Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 250246
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
1046 PM EDT Sat Jun 24 2017

.SYNOPSIS...
A slow moving cold front will be in the region through Monday.
Showers and thunderstorms will be associated with the front.
Drier and cooler weather will follow the front by the middle of
next week.

&&

.NEAR TERM /UNTIL 8 AM SUNDAY MORNING/...
Convection has greatly diminished over the CWA during the last
few hours as the low level atmosphere has stabilized
considerably due to the loss of daytime heating, as well as some
additional cooling from earlier rains. There is still enough
moisture around to maintain some light clusters of showers over
the next several hours, but the significant convection is over,
so I have taken thunder out of the forecast.

The remainder of the changes to the forecast grids were cosmetic
in nature to keep up with current temp trends, but are generally
insignificant in the big picture of tonight`s forecast.

&&

.SHORT TERM /8 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Frontal boundary will be slowly sinking south through the area
on Sunday. Some question as to how far south it will be during
the morning hours and where it might be when convection
initiates from heating. Should be a strong gradient in
precipitable water values across the forecast area with values
around 1.5 inches northern and western Midlands increasing to
near or above 2 inches in the southeastern Midlands. Drier air
will be working into the area from the northwest through the
day but it may be slow and will carry a gradient in pops from
slight chance northwest to high chance in the southeastern
parts of the forecast area. Debris clouds from convection today
may limit initial heating and instability on Sunday but expect
convection to develop in the vicinity of the boundary across
the southeastern Midlands and shift southeast through the
afternoon. Temperatures will be slightly cooler Sunday compared
to today but still in the upper 80s to around 90 degrees.

Cooler and drier air will filter into the region Sunday night
ending precipitation chances and supporting overnight lows in
the 60s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Reasonable agreement among the medium range models regarding
the overall pattern during the extended forecast period which
should support generally cooler and drier conditions.

The upper level pattern on Monday will feature a broad trough
across the eastern half of the country with a ridge over the
intermountain west and along the west coast. The cold front
that pushed through the area will be stalled offshore as high
pressure and northerly flow dominate across the region with
dewpoints dropping into the 50s to lower 60s. Atmospheric
moisture will be unseasonably low with precipitable water
values below an inch resulting minimal to no instability.

The broad upper trough will amplify a bit late Monday night and
Tuesday with shortwave energy diving across the Ohio Valley and
Mid- Atlantic region which will bring another surge of cooler
and drier air to the forecast area Tuesday night. There is some
uncertainty with how much moisture will be available to
interact with the shortwave and whether or not it will be
enough to produce precipitation. The ECMWF is more aggressive
with better moisture and higher pops compared to the
GFS/Canadian. Will continue with previously dry forecast which
is also in line with WPC. The cooler and drier weather will
continue through mid week with surface high pressure in control
at the surface and northwesterly 500mb flow becoming more zonal
on Wednesday and Thursday.

Differences become more pronounced late in the period. The
upper ridge over the western Atlantic builds back over the
southeastern states Thu/Fri with increasing low level moisture
Fri/Sat as the surface high shifts offshore and a moist
southerly flow returns. The GFS is depicting a digging trough
over the upper midwest and Great Lakes region Fri/Sat with
precipitable water values increasing back to around 2 inches
while the ECWMF is less amplified with that feature, keeping a
stronger ridge over the southeast with less deep moisture
available. Will carry low pops Fri/Sat for mainly diurnal
convection at this time. Temperatures through the period will
be near normal Monday then below normal Tue/Wed and returning
back to near or above normal by the end of the extended period.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Low confidence forecast overnight with a cold front moving into the
area.

Line of showers associated with a cold front is expected to cross
the TAF sites in the 03Z-08Z time-frame. Models are inconsistent on
timing and extent of CIG/VSBY restrictions. Should see deterioration
to MVFR conditions as showers ahead of the front moves into the TAF
sites. The Cold front will slowly cross area overnight into Sunday
morning...then stall over the eastern Midlands or Lowcountry of SC.
Have indicated fog at all sites during the early morning hours given
abundant low level moisture and near calm wind. Should see VFR
conditions returning to all TAF sites in the 12Z-14Z time-frame.
Could see afternoon convection develop at OGB given the proximity to
the frontal.

EXTENDED AVIATION OUTLOOK...No significant restrictions
expected.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.

&&

$$AVIATION...99



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