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Area forecast discussion 
National Weather Service Columbia SC
1017 am EDT Wednesday Aug 20 2014

Synopsis...
drier air and a building upper ridge just to our west will reduce
thunderstorm chances through Friday...and lead to hotter high
temperatures. An approaching cold front and increasing moisture
will increase the thunderstorm chance over the weekend.

&&

Near term /through tonight/...
this morning/S analysis showed surface ridging continuing to our
south with weak troughing in the forecast area. There was 850 mb
moisture with dew point temperatures near 12 c. It was relatively
dry above this level. There was 500 mb cold advection with
temperatures -7 to -8 c upstream in Georgia and Alabama. The water
vapor imagery indicated a shortwave trough along the Appalachians.
The stronger lift associated with this feature was supporting
thunderstorms well north of the forecast area. The high-resolution
models display just isolated thunderstorms in the forecast area
this afternoon with the more significant development upstream in
the mountains likely associated with the shortwave trough and
differential heating. The models show these thunderstorms
diminishing as they move into the forecast area this evening. The
forecast of just slight chance probability of precipitation still appears on track because
of shallow moisture and little convergence into the weak surface
feature.

Forecast sounding indicate an inverted-v profile and moderate
instability. Damaging wind could possibly occur with any
thunderstorms. The temperature forecast is on track with highs in
the middle 90s.

The thunderstorm chance should further diminish overnight with the
loss of heating and middle-level shortwave ridging. Nocturnal cooling
with dry air aloft and light wind should help support areas of fog
toward sunrise. The temperature guidance was consistent with lows
in the lower and middle 70s.

&&

Short term /Thursday through Friday/...
upper ridge continues centered to the west of the area. Models
suggest low level warming through the period. Temperatures likely
near 100 degrees. Guidance indicates dew points mixing down into
the middle to upper 60s across the northern and western counties to
near 70 across the southeast midlands. This should keep heat
indices just below our heat advisory criteria of 110f. Only slight
chance of showers/thunderstorms expected due to drier air and building
ridge aloft.

&&

Long term /Friday night through Tuesday/...
upper ridge to our west with upper trough and closed low to our
NE...providing a northwest flow aloft for our forecast area. Some timing
uncertainties...but models suggest a back door front will move
down the East Coast...reaching our forecast area some time this weekend. This
would increase probability of precipitation along and south of the boundary...and lead to
cooler temperatures north of it. Will maintain trend in the ongoing
forecast of probability of precipitation trending higher and temperatures trending lower during
that time.

&&

Aviation /14z Wednesday through Sunday/...
expect mainly VFR conditions through the period.

The latest analysis shows surface ridging to our south with weak
troughing in the forecast area. Strong heating plus some support
associated with the surface feature and a middle-level shortwave
trough could help cause thunderstorms. However...moisture is
shallow and convergence into the surface feature should remain weak.
Much of the lift associated with the middle-level shortwave trough
will stay north of the area. Expect just isolated thunderstorm
coverage this afternoon and evening with the chance too low to
include in the terminal forecasts at this time. The isolated
coverage is supported by the high resolution models. Forecast
soundings indicate an inverted-v profile and moderate instability.
Therefore...very strong wind may occur near any thunderstorms.

The thunderstorm chance should further diminish overnight with the
loss of heating and middle-level shortwave ridging. Nocturnal cooling
with dry air aloft and light wind should help support areas of fog
toward sunrise. Most of the NAM and GFS MOS indicate MVFR or IFR
fog with the greater restrictions at the River Valley terminals of
ags and dnl.

Extended aviation outlook...MVFR or IFR conditions possible in late
night and early morning fog through the period. Isolated afternoon
and evening thunderstorms may also bring restrictions.

&&

Cae watches/warnings/advisories...
SC...none.
Georgia...none.
&&

$$

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