FXUS62 KCHS 240613 AFDCHS
Area Forecast Discussion National Weather Service Charleston SC 113 AM EST Mon Nov 24 2025
...RISK FOR DENSE FOG THIS MORNING...
.SYNOPSIS...
High pressure will prevail early this week, before a cold front impacts the area mid week. High pressure is expected to return for Thanksgiving and into the weekend.
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.NEAR TERM /THROUGH TONIGHT/...
A Dense Fog Advisory has been issued for areas roughly along and west of I-95 through 10 AM. The advisory goes not include the coastal zones of Chatham, Bryan and Liberty Counties per latest satellite trends, but as the fog expands over the next few hours, it may very well need to be expanded into these zones along with Coastal Jasper, Beaufort, Coastal Colleton and possibly Dorchester into the western portions of Charleston Counties.
The risk for fog will steadily increase through daybreak within a decoupled boundary layer. Surface observations show a few observation sites have already dropped below 1SM, but regional webcams suggest the fog is still fairly shallow and somewhat patchy. 1000 hPa condensation pressure deficits are only marginal favorable for dense fog, but given fog is already starting to form so early in the night with surface dewpoint depressions approaching zero, the fog has plenty of time to expand and thicken with time. The risk for significant dense fog with visibilities 1/4 mile or less looks highest roughly along/west of the I-95 corridor where the lowest condensation pressure deficits are progged and 24/00z HREF probabilities for <1/4 mile are averaging 50-80%. A Special Weather Statement has been issued to address the going fog situation, but a Dense Fog Advisory may eventually be needed prior to daybreak. The fog should mix out by mid-morning.
High pressure will prevail across the region through tonight as ridging aloft persists. A weak onshore flow will develop later this afternoon and especially tonight as the center of the surface high shifts offshore of the Mid-Atlantic coast and a subtle coastal trough forms just the beaches. A rough shower or two could approach mainly the lower South Carolina early Tuesday morning, but most of the overnight hours will feature dry conditions with marine-based stratocumulus propagating onshore and a veil of thick cirrostratus aloft spreading in from the southwest ahead of the storm stream shortwave ejecting out of the Southern/Central Plains. Highs today will warm into the lower-mid 70s across the Lowcountry, the mid-upper 70s across Southeast Georgia with mid-upper 60s at the beaches. Overnight lows will range from the lower-mid 50s well inland to the lower- mid 60s at the beaches.
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.SHORT TERM /TUESDAY THROUGH THURSDAY/...
Tuesday: High pressure at the surface will shift off the Mid- Atlantic coast while the upper level ridging originally over the southeastern states progresses eastward over the adjacent Atlantic waters. A weak shortwave trough aloft will ripple across southwesterly flow over the southeastern states. This weak disturbance could trigger some showers across mainly the Charleston Tri-County area, with 15-20% PoPs in the forecast. Temperatures will be above normal again, with mid 70s across southeastern SC and locations across southeastern GA reaching into the low 80s. Overnight lows will similarly be above normal, only dipping into the low 60s.
Wednesday and Thursday: The pattern aloft will shift to a large trough moving into the eastern CONUS, driving a cold front across the region Wednesday night into Thursday. Wednesday will feature highs once again in the upper 70s to low 80s as the region is situated within the warm sector. Ahead of the front a line of showers will approach the region Wednesday afternoon, however the showers will likely be in a diminishing state and is not expected to be a significant rain-maker. Accumulations across the region are only forecast to be a few hundredths, which matches ensemble guidance and NBM probabilities. Areas west of I-95 have the best chance at seeing rainfall, as the showers are likely to diminish as they approach the coastline. Post-FROPA temperatures Wednesday night will dip into the upper 30s inland and 40s along the coastal counties. Thursday will feature plentiful sunshine, however temperatures are expected to only top out in the low 60s, with some locations not getting out of the 50s.
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.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Broad troughing aloft will transition to zonal flow into the weekend, while high pressure dominates at the surface. This pattern will yield dry and noticeably cooler weather through the weekend. Low temperatures Thursday and Friday nights are forecast to dip below freezing across far inland locations. A reminder that the local frost/freeze program has ended due to the widespread freeze earlier this month.
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.AVIATION /06Z MONDAY THROUGH FRIDAY/...
24/06z TAF Discussion: KCHS/KJZI: Main concern through daybreak is the development of fog. Conditions favor dense fog south and west of both terminals, but there could still be impactful levels of lower visibilities. Vsbys could occasionally drop below IFR between 08-10z with a period of prevailing IFR vsbys 10-13z. Lowest vsbys are expected to bottom out solidly below airfield minimums during this time and could even approach airfield minimums at times, especially at KJZI. Until confidence increases, vsbys were limited to 1SM at KCHS (below alternate minimums) and 1/2SM at KJZI (just below airfield minimums). Conditions should rapidly improve after 14-15z with VFR returning and prevailing through 25/06z.
KSAV: Confidence is increasing that significant fog will impact the terminal early this morning. Current near term guidance and observational trends suggest dense fog will impact the terminal prior to daybreak with vsbys and possibly vertical visibilities dropping falling below airfield minimums. The risk for such conditions is highest between 10-13z and prevailing 1/4SM FG VV002 was highlighted during this time. Pockets of dense fog could occur as early as 08-10z which was handled by a TEMPO group. The fog should mix out by mid-morning with conditions returning to VFR, which will persist through 25/06z.
Extended Aviation Outlook: Prevailing VFR.
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.MARINE...
Visibility trends are being monitored closely in the Charleston Harbor where some fog could bleed in from the west/southwest. A Marine Dense Fog Advisory could be needed for vsbys 1NM or less, but confidence in dense fog reaching the harbor is not high enough at this time to hoist the advisory.
Through Tonight: Northeast winds will gradually veer east and southeast through tonight as high pressure to the north gradually shifts offshore of the Mid-Atlantic coast. Winds will average less than 15 kt through the period with seas 4 ft or less.
Tuesday through Thursday: High pressure will dominate early this week, with a cold front pushing through the region Wednesday night. SE winds around 10 knots Tuesday will shift to the SW on Wednesday, and eventually the NW on Thursday. After the cold front pushes through winds on Thursday are forecast to surge to 15 to 20 knots, with some gusts approaching 25 knots. Small Craft Advisories may eventually be needed for portions of the marine waters. Seas are forecast to average 2 to 3 ft with some 4 ft seas in the 20 to 60 nm offshore GA waters.
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.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Dense Fog Advisory until 10 AM EST this morning for GAZ087-088-
099>101-114>116-118-137-138-140-141.
SC...Dense Fog Advisory until 10 AM EST this morning for SCZ040-042-
043-047.
MARINE...None.
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