FXUS62 KCHS 062107 AFDCHS
Area Forecast Discussion National Weather Service Charleston SC 407 PM EST Thu Mar 6 2025
.SYNOPSIS...
High pressure will prevail into Saturday. A cold front is expected to move through the area Saturday night into Sunday as low pressure develops along it, and pulls away over the Atlantic early next week.
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.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Through Sunset: Ongoing cold air advection and an enhanced pressure gradient is maintaining breezy W/NW winds across our area, with gusts to 25-30 mph. The cold air advection will quickly wane around sunset and the pressure gradient will level off. This will cause these winds to rapidly ease.
Tonight: The mid-levels will consist of a negatively tilted trough moving further into the Atlantic. Meanwhile, weak ridging over the MS Valley in the evening will shift eastward and weaken. The result will be northwest winds overhead initially will become more westerly late as zonal flow develops. Surface High pressure near the mouth of the MS River in the evening will shift over the Southeast U.S. late. The High will bring dry conditions. Though, there should be some higher cloud cover floating over our region. This along with very light to calm surface winds will lead to decent radiational cooling. Temperatures are expected to bottom out in the lower to middle 30s across most areas, except warmer at and near the beaches. All of this will cause areas of frost to form across inland areas. Therefore, we have a Frost Advisory in effect. Closer to the coast, the frost should be more patchy, so we don't have an advisory there at this time.
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.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Friday: The day begins cool with frost many places inland from US-17. But with zonal flow to prevail aloft, it will allow for surface high pressure initially directly overhead to move offshore for the afternoon. With the strengthening March sun, and warm advection, highs will be 5-10F warmer than on Thursday. The immediate coast will be considerably cooler with a resultant afternoon sea breeze.
Friday night: It'll also be a warmer night with a 35-45 kt low level jet passing through, keeping things well mixed within the boundary layer. This occurs in response to an upstream cold front and high pressure to the south and southeast. Lows only look to be within a few degrees either side of 50F.
Saturday: A deep downslope flow will dominate the region ahead of a cold front not far to the north of the area. This along with warm advection will promote a very warm day for this time of year, and provided there is enough sunshine available ahead of a developing system in Texas, highs will reach into the mid and upper 70s, with gusty westerly breezes The sea breeze will be pinned close to the coast within this pattern, But keep in mind if you're going to the beaches, they will be much cooler in the afternoon due to the eventual development of that sea breeze. Most if not all of the day will be rainfree, with just a slight chance late southern areas as a weak short approaches.
Saturday night and Sunday: The next system to impact the local vicinity will be in response to a backdoor cold front that passes into the area late Saturday night, and clears most, if not all locations Sunday. Low pressure rides eastward along the front from the Deep South, and within a moister flow out of the Gulf, and isentropic ascent, we look for showers to spread into the area. Guidance is still somewhat mixed regarding how quickly his occurs, but given forcing for ascent with short waves aloft, the right entrance region of the jet nearby, and some indications of 850-700 frontogenesis, it promises to be a wet period. PoPs as of this time are 60-80%, but 90-100% PoPs will likely be required at some point. The risk for any thunder is limited due to minimal CAPE. But since thunder was already mentioned in the forecast, there is some elevated instability, and the NBM has low chances, we do show slight chance t-storms during Sunday. Most lows Saturday night won't drop out of the 50s, and highs Sunday will be much cooler than on Saturday. Depending upon the exact track of the surface low and how far south the cold front pushes, adjustments could be forthcoming.
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.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A strong short wave drops through the area early in the week, causing the surface low to deepen off the Southeast coast. This low then pulls away either late Monday or Monday night, before high pressure builds in again through Wednesday. Another short wave and possible surface low could approach from the west Thursday. It still looks wet Sunday night into Monday, with eventually drier weather to return late in the period. Cool conditions Monday, then much warmer thereafter.
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.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
18Z TAFs: VFR. The combination of cold air advection and an enhanced pressure gradient will cause gusty WNW winds to prevail through late this afternoon. Winds will quickly diminish around sunset, then be light to calm overnight.
Extended Aviation Outlook: There could be LLWS Friday night into early Saturday as a 35-45 kt low level jet moves through. A storm system could bring flight restrictions to the area late Saturday night or Sunday into Monday or Monday night.
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.MARINE...
Tonight: High pressure near the mouth of the MS River in the evening will shift over the Southeast U.S. late. Cold air advection will quickly wane around sunset and the pressure gradient will level off. This will cause winds to rapidly ease. Hence, the Small Craft Advisories should expire by midnight.
Friday and Friday night: High pressure is in control, and the gradient is light enough during Friday for afternoon sea breeze circulations. Winds though remain no more than 10 or 15 kt. However, the gradient does start to tighten Friday night as an upstream cold front begins to draw closer, and a 35-45 kt low level jet moves in. Warm advection will temper the amount of mixing of these winds at night, but there could be some gusts of 20 or 25 kt at times.
Saturday through Tuesday: High pressure eventually gives way to a cold front late Saturday night and early Sunday, as low pressure rides along the front, and deepens not far away from the local waters into Monday or Monday night. As that feature pulls away thereafter, high pressure builds in from the west. Conditions could be close to advisory levels with a pinched gradient Sunday through Monday.
Mariners are advised that a few t-storms are possible Sunday into Sunday night given some elevated instability. Nothing severe however.
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.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Frost Advisory from 1 AM to 8 AM EST Friday for GAZ087-088-
099>101-114-115.
SC...Frost Advisory from 1 AM to 8 AM EST Friday for SCZ040-042>045.
Lake Wind Advisory until 5 PM EST this afternoon for SCZ045.
MARINE...Small Craft Advisory until 6 PM EST this evening for AMZ330-
354. Small Craft Advisory until 9 PM EST this evening for AMZ350- 352. Small Craft Advisory until midnight EST tonight for AMZ374.
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NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE...