. Tuesday and Wednesday: Guidance indicates a wet period as a pool of PWAT values around 2 inches settles over the region. However, timing/coverage of showers/thunderstorms will be linked with strength of the surface high N/NE of the region and to the uncertain evolution of a surface trough/surface low S/SE of the area. The latest forecast ramps PoPs up to likely all but far northern/inland counties Tuesday. Then, PoPs vary from likely along the SC coast to chance elsewhere Tuesday night. Wednesday, PoPs range from likely north to chance south. However, forecast confidence decreases Tuesday night and remains rather low through Wednesday. The potential for locally heavy rain will increase Tuesday through Wednesday, especially near the coast where tides will be elevated due to persistent E/NE flow. If stronger low pressure tracks over or inland from the coast Tuesday night through Wednesday, the potential for severe weather could increase. Also of note, greater than expected coverage/persistence of clouds/precipitation could translate to cooler daytime temperatures than indicated within the latest forecasts. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... The start of this period remains uncertain and will depend on whether surface low pressure remains in the vicinity into Thursday. Otherwise, on the western periphery of Atlantic surface high pressure/beneath a weak ridge of high pressure aloft, a surface trough should linger over the region with above normal precipitation and temps into this weekend. A cold front could approach or move into the area by late next weekend. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... Prior to the 6Z TAFs, a backdoor cold front was pushing across the Santee River basin. Surface based observations along and north of the front were observing LIFR to IFR ceilings with MVFR visibilities. Based on the latest run of the HRRR, it appears that a period restrictive ceilings will pass over KCHS between 07-11Z and KSAV between 10-13Z, highlighted with TEMPO groups. The pressure gradient between a developing tropical wave over FL and high pressure across the Mid-Atlantic states will increase this afternoon. Gusty SE winds should develop by mid-day and remain until around sunset. Conditions tonight should feature steady east winds with VFR ceilings. Extended Aviation Outlook: Periods of flight restrictions, especially related to showers/thunderstorms in the area, should persist into late week. && .MARINE... Tonight: South to southeast winds will gradually back as a weak cold front approaches. Speeds will remain <10kt with seas 1-2 ft nearshore waters and 2-3 ft offshore waters. Monday through Friday: On Monday, as a high pressure system builds over the area throughout the day, winds will increase as the pressure gradient tightens. Then, as a low pressure system lingers off the east coast of Florida, the pressure gradient will tighten more, causing winds and seas to gradually increase. Small Craft Advisories will likely be needed starting Tuesday afternoon into at least Wednesday morning. While there is still some uncertainty about the track of the low over or close to the Southeast coast mid to late week. Some guidance suggests that the pressure gradient starts to relax mid to late week, but the low pressure could maintain elevated winds and seas through Friday. && .TIDES/COASTAL FLOODING... Persistent E/NE flow will support elevated tides this week. Mid to late week, there exists a low probability for minor salt water flooding around the times of the overnight high tides. Also, we`ll continue to assess the potential for heavy rainfall to coincide with high tides at the coast, especially during the Tuesday-Thursday period. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...NED SHORT TERM... LONG TERM... AVIATION...NED MARINE... TIDES/COASTAL FLOODING...

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