Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1006 am EDT Wednesday Jun 19 2013
Synopsis...
an upper level disturbance will cross the region from the northwest
today...with a weak surface cold front then settling southward along
the appalachian mountain chain into Thursday. High pressure will
build over the area from Friday Onward...with increasingly warm and
humid conditions developing into early next week.
&&
Near term /through tonight/...
as of 1000 am EDT...the scattered showers that developed around
sunrise over ther western upstate due to a passing vorticity are slowly
dissipating as they moved eastward. Have adjusted the pop field for
this trend. The convection allowing models are still advertising
that at least some widely scattered showers/thunderstorms will
develop over the mountains this afternoon due to the weak upslope
flow and heating. Current probability of precipitation are solidly in the scattered range...which
which could be a little on the high side....but will leave as is for
this update.
The models are advertising the passage of a weak short wave this
evening with some light quantitative precipitation forecast response over the NC foothills/
northern Piedmont. Have added some low end probability of precipitation in that area late
this afternoon and evening.
Previous discussions:
as of 0745 am EDT Wednesday...some showers have developed over the
SC upstate in response to an upper impulse moving through the area.
Hence...have made a quick updtate to include some scattered showers to the
forecast for mainly just the morning hours outside of the mountains.
Still expect scattered afternoon convection over the mountainss.
As of 230 am EDT Wednesday...conditions will continue to improve
across northeast Georgia and the Carolinas over the next 24 hours as
upper level cyclonic flow shifts east allowing for building surface
high pressure. Cold front that moved through the region Tuesday
that spawned numerous showers and thunderstorms has pushed into the
midlands/low country of SC. Behind the front...much drier air can
be seen on the surface analysis as most sites across NC are reporting
dew points in the upper 50s to lower 60s. This drier airmass will
continue advecting southward allowing for a fairly nice day across
the region with the only exception being some mechanically forced
convection in the higher terrain during the afternoon hours. High
temperatures on Wednesday will be slightly below normal as middle 80s
are expected across the Piedmont...and upper 70s to lower 80s
elsewhere. Towards the end of the near term period...the ridge
slides further to the northeast allowing for a return to easterly
flow prompting some increases in boundary layer moisture which will
lead to increasing cloudiness for Thursday morning. Lows on
Thursday morning will be slightly below normal.
&&
Short term /Thursday through Friday night/...
as of 230 am EDT Wednesday...surface high pressure will stretch from the middle
Atlantic coast through the western Carolinas on Thursday. This will
produce some easterly flow in the boundary layer over the
area...contribute a very light upslope...and halt any brief near
surface drying. The combination of light upslope...wind field
convergence in the Southwest Mountains...and conditional instability in
the profiles will likely produce scattered convections over the mountains
and isolated coverage in the adjacent foothills during the diurnally
favored afternoon and evening periods. Will continue to feature maximum temperatures
about a category below climatology.
Upper level heights will start to rise in earnest from the west on
Friday. The SW NC mountains appear to have the best chance of any isolated
to scattered convection again on Friday afternoon in the best low level
convergence...however...pops will be less than Thursday since profiles
are a bit drier. Maximum temperatures may recover 1 to 2 degrees in most
locations...but remain quite comparable to Wednesday values.
&&
Long term /Saturday through Tuesday/...
as of 240 am EDT Wednesday...a 591 dm 500 mb ridge will remain dominant over
the southeast through the medium range period. Anticipate a mainly diurnal
trend of isolated to scattered afternoon probability of precipitation through the period...with
the mountains being the primary focus. The GFS is the most aggressive in
bringing an inverted coastal trough back inland along the Savannah
on Saturday...but the other operational and ensemble mean solutions
keep the system along the immediate coast with the ridge persisting
over the western Carolinas. The diurnal pattern of isolated to scattered showers
and thunderstorms should thus continue Sat through Tuesday...with
temperatures steadily warming under the upper ridge. Expect maxes to
reach climate normals by Sunday and then exceed them Monday and Tuesday.
&&
Aviation /14z Wednesday through Sunday/...
at kclt...ceilings have lifted across the Piedmont of North Carolina
thus allowing for a VFR forecast through the period. However...some
rain showers have developed over the SC upstate in response to an upper
level impulse passing through. These are moviong eastward and have
included a vcsh around midday with lowering VFR ceiling. Could be a
brief visibility restriction but confidence too low for now to include in
taf. Drier air advects in from the north later today as and high
pressure ridges into the region. Expecting nothing more than a few
scattered middle clouds and high level ceilings tonight. Winds will be light NE
through most of the period before shifting to an easterly component
towards the end of the forecast cycle.
Elsewhere...rain showers over the SC upstate lwering visibilities to MVFR at gsp
and gmu. Conditions should continue improve by late morning as srra
move east. Not expecting any precipitation at any of the SC sites
this afternoon as high pressure begins to dominate and capping
inversion holds. However...for the NC sites...went with prob30 at
kavl as short term convection allowing guidance indicates some
updrafts being able to overcome the cap with the aid of mechanical
forcing. Beyond that...latest guidance indicates a lowering of ceilings
to high end MVFR across most sites this evening as boundary layer
moisture increases. Winds will be light and northerly through most
of the period before shifting to an easterly component towards the
end of the forecast cycle.
Outlook...increasing moisture towards the end of the work week will
allow some diurnal convection to develop each afternoon.
Otherwise...most areas should see dry conditions. Some early
morning stratus will also be possible on Thursday and Friday perhaps
causing some restrictions.
Confidence table...
14-20z 20-02z 02-08z 08-14z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 100% high 100% high 88%
khky high 100% high 100% high 100% high 85%
kgmu high 100% high 100% high 100% high 100%
kand high 100% high 100% high 100% high 100%
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...hg
near term...lg
short term...hg
long term...hg
aviation...cdg
