Scientific Forecaster Discussion
fxus62 kcae 241816
Area forecast discussion
National Weather Service Columbia SC
216 PM EDT Sat Jun 24 2017
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
Near term /through tonight/...
a shortwave upper trough moving through northern Alabama this
afternoon will progress into North Carolina by Sunday morning.
The trough is spurring a broad area of shower and thunderstorm
development across Georgia and into the northwest half of South
Carolina. Expect this activity to persist the remainder of the
afternoon into tonight. Localized flash flooding will be
possible when thunderstorms train. Activity will diminish
toward Sunday morning.
Short term /Sunday 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
Long term /Monday through Friday/...
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 European model (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 /18z Saturday through Thursday/...
MVFR ceilings and visibilities are likely from 18z to 03z at
taf sites due to showers and thunderstorms. There is a better
chance of VFR conditions after 06z as a cold front continues to
sag southward toward the Georgia/SC coasts.
Extended aviation outlook...no significant aviation related