084 FXUS62 KCHS 180811 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 311 AM EST Wed Jan 18 2023 .SYNOPSIS... A stationary front will lift north of the area today. A cold front will move through Thursday night, followed by high pressure late this week. Low pressure is expected to impact the region this weekend. High pressure should build into the area early next week, before another low pressure impacts the region around the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... Today: Aloft, high amplitude ridging that extends north of the Great Lakes will shift eastward across the eastern third of the CONUS. At the surface, the day will begin with a subtle stationary boundary draped across the forecast area from west to east. This boundary will lift northward through the day and clear the entire forecast area by late afternoon. The day will begin with plentiful low stratus and fog that will take some time to mix and scatter out. This will slow the warming trend through the morning, but we should see enough sun in the afternoon to yield highs in the low to mid 70s (nearly 15 degrees above normal). The other forecast issue to keep an eye on is the potential for showers to develop across the interior this afternoon as the stationary boundary lifts northward. Models all try to generate some weak shower activity across central Georgia where the best ThetaE surge takes place, and the eastern extent of this could pass through areas across Tattnall, Candler, Evans, Bulloch, Screven, and Jenkins counties. If showers to develop they shouldn't amount to much, but we did include a small area of 20 percent rain chances. Tonight: The forecast area will sit in the warm sector ahead of an approaching cold front. The forecast is dry and mild with lows in the mid to upper 50s. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... Thursday: Ahead of a cold front, expect much above temperatures and gusty south winds. Clouds will increase, and a few showers could push into inland counties during the afternoon. Away from the coast, highs 75-80F will be common, near records for KSAV and even KCHS. On the coast, the marine influence should hold temperatures in the lower to middle 60s. Thursday night: Guidance continues to depict a decrease in precipitation coverage as a cold front crosses the region. Slight chance PoPs are in order for much of the area through the evening, but many locations will probably remain rain-free. Post cold-fropa, expect strong drying, but cooling will remain unimpressive, with lows ranging from the upper 40s inland to the middle 50s near the coast. Friday: High pressure will nudge into the region from the west. Weak cold air advection will be offset by downslope/westerly flow. Thus, although high temperatures will average around 10F cooler than those of Thursday, highs in the middle/upper 60s will remain above average for mid-January. Meanwhile, morning sunshine will give way to increasing mid/high level clouds as the next wave of low pressure takes shape upstream. Friday night: Under mid/high level cloud cover, expect a seasonally cool night, with lows in the upper 30s far inland and lower/middle 40s most other locations Saturday: Clouds will continue to increase/thicken within broad area of ascent ahead of surface low pressure developing over the northern Gulf of Mexico/an associated deep upper trough approaching from the west/northwest. However, low levels will remain quite dry, so PoPs remain below 15 percent with no mention of precipitation until Saturday night. With cloud cover and winds turning to the northeast, high temperatures Saturday afternoon will struggle to reach 60F. Lake winds: The probability for S/SW wind gusts 25 knots remains quite high on Lake Moultrie Thursday. A Lake Wind Advisory could eventually be required. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... Saturday night through Sunday, surface low pressure will eject NE along baroclinic zone/ahead of a deep longwave trough aloft. Many parameters, including the strong transport of deep subtropical moisture/PWAT values around 1.50 inches and ascent enhanced by the low-level cold air damming regime over the area, point toward significant rainfall, perhaps in the 1-2 inch range, across the region. Between the onset of showers Saturday evening and the gradual decrease in shower coverage Sunday afternoon and Sunday night, categorical PoPs span the period from later Saturday night through midday Sunday. A cold front should advance through the region Sunday night. Then, slight chance PoPs linger Monday into Tuesday as the baroclinic zone will remain close to the region. However, high pressure could expand into the region and could provide a break in precipitation later Sunday night into Tuesday. Then, east of deep layered low pressure, another broad area of moisture transport/overrunning and associated rain could overspread the region later Tuesday into midweek. Otherwise, expect seasonally cool conditions during the first half of next week. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... At 06z, VFR conditions and very light rain are occurring at KCHS, KJZI, and KSAV. Model guidance, and upstream observations, both strongly suggest that ceilings will lower into the MVFR and IFR range over the next few hours. IFR conditions are in the TAF's from around 09z and then lingering through late morning. At this time it appears that any significant fog and lowered visibilities will remain inland of the terminals. Ceilings should scatter and lift back to VFR by around midday and remain VFR through the rest of the period. Extended Aviation Outlook: Flight restrictions, mainly in lower ceilings, possible Thursday into Thursday night. Then, VFR through Saturday. Flight restrictions appear likely Saturday night into Monday. && .MARINE... Today through tonight: Expect modest southerly flow by the afternoon with wind speeds topping out around 10 knots. Overnight, winds will remain southerly and pick up a bit, becoming 10-15 knots late. Seas will average 1-3 feet through the period. Thursday: Ahead of an approaching cold front, a tightening surface pressure gradient/strengthening low-level southerly winds probability for Small Craft Advisory wind gusts. Thursday night through Friday night: Even after the cold front pushes through the coastal waters Thursday night, elevated offshore winds will persist through Friday and into Friday night, and some gusts could reach 25 knots, especially beyond 10-20 nm from shore. Saturday: Winds will turn toward the northeast as a wedge of high pressure expands into the region. Winds/seas should remain below SCA levels. Sunday: Expect variable/changeable winds as low pressure passes over or close to the waters. Wind direction/speed and associated seas remain uncertain and will depend on the strength/track of the surface low and the wedge of high pressure. Sunday night and Monday: A cold front is expected to push through the coastal waters Sunday night, and offshore winds/elevated seas could reach Small Craft Advisory levels. && .TIDES/COASTAL FLOODING... New moon and perigee both occur Jan 21. Offshore winds could veer toward the northeast as a wedge of high pressure builds into the region Saturday. Then, low pressure is expected to impact the region Sunday. While the track/strength of the low and associated wind direction/speed remain uncertain, the overall synoptic setup should add to the already elevated astronomical tide levels. Thus, the probability for Minor coastal flooding along the Charleston/Colleton County coasts will increase with the morning high tides this weekend. If heavier rainfall occurs Sunday morning, the potential for poor- drainage area flooding will increase near the coast, including downtown Charleston. && .CLIMATE... Record maximum temperatures for January 19th... KCHS: 78F degrees set in 1950 and previous KSAV: 79F degrees set in 2017 and previous KCXM: 77F degrees set in 1950 and previous && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...BSH SHORT TERM...SPR LONG TERM...SPR AVIATION...BSH/SPR MARINE...BSH/SPR TIDES/COASTAL FLOODING... CLIMATE...