Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
300 am EDT Wednesday Aug 5 2015
Hot and generally fair weather expected to continue today. A weak
surface trough will remain over the central Carolinas and Georgia
today. An upper trough and increasing moisture will lead to better
precipitation chances Thursday and Friday...followed by expectations
of drier air returning for the weekend. A front may affect the
region early next week.
Near term /through tonight/...
Upper ridge over the west Continental U.S. With weak upper trough east Continental U.S.. a
weak surface trough appears to have settled into the central
Carolinas and Georgia...where it appears it will remain nearly
stationary today. A relatively dry atmosphere remains in place
over our forecast area (fa). A little better moisture exists to
our south and west. As surface wave near the Outer Banks moves
farther NE...lower level flow expected to become more SW and
increase a little...and may allow a little better moisture to
shift towards our southern and western forecast area. In addition...appearance
of weak upper impulse traversing the region today...followed by a
little stronger impulse this evening and early tonight...mainly
north. Think slight chance...to possibly low end chance...mainly
diurnal probability of precipitation plauisible. Weak to moderate instability today...with
slightly better shear but still relatively low. Forecast soundings
indicate plenty of middle level dry air...and a deep low level
inverted v. If a strong storm does develop...it would have
potential for damaging winds with strong dcape around ~1500 j/kg
and windex value of 72.
Though we appear to lose the low level downslope flow today that
contributed to the hot maximum temperatures Tuesday...guidance pointing to
maximum temperatures near or just above 100 for the normally famouslyhot
locations. Due to good insolation and dry soil conditions...will
go with slightly higher than guidance numbers for maximum
temperatures...expected to result in triple digits many areas. Mixing
down of dewpoints during the afternoon appears to keep heat index
values below our heat advisory criteria.
Short term /Thursday through Friday night/...
Upper ridge center will shift east from The Four Corners region to
the Southern Plains...with mean upper long wave trough remaining
over the east Continental U.S.. significant middle level shortwave trough will
approach the region Thursday...with latest model runs trending a
little faster with it...and move through Friday...with significant
increase in atmospheric moisture prognosticated as moisture from the Gulf
shifts north ahead of it. GFS projected precipitable water values
increase to around 2 inches. So...probability of precipitation will increase Thu/Fri.
Long term /Saturday through Tuesday/...
Upper trough and best moisture appear to shift offshore...with a
drier atmosphere for our forecast area...Sat/sun. Models indicate upper ridge
will shift back to the west some...with upper trough deepening over
the east Continental U.S....early to middle next week. This along with some expected
increase in moisture and indications of a possible front suggests
trend towards increasing probability of precipitation. Generally accepted blend of guidance.
Aviation /07z Wednesday through Sunday/...
expect mainly VFR conditions through the taf period.
Drier air was noted over the region early this morning compared to
24 hours ago and model guidance is showing a low level jet which
is confirmed by the VAD wind profile product. Therefore not
anticipating any fog/stratus issues like we experienced Tuesday
Strong heating and convergence into the heat trough in the
forecast area may help support thunderstorms Wednesday
afternoon...but with continued shallow moisture coverage should be
isolated. The thunderstorm chance is too low to include in the
terminal forecasts at this time.
Extended aviation outlook...restrictions possible in late
night and early morning fog and afternoon and evening