Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 202058

Area Forecast Discussion
National Weather Service Columbia SC
458 PM EDT Wed Sep 20 2017

Surface high pressure will remain in the region during the rest
of the week. Upper troughing will be over the area through
Friday, which should help support scattered thunderstorms. Upper
ridging will begin to push back into the area Saturday and help
diminish the thunderstorm chance.


An upper trough will remain over the Southeastern US through
tonight with weak high pressure ridging into the forecast area
at the service. Regional radar as of 18Z shows isolated showers
and thunderstorms mainly north of Columbia. GOES-16 satellite
imagery shows precipitable water values ranging from 1.4 inches
west to 1.6 inches east across the area. LI values are around
-5 to -7. Westerly downsloping winds are working against convective
 development by drying the atmosphere. There is also not much
 of a trigger, nor divergence aloft. As such, have continued to
 indicate only a slight chance of thunderstorms through the
 evening hours. DCAPE values are around 700 to 1000 J/kg, so if
 a storm does get going, strong winds may be possible. With
 sunset and loss of heating, potential for convection will
 quickly diminish with partly cloudy skies overnight. High
 temperatures are on track this afternoon and are expected to
 max out in the lower 90s. Overnight lows in the middle to upper


The models display surface ridging continuing in the region.
Aloft, troughing is depicted with h5 temperatures -9 to -10 C.
Instability associated with the upper feature combined with
strong surface heating should help support thunderstorms, but
expect little coverage because of shallow moisture and lack of a
well defined surface convergence feature. The guidance consensus
supports pops around 20 percent. Expect moderate instability.
The NAM has surface-based LI values -6 to -7. This instability
plus dry air in the mid levels aiding downdrafts could help
support strong wind with any thunderstorms. The temperature
guidance has been consistent with continued above normal values.


The GFS and ECMWF display surface ridging continuing in the region
through the medium-range period. Upper troughing is depicted
weakening or being suppressed farther southwestward. Most GFS and
ECMWF ensemble members indicate very low pops through the period.
The ensemble mean plus an average of the GFS and ECMWF MOS support
pops 20 percent or less. The guidance shows continued above normal

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 most reliable models have
been consistent with this solution. Please see the latest advisory
on Maria from the National Hurricane Center.


VFR conditions expected outside of diurnal convection and early
morning fog.

An upper trough moving through the area will bring a slight
chance of showers and thunderstorms to the terminals through
this evening. The chance is too low to include in current TAF
issuance, but will amend based on radar trends through the
afternoon and evening. The chance of showers and storms will
diminish tonight with the loss of heating. Models indicate
potential for fog/stratus development late tonight into early
Thursday morning. Have continued to indicate MVFR/IFR fog
development at fog prone AGS/OGB 09Z through 12/13Z. Diurnal
convection will be possible again on Thursday although the
chance is too low to mention in current TAF issuance.

EXTENDED AVIATION OUTLOOK...Late night/early morning
fog/stratus possible each morning, mainly at AGS and OGB.
Scattered diurnal convection possible Thursday and Friday.




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