409 FXUS62 KCHS 301401 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1001 AM EDT Sat Mar 30 2019 .SYNOPSIS... Warm high pressure will prevail into Sunday. A cold front will then move through late Sunday, followed by a coastal storm which will produce much below normal temperatures and some showers Monday and Tuesday. Warmer and drier high pressure will then build over the region until late week when another cold front could affect the area. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A pronounced vorticity maximum centered just north of KCSG at 30/12z per upper air analysis and GOES-E water vapor imagery will move steadily east today, pushing offshore by mid-afternoon. Extensive mid/high-level cloud decks streaming north ahead of this feature will gradually diminishing in coverage as the shortwave pushes through. This should give way to a good bit of sunshine and the formation of a shallow cumulus by mid-late afternoon which will help drive highs to near 80 across the interior. A robust sea breeze circulation will develop along the land/sea interface by early afternoon and move steadily inland. Any cumulus that develops should scour out in the wake of the sea breeze. Beach temperatures will be limited to the upper 60s to lower 70s. Dry conditions will persist. For the mid-morning update: * Raised afternoon highs by a degree or two across interior Charleston County. * Improved cloud timing slightly based on a blend of the RAP and HREF simulated cloud output. * Increased winds by several knots within the sea breeze circulation. && .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/... Tonight: Sfc low pressure will continue to deepen and organize over eastern Canada. A cold front associated with the low will sweep across the southern Appalachians around midnight. By sunrise Sunday, the cold front is forecast to remain along the Interstate 20 corridor across SC and GA. A few showers will likely develop along and ahead of the front, possibly reaching Jenkins and Allendale Counties by 12Z Sunday. Otherwise, low temperatures are forecast to range from the upper 50s inland to around 60 along the coast. Sunday through Tuesday: Moderate confidence this period. A cold front will be approaching the forecast area from the west early Sunday and then push offshore in the afternoon bringing some showers and possibly a few thunderstorms. The rain should end for most of the area by the evening, although could linger along the GA coast most of the night. Instability will likely be minimal so don't expect severe storms at this time. Cooler high pressure will then build into the area from the north Sunday night as some upper-level energy helps a surface low pressure system develop along the stalling cold front across the northern Gulf of Mexico and/or off the Southeast U.S. coast. There is more confidence now that the low will pass just offshore Tuesday. Although there could be a few showers Monday, especially near the coast, the best rain chances should come later Monday night into early Tuesday when deeper moisture and strong upper forcing move into the area. Rain amounts are a bit uncertain still as the exact track of the low remains elusive. It will also be breezy near the coast beginning late Sunday night. Temperatures look cooler than previously forecast on Sunday given the slightly quicker pace of the front, although could still end up near normal. A drastic cool down is then expected Sunday night through Tuesday due to the chilly high pressure wedge pattern. We trended cooler than MOS guidance as a result with temperatures expected to remain well below normal in the 50s most places during the day, possibly even 40s where rain/clouds are most abundant and/or high pressure is strongest. Temperatures Monday night could dip into the upper 30s well inland but not expecting frost. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... Moderate confidence this period. High pressure will build back into the area from the northwest Tuesday night as strengthening low pressure moves farther away to the northeast. Temperatures will modify through Thursday as the high shifts offshore and a return flow sets up which could also lead to a few showers, mainly near the coast. Rain chances look to increase Thursday night however as another cold front and upper disturbance approach from the west. The front could push offshore Friday night, although this is uncertain. Below normal temperatures should persist through Wednesday before returning back closer to normal later in the week, possibly getting above normal Saturday if the frontal passage is delayed. Some inland spots could dip into at least the upper 30s Wednesday morning and with diminishing winds we could see some frost in the normally colder locales. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... VFR. Extended Aviation Outlook: Restrictions possible late Sunday and Sunday night, then more likely Monday into Tuesday as a cold front and then low pressure system affect the area with low clouds and rain. && .MARINE... Today and tonight: Increased winds to a solid 15 kt with the passage of the sea breeze in Charleston Harbor this afternoon. The rest of the forecast is on track. The marine zones will remain between high pressure to the east and a cold front to the west. This pattern will support steady south winds around 10 kts today, veering from the southwest and increasing to 10-15 kts tonight. Seas will remain between 2-3 ft within 20 NM, 3-4 ft beyond 20 NM. Sunday through Thursday: Southwest winds will begin to increase Sunday ahead of a cold front but will increase more dramatically Sunday night and remain strong into Tuesday as low pressure passes over or just east of the local waters. Small Craft Advisories will be needed Sunday night through Tuesday for the nearshore waters and into Wednesday in the offshore waters. Gale force gusts around 35 knots are also not out of the question Monday and Tuesday, especially in the offshore waters. && .TIDES/COASTAL FLOODING... Tides are expected to be above normal Monday and Tuesday as a coastal low pressure system affects the area causing strong northeast winds at least into early Tuesday before winds shift more offshore as the low passes by to the north. Thus, coastal flooding will be possible in typically vulnerable coastal locales around times of high, especially if moderate to heavy rainfall also occurs during these periods. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$