Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 130537 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 137 AM EDT Thu May 13 2021 .SYNOPSIS... High pressure will build into the area tonight as cold front becomes nearly stationary near the northern shore of the Gulf of Mexico. A series of weak low pressure areas will track along the stationary front well south of the region through Thursday. High pressure will expand into the region late in the week and likely persist into early next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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As of 130 AM: KCLX detected a ragged band of light returns over the CWA, associated with drizzle. Based on the radar trends, drizzle should largely end over the next couple of hours. In addition, wind observations near the lake have remain well below Lake Wind Advisory (LWA) criteria, based on the forecast winds the LWA has been cancelled. Otherwise, the forecast appears on track with temperature expected to remain generally steady through the rest of the night. Previous Discussion: Tonight: High pressure will spread across the region behind a cold front now south of the area. As this process continues to unfold, chances of precip will become considerably lower as the bulk of mid- lvl moisture is scoured out of the area. However, a fair amount of low-lvl moisture will linger through the night, helping produce bouts of light rain and/or mainly drizzle. Low stratus and lower vsbys should also accompany drizzle, but lowest vsbys should be temporary. Cold air advection across the region associated with a north-northeast sfc wind favors noticeably cooler sfc temps than the previous night. In general, temps should dip into the mid-upper 40s inland to low-mid 50s closer to the coast late tonight. This is around 10-12 degrees below normal. Lake winds: Gusty north-northeast winds will persist over Lake Moultrie tonight as high pressure builds in from the northwest behind a departing cold front. A Lake Wind Advisory remains in effect through tonight.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH SATURDAY/... Thursday and Thursday night: a surface cold front is expected to be stalled well south of the region as high pressure builds well to the north over the OH River Valley. Models all show that the best deep layer moisture will slowly move south of the region, and have therefore continued to trend PoPs down from low chance to slight chance through the morning and into the afternoon. Any precip. is expected to be in the form of light showers, with little/no thunder. Model guidance continues to indicate that high temperatures will be cool for this time of year, in the mid to upper 60s, potentially flirting with record low max values. For Thursday night, there could still be enough deep layer moisture over the eastern third of the area for a slight chance for showers, but precip. chances are expected to drop off completely before midnight. Lows will be cool, ranging from the upper 40s well inland, to the lower to mid 50s else where. Friday and Saturday: An upper level trough will still be centered north of the area through Friday, then upper heights are expected to begin rising slowly by Saturday. At the surface, high pressure will be north of the region on Friday, shifting to off the mid Atlantic coast by Saturday. This pattern will keep generally low level northeast winds on Friday, becoming light and variable on Saturday as the pressure gradient becomes very light. Temperatures are expected to continue below normal, with a gradual warming through the period. Highs in the lower to mid 70s on Friday, warming to the mid to upper 70s on Saturday. Lows Friday night in the mid 40s to around 50s inland, and the lower to mid 50s near the coast. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Through Monday, models continue to show a relatively dry/quiet period. A broad upper ridge is expected to develop near or just to the west of the region with surface high pressure situated well to the northeast. Temperatures will start off below normal, likely moderating back closer to normal by Monday. By Tuesday and Wednesday, models begin to indicate that better deep layer moisture will return as the mid/upper level ridge tries to retrograde/build further west. Have kept slight chance PoPs for the western zones for Tuesday and all zones by Wednesday as low level southeast flow and some return of instability should allow for the potential for mainly afternoon showers/thunderstorms. Temperatures expected to be close to seasonal normals. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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Prior to the 6Z TAfs, IR satellite indicated that the clearing line was located generally over the Fall Line of SC and GA. Based on the satellite trends, restrictive ceilings and patchy drizzle may linger over the terminals until daybreak, possibly into the early daylight hours at KSAV. The rest of the period should feature steady NE winds and VFR conditions. Extended Aviation Outlook: Friday through Monday: Expect VFR to prevail.
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&& .MARINE... Tonight: A tight pressure gradient between high pressure building south behind a cold front and low pressure exiting further offshore will favor gusty north-northeast winds and elevated seas across all local waters through the night. Small Craft Advisories will remain in place for all waters with winds gusting upwards to 25-30 kt and seas building as high as 6-8 ft (highest seas across offshore Georgia waters late). Thursday and Friday: the waters will be between high pressure to the north and a stalled front and lower pressure well to the south. This pattern is expected to maintain a moderately strong pressure gradient and SCA conditions. Expect northeast winds of 15 to 20 kts, with gusts of 25+ kts, and seas generally 4 to 6 ft within 20 nm, and 6 to 8 ft beyond 20 nm. Later Friday through Monday: Winds and seas are expected to gradually decrease, with no highlights expected after Saturday evening. Northeast winds through Saturday, will likely veer to east and then southeast Sunday and Monday. Rip currents: An elevated risk of rip currents is possible through late week due to gusty northeast winds. && .CLIMATE... An unseasonably cool air mass, accompanied by clouds and showers, could challenge the following record low maximum temperatures Thursday 5/13. CHS 5/13 68 (1996) CXM 5/13 68 (1996) SAV 5/13 69 (1928) && .CHS WATCHES/WARNINGS/ADVISORIES...
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GA...None. SC...None. MARINE...Small Craft Advisory until 5 PM EDT this afternoon for AMZ330. Small Craft Advisory until 10 PM EDT Friday for AMZ350-352-354. Small Craft Advisory until 10 PM EDT Saturday for AMZ374.
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&& $$ NEAR TERM...NED SHORT TERM...RFM LONG TERM...RFM AVIATION...NED/RFM MARINE...DPB/RFM CLIMATE...

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