Area Forecast Discussion
Issued by NWS Columbia, SC

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000 FXUS62 KCAE 201918 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 218 PM EST Fri Jan 20 2017 .SYNOPSIS... A very active weather pattern expected to bring several rounds of showers and storms to the region over the weekend with severe weather possible. A deep upper low pressure system will move over the area Sunday night and Monday followed by a couple of days of high pressure and dry weather early next week. Above normal temperatures early in the period then cooler late week. && .NEAR TERM /THROUGH TONIGHT/... Temperatures once again have risen above guidance with warm advection over the forecast area in the wake of a passing warm front earlier. Skies have been improving allow for more sunshine and warmer temps. Adjusted max temperatures to the mid/upper 70s this afternoon and cannot rule out a new record high at Columbia with the old record at 76 last set in 1890. Shallow low level moisture in place may still support an isolated shower or two this afternoon but no widespread rain is expected through evening but will hold on to a slight chance pop. Southwesterly flow aloft later tonight associated with upper trough over the middle of the country will allow another shortwave lifting northeastward from the gulf coast to approach the area by dawn Saturday. Precipitable water values will surge again as values rise over 1.25 inches after 06z and support an increase in pops through the early morning hours from southwest to northeast, especially in the CSRA. Will reflect a gradient in pops from southwest to northeast. Abundant low level moisture overnight will support stratus development with most guidance suggesting low clouds developing during the 06-09z time frame which will limit radiational cooling and keep overnight lows mild in the 50s. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... There is a risk of severe thunderstorms over the weekend with several rounds of convection moving through the area. A warm front should be in area Saturday and Saturday night as strong moisture flux and isentropic lift develops with deep southwest flow aloft. Higher theta-e air will advect north into the region during the day Saturday and air mass will become increasingly unstable. Strong upward vertical motion early afternoon across the Southeastern States associated with strong upper level divergence ahead of deepening low pressure system in the Plains. Deep layer shear increasing with helicity possibly maximizing in the west Midlands and Piedmont during the afternoon as suggested by NSSL WRF model. High resolution models point to organized convective system moving through the region during the late morning through early afternoon. Convection in southeast Georgia and Florida may cut off moisture advection into SC/East central Georgia. But continued categorical pops and mild temperatures. There may be a lull in the thunderstorms during Saturday evening period. Another round during the late overnight and early Sunday period possible as deepening low pressure approaches from the west. The main event may develop Sunday afternoon as anomalously deep upper low moves into the lower Mississippi valley. although dry slot may develop early in the day...this may result in strong heating and increasing instability. Global models...EC/GFS show deep surface low moving through the Upstate region. Strong instability/deep moisture and strong deep layer shear supports threat for severe thunderstorms across the area. Tight surface pressure gradient supports gusty winds especially in the afternoon and evening. The main severe weather threats will be damaging winds with bow echoes and isolated tornadoes along quasi-linear convective lines. Followed the WPC rainfall forecast although trended slightly higher given strong south moisture flux into the area. Heaviest amounts Saturday night and Sunday. Forecasted weekend totals of 2 to 3 inches. Elevated threat for localized flooding although convection should be moving rapidly through the area in waves. && .LONG TERM /MONDAY THROUGH FRIDAY/... The GFS and ECMWF display the upper low beginning to lift northeast of the region Monday. Wrap-around moisture and instability associated with the low supports a continued chance of showers. Dry ridging should dominate Tuesday with an approaching cold front Wednesday. The models show the front in the area Thursday. Moisture appears limited with front mid to late week. Model differences late in the period but trending cooler. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... High confidence in VFR conditions through the evening hours followed by deteriorating conditions during the predawn hours Saturday. Lower clouds have dissipated in the wake of a warm front that crossed the area earlier. Southwesterly to westerly winds around 10 knots will continue through the afternoon then become light and variable with a predominant southwesterly direction overnight. Abundant low level moisture will support redevelopment of stratus and fog during the predawn hours Saturday and supported by most of the guidance. Bring MVFR cigs after 07z with a further reduction to LIFR cigs by 09z-11z all terminals with possible IFR or lower vsbys. More uncertainty on when or if conditions improve after 12z Saturday as an upper disturbance moves into the region from the southwest with rain overspreading the terminals after 15z. Thunder may be possible towards the end of the forecast but not included at this time. EXTENDED AVIATION OUTLOOK...Showers...and associated restrictions... are likely Saturday through Monday as several waves of low pressure cross the region. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$

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