Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
710 PM EDT Wednesday Sep 17 2014
high pressure will bring dry weather and below normal
temperatures to the area Thursday through the weekend. Another
cold front will bring a chance for showers and thunderstorms early
Near term /until 6 am Thursday morning/...
update this afternoon to raise probability of precipitation in the southeastern counties
as convection developed along a surface convergence boundary aided
by shortwave energy moving through the base of the upper trough.
Moderate instability in place provided the fuel for storms to
become severe with some reports of quarter size hail and trees
downed. Storms are beginning to weaken and shift towards the coast
and expect a general downward trend in activity through the
evening as the trough axis pushes east of the area. Expect fair
weather later tonight with the cooler and drier air working into
the area from the north. Low cloudiness and possibly fog
expected to develop late tonight.
Short term /6 am Thursday morning through Friday night/...
the upper trough over the eastern Continental U.S. Is forecast to deepen
with a cut off low developing over southeast Georgia on Friday. 500 mb
temperatures are forecast as low as minus 11c. Weak instability is
forecast for the midlands and csra with moderate instability
farther south beneath the upper low. A large area of surface high
pressure crossing southern Canada and the Great Lakes will move
east to the North Atlantic coast. All models forecast the high
pressure to ridge into our area bringing northerly winds and cold
air advection through Friday night. Expect several hard to time
weak short waves to cross the are in northwest flow aloft.
Moisture appears to be shallow...so kept the forecast dry...but
increased cloud cover. The 12z models have begun to increase probability of precipitation
across the area both Thursday and Friday. Given shallow moisture
and lack of Omega...will not follow.
High temperatures will be in the upper 70s to lower 80s with
overnight lows in the lower to middle 60s.
Long term /Saturday through Wednesday/...
both the GFS and European model (ecmwf) indicate weak cyclonic upper flow across the
northern tier states Saturday with a with cutoff low off the
southeast coast. The trough is prognosticated to deepen over the eastern
Continental U.S. Through early next week. Wedge conditions will persist across
the forecast area Saturday and Sunday with the next cold front
ejecting The Wedge as it moves into the region Monday. This will
keep dry conditions over the region through Sunday with low chance
probability of precipitation Monday and Tuesday as the front crosses the forecast area.
Given moist onshore flow and above average probability of precipitation shown by the GFS
ensembles...will keep low chance probability of precipitation for Wednesday, also.
Temperatures through the long term will be below normal.
Aviation /23z Wednesday through Monday/...
widely scattered showers/thunderstorms continue over portions of the
southern midlands and csra at this time. Will keep mention of thunderstorms and rain
at ags and dnl until around 01z. Some convection may threaten ogb
over the next couple of hours but will amend taf as necessary.
Expect convection across the area to diminish after sunset.
Lingering low level moisture plus dry air aloft and light surface
winds will provide threat of fog/stratus late tonight/early Thursday
morning. Latest guidance suggesting low ceilings the main threat...with
some visibility restrictions. A slow return to VFR expected by Thursday
Extended aviation outlook...late night and morning fog/stratus
possible through Saturday.