Area forecast discussion
National Weather Service Columbia SC
1112 am EDT Wednesday may 22 2013
Synopsis...
high pressure off the southeast coast will circulate a moist
southerly flow into the forecast area ahead of a slow moving cold
front through Thursday. The cold front will move through the area
Thursday night. The dry air mass behind the front will dominate
during the weekend.
&&
Near term /until 6 PM this evening/...
update...satellite imagery and surface observation show fog continues to
lift across the area with low clouds continuing to linger across
much of the area. Expect the clouds to break up a bit producing
partly sunny skies during the late morning to early afternoon
hours. With high pressure offshore and southerly winds persisting
over the area there will be another chance of afternoon and
evening showers and thunderstorms. The main threat will again be
heavy rain as precipitable water values remain 1.6 inches or greater. Severe
thunderstorm potential remains low...however an isolated severe
cell is possible with gusty winds and large hail. With the cloud
cover across the forecast area this morning have lowered high
temperatures a degree or two with afternoon high temperatures in
the middle 80s.
Previous discussion...high pressure off the southeast coast will
continue to circulate moist air into the forecast area today. The
NAM and GFS continue to indicate a weak middle-level shortwave trough
lingering over the forecast area. Expect scattered thunderstorms
mainly during the time of maximum heating. Used an average of the
GFS and NAM MOS probability of precipitation. Precipitable water near 1.7 of an inch and
slow storm movement supports heavy rain will some of the
thunderstorms. Heavy precipitation loadings and possibly moderate
instability with 500 mb temperatures around -10 support a possibility
of damaging wind. Used the warmer temperature guidance for today
based on yesterday/S verification.
&&
Short term /6 PM this evening through Thursday night/...
a continued moist south flow associated with the offshore high
plus a pre-frontal trough support thunderstorms tonight. Coverage
will likely be limited by diurnal cooling and previous convection.
The NAM and GFS MOS are in good agreement with probability of precipitation 30 to 40 percent.
The models show the pre-frontal trough lingering Thursday but
deeper moisture appears to shift east of the forecast area early
ahead of a middle-level shortwave trough. The NAM and GFS MOS
indicate very low probability of precipitation...but maintained chance probability of precipitation because of
convergence associated with the pre-frontal trough Thursday and
the cold front Thursday evening. Further drying should occur
behind the front by late Thursday night. The temperature guidance
was close.
&&
Long term /Friday through Tuesday/...
the dry air mass behind the cold front should dominate during the
weekend. The GFS and European model (ecmwf) indicated a warm front developing
Monday with much of the moisture north of the forecast area Monday
and Tuesday. The GFS and European model (ecmwf) MOS plus GFS ensemble mean supports
very low probability of precipitation. Expect below normal temperatures during the
weekend and near normal during the rest of the medium range
period.
&&
Aviation /14z Wednesday through Sunday/...
mainly VFR conditions through the taf period.
Fog has eroded across the area with some low clouds
remaining...which will dissipate over the next hour or so. Main
concern through the period will be afternoon and evening
convection. Expect scattered showers and isolated thunderstorms
to develop this afternoon and linger into this evening. Confidence
in coverage and timing remain too low to include in tafs at this time.
Potential for fog overnight remains low as front approaches from
the west...however with a 25 knot low level jet across the area
low stratus will be possible. Much of the stratus potential will
depend on afternoon showers so have kept stratus out of tafs at this time.
Extended aviation outlook...scattered showers and
thunderstorms...mainly afternoon and evening...possible through
Thursday night. Late night/early morning fog/stratus also
possible.
&&
Cae watches/warnings/advisories...
SC...none.
Georgia...none.
&&
$$
