567 FXUS62 KCHS 060905 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 405 AM EST Fri Dec 6 2019 .SYNOPSIS... High pressure will move away today, with a stronger high to build from the north tonight and prevail through the weekend. A warm front will lift north of the region Monday, before a cold front sweeps through the area late Tuesday. Strong high pressure will then return Wednesday through Friday. && .NEAR TERM /THROUGH TONIGHT/... Pre-dawn: Skies have been mainly clear overnight with some thin high clouds over GA and patchy mid level clouds across our northwest zones. Strong radiational cooling has lead to temps in the lower to mid 30s inland northwest zones with readings dipping toward the mid 30s inland from I-95 in Southeast GA. Shallow ground fog appears to be common along coastal SC zones prior to sunrise. Today: A very progressive pattern both at the surface and aloft across the southeast states. A short wave near the Red River region of TX/OK pre-dawn is forecast to race ESE and slowly dampen, reaching GA early this evening. Hallmarks of this upper level disturbance will be an increase in layered clouds across our forecast region today with chances for late afternoon showers mainly to the north of I-16 in GA. Along the northern half of our SC zones, models indicate a quick window where upper forcing and deeper 850-500 MB moisture co-exist a couple hours around sunset. We have scattered showers in the forecast across the Charleston Tri-County region during this period with light rainfall amounts generally less than a tenth of an inch. Elsewhere, low level moisture lacking but we could see spotty showers just about anywhere as upper difluence spreads over the region later today. Temps a bit on the tricky side with the timing for the cloud cover. We still allowed readings in the upper 60s to near 70 degrees today before mid clouds thicken late. Tonight: The disturbance aloft will shift quickly offshore with surface high pressure building from the north overnight. There will be some lingering mid level clouds through the night while lower levels tend to dry further after midnight. There could be some patchy fog along coastal areas or where and light rains fell but nothing significant anticipated. Low temps should average out in the lower to mid 40s from north to south. && .SHORT TERM /SATURDAY THROUGH MONDAY/... Saturday: A zonal west to northwest flow will develop aloft, as surface high pressure initially over the Ohio Valley and eastern Great lakes traverses east through the day. The high will extend south as it builds overhead, and becomes sandwiched between two weak areas of low pressure; one a few hundred miles off the coast and another in the northern Gulf of Mexico. The air mass is void of any deep moisture, and that along with the lack of forcing should keep us rainfree. There's enough insolation and downslope flow above the boundary layer to support max temps in the lower and middle 60s inland from the coast. Lows Saturday night will be close to climo, as the high to the north strengthens further and develops into an inland wedge over the Southeast. North and northeast breezes through the period will increase to between 20 and 25 mph at times, especially along the coastal corridor as the gradient tightens between the inland high and a baroclinic zone offshore. Sunday: Even though the parent high will pull off the coast of New England, the inland wedge will intensify as an inverted trough or warm front sharpens off the coast. Moisture steadily increases, and as isentropic ascent strengthens and we are nearby to the offshore trough, we look for isolated to perhaps scattered showers near and east of I-95 in South Carolina. Considerable moisture is trapped beneath the wedge inversion and with neutral or weak warm advection, temps will be several degrees cooler than on Saturday. Those gusty northeast breezes will again prevail between the inland wedge of high pressure and the offshore trough. Monday: While there is a zonal west-southwest flow aloft, at the surface the pre-existing trough/warm front will have lifted to the north. The local region will become situated between a huge oceanic high that extends across Florida into the Gulf, and an upstream cold front that trails from a low in the western Great Lakes region to southeast Texas. The best chance of showers will be off to the north- northeast near the warm front and to the distant west-northwest in association with the cold front. Impressive warm advection will occur as H85 temps peak at 11-12C or between the 75th and 90th percentile for this time of year. So despite plenty of cloud cover, max temps will climb far above normal, with a huge range from the cooler coast to the warmer inland sections. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... The mid and upper trough will amplify to our west early next week, allowing for a cold front to approach from the west late Tuesday, which will likely pass through Tuesday night. There remain enough timing differences between the global models to not show anything higher than chance PoP ahead of the front, but higher chances will be required at we draw closer to the event. Any t-storm risk is too low to include this far in advance. Confidence is excellent that it'll be unseasonably warm, with H85 temps as great as 12-13C Tuesday. Behind the cold front a large and robust high pressure system with dry and colder weather will dominate the local vicinity Wednesday and Thursday, before it gives way to another upstream cold front late in the week. An extended period of breezy to windy conditions will prevail through the period with large pressure rises and a tight gradient around the high. && .AVIATION /09Z FRIDAY THROUGH TUESDAY/... VFR. Risk for shower impacts will increase in the late afternoon and early evening at KCHS. We maintained VCSH from 21z to 01Z/07. Cigs will also become established, roughly 4-6kft. Extended Aviation Outlook: The potential exists for flight restrictions late tonight into Saturday morning before strong high pressure builds in from the north. Another round of flight restrictions is possible Saturday night into Sunday as a wedge of high pressure exists across the area. Additional sub-VFR weather could occur late Tuesday as SHRA develops in association with a cold front next week. && .MARINE... A weak pressure pattern across the waters today. Winds speeds mainly 10 kt or less with a good amount of directional variability. Seas will continue slight, in the 1-2 ft range. Tonight, weak winds in the evening should pick up a bit late as high pressure to the north begins to build in. Around daybreak on Saturday, NNE winds may be up as high as 15 kt with seas increasing to 2-4 ft, highest beyond 20 NM. Saturday through Sunday; Conditions will steadily deteriorate across the local waters as high pressure builds from the north and develops into a wedge across inland areas of the southeast. At the same time there will be the gradual formation of a nearby trough or warm front that strengthens later Saturday night and Sunday. The resulting packing of the isobars between these two systems will lead to the raising of Small Craft Advisories. Since this won't happen until late in the 3rd period of the forecast, we have opted not to hoist the advisory just yet. Nevertheless, mariners can expect N-NE winds as high as 20-25 kt and gusty, with the resulting seas building to as high as 6 to 8 ft. Monday through Wednesday: The warm front offshore will pass to the north early Monday, is replaced by extensive Atlantic high pressure into early Tuesday, before giving way to a cold front late Tuesday. behind that front will be another strong area of continental high pressure that returns. Additional Small Craft Advisories are possible. Sea Fog: Conditions still point to at least a chance of sea fog on Monday as temps and dew points climb greater than the underlying waters. Should this occur the most likely time frame would be Monday within a favorable S-SW fetch and before winds increase too much. Confidence is not yet supportive of adding mention to the forecast, nor to the Hazardous Weather Outlook. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...33 LONG TERM...33 AVIATION...33 MARINE...33