064 FXUS62 KCHS 090917 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 417 AM EST Sat Feb 9 2019 .SYNOPSIS... High pressure will prevail through the weekend. A warm front will lift north through the area Monday, followed by a cold front late Tuesday. High pressure returns for the middle of next week, before another cold front impacts the area late in the week. && .NEAR TERM /THROUGH TONIGHT/... Today: High pressure will extend across the region through tonight with the surface high evolving into a inland wedge after sunset. The pinched gradient between the developing inland wedge and a subtle coastal trough off the northeast Florida coast will keep breezy to locally windy conditions in place at the coast. Gusts could reach 30-35 mph at times along the beaches, especially from Hilton Head and points south, including Tybee Island. These gusts are just below Wind Advisory thresholds. It will be considerably cooler today with the H8 thermal advection pattern becoming neutral after daybreak. H8 temperatures of 5-7C filtered through a thickening cirrus canopy will only support highs from the upper 50s north to lower 60s south, warmest in the area south of I-16 and west of I-95 in Southeast Georgia. This is ~20F cooler than the high temperatures observed over the past several days. Tonight: The coastal trough well to the south will redevelop off the Georgia and far southern South Carolina coast after midnight as the inland wedge holds. Guidance suggests any isentropic assent atop the wedge will be slow to develop with the bulk of any meaningful lift holding off until after daybreak Sunday. The NAM is certainly the wettest of the various 09/00z global guidance members and brings shower activity to the Georgia coast as early as midnight. The NAM looks overly aggressive in this scenario and is showing a typical bias in bringing rain inland from off the Atlantic way too quickly. None of the other various guidance support rainfall this early, including all of the available HREF members. Will keep conditions rain-free through the overnight period. There will be a large gradient in overnight lows, ranging from the mid 30s far northern portions of Dorchester and Berkeley Counties away from Lakes Marion and Moultrie to the lower 50s along the Georgia coast. Lake Winds: A marginal Lake Wind Advisory remains in place through sunset for Lake Moultrie. Confidence that frequent gusts to 25 kt will occur over the open lake waters is moderate at best given mixing will be curtailed over the cold lake waters and the tightest pressure gradient is forecast to remain displaced to the south. However, there is not enough evidence at this time to justify a cancellation so the advisory will be maintained for now. Northeast winds 15-20 kt with gusts to 25 kt will be maintained with waves 1-2 ft. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... Sunday: The mid-levels will consist of a broad area of high pressure over the Bahamas in the morning while zonal flow prevails over our area. The high is forecasted to move eastward with time while weak ridging develops over the Southeast. At the surface, high pressure will be centered over the Mid- Atlantic States in the morning while a weak trough is just off our coast and a stationary front is spread across FL. The high is forecasted to move offshore while the stationary front lifts northwards with time, merging with the coastal trough and possibly reaching our area late. Moisture will increase across the area, especially overnight. Though, PWATs will only rise a little above 1". The meager moisture combined with the broad area of lift should limit the overall shower coverage. Models generally show showers increasing in coverage with time, especially overnight. Though, their are still some differences on the exact location and QPF. Our blended forecast has them starting over our GA counties during the day, increasing across our entire area by the evening and overnight. QPF may only be a few hundredths. Gusty northeast winds along the coast in the morning should ease during the day. Additionally, the northeast winds and cloudy skies will make it hard for high temperatures to reach the 60 degree mark for most locations. Though, they should make the lower 60s in some of our GA counties. Low temperatures will be above normal. Monday: The mid-levels will consist of a broad area of high pressure east of the Bahamas in the morning and weak ridging over the Southeast. The high will shift eastward with time while a ridge amplifies along the East Coast, partly caused by a strengthening trough in the Plains. The result will be southwest flow over our area. At the surface, a storm system to our west be intensifying as it slowly moves eastward. A stationary front over or just south of our area in the morning will transition into a warm front and lift north through our area during the day, continuing its northward movement into the night. At the same time, a cold front associated with the storm system will be approaching from the west. It is not forecasted to reach our area during this time period. Models do have a small band of higher moisture associated with the front. Likewise, that's where the best shower activity will be. Highest POPs initially