210 FXUS62 KCHS 200326 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1026 PM EST Tue Jan 19 2021 .SYNOPSIS... High pressure will prevail through Wednesday. A cold front is forecast to move through the region on Friday, followed by high pressure for the weekend. A stronger cold front is expected to affect the area early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... The leading edge of the stratocumulus and altocumulus clouds are starting to develop and/or advance into the forecast area ahead of the weak cold front. Cloud cover will steadily increase from west to east through the overnight, and this will create a rather atypical diurnal temperature curve. Temps will still have time to radiate a bit more early on, before temperatures steady off or even rise a tad once the thicker clouds move in. The combination of these clouds and a 30-40 kt low level jet that moves in after 06Z will result in the mildest night for many places in a week. Previous discussion... No significant changes with the early evening update other than to open a larger range of temps from some far inland locations to the immediate coast. 342 PM discussion... The surface high will gradually push offshore tonight. A shortwave trough will pass by to the north, pushing a dry cold front through the area overnight. This evening, the boundary layer may partially decouple, which along with mostly clear skies should allow temperatures to drop quickly. Late this evening and overnight, however, surface winds will pick up and some mid and high clouds will overspread the area. Temps will thus only slowly fall after midnight or perhaps remain nearly steady. Lows will be in the low to mid 40s. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... Wednesday: A shortwave will pass to our north during the morning. It's forecasted to become a strengthening trough off the coast in the afternoon, moving further away with time. Weak ridging will pass to our north overnight, with west northwest flow prevailing overhead. Surface high pressure will prevail over the Southeast, bringing dry conditions. Expect mostly sunny skies during the day, with increasing high clouds from the west overnight. Temperatures should be a few degrees above normal during the day and near normal at night. Thursday into Friday: West northwest flow prevails in the mid- levels on Thursday, becoming westerly on Friday. At the surface, high pressure centered over the Southeast Thursday morning will shift over Southern FL and the Bahamas Thursday afternoon, then move further away into Friday. Meanwhile, a front will approach from the west Thursday, then spread across our area on Friday. Decent moisture is expected with the front, with PWATs approaching 1.5" by Friday. As for the shower potential, models have come into better agreement overall. Thursday morning is expected to be dry, with showers developing/overspreading the area from the west Thursday afternoon and evening. POPs really ramp up overnight, especially across our GA counties. By Friday showers will overspread the entire area. We have categorical POPs for most locations, but expect these to be raised more if forecast trends persist. Rainfall amounts should generally be 0.25-0.5" into Friday. As for temperatures, warm air advection and some breaks in the clouds should yield high temperatures in the low to maybe mid 60s Thursday. The rainfall on Friday will limit them to the mid 50s to around 60 degrees. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Building high pressure and drier conditions are expected Sunday/Monday in the wake of a cold front. A slightly stronger cold front will approach the area Tuesday. Temperatures should return to near normal early in the week with the cooler air mass over the area, before they begin to warm prior to the approach of the front. Showers associated with the front are likely to effect the region late Monday night through Tuesday night. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... VFR through 00Z Thursday with some gustiness to the W and NW winds on Wednesday at both KCHS and KSAV Extended Aviation Outlook: VFR through Thursday. A cold front will bring flight restrictions Thursday night into Friday night. && .MARINE... Overnight: Guidance has been consistently showing wind gusts of 25-30 kt late tonight into Wednesday morning across the Charleston County Atlantic waters. After coordinating with WFO Wilmington, we have raised a Small Craft Advisory for AMZ350 from 08-16Z Wednesday. The other waters could briefly reach advisory conditions due to wind gusts, but for now we held off on issuing an advisory elsewhere. Expect elevated winds Wednesday morning with gusts to 20 kt. Gusts could approach 25 kt across the easternmost portion of the Charleston waters. But the areal coverage is small enough and the time period short enough where we won't need a Small Craft Advisory. If observations or model runs increase winds a bit, then an Advisory will be needed. Winds are expected to ease Wednesday afternoon into the overnight period. Though, they'll increase again Thursday as a cold front slowly approaches from the west. Gusts should approach 25 kt Thursday night for portions of the waters and Small Craft Advisories will probably be needed, mainly for the SC waters and the GA waters beyond 20 nm. The front is expected to move offshore late Friday, with winds/seas lowering. A secondary surge in the winds is expected Saturday as the front moves further offshore. Conditions should remain below Small Craft Advisory criteria, however. Winds/seas are expected to gradually decrease/subside Sunday. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory from 3 AM to 11 AM EST Wednesday for AMZ350. && $$ NEAR TERM... SHORT TERM...MS LONG TERM...BRM AVIATION... MARINE...