Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 202329

Area Forecast Discussion
National Weather Service Columbia SC
729 PM EDT Fri Oct 20 2017

Fair weather will continue through early Sunday. A cold front
will bring a chance of showers and thunderstorms Monday and
Tuesday, followed by much cooler temperatures for mid to late
next week.


Dry high pressure will ridge into the forecast area from the
north. Wind will be light and variable with a weak pressure
gradient along the ridge axis. Expect temperatures a few
degrees higher than yesterday because of air mass modification.
Strong net radiational cooling will occur again tonight. Most
of the MOS guidance plus in-house radiation scheme support lows
in the middle 40s to around 50. The cooling and some recovery of
low-level moisture may help support areas of stratus and fog
during the early morning hours. The threat will be greatest near
bodies of water. We forecasted just patchy late night fog
thinking it will remain limited because of the dry air mass.


Strong upper ridge will remain over the SE CONUS Saturday, with
surface high pressure centered over the Mid Atlantic coast,
providing warm and dry conditions. The upper and surface ridges
will shift to our east offshore by late Sunday ahead of an
approaching upper trough and surface front. Low level flow to
gradually veer to ESE/SE and pick up some Atlantic moisture,
with indications of showers possible by afternoon mainly S FA/


Upper trough to shift east into the central CONUS Sun nt into Mon
with cut off low developing over the Lower Mississippi valley.
Upper low to open and shift to the ENE Mon nt and Tue ahead of
deepening upper trough. Surface low to develop along the Gulf
coast and track NE into the Ohio Valley and southern
Appalachians. Increasing moisture and dynamics along and ahead
of the upper trough and surface front sets the stage for
increasing chances of showers and thunderstorms. Some slight
timing differences and uncertainties with the timing of the
system, but latest model consensus has highest POPs generally in
the late Monday into early Tuesday time period. Indications of
moderate to strong wind fields and shear, but only weak
instability, provides some severe threat but with limited
confidence at this time.

Models also continue to indicate a significantly deepening upper
trough over the E CONUS behind this system, with indications of
much cooler air coming in Wednesday, with breezy conditions
possible. Despite drier air entering the region behind the
system Tue nt and Wed, indications of strong upper lift, and
some instability associated with very cold temps aloft, with the
next upper trough Wednesday could possibly provide a few
showers, although dry low level air and downslope flow could
allow virga. Model consensus indicates a slight chance.

Fair and cool late week. Some model differences on position of
high center and therefore some uncertainties on extent of
radiational cooling conditions for Thu/Fri mornings. Too early
to speculate on frost potential but will continue to monitor.
Next system to come in next Sat or Sun, beyond the current
forecast period.


High confidence in VFR conditions through much of the period
with the exception of possible brief fog/stratus at favored
AGS/OGB during the predawn hours.

Dry high pressure continues to dominate over the region tonight
and Saturday with an upper ridge aloft. Winds have gone calm
with sunset this evening and will remain calm overnight.
Nocturnal cooling and recovering dewpoints may support isolated
fog late tonight. Crossover temperatures down into the mid 40s
so do not anticipate dense fog development but will include
brief MVFR vsbys at AGS/OGB with possible IFR vsbys at AGS due
to river valley fog.

Light winds pick up by 15z around 5 knots from the east.

may occur in stratus and fog during the early morning hours
Sunday. A frontal system may bring widespread restrictions in
showers late Sunday into Tuesday, with thunderstorms possible
Monday and Tuesday.




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