Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
251 am EDT Wednesday Apr 1 2015
a cold front will push south of the forecast area early today. The
high pressure center behind the front will briefly ridge into the
area today and tonight. The high will be off the coast Thursday
with an onshore flow into the forecast area. A warm front will
also be just south of the area Thursday.
Near term /through tonight/...
the backdoor front will push south of the forecast area early
today. Convergence ahead of the front may help support
showers but deeper moisture is suppressed south of the area. Radar
trends support just scattered showers in the extreme south part
early this morning. Further drying will occur behind the cold
front later this morning with rising 500 mb heights today. We will
get off to a relatively warm start because of mixing associated
with the cold front. The temperature guidance was close with highs
in the lower and middle 70s north to near 80 south.
It will remain dry tonight with surface high pressure centered in
eastern North Carolina. The 500 mb ridge will extend through the area.
Used the guidance consensus for the low temperature forecast.
Short term /Thursday through Thursday night/...
high pressure off the coast will direct an onshore flow into the
forecast area through Thursday night. The models display a warm
front in Georgia with isentropic upglide in the forecast area.
There should also be moisture and instability associated with a
middle-level shortwave trough shown by the NAM and GFS Thursday
afternoon or evening. The NAM and GFS MOS support probability of precipitation of 30 to 40
percent with the greater chance Thursday afternoon ahead of the
shortwave trough and near the time of maximum heating. There may
be enough instability for thunderstorms especially in the south
part where the NAM lowers surface-based Li/S to near -4. Used the
guidance consensus for the temperature forecast.
Long term /Friday through Tuesday/...
the models have been consistent showing much of the isentropic
lift shifted northeast of the forecast area Friday. Forcing
associated with the approaching cold front should remain north of
the region through the day. The shower chance appears low. We
used the warmer temperature guidance because of expected heating
just ahead of the cold front.
Convergence ahead of the cold front supports an increased shower
chance Friday night. There may be enough instability for
thunderstorms but this support should be limited because of
nocturnal cooling. The models display the deepest moisture late
Friday night into early Saturday morning. Drying behind the cold
front should dominate beginning late Saturday morning or early
Saturday afternoon. Used the warmer temperature guidance Friday
night because of cloudiness and mixing associated with the front.
The guidance may be too cool Saturday because of a relatively warm
start and downslope winds behind the front.
The high pressure center behind the front should be near the
forecast area by late Saturday night. Expect mostly clear skies
and light winds with strong nocturnal cooling. The GFS and European model (ecmwf)
MOS have lows in the upper 30s to around 40. The dry air mass
should remain in place through Sunday and the MOS has highs near
The high will be off the coast Monday and Tuesday. The models
indicate an associated onshore flow plus isentropic lift in the
forecast area. The GFS and European model (ecmwf) MOS have probability of precipitation of 20 to 30 percent.
Aviation /06z Wednesday through Sunday/...
VFR conditions expected through the taf period...except possible brief
MVFR visibilities early this morning due to fog.
A cold front approaching the region from the north will cross the
taf sites during the early morning hours. Cannot completely rule
out a brief shower affecting ags/dnl although probability is much
too low to include in tafs. Model soundings and guidance indicate
that a brief period of MVFR visibilities is possible before dawn
this morning. Confidence remains too low to include in current
issuance as winds may inhibit fog development. Winds will be
southwesterly around 5 to 7 knots and will become northerly behind
the front early Wednesday while gradually weakening toward
daybreak. Surface high pressure will build into the region for
Wednesday promoting light northeasterly winds and VFR conditions.
Extended aviation outlook...restrictions possible Thursday
afternoon through Saturday as another frontal boundary stalls
across the region.