Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 172320 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 620 PM EST Sun Feb 17 2019 .SYNOPSIS... An unsettled pattern is expected as a series of frontal systems affect the area through next weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 17/23z surface observations show the warm front across Southeast Georgia is beginning to move north. The front should pick up speed over the next few hours as surface pressures continue to fall across the interior and to the north. Nighttime lows (6pm- 6am) will occur over the next few hours before temperatures begin to rise in the wake of the warm front. Expect temperatures to be in the mid-upper 60s by daybreak Monday. Sea fog developing off the Georgia and far southern South Carolina coast will continue to expand over the coastal waters this evening. Some of this could propagate inland across the coastal counties as the warm front lifts north and winds turn more southerly. In fact, there are signals some degree of sea fog could reach as far inland as Walterboro and Moncks Corner by late evening before wind fields begin to pick up in response to strengthening low-level jetting ahead of the approaching cold front. Any inland dense fog should retreat back to the immediate coast during the early morning hours Monday and there could be very little in the way of significant fog over land by daybreak. && .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/... Monday: A weak cold front will be pushing through the area during the morning, then offshore by afternoon. Moisture and large scale forcing seem to be diminishing as this front pushes through. Therefore, have maintained only low end chance PoPs for light precipitation amounts. Despite the front moving through, high temperatures are still expected to be quite mild, around 70, likely helped by a little downslope flow. Monday night: A strong wedge of high pressure develops north of the area with increasing northeast low level winds. Deep layer moisture begins to return/overrun the cooler low level airmass late, but only have slight chance PoPs by late night south of the Savannah River. Lows relatively mild, in the mid to upper 40s north and lower 50s south. Tuesday: A strong wedge of high pressure looks to hold north and east of the area with northeast early, to east-northeast winds late. Deep layer moisture continues to move northward and overrun the lower level cooler air, while a weak coastal trough tries to develop over the Atlantic waters. Models continue to differ a bit on precip. chances, but have continued a slow trend upward from slight chance to chance PoPs during the afternoon. Best chances expected to be well inland and over the near shore waters in the coastal trough. Highs expected to remain cool, in the mid 50s north to around 60 south. Tuesday night and Wednesday: The surface wedge pushes off to the northeast as a weak surface low pass well to the northwest. Deep layer moisture and some upper level forcing should result in scattered to numerous light showers, likely decreasing later in the day on Wednesday. Temperatures Tuesday night in the mid to upper 40s inland, warming to mid to upper 60s north and lower to mid 70s south on Wednesday. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... The warm front will linger north of the area Wednesday night through Friday while a series of upper shortwaves move through. Isolated to scattered showers will remain possible. Temps will be 10-15 degrees above normal due to strong warm air advection. A cold front might sweep through late in the weekend. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... KCHS: IFR cigs will could improve if low-end MVFR by 05z as a warm front lifts north. Risk for IFR cigs will still be present, however. Will carry prevailing IFR through 05z, then TEMPO IFR 09-12z. FROPA looks to occur at 15z and could be accompanied by a band of light rain. VFR will return by early afternoon Monday. KSAV: Low cigs will persist for much of the night. Watching an area of sea fog off the coast. There are signals some of this could spread inland and impact the terminal over the next few hours. Could see vsbys drop as 2 miles before visibilities improve. Cigs should rise to MVFR around daybreak as a cold front approaches. FROPA looks to occur at 15z and could be accompanied by a band of light rain. VFR will return by early afternoon Monday. Extended Aviation Outlook: Monday: Mainly VFR expected. Late Monday night through early Wednesday: Periods of flight restrictions, mainly due to low CIGS and possibly lower VSBYS with fog. Wednesday night through Friday: A return to mainly VFR conditions expected. && .MARINE... Tonight: Sea fog has rapidly developed off the Georgia and far southern South Carolina where coastal webcams show vsbys have dropped below 1 NM. A Marine Dense Fog Advisory has been issued for the Georgia and Beaufort county nearshore zones through 1 AM. The sea fog should expand up into the Charleston County waters and Charleston Harbor later this evening and an expansion of the advisory appears likely. Winds should increase after midnight as low-level jetting intensifies ahead of an approaching cold front. It is unclear how much fog will persist overnight, but given the stable conditions within 10 NM or the coast, the risk for dense fog could linger beyond 1 AM. Monday: No highlights expected as a weak cold front pushes through the waters. Winds southwest at 15 to 20 knots ahead of the front in the morning, veering to northwest 15 knots in the afternoon. Seas 3 to 4 feet, highest beyond 20 nm. Monday night through Tuesday night: Small Craft Advisory conditions expected as a strong high pressure builds north of the waters. Sustained northeast winds will likely increase to around 20 knots with gusts of 25 to 30 knots, with seas building to 5 to 9 feet, highest offshore. Winds may decrease to 15 to 20 knots later Tuesday night, but seas are expected to remain at advisory levels. Wednesday and Thursday: Winds and seas are expected to fall below advisory levels as the surface ridge pushes farther northeast and the low level flow veers to east-southeast on Wednesday and Wednesday night, then south-southwest on Thursday. Sea Fog: Conditions may become favorable for more sea fog Wednesday night and Thursday as the low level flow become southerly, which will help to advect warmer, more moist air northward. && .TIDES/COASTAL FLOODING... Tide levels may reach marginal coastal flood advisory levels during the Monday morning high tide, but winds will not be favorable, then they will be parallel to the coast then offshore by afternoon. By Tuesday and Wednesday, the low level flow is still expected to increase from the northeast, strongest on Tuesday. Tide guidance is still indicating coastal flood advisory conditions for both Tuesday and Wednesday, mainly for the morning high tides. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Dense Fog Advisory until 1 AM EST Monday for AMZ352-354. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.