Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
622 am EDT Monday Sep 1 2014
surface high pressure will extend into the forecast area from the
Atlantic through the middle of the week. A persistent upper ridge
will help maintain the hot temperatures.
Near term /through tonight/...
low-level moisture has increased and expect much of the forecast
area will have stratus and fog early this morning. Heating and
mixing should dissipate the fog by 900 am. The surface ridge will
remain east and south of the forecast area with weak Lee-side
troughing in the area. The upper ridging will continue but the NAM
especially shows a middle-level shortwave trough moving into the
ridge over the forecast area late this afternoon and evening. The
combination of strong heating...convergence into the Lee-side
trough...and an increase of moisture and instability associated
with the middle-level shortwave trough should support thunderstorms
but there is more than normal uncertainty with the coverage. The
Storm Prediction Center WRF shows scattered coverage in the afternoon becoming widespread
during the evening. However...the NAM and GFS MOS indicate low
probability of precipitation with the consensus around 20 percent. The upper-level
feature does not appear particularly strong on the water vapor
imagery. Also...storm motion should be slow limiting coverage
because of the upper ridging. We maintained slight chance probability of precipitation.
The slow storm motion and precipitable water near 2 inches should
support locally heavy rain. The models indicate moderate to
strong instability. The NAM has surface-based Li/S near -7. The
thunderstorms may contain strong winds as well. We forecasted
temperatures a few degrees above the guidance because of the
recent cool bias.
Short term /Tuesday through Tuesday night/...
surface ridging should continue east and south of the forecast
area. Expect weak Lee-side troughing in the area. Strong heating
and convergence into this feature should help support
thunderstorms...but continued upper ridging should limit coverage.
Also...the surface feature should remain weak. The NAM and GFS
MOS have low probability of precipitation with the consensus around 20 percent. It will
remain hot. Used the warmer temperature guidance based on recent
Long term /Wednesday through Sunday/...
the GFS and European model (ecmwf) show a weakening front stalling before reaching
the area during the middle of the week. The models show another
front may reach the area late in the medium-range period. The
models indicate upper-level ridging continuing. The
GFS...ECMWF...and ekd MOS show above normal temperatures with probability of precipitation
20 to 30 percent through the period.
Aviation /10z Monday through Friday/...
some convective debris clouds linger from precipitation yesterday.
Still a potential for fog until around 13z this morning especially
at ags...but stratus may be possible at other taf sites as well. Fog
and stratus which develop will mix out by 13z with diurnal cumulus
from midday through the end of the period. Potential for convection
at the taf sites from 18z Onward remains too low to include in tafs
at this time. Some MVFR fog possible early Tuesday morning at ags and ogb.
Extended aviation outlook...restrictions possible in late night
and early morning stratus and fog. Scattered mainly afternoon
showers and thunderstorms Tuesday through Friday.