Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
1242 PM EDT Sat Sep 5 2015
an upper-level low off the Carolina coast will drift west into the
southeastern states this weekend. A back door cold front will keep
the chance for showers and cooler temperatures into early next
week. The upper ridge will try to build back over the area by the
middle of next week along with warming temperatures.
Near term /through tonight/...
a weak backdoor cold front is expected to push across the
southern midlands and csra today providing a focus for convection
once again. An upper level low off the Carolina coast will drift
westward across southern South Carolina into Georgia overnight.
The best instability and convergence should focus highest probability of precipitation in
the southern midlands and csra with lower chances to the northeast.
Cannot rule out the possibility of isolated pulse severe
storms...though the environment does not look as conducive with
less dry air aloft available compared to Friday. Temperatures will
be several degrees cooler than on Friday with maximum temperatures in the
middle 80s to around 90. Overnight lows will be near normal in the
upper 60s to around 70 degrees.
Short term /Sunday through Monday night/...
upper level low is forecast to be centered just to the west of the
csra during the day Monday. This low will continue to slowly
retrograde westward...becoming centered over the northern Gulf late
Monday night. This flow pattern will keep a relatively moist and
deep easterly wind through much of the period. Precipitable water values will
remain high with all the moisture...with readings possibly
approaching 2 inches in places. Do expect some diurnal showers and
thunderstorms to develop in this flow pattern...especially with the
slightly cooler temperatures aloft associated with the upper low. With
plenty of moisture to work with...periods of heavy rain may occur
with any slower moving storms. For the most part have continued
with chance probability of precipitation through the period. At the surface...high
pressure centered across portions of the Middle-Atlantic States will
nudge southward into the region through the period. This will
bring slightly cooler air into the region. This means the
forecast highs are slightly cooler than normal...while overnight
lows will be close to normal for this time of the year.
Long term /Tuesday through Saturday/...
westward and out of the region it is forecast to weaken and
eventually transition more into an open trough across the lower
Mississippi River valley region. Across our area...upper level
ridge that has been over the western Atlantic will push back into
the region. This brings more of a southwesterly flow aloft. The
area will still have good low-level moisture...so do expect to see
scattered afternoon showers/storms through much of the forecast
period. Better chances for organized rainfall may occur late in
the period as upper level energy moves southeastward out of the
plains states. This will deepen the trough across the middle of
the country...eventually pushing the trough towards the
southeastern states by Friday. Best chance for rainfall will occur
Friday through Saturday. Temperatures rise a few degrees in the long
term...but for the most part afternoon highs close to climate
normals...while overnight lows slightly above normal.
Aviation /18z Saturday through Thursday/...
northeast winds 5 to 10 knots across the taf sites as high
pressure ridges in from the north. Moisture and instability
combined with daytime heating will bring scattered convection to
the region this afternoon and evening. Best chance for convection
will be across the csra near a backdoor cold front pushing through
the area. Have not included thunderstorms in tafs at this time given timing and
coverage uncertainty. Models indicate low clouds to develop late
tonight bringing MVFR/IFR conditions to all taf sites around 09z.
Extended aviation outlook...late night/morning fog/stratus
possible...with a chance of showers and possible thunderstorms.