Area Forecast Discussion
Issued by NWS Columbia, SC

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000 FXUS62 KCAE 241008 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 608 AM EDT Wed May 24 2017 .SYNOPSIS... Several waves of low pressure moving along a frontal boundary stalled near the forecast area will bring periods of showers and thunderstorms to the region through tonight. A cold front will finally be moving east of the region Wednesday night, with drier and cooler air taking hold by the end of the week. && .NEAR TERM /THROUGH TONIGHT/... Early morning analysis reveals surface low pressure over southern Indiana with a cold front extending southwestward through the Tennessee Valley to the western Gulf coast. Another weaker nearly stationary boundary was located near the forecast area but is subtle and diffuse. Sounding analysis indicates the mid levels have dried a bit since Tuesday afternoon but abundant low level moisture remains in place. Regional radar showing some scattered convection lifting northeastward from central Georgia into the forecast area ahead of a weak northeastward lifting shortwave trough. Expect scattered convection to continue lifting into the forecast area through the early morning hours but then may see a bit of a lull for a few hours in the wake of the passing shortwave. More widespread convection is expected this afternoon and evening as another surge of deep moisture moves over the area with backed south to southeasterly low level flow in response to deepening surface low pressure over the Tennessee/Ohio Valleys. Precipitable water values will push back up close to 1.75 inches and warm layer cloud depth will be greater than 10kft supporting efficient rain processes and continuing the flood threat. Therefore will continue to carry the Flash Flood Watch already in effect through 8pm tonight. Severe weather is also possible with strengthening mid level flow and the nose of a 130 knot upper jet pushing into the region during peak heating this afternoon. Diffluent 500mb flow will also provide large scale lift combined with moderate to strong instability leading to possible damaging wind and hail threat, and tornadoes cannot be ruled out although that risk is lower. Expect convection to develop over central GA and spread northeastward into the forecast area this afternoon and continue through the evening until a cold front off to the west pushes into the region and shifts the deeper moisture to the east overnight. SPC has expanded the slight risk area to encompass all of the Carolinas and most of Georgia into Florida and MOS guidance severe pops are quite high, over 50 percent. Will carry categorical pops across most of the area this afternoon into early evening with pops decreasing overnight from southwest to northeast behind the front. Temperatures today will be highly dependent on cloud cover and therefore confidence is low but think the eastern Midlands could see some temps around 80 to lower 80s while the remainder of the region remains in the 70s. Overnight lows tonight will be dictated by cool advection behind the front and we should see lows ranging from the upper 50s western Midlands and upper CSRA to lower 60s eastern Midlands. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... The upper trough axis will swing through the forecast area on Thursday with a pocket of very cold 500mb temperatures at -20C which is quite cold for late May. Expect the cold temperatures aloft will result in scattered showers with steep mid level lapse rates and could even see a bit of graupel with some of the stronger cells. By late afternoon the cold pool will have shifted east of the forecast area and precipitation chances should diminish along with cooler, drier air building into the region. Highs on Thursday will be limited by cloud cover and weak cool advection. Overnight lows Thursday night will fall into the 50s. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Dry and fair weather expected to close out the week with surface high pressure building over the area with generally zonal westerly or northwesterly flow at 500mb. Temperatures will be slightly below normal on Friday in the lower 80s but will quickly warm back above normal on Sat/Sun with southerly flow returning and weak upper ridging building over the area. The next weather system will impact the forecast area on Sun/Mon as a deep trough dives southeastward into the middle of the country and 500mb flow veers to the southwest allowing moisture to increase again over the area. The combination of weak shortwave energy and increasing moisture will warrant small chance pops Sunday into Monday. && .AVIATION /10Z WEDNESDAY THROUGH SUNDAY/...
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Widespread stratus in place, with IFR CIGs. Will expect IFR CIGs to continue into mid morning, then a gradual diurnal CIG improvement during the day. Otherwise, main focus will then shift to shower and scattered thunderstorm activity this afternoon and early evening, some possibly severe. Bulk of moisture to shift out of the region tonight, with drier air filtering in along with some wind expected to preclude restrictions. EXTENDED AVIATION OUTLOOK...Scattered showers and a few thunderstorms possible Thursday afternoon, mainly north. Breezy conditions expected Thu.
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&& .HYDROLOGY... Significant rainfall over the past few days has resulted in runoff into the mainstem rivers. Additional rainfall is expected today and tonight, therefore over the next several days we will see rises in rivers and streams across the area which could result in river flooding. Additional rainfall and flood potential will continue to be closely monitored. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...Flash Flood Watch through this evening for GAZ040-063>065-077. SC...Flash Flood Watch through this evening for SCZ015-016-018- 020>022-025>031-035>038-041. && $$

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