Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
113 PM EDT Friday may 22 2015
dry Canadian high pressure will linger atop the region through the
Holiday weekend. A southerly flow of moisture around Bermuda high
pressure will gradually return next week.
Near term /through tonight/...
as of 100 PM EDT Friday...current forecast remains on track therefore no
sig changes needed/made with this update. Thus...only minor tweaks
to temperatures/dews were made to better align with most recent observation.
As of 630 am...updated the sky grids and temperatures to match up with
trends. Clouds have been a little slower to clear out than what the
guidance was indicating earlier. Temperatures were running warmer than
expected where the clouds have persisted. Still...overall trends are
on track...so no major changes with this update.
As of 230 am...a broad upper level trough axis will begin to shift
east...with the axis from the Appalachians today to the East Coast
tonight. This will allow heights to start rising atop the County warning forecast area...and
make for mostly clear skies. At the surface...a large area of dry high
pressure will continue to build in across a huge portion of the eastern
Continental U.S.. low level thicknesses will support temperatures a category or two below
normal with low humidity and light winds...making for a very
pleasant day. Min temperatures tonight will be about a category below
Short term /Saturday through Sunday night/...
as of 150 am Friday...an upper level ridge builds across the southeastern US
through the period. At the surface...the center of high pressure moves from
the Middle Atlantic States off shore during the day Sat...but remains
ridged across the area. The center slowly moves east into the
Atlantic through the rest of the period...but remains ridged into the
area during this time. There is no instability across the area
during the period and deep moisture remains off to the west.
Therefore...the dry forecast will continue. However...there could be
some clouds early Sat and sun as weak upslope flow interacts with
some lingering low level moisture. Better chance of clouds Sun
afternoon and night as low level moisture and upslope flow increase.
Highs near to a little above normal Sat rise a couple of degrees on
Sunday. Lows a few degrees above normal Sat night rise a few degrees
on Sun night.
Long term /Monday through Thursday/...
as of 325 am Friday...the pattern takes on a definite Summer feel through
much of the medium range with ridging surface and aloft. The ridge axis
is far enough east and the surface ridge axis is far enough south for a
moist southwesterly flow to develop across the area Monday through Wednesday. Instability
and moisture increase each day bringing an increase in diurnal
convective coverage each day. Still...best precipitation chance each day will
be over the mountains farther from the ridge axes creating better
moisture and higher instability. Some differences creep in on Thursday.
The European model (ecmwf) keeps the upper ridge stronger dampening the approaching
short wave and moving it farther north. The GFS has a stronger short
wave which knocks down the ridge and moves across the area.
Therefore...the European model (ecmwf) has less convective coverage while the GFS is
higher. Have gone with a blend which keeps coverage similar to Wednesday.
Temperatures start out above normal and rise a couple of degrees each day.
Aviation /17z Friday through Tuesday/...
at kclt and elsewhere...VFR through the period with winds being the
only minor issue for all sites. Rising upper heights amidst
building high pressure at the surface will allow for sky clear...with
perhaps a few occasional high cirrus on Saturday. Said surface
ridge will shift through the Ohio Valley today/tonight...then east
over the central Apps on Saturday. In response...light/northerly
winds this afternoon will calm overnight before veering
east/southeast late in the period...however generally around 5kts or
Outlook...deep high pressure will settle over the region over the
weekend...then shift east early next week...allowing moisture to
gradually return out of the south. Conditions should remain
generally fair through the period.
17-23z 23-05z 05-11z 11-12z
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 100%
khky high 100% high 100% high 100% high 100%
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)