685 FXUS62 KCHS 170748 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 348 AM EDT Tue Apr 17 2018 .SYNOPSIS... High pressure centered to the south will persist through Wednesday. A dry cold front will then pass through Thursday, followed by cooler high pressure through the end of the week. Unsettled weather is expected early next week as low pressure passes to the south. && .NEAR TERM /THROUGH TONIGHT/... Today: After a chilly start with temperatures in the 30s inland, temperatures will modify quite a bit compared to yesterday afternoon given the warmer low-level air mass. Highs should be about 8 degrees warmer than yesterday, reaching the lower 70s most locales except mid 70s near and south of I-16. However, such readings will still be about 5 degrees below normal. The decent pressure gradient will persist given the developing lee- side trough to the northwest and thus it will be breezy again with gusts near 25 mph this afternoon. Tonight: Surface high pressure will be centered over FL as lee-side troughing persists to the north. This will keep a decent low-level gradient in place and with the warmer air mass across the region we think temperatures will be milder than this morning with lows closer to 50 degrees inland with mid 50s closer to the coast. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... Wednesday: Flat ridging will prevail aloft as a progressive closed low and associated short wave trough travel east through the upper Midwest. At the surface we find high pressure from the SW Atlantic into the Gulf of Mexico, as low pressure and its trailing cold front move from the Plains eastward through the day. Considerable dry air, downslope flow will combine with H8 temps and full insolation to boost temps into the mid and upper 80s away from the "cooler" immediate coasts. Deep mixing will tap into 25-30 kt of low level winds to produce a breezy to windy day, and we'll be close to the threshold of needing a Lake Wind Advisory near and along the shores of Lake Moultrie. Wednesday night will be mild with turbulent mixing ahead of the upstream cold front to prevent temps from dropping any lower than the upper 50s-lower 60s most places. Thursday: A phasing of short waves in the northern latitudes will develop into a closed low that spins near the St. Lawrence River Valley and north of the eastern Great Lakes. A widening and progressive long wave to the south of these features over the eastern third of the nation will send a dry cold front through the local area, accompanied by scattered to perhaps occasional broken cumulus and cirriform clouds. Another day with a deep westerly flow and dry air will again allow conditions to warm above normal, but not as warm as Wednesday will be. Yet again we have deep enough mixing to tap into higher winds within the boundary layer, producing another breezy day, and very close to the requirement for a Lake Wind Advisory on Lake Moultrie (mainly near and along the lakeshore). Friday: The closed low aloft will swing off the New England coast and near Nova Scotia and Newfoundland in Canada, while a sprawling Canadian high builds in from the NW. Conditions will be considerably cooler, with H8 temps down around 4-6C or near just the 10th percentile for this time of year. With a N-NE synoptic flow highs will only be 70-75F most places, a little cooler on the coast and near the Santee River. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... Mid and upper ridging will develop across the area into the weekend, as a deep cutoff near the Four Corners at the start of the extended period, reaches into the SE states or Gulf of Mexico early next week. The cyclone aloft will only make it so far east, before it stalls with what appears to b a blocking Rex Block as an anticyclone forms and strengthens to the north of the cutoff low. Surface low pressure will form in response to the low aloft, while a high pressure wedge develops early next week. Considerable upper difluence ahead of the cutoff low, and plentiful moisture advection and convergence from the Atlantic will lead to an increased risk of wet weather late in the forecast period. Daytime highs will be below normal, while night time lows will average near or above normal through the entire period. && .AVIATION /07Z TUESDAY THROUGH SATURDAY/... VFR at KSAV/KCHS through 06Z Wednesday. Main concern will be gusty winds near 20 kt Tuesday afternoon. Extended Aviation Outlook: VFR conditions are expected at both CHS and SAV terminals through Saturday, but with gusty west/southwest winds both Wednesday and Thursday afternoon. && .MARINE... Today and Tonight: Breezy conditions will persist most of the period, especially this morning when cold advection will be strongest. Advisories remain in effect until around daybreak for all waters except Charleston Harbor. Wednesday: A tightening gradient between high pressure to the south and low pressure and a cold front to the NW, aided by a boost from the resultant sea breeze will lead to elevated winds and seas and possible Small Craft Advisory conditions, mainly in Charleston Harbor. Thursday: A cold front will pass through the local waters, but a tight pressure pattern again persists. This will lead to a chance of Small Craft Advisory conditions for not only Charleston harbor, but also over parts of the Atlantic. Friday and Saturday: Continental high pressure on Friday breaks into a separate center to the north of Saturday, leading to veering winds from the NE around to the E through the late week. Wind and seas will likely be near advisory levels on mainly the outer GA waters during this time. Sunday: High pressure begins to relax its influence on the marine area as low pressure forms over the lower MS valley. Onshore trajectories will continue, leading to elevated winds and seas, and perhaps additional advisory conditions. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory until 7 AM EDT this morning for AMZ350- 352-354-374. && $$ NEAR TERM...RJB SHORT TERM...33 LONG TERM...33 AVIATION...33/RJB MARINE...33/RJB