Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 240534

Area Forecast Discussion
National Weather Service Columbia SC
134 AM EDT Mon Jul 24 2017

Upper level ridging will continue to weaken across the area as
the upper level trough digs over the eastern US. However. a
Bermuda high will provide very warm and humid conditions
through Monday with scattered afternoon and evening showers and
thunderstorms. A weak cool front will stall over the area
Tuesday, then move southward into southern Georgia on Wednesday
before dissipating, providing somewhat cooler weather and a
continued threat for scattered thunderstorms. High pressure will
become re- established for the end of the week.


Strong thunderstorms moved through the area late in the
afternoon and evening. Satellite and radar trends suggest
continued weakening during the late evening as the storms move
to the south. Storms produced damaging winds and flooding. 2 to
4 inches rain fell in downtown Columbia.

Lingering showers could continue through much of the night, then
will end during the early morning hours with some mid and upper
level debris cloudiness through daybreak keeping low temperatures
in the mid to upper 70s for most locations. Low level jet should
limit fog late tonight although stratus possible.


The forecast area will remain on the western edge of the Bermuda
high through Tuesday night, while heights aloft slowly drop as a
longwave trof becomes established over eastern North America.
This combination will lead to hot afternoons with max temps
generally in the lower to mid 90s, and maximum heat indices a
little above 100. The combination of developing steep low level
lapse rates each afternoon and weak vorticity aloft will lead
to scattered afternoon and evening convection. PWs will range
from 1.8 inches to 2.2 inches across the CWA, so any slow moving
convection could dump some locally heavy rain in spots.

Min temps will remain quite warm with lows in the mid to upper
70s most places.


On Wednesday, a weak front will slowly slide through the CWA as
a small area of low pressure develops off of the South Carolina
coast and moves to the northeast. It`s main impact will be to
dry the air out a little bit Wednesday night and Thursday, but
max temps on Thursday afternoon will still be in the 90s as an
increase in sunshine will offset any weak cool advection that
tries to set up. Thursday will also see the lowest chance for
afternoon and evening convection for the week.

By Friday, the main global models begin to diverge with details,
but the overall pattern indicates a digging shortwave will move
into the southeastern states on Friday. This will cause an
increase in the deep southwesterly flow, allowing moisture to
quickly return in the form of clouds and scattered convection,
especially during the second half of the day. The weekend
contains a lot of uncertainty as the GFS shows a rather strongly
amplified pattern for july with a significantly deep trough
carving out over the southeastern states, while the ECMWF is
much more progressive with the digging shortwave on Saturday and
instead is more focused on the next shortwave, which is in the
7-10 day period and not part of this package. I have gone for
generally unsettled weather due to the mean trof, without
concentrating too much on the individual shortwaves. This means
slightly above normal chances for rain and slightly below
normal afternoon temps due to increased cloud cover.


Thunderstorms threat has diminished but scattered showers are
still possible through the night. Increased moisture will also
cause MVFR/IFR ceilings at times through morning. Fog appears a
lower threat than stratus due to low level jet, but with
rainfall cant rule out visibility restrictions, especially at
AGS. Cumulus will redevelop during the late morning hours
through the end of the period as another round of convection is
expected Monday afternoon.

EXTENDED AVIATION OUTLOOK...Increasing confidence in
restrictions in mainly afternoon/evening thunderstorms through
Wednesday. We could also see some morning cig restrictions from
stratus. The convection looks to decrease on Thursday, but
should pick back up again by Friday.




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