227 FXUS62 KCHS 152104 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 404 PM EST Tue Jan 15 2019 .SYNOPSIS... Dry high pressure will build from the west and prevail into Thursday. A weak cold front will approach the area Friday, then lift north as a warm front Saturday. A stronger storm system will then impact the area Saturday night and Sunday with much colder temperatures to follow starting Sunday night. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... A weak shortwave will pass over the region this evening. At the surface, high pressure centered to the west will slowly build to the area. We're not expecting any rainfall or sprinkles with the wave. However, it may impact the cloud cover. Satellite imagery indicates clouds have been slower to dissipate than what was expected. We upped the cloud cover, especially this evening, then have it gradually trending down overnight. But the models hint that the coverage may still be higher than what we currently have forecasted. This will be the main forecast challenge. If this occurs, temperatures will need to be raised, especially late tonight. For now, we have clouds scattering out late and lows generally in the mid to upper 30s inland and around 40 degrees at the beaches. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... Quiet conditions Wednesday through Thursday, as a dry west-northwest flow prevails aloft, and high pressure initially centered along the northern Gulf cost slides into the Atlantic the second part of Thursday. PWat less than 1/2 inch and large scale subsidence will support mostly clear/clear conditions Wednesday/Wednesday night. A subtle increase in moisture and forcing from the approach of a 115 to 135 kt upper jet Thursday will lead to increasing high level cloudiness. Downslope flow and considerable sunshine Wednesday will bump temps to the upper 50s and lower 60s, while strong radiational cooling Wednesday night will generate lows mostly in the mid and upper 30s. Warm advection on Thursday will support max temps reaching at least the lower and middle 60s away from the cooling effects of the ocean. Thursday night and Friday: A fast moving short wave will slide by to the north Thursday night, and gives way to short wave ridging or a zonal flow Friday. This will initially push an anemic cold front toward the area, before it stalls or becomes diffuse to the north on Friday. An increase in vertical moisture, with PWat climbing above 3/4 inches and forcing from the upper jet and nearby short wave, might be enough to produce isolated showers, mainly after midnight Thursday night into the early morning hours on Friday. Increasing cloud cover will hold temps about 8-10F higher than the previous night, before warm advection bumps temps into the mid and upper 60s on Friday. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Moderate forecast confidence this period. Surface high pressure will build to the north Friday night as a weak cold front stalls near the SC/NC border before shifting north as a warm front ahead of low pressure near the Mississippi/Tennessee Valleys. The surface low should reach close to Philadelphia early Sunday with its trailing cold front likely reaching inland portions of southeast SC/GA, although there remains a bit of uncertainty in this timing. Although some light showers are possible Saturday as low-level isentropic ascent increases near the warm front, the best rain chances should hold off until Saturday night and Sunday along and ahead of the front when upper forcing peaks. Most locales should see a half inch to maybe 1 inch. Although deep layer shear is strong we don't see a lot of instability so not overly concerned about the severe thunderstorm threat at this point and in fact we don't even have any mention of thunderstorms. After the strong front passes we should see much colder air move into the region with most areas likely well below freezing Sunday night and struggling to warm past the 40s Monday with another cold night on Monday night. Elevated winds Sunday night will lead to wind chills in the teens, possibly nearing Wind Chill Advisory territory. It will also be breezy Sunday through Monday and a Lake Wind Advisory may be needed for Lake Moultrie. Temperatures will stay well above normal ahead of the front at least through Saturday night before falling back quite a bit below normal through Tuesday morning. Some model guidance even suggests some inland areas could get into the upper teens Monday morning. && .AVIATION /21Z TUESDAY THROUGH SUNDAY/... 18Z TAFs: VFR. Extended Aviation Outlook: Flight restrictions expected Saturday night into Sunday with a cold front. Breezy/gusty conditions expected behind the front Sunday. && .MARINE... Tonight: High pressure centered to the west will allow generally N winds ranging from 5-10 kt. Seas will range from 1-2 ft within 20 nm and 2-4 ft beyond. Wednesday through Sunday: No significant concerns through Saturday though conditions will be deteriorating significantly Saturday night and Sunday as a strong cold front affects the area with some heavy showers and possible thunderstorms (mainly near the Gulf Stream). Wind could even gust near gale force across the GA waters beyond 20 nm. Otherwise, Small Craft Advisories are likely for all waters. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM... LONG TERM...RJB AVIATION... MARINE...