Area Forecast Discussion
Issued by NWS Columbia, SC

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000 FXUS62 KCAE 212258 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 658 PM EDT Thu Sep 21 2017 .SYNOPSIS... Surface high pressure will remain in the region through the weekend. Upper troughing will be over the area through Friday night, which combined with strong surface heating should help support scattered thunderstorms. Upper ridging will begin to push back into the area Saturday and help diminish the thunderstorm chance. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Weak high pressure at the surface will remain over the region through tonight along with a weak upper level trough. Scattered thunderstorms continue across the eastern third of the cwa late this afternoon, with activity expected to once again diminish by Midnight. Overnight lows in the upper 60s to near 70. Patchy fog development possible early Friday morning. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/... The models display surface ridging continuing in the region. Aloft, troughing is depicted with h5 temperatures near -10 C through Friday night. Some weakening of the trough is forecast Saturday with temperatures near -9 C. Instability associated with the upper feature combined with strong surface heating should help support thunderstorms Friday, but expect limited coverage because of shallow moisture and the surface ridging. The thunderstorm chance should further diminish Saturday with less upper support. The guidance consensus supports pops around 20 percent Friday and less than 20 percent Saturday. Expect moderate instability Friday afternoon because of the cold air aloft and strong surface heating with highs in the lower 90s. The NAM displays surface-based LI values -7 to -8. This instability plus dry air in the mid levels aiding downdrafts could help support strong wind with any thunderstorms. Forecast wet bulb zero heights around 10,500 feet indicates possible hail as well. The temperature guidance has been consistent with continued above normal values. && .LONG TERM /SUNDAY THROUGH THURSDAY/... The GFS and ECMWF display surface ridging continuing during most of the medium-range period. Some weakening is noted toward the end of the period ahead of an approaching cold front. The models also exhibit upper ridging during the period. The pattern supports a diminished thunderstorm chance with above normal temperatures. The GFS and ECMWF MOS plus ensemble means support pops 20 percent or less through the period. A weakness in the ridging north of Hurricane Maria plus upper troughing over the Southeast States should steer the storm northward and well east of the forecast area. The models have been consistent with this solution. Please see the latest advisory on Maria from the National Hurricane Center. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... Colliding boundaries and some upper level energy may provide continued impetus for at least isolated convection through this evening into early tonight. Will maintain VCSH/TS for now. Otherwise, will expect skies to become mostly clear, with winds becoming light. Late afternoon dewpoints/crossover temps a little on the low side in the lower to mid 60s. However, some precip or outflow cooling may provide some fog potential. Guidance indicating fog at the fog prone sites AGS and OGB, less so at the other terminals. Slight chance diurnal thunderstorms again Friday, chances may be too low to include mention in the TAFS at this time. EXTENDED AVIATION OUTLOOK...Late night/early morning fog/stratus possible, mainly at the fog prone sites AGS and OGB. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.