Area Forecast Discussion
Issued by NWS Columbia, SC

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000 FXUS62 KCAE 232159 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 559 PM EDT Sun Apr 23 2017 .SYNOPSIS... An approaching low pressure system will slowly cross the region tonight through Monday night bringing showers and thunderstorms. Dry weather and above normal temperatures will return by Wednesday as high pressure takes control. && .NEAR TERM /THROUGH TONIGHT/... Latest analysis continues to show a nearly stationary front extending from joust south of Augusta to Orangeburg to just south of Myrtle Beach. Closed upper low has developed over northern Alabama with surface lows over northern and east central Georgia. Scattered showers and thunderstorms have developed across the Midlands, and will increase in coverage this evening. There is the possibility of isolated supercells tonight with moderate instability and strong mid level cooling. A squall line type feature is expected push across the region between 10 PM and 5 AM. A small tornado threat also exists given the increased helicity values in vicinity of the frontal boundary. SPC has the area outlooked in a slight risk for severe weather. Precipitable water values peak overnight with anomalously high values close to 1.7 inches and with the slow movement of the convection and orientation which may favor some training there is the threat of heavy rainfall and possible isolated flooding, certainly in the urban areas and other typical low lying locations. SREF and GFS ensemble guidance suggest 48hr mean total rainfall 2-2.5 inches with some higher totals as high as 4 inches possible. A flash flood watch has been issued for the entire area from this evening through the day Monday. WPC has part of the area outlooked in a slight risk of excessive rainfall. There continues to be a great contrast in temperatures on either side of the stationary front this evening. North of the front, temperatures range from the upper 50s over the extreme north to the lower 70s in the central Midlands, while south of the front, temperatures have warmed into the mid 80s. Overnight lows tonight will remain above normal but will feature a gradient from the mid 50s western Midlands and upper CSRA to mid 60s eastern Midlands. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... The closed upper low to the west will shift eastward across Georgia to off the southeast coast Monday into Monday night bringing the coldest 500mb temperatures (as low as -18C) over the forecast area creating steep lapse rates. Moderate instability is forecast on Monday and the axis of highest moisture will pivot over the Midlands and keep chances of rain high. Heavy rain will remain a threat across the northern and eastern Midlands with training convection likely. Could see strong storms once again. SPC has the central and eastern Midlands outlooked in a marginal risk. Extensive clouds and rain will hold temperatures in the mid 60s northwest to mid 70s southeast. The surface low and upper low will lift northeast of the area Monday night and allow for cool advection resulting in overnight lows in the mid 50s. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Generally fair weather and a return to well above normal temperatures expected by the middle of the week. An upper level ridge will traverse the forecast area on Wednesday with southerly low level flow which will support warm advection. A weakening upper trough lifting northeast from the Mississippi Valley into the Ohio Valley Wednesday night into Thursday will push a weak cold front into the area by Thursday night into Friday morning bringing a low chance for rain. The front will become diffuse Friday into the weekend as the upper ridge builds back over the southeastern states. Increasing moisture and instability will bring another chance for diurnal convection Sunday. Temperatures during this period will be well above normal with highs in the mid 80s to around 90 degrees with lows in the 60s. && .AVIATION /22Z SUNDAY THROUGH FRIDAY/... A nearly stationary front is currently draped across the CSRA and southern Midlands. Scattered showers and thunderstorms have developed across the area and coverage will increase this evening. A squall line is expected to cross from west to east between 02Z and 08Z with heavy rain and strong wind gusts. MVFR ceilings in between showers, with IFR restrictions likely in rain through Monday. EXTENDED AVIATION OUTLOOK...CIG restrictions continuing Monday night/Tuesday morning. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...Flash Flood Watch through Monday evening for GAZ040-063>065- 077. SC...Flash Flood Watch through Monday evening for SCZ015-016-018- 020>022-025>031-035>038-041. && $$

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