Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
243 PM EDT Thursday Jul 10 2014
a surface trough and an approaching frontal boundary will provide
increased chances of showers and thunderstorms across the area
today. The weak front will push into the area on Friday and
stall...eventually becoming diffuse this weekend. Another upper
trough and approaching front will bring increased chances for rain
again early next week.
Near term /through tonight/...
regional radar early this afternoon shows numerous showers and
thunderstorms across Georgia and up through the western Carolinas.
Showers and thunderstorms have also begun to pop up across the
midlands. Expect coverage to increase through the late afternoon
and early evening hours.
18z laps sounding shows moderate instability present this
afternoon with precipitable water values near 2 inches. The
additional atmospheric moisture results in a lower level of free
convection and shallower and less pronounced low level inverted v
on model forecast soundings...and lower windex values as compared
to yesterday. However...moderate instabilities could still provide an
isolated severe wind gust threat. Main concern will be locally
heavy rain and isolated flooding potential given high precipitable water values.
Cannot totally rule out probability of precipitation overnight with a boundary in the
area so will hold on to probability of precipitation all night though gradually lowering
them towards the predawn hours. Temperatures are on track this
afternoon. Still expect temperatures to maximum out in the upper 80s
to lower 90s. Temperatures will struggle to fall tonight under
mostly cloudy skies and elevated dewpoints...with lows expected in
the lower 70s.
Short term /Friday through Friday night/...
the frontal boundary will move into the forecast area and will
weaken and become stalled over the midlands as the upper trough axis
shifts overhead. The axis of highest precipitable water values also
shifts toward the coastal plain by Friday. By late Friday some drier
air will build into the region from the west as a west to east
gradient in precipitable water sets up with values close to 2 inches
in the eastern midlands and down to around 1.5 in the western
midlands. This will support higher probability of precipitation in the east closer to the
better moisture and the frontal boundary. Temperatures will
again be near climatology in the lower 90s.
Long term /Saturday through Thursday/...
on Saturday the upper flow becomes more zonal with a bit drier
airmass in place as precipitable water values fall below 1.5 inches across most of
the area. The atmosphere becomes less unstable as upper heights
attempt to build over the region. Continued to lower probability of precipitation across the
forecast area but continuing to show a gradient with probability of precipitation higher in
the southeastern midlands. Temperatures will rebound with highs in
the middle 90s...although it will be slightly cooler in the eastern
midlands. Sunday appears to be mainly hot and dry but a typical
Summer time diurnal thunderstorm is not out of the question during
the afternoon. Chances for afternoon thunderstorms are higher
on Monday with the upper ridge centered over the deep south ridging
eastward over the area atop a shallow moist boundary layer with
southerly flow around the Bermuda high. Temperatures back above
normal sun-Tuesday with highs in the middle to upper 90s. A deep closed
upper low is forecast to dig southward into the Great Lakes region
Monday into Tuesday resulting in low pressure tracking across the
Ohio Valley. A cold front will move southeastward into the forecast
area on Tuesday and stall over the region on Wednesday. Higher probability of precipitation
warranted for Tuesday-Wednesday with the approaching front. Precipitable water values rise
back above 2 inches during this time supporting a heavy rain threat
as well as increasing the instability of the atmosphere. Possible
severe weather Tuesday or Wednesday cannot be ruled out.
Aviation /18z Thursday through Tuesday/...
VFR conditions expected for a majority of the taf period. Restrictions
possible in thunderstorm activity and early morning fog.
A frontal boundary slowly moving toward the area along with a
moist atmosphere and daytime heating will result in likely chances
of shower and thunderstorm activity late this afternoon through
early tonight. Current regional radar loop early this afternoon
shows numerous showers and thunderstorms stretching from
southwestern Georgia up through the western Carolinas. Expect this
activity to continue to make its way into the midlands and csra
this afternoon and evening in addition to activity that develops
along the sea breeze. The two areas could converge over our
forecast area....appearing to provide good confidence of sh/thunderstorms and rain
affecting the terminals...mainly during the late afternoon and
evening hours. Due to uncertainty in exact timing and
coverage...have continued to convey threat with a vcsh group from
18z to 02z...with an embedded tempo thunderstorms and rain from 21z to 24z to
highlight best timing threat.
After diurnal convection dissipates...fog may develop late tonight
into early Friday morning. Have introduced MVFR visibilities at
all sites toward daybreak Friday morning with improvements after
13z. Calm winds and low level moisture overnight support fog
development as well as the persistence forecast and model
guidance. Cloud cover will likely be the limiting factor.
Extended aviation outlook...
scattered afternoon/evening thunderstorms.