789 FXUS62 KCHS 152320 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 620 PM EST Sun Jan 15 2023 .SYNOPSIS... High pressure will persist into Monday. A weak cold front will approach late Tuesday and dissipate north of the area. Another cold front will move through Thursday night, with a storm system to likely impact the region next weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Tonight: A quiet, but cold night is on tap for tonight as high pressure settles overhead. The boundary layer will decouple quickly after sunset and temperatures will plummet shortly after. Clear skies, calm winds and low dewpoints will promote strong radiational cooling with lows expected to drop into the upper 20s inland with mid to upper 30s along the beaches and Downtown Charleston. Locations that usually see the coldest temperatures could even drop down as low as 25 degrees, such as spots within/near the Francis Marion National Forest and interior Berkeley, Dorchester, Colleton counties. && .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/... Monday: Short wave ridging prevails aloft, while high pressure at the surface originally overhead shifts south across Florida. Meanwhile, an intense but vertically stacked low will be situated southeast of New England. Upstream we find another deep low and associated strong short wave moving through Iowa. South of this feature a potent upper jet punches east into the Ohio and Tennessee Valley, which brings an increase in high level cirrus clouds to the local communities. Simulated satellite products and cross-sections indicate that the majority of these clouds will be thin enough to not have much impact on temps. As a result, given 1000-850 mb thickness climbing to about 1345-1350 meters and some downslope component in the boundary layer, we look for max temps of at least 60-64F. Monday night: More extensive cloud cover and maybe a little mixing within the boundary layer will provide us with a warmer night than the past few nights. Looking at min temps 40-43F degrees inland, mid and upper 40s elsewhere. Tuesday: A zonal flow prevails aloft with various mid level impulses riding quickly east, but staying north of the local counties. At the surface, high pressure over Florida will reorganize east of the Bahamas, while stacked low pressure heads toward the western Great Lakes. A cold front trailing from that low will draw closer to the area, and that along with deeper moisture pulling into the region (Pwats of 1.25 inches or more) could allow for isolated to maybe scattered showers to impact our northwest tier late. However, the better dynamics stay outside the area, isentropic ascent is minimal and convergence is weak, so QPF looks to be very minor. With the front to become parallel to the flow aloft, the front will never reach here, and looks to eventually dissipate to our north. Both 850 mb temps and low level thickness climbs further, so despite the cloud cover, parts of georgia will hit 70F degrees or greater, with upper 60s elsewhere away from the much cooler beaches with a decent southerly sea breeze. There are indications of fog from the build down of stratus Tuesday night. But since there is too much mixing we didn't include in the forecast at this time. Wednesday: The aforementioned cold front will have already dissipated or will do so early in the day as high pressure extends from the Atlantic into the Southeast, and a zonal flow or flat ridging dominates aloft. Further upstream an area of low pressure will move into the Oklahoma and Texas panhandles, with an associated west-east warm front to extend into the Tennessee Valley. There will be extensive cirriform clouds spreading into our area with this system, along with some lower level clouds within a southwest boundary layer flow. Despite this, warm advection will persist, leading to temps climbing even warmer than on Tuesday. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... The northern branch of the westerly flow aloft will feature fast moving short waves that stay well to our north, while a closed low that forms over the Four Corners by late week, tracks eastward. At the surface, a weak cold front moves through Thursday night, followed by high pressure into early Saturday, which at some point gives way to a southern stream storm system thereafter. there is some better forcing and a little instability and shear in association with the cold front Thursday. So we have PoPs up to 50%. We didn't include it, but there could be a low end chance of a few t- storms, but no severe weather at this time. Closed lows in the south or southwest states are always problematic for our region regarding the timing of precipitation. So our forecast for next weekend is uncertain at this time, but could be somewhat unsettled. Temps are far above climo, but currently below any records for Thursday, then trending cooler behind the cold front (although still above normal). && .AVIATION /23Z SUNDAY THROUGH FRIDAY/... KCHS/KJZI/KSAV: Solid VFR conditions through 00Z Tuesday. Extended Aviation Outlook: Mostly VFR conditions. Any potential for flight restrictions might occur in low stratus and maybe some fog late Tuesday night and early Wednesday, and maybe again in a few showers late Thursday associated with a cold front. && .MARINE... Tonight: High pressure will settle over the local waters. Northwest winds will continue overnight and will decrease to around 5-10 kt with seas falling to around 2-4 ft. A tighter pressure gradient will exist to the northeast well offshore closer to a strong surface low. This should keep winds in the Charleston County nearshore waters slightly more elevated than its adjacent waters through at least midnight, with winds 10-15 kt. Winds near the Charleston-Edisto Buoy (41004) could even gust up to 20 kt at times through late evening. Monday: This will be the best period for mariners under the influence of high pressure, leaving us with winds no more than about 10 kt and seas of 2-4 feet (highest across the 20-60 nm Georgia waters). Tuesday and Wednesday: A weakening cold front will attempt to approach, but washes out to our north before ever reaching here. Instead, high pressure from the Atlantic and extending west across Florida will hold firm. There is some tightening of the gradient Tuesday into Tuesday night, which could cause marginal Small Craft Advisories over some of the waters. Thursday and Friday: Another cold front approaches Thursday and then moves through at night, followed by continental high pressure in its wake. Conditions might flirt with advisories on some of the waters Thursday and Thursday night. Sea fog: Abnormally warm air will overspread the waters Tuesday through Thursday. However, initially dew points aren't very high, and winds might be too strong through the period. For now there is no mention of any sea fog, but given the warmth of the air mass, it does bear watching. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$