Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1026 am EDT Monday may 20 2013
Synopsis...
a weak upper level trough will remain over the region through
Tuesday. The forecast area will remain in a moist and rather
unstable airmass...before a cold front crosses through late in the
week.
&&
Near term /through tonight/...
as of 1010 am EDT...the widespread fog has been lifting over the
past hour or so and thus the dense fog advisory was allowed to
expire at 10am. Low ceilings continue to persist over most of the SC
upstate and the Piedmont and foothills of NC. The NC mts have been
showing some clearing over the past few hours. Scattered showers have
been moving southeast over portions of the NC Piedmont and foothills with
a couple lightning strikes already detected just west of Hickory.
Still expecting scattered sh through the remainder of the morning with
convection likely to increase into the afternoon. The potential
remains for some isolated severe wind and/or hail events...but
widespread events are not expected. Temperatures are still on track to
top out a few degrees above climatology this afternoon with dewpoints
remaining juicy tonight.
&&
Short term /Tuesday through Wednesday night/...
as of 330 am Monday...guidance now shows energy from the upper trough
currently over the area remaining in place for Tuesday even as an upper
ridge tries to build. While the forcing will not be that strong...
there is now a lack of a subsidence inversion. Moderate instability
develops during the afternoon. This should lead to another day of scattered
convection...with slightly better chance over the mountains and western County warning forecast area
where instability is better. Convection will linger a little longer
over the mountains Tuesday night...but it should still be mainly diurnal in
nature. Highs will be 5 to 10 degrees above normal and lows around 5
degrees above.
Any attempt at ridging ends Wednesday as a trough rotating around another
upper low moves into the area. Although instability will not be as
strong...forcing will be much better. Therefore...expect numerous
coverage of convection over the mountains and high scattered elsewhere by
afternoon. Convection still looks to be mainly diurnal as the trough
and forcing move east of the area overnight. Although instability
will be less...shear and forcing will be higher...so isolated severe
storms are possible. Highs will be a few degrees lower...while lows
will be nearly steady.
&&
Long term /Thursday through Sunday/...
as of 400 am Monday...GFS and European model (ecmwf) in good agreement on an upper
trough moving into the area Thursday and across the area Friday. This leads to
scattered mainly diurnal convection each day. Highs Thursday about 5 degrees
above normal and near to slightly above normal Friday. Lows about 5
degrees above normal Thursday night and near normal Friday night.
Weak ridging builds in Sat with short waves moving by just north of
the area sun. At the surface...the GFS shows dry high pressure Sat and
sun. The previous ecwmf was wet for the weekend. However...the latest
run shows a mainly dry back door cold front moving in on sun.
Therefore...have gone with a dry forecast both days. Highs and lows will
be near normal both days.
&&
Aviation /15z Monday through Friday/...
at kclt...shower activity has moved east of the field...but
restrictions will linger into middle morning until heating causes the
ceiling to rise and fog to erode. Kclt will be close to the upper trough
axis...and clouds cover will likely keep a low VFR ceiling through the
day. Greater instability today will support scattered convection
this afternoon into this evening. Light south winds will prevail.
Model guidance is not supportive of restrictions early Tuesday
morning...but if the field experiences heavy rainfall from a
thunderstorm...restrictions would be more likely.
Elsewhere...restrictions are expected to lift around middle morning as
heating occurs under an approaching upper ridge. Low VFR ceilings will
persist into the afternoon...after which model data supports
lessening cloud cover at low levels. Although precipitation coverage
should be less as an upper trough departs to the east...instability
will be greater...and be more supportive of thunderstorms this
afternoon and early evening. Light south winds will persist in the
foothills. Winds will initially be light northwest in the mountains...
becoming southerly by afternoon. Model guidance supports MVFR fog at
kavl and kand early Tuesday morning...with low VFR visibility at other
sites.
Outlook...scattered showers and thunderstorms...and associated
restrictions...are expected to continue during the week...but should
become more focused during the afternoon and evening.
Confidence table...
14-20z 20-02z 02-08z 08-14z
kclt high 81% high 100% high 95% medium 78%
kgsp high 97% high 100% high 94% medium 70%
kavl high 97% high 100% high 83% high 86%
khky high 90% high 100% high 88% low 56%
kgmu high 86% high 100% high 91% medium 73%
kand high 97% high 100% high 100% high 80%
The percentage reflects the number of guidance members agreeing
with the scheduled taf issuance flight rule category. Complete
hourly experimental aviation forecast consistency tables and ensemble
forecasts are available at the following link: (must be lower case)
Www.Weather.Gov/gsp/aviation_tables
&&
Gsp watches/warnings/advisories...
Georgia...none.
NC...none.
SC...none.
&&
$$
Synopsis...rwh
near term...jpt
short term...rwh
long term...rwh
aviation...jpt
