394 FXUS62 KCHS 130823 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 423 AM EDT Wed Jun 13 2018 .SYNOPSIS... A stationary front will dissipate across the region today while a trough prevails inland through Thursday. A southward moving cold front will slowly move through the area Friday and Saturday, dissipating south of our area early next week. && .NEAR TERM /THROUGH TONIGHT/... Today: The forecast area will remain within a baggy mid/upper level trough in the weakness between the ridge near the Four Corners region and the ridge over the Atlantic. At the surface, a weak stationary front will remain near the area, meandering around along the coast and dissipating through the afternoon. Early morning convection looks as though it will be mainly confined to the Charleston County coast, and any lingering boundaries produced by this convection should be enough to keep this area as the focus through the mid to late morning hours. Then as we transition to the afternoon, the focus for convection is expected to shift further to the west and into southeast Georgia. Rain chances increase into the 50-60 percent range during this time and the convection is expected to shift to the east and southeast with time, such that by the evening hours the best chances will be along and south of I-16. Storm motions will be quite slow (less than 10 knots), with precipitable water values in excess of 2 inches. This means locally heavy rainfall will be the main concern for today with almost no severe threat due to the very weak flow through the depth of the atmosphere. High temperatures are expected to reach into the upper 80s for most areas, though hourly temperatures could fluctuate significantly depending on where showers and thunderstorms occur. Tonight: An upstream cold front will begin moving into the Tennessee Valley and the southern Appalachians, which will promote a more uniform southwesterly flow across the forecast area. Evening convection should be mainly confined to southeast Georgia and should dissipate by the late evening. Overnight, the best rain chances are expected to be over the coastal waters with isolated showers and storms possible right along the coast. Overnight lows will only fall into the low 70s. There could again be some patchy shallow ground fog, but not enough coverage is expected for inclusion in the forecast. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... The mid-levels will consist of a weak trough over the Southeast Thursday. Friday the trough begins to shift offshore while a strong ridge builds in from the west. By Saturday the trough axis is off the East Coast while the strong ridge stretches from the Gulf of Mexico northward into the Great Lakes Region. At the surface, an inland trough will prevail Thursday with high pressure far in the Atlantic. A cold front will approach from the north Friday. The front will slowly move southward through our area Friday night into Saturday, eventually becoming located just south of our area late Saturday. The synoptic pattern keeps ushering plenty of moisture into our area through Saturday. PWATs are expected to remain ~2". Though, their are indications they can pool up to 2.25" just ahead of the southward moving front. We have chance POPs Thursday, highest during the afternoon and along the sea breeze. POPs Friday and Saturday are highly dependent on the location of the front. We raised them to likely on Friday to account for the increased lift with the approaching front, but kept them capped at high end chance on Saturday. Though, POPs both days may still be too low. Another factor is the instability and how much is in place with ahead of the front. The models seem to be mixed on how much will be in place Friday, with lower amounts on Saturday. These details will need to be refined further with upcoming forecasts, including severe potential. The main threat now appears to be heavy rainfall and locally gusty winds. Nothing significant to note with the temperatures as daytime highs remain near normal and nighttime lows hover a few degrees above normal. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... A cold front is forecasted to be over or just south of our forecast area Saturday night, bringing unsettled weather to portions of GA. This slow moving front is expected to keep moving south Sunday and dissipate, pushed by high pressure centered off the coast of the Outer Banks. In the wake of this front will be a lower risk of thunderstorms and slightly cooler temperatures Sunday. On Monday and into Tuesday the high is forecasted to move further offshore, allowing a trough to develop inland. This will allow both temperatures and the thunderstorm potential to increase both of these days. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... The biggest concern through the next 6 hours is the potential for stratus at both sites. KCHS has already had some IFR stratus and surrounding observations show that it is still out there. Therefore, will go with TEMPO IFR for a few hours and then prevailing IFR by close to sunrise. At KSAV it will likely take a bit longer for stratus to develop, but have introduced it there in a TEMPO at 10z. Stratus should scatter out and lift by 13z at both sites. Attention then turns to thunderstorm potential. Current thinking is that KCHS will see the best chances in the 14-18z time period and 19-23z at KSAV. Kept TSRA MVFR for now but if direct impacts do occur, brief IFR periods of IFR will be possible. Extended Aviation Outlook: Mainly VFR. Brief flight restrictions are possible in showers and/or thunderstorms, mainly each afternoon and early evening through Saturday. && .MARINE... Today: A weak stationary front is expected to dissipate across the region, with modest southwest flow in the 10-15 knot range expected by the afternoon hours. Seas are expected to be in the 2-3 foot range. The main concern for the coastal water will be in the morning when light winds and very moist conditions could combine to create a favorable environment for water spouts. My midday the water spout risk should be significantly reduced. Tonight: Expect southwest winds mainly in the 10-15 knot range, with some brief periods where speeds could increase a bit. Seas will tick upwards and average 2-4 feet. Extended Marine: Thursday the waters will remain between an inland trough and high pressure in the Atlantic. This synoptic flow will allow southwest winds to prevail. The exception will be during the afternoon near the coast where winds will likely turn south and increase a bit due to the sea breeze. A southward moving cold front will slowly move through the area Friday into the weekend. Winds will transition this weekend with the front, but they will not increase to the point that we would need advisories. The front will dissipate south of our area early next week. Occasional thunderstorms could bring gusty/erratic winds and frequent lightning, especially during the overnight hours through Saturday. && .TIDES/COASTAL FLOODING... The approaching new moon and perigee could produce shallow coastal flooding with the evening high tide. A Coastal Flood Advisory could be needed. The combination of the new moon and occasional onshore winds should allow the evening high tides Thursday, Friday, and maybe Saturday to reach coastal flood advisory levels. Any heavy rain near the times of these high tides will increase the risk of flooding. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...BSH SHORT TERM...MS LONG TERM...MS AVIATION...BSH/MS MARINE...BSH/MS TIDES/COASTAL FLOODING...