Area Forecast Discussion
Issued by NWS Columbia, SC

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000 FXUS62 KCAE 290808 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 308 AM EST Sun Nov 29 2020 .SYNOPSIS... An approaching warm front will provide increasing chances of rain late this afternoon and evening. The warm front will move north through our forecast area (FA) tonight, followed by a cold front moving through Monday morning. Expect showers and some thunderstorms with this system. Drier air and increased winds expected Monday behind the cold front. Significantly cooler air will then filter into our region through Wednesday. The air mass will begin to modify Thursday and Friday, as moisture begins to move back into our region Thursday night through Friday night. Another cold front will bring a return to cooler and drier conditions by Saturday or Sunday. && .NEAR TERM /THROUGH TONIGHT/... Widespread fog continues to blanket most of the forecast area and therefore have issued a dense fog advisory through 14z. Thought the thicker high/mid clouds arriving may help improve visibilities but that has not been the case. Surface high pressure centered over West Virginia continues to ridge down across the southeastern states with a stalled front extending across central Florida westward to a weak surface low off the southeast TX coast. 500mb analysis reveals a deep closed upper low along the TX/OK border with moist southwesterly flow across the Gulf Coast states. Current precipitable water values are relatively low around a half inch across the forecast area. However, the southwesterly flow ahead of the approaching upper trough will combine with increasing southeasterly low level flow off the Atlantic through the day resulting in PWATs rising to between 1.25-1.5 inches by 00z Monday which is 200-225 percent of normal. As high pressure shifts eastward off the coast and the surface low over the western Gulf of Mexico lifts northeastward through the day, isentropic lift will increase over the forecast area from midday through the early evening hours as a weak inverted trough along the coast lifts northward. This will provide likely to categorical pops during the afternoon and evening hours especially across the eastern and central Midlands, shifting northward into the Pee Dee and northern Midlands this evening. Temperatures today will be slow to rise due to abundant cloud cover and the development of rain this afternoon. Expect highs today to generally be in the lower to mid 60s. Tonight: The upper trough will lift northeastward into the southern Appalachians tonight with the surface low also lifting northeastward to near the TN/NC/SC border area by 06z. The warm front to our south will lift northward and isentropic lift north of the front producing moderate rainfall will then shift north of the forecast area overnight into North Carolina which may bring a brief break in the rain, especially across the eastern Midlands as forecast by the hi- res CAMs. A surge in moisture advection ahead of the surface low and associated cold front will push PWAT`s to near 1.5 inches and 250 percent of normal during the 03z-09z time frame. There is expected to be a broken line of convection along and just ahead of the cold front lifting northeastward into the forecast area during the 06z- 12z time frame. This is a very dynamic system with strong jet dynamics present and an 850mb jet around 50-60 knots which will provide the potential for damaging wind gusts with stronger storms that may occur. The limiting factor regarding severe weather potential is instability. The NAM is more aggressive in showing surface based CAPE trying to work into the area just ahead of the cold front compared to the GFS but both are not showing very much so think the severe threat is limited. However, given the strong wind fields, any storms that develop will have potential to produce damaging wind gusts and isolated tornadoes cannot be ruled out in a brief 2-3 hr window just ahead of the front where whatever instability is present will be best. QPF has been trending downward on the past several model runs, but it should be noted that the models struggled with the past 2 precipitation events under forecasting them and the moisture associated with each system. Expecting generally less than an inch of rain with this event but cannot rule out some locally higher amounts. Lows tonight will be driven by the location of the front and cold advection behind it but have overnight lows ranging from the lower 50s west to upper 50s east. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... The cold front, and associated band of showers and some thunderstorms, will move east through our FA early to mid Monday morning. Weak instability but strong wind fields will provide a continued possibility of severe weather Monday morning. Upper low expected to cut off over the Midwest Monday while surface low will intensify and move rapidly to our NE. Pressure gradient between the low to our NE and surface high to our west expected to result in breezy west winds Monday. A lake wind advisory may be required Mon/Mon nt. Best cold advection appears will be behind a secondary front late Monday and Monday night. Upper trough to move through our region Tue/Tue nt. Models indicate any associated moisture/lift to remain to our north. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... Surface high pressure will build in for Wednesday and Thursday. Some airmass modification expected Thursday as a weak shortwave ridge moves overhead. SW flow aloft expected late Thursday and Friday as upper low cuts off over the Plains and moves east into the Miss valley. Some timing differences with the next system, with GFS indicating moisture return and isentropic lift as early as Thursday night, while EC holds it off towards Friday or Friday night. Cold frontal passage expected over the weekend to bring in drier and cooler air again under possibly breezy conditions. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... High confidence in LIFR/IFR restrictions through 09z or so with some brief improvement expected after that into the early afternoon but then restrictions return for tonight. Widespread LIFR fog impacting all terminals except OGB to start the forecast period. Some thicker high and mid level clouds will move over the area by 08z-10z which may improve vsbys due to warming surface temps but confidence is limited in that scenario so will show that improvement in a tempo group. A deep upper trough and associated front will approach from the west this afternoon. Ahead of this system, southeasterly flow will increase today allowing Atlantic moisture to stream over the region and expect MVFR cigs to spread northwestward over the terminals during the late morning into afternoon. An inverted trough along the coast will lift northward and bring scattered showers to parts of the central and eastern Midlands so will include VCSH at OGB after 16z and CAE/CUB after 19z. More significant rain is expected to develop by 00z across the region as a warm front sets up to our south and increasing isentropic lift will result in lowering cigs and development of widespread rain with MVFR/IFR vsbys expected. Winds will generally be light and variable through 15z then increase to around 5 to 7 knots from the east through the afternoon before diminishing again around 00z. EXTENDED AVIATION OUTLOOK...Restrictions likely to continue into Monday morning as a low pressure system moves through the region. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...Dense Fog Advisory until 9 AM EST this morning for GAZ040- 063>065-077. SC...Dense Fog Advisory until 9 AM EST this morning for SCZ016-018- 020>022-025>031-035>038-041-115-116. && $$

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