start over our GA counties, then trend into SC during the afternoon. Decreasing shower coverage is anticipated overnight, especially in our GA counties, as some drier air tries to build in from the south. Despite the cloudy skies and eventual showers, models show us in the warm sector of the overall storm system. This equates to above normal daytime and nighttime temperatures. Tuesday: The mid-levels will consist of a ridge offshore and a trough over the Plains states. Both features will amplify with time and move eastward. This means the trough should start passing over the Southeast during the evening. At the surface, a warm front north of our area in the morning will be lifting away while a cold front rapidly approaches from the west. The cold front is expected to reach our area during the evening hours. A narrow band of high PWATs ~1.5" are anticipated ahead of the front. This moisture combined with good lift will equate to widespread showers across the area. We have likely POPs, but expect they'll need to be raised as the front's timing gets narrowed down. A brief period of moderate to locally heavy rainfall is a possibility. QPF could be ~0.25". Models do show instability with the front. It's not overly impressive. However, the shear with the front is. We'll certainly have to monitor for any gusty wind potential. The models insist temperatures will again approach record values. This might be a stretch given the timing of the precipitation and the mostly cloudy skies. Regardless, temperatures will be well above normal. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... A cold front will quickly move through the region Tuesday night, allowing showers to decrease. High pressure returns with dry conditions Wednesday into Thursday. Models then show another intensifying storm system bringing potential impacts to our area on Friday. However, these impacts will depend on the exact track of the storm, which may be just to our north. && .AVIATION /07Z SATURDAY THROUGH WEDNESDAY/... VFR. Gusty winds will impact the terminals next 24 hours, greatest gusts occurring 15-21z. Extended Aviation Outlook: A warm front moving through the area could bring brief flight restrictions Sunday night into Monday night. Flight restrictions are expected with the passage of a cold front Tuesday into Tuesday night. VFR Wednesday. && .MARINE... Today: Hazardous conditions will persist across the coastal waters today as a pinched gradient between inland high pressure and a weak coastal trough off the northeast Florida coast holds. Expect northeast winds of 20-25 kt with gusts to 30 kt nearshore waters and 25-30 kt with gusts to 35-40 kt over the Georgia offshore waters. Small Craft Advisories remain in force for all nearshore legs and Charleston Harbor with a Gale Warning for the Georgia offshore zone. The risk for gales will be highest beyond 40 NM where mixing will be enhanced in a region of water sea surface temperatures. Seas will build to 5-8 ft nearshore and 9-11 ft offshore. Tonight: Elevated winds and seas will remain in place as the coastal trough redevelops off the coast. Gales should end over the Georgia offshore waters by sunset with both winds and seas remaining well into Small Craft Advisory thresholds for all legs except Charleston Harbor. Northeast winds will average 20-25 kt with seas subsiding to 4-7 ft nearshore and 8-9 ft offshore. Sunday through Wednesday: A complex weather pattern is expected. A coastal trough will be over or near us Sunday. A stationary front across FL will shift northward, becoming a warm front and merging with the coastal trough. This front will lift north of our area on Monday, followed by a cold front late Tuesday. High pressure is expected midweek. Small Craft Advisories will gradually expire Sunday as conditions improve. However, another round of advisories are possible Tuesday and Tuesday night for some of our waters due to winds and seas. Sea fog: There could be some potential for sea fog Monday night into Tuesday in advance of the front. Though, the increasing wind speeds and marginal dew points may limit its potential. && .FIRE WEATHER... An enhanced risk for wildfires will occur across the inland portions of the coastal counties of Southeast South Carolina and parts of Southeast Georgia from late morning into the late afternoon. Expect wind gusts to peak 25 mph in this area with RH values dropping to about 22-25% for about 3-5 hours. 10-hr fuels in this region have dried to 7-10% per RAWS/WFAS analysis which is just above critical levels. State and federal users indicate fuels are a bit wetter at the immediate coast, so the risk there will be less. Farther inland, lower wind speeds will occur which will mitigate the risk somewhat. A Fire Danger Statement will be issued for Charleston, Tidal Berkeley, Coastal Colleton, Beaufort, Jasper, Effingham, Inland Chatham, Inland Bryan and Inland Liberty Counties Noon through 8 PM. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...Lake Wind Advisory until 4 PM EST this afternoon for SCZ045. MARINE...Small Craft Advisory until 1 PM EST Sunday for AMZ350-352-354. Gale Warning until 7 PM EST this evening for AMZ374. Small Craft Advisory until 7 PM EST this evening for AMZ330. && $$