Area Forecast Discussion
Issued by NWS Columbia, SC

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000 FXUS62 KCAE 181824 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 224 PM EDT Fri Aug 18 2017 .SYNOPSIS...
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A weak frontal boundary will cross the area overnight and stall over the Coastal Plain through the weekend. Drier air will work into the region providing dry weather Saturday and Sunday for much of the region except the eastern Midlands. Moisture will increase again early next week as an upper ridge builds back over the southeastern states.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Atmosphere is a bit more stable today compared to yesterday due in large part to lower atmospheric moisture. Precipitable water values are quite a bit lower this afternoon around 1.6-1.7 inches compared to Thursday when they were over 2 inches. A subsidence inversion around 700mb was evident on HRRR forecast soundings and current visible imagery showing generally fair weather flat cumulus clouds across the forecast area. Some enhanced cumulus noted over eastern TN into the mountain of NC associated with shortwave energy lifting into the Mid-Atlantic region but that should remain north of our area. Hi-res model guidance continues to show minimal convection over our area through early evening with some storms possibly developing on the front that is approaching from the west during the evening and overnight hours through 06z but mainly focused across the northern Midlands. Will hold on to slight chance pops through the afternoon and chance pops in the northern Midlands this evening before diminishing pops overnight with the loss of daytime heating. Storms that do develop will have the potential to produce strong gusty winds with significant dry air aloft and downdraft CAPE values at or above 1000 J/kg. Skies should clear late tonight behind the front with winds turning more northwesterly albeit light. Overnight lows expected in the mid 70s with some patchy fog possible in the eastern Midlands where moisture may pool a bit ahead of the weak front.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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A weak cold front will stall over the area on Saturday. However, it should be mostly dry as the models have more significant moisture shifted farther east ahead of upper troughing, with little recovery Sunday because of a building ridge. Mid-level temperatures are forecast to remain relatively warm and dry with h5 temperatures around -5 C. There will be a capping inversion that will limit instability and thunderstorm coverage. The slightly drier air should also result in lower heat index values. However, it will remain hot with forecast maximum heat index readings 100 to 105.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/...
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The models show upper ridging building over the region Monday as surface high pressure strengthens over the western Atlantic. Low-level moisture will increase due to a southeast flow off the ocean. The pattern supports partly cloudy skies with a chance of mainly afternoon thunderstorms. Thunderstorms will be most likely across the CSRA and southern portions of the forecast area. Areas north and west of Columbia will have lesser chances. Similar weather is expected Tuesday. Another weak cold front is forecast to approach Wednesday and be in the area Thursday which will bring an increased chance of thunderstorms. The GFS and ECMWF MOS have pops 20 to 30 percent Monday and Tuesday, and 30 to 40 percent Wednesday and Thursday. The MOS supports above normal temperatures lowering to about normal Thursday. Drier westerly flow is expected Friday. Expect maximum heat index values 100 to 105 through the period.
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&& .AVIATION /18Z FRIDAY THROUGH TUESDAY/...
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Generally VFR conditions through the period. Diurnal cumulus clouds will blanket the are this afternoon with isolated showers or thunderstorms developing along a weak frontal boundary crossing the region this evening. Coverage is widely scattered with low confidence in any terminal being affected so not including in the forecast at this time. Winds will be from the southwest 5 to 10 knots through 00z then diminish to less than 5 knots and become light and variable overnight. Winds will pick up from the west around 5 knots after 15z with some diurnal cumulus clouds developing by the end of the forecast period. EXTENDED AVIATION OUTLOOK...Scattered mainly afternoon and evening showers and thunderstorms possible each day. Also, low- level moisture could result in early morning fog and/or stratus.
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&& .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$

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