Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1034 am EDT sun may 24 2015
dry Canadian high pressure will remain atop the region today. The
high takes on a summertime Bermuda high pattern on Memorial Day and
remains there through the week. A moist southerly flow develops with
increasing chances for convection.
Near term /through tonight/...
as of 1030 am EDT Sunday...other than tweaks to sky grids to account
for cumulus/stratus over portions of the southwest NC and northeast Georgia
mountains...no significant change were made to the forecast.
Temperatures continue to climb into the 70s...on their way
toward/into the lower 80s amongst increasing dewpoints thanks to
southeasterly flow at the surface.
As of 230 am...a large upper ridge will remain over the area
today...while the center of the surface ridge sets up off the middle
Atlantic coast. The increasing southeasterly low level flow atop the County warning forecast area
should begin to transport some shallow Atlantic moisture into the
area. However...middle level subsidence will result in another dry day.
Thicknesses will be similar to yesterday...with maximum temperatures about a
category above normal.
Tonight...models in good agreement on a shallow moist layer reaching
the upper Savannah valley and southern Blue Ridge Escarpment
overnight. So expect stratus to develop...at least across the western
half of the County warning forecast area by daybreak Monday. Most of the guidance tries to
squeeze out a few light showers along the Escarpment within the
southeasterly upslope flow. However...forecast soundings show the depth of
the near-saturated layer to be very shallow. So will go with a dry
forecast overnight. Temperatures will be a couple categories above normal
within the southeast flow and increasing clouds late.
Short term /Monday through Tuesday night/...
as of 155 am Sunday...the upper ridge axis over the area slides to
the coast on Monday allowing a southwesterly flow to develop. This pattern
holds on Tuesday with a series of weak short waves sliding through the flow
and over or near the County warning forecast area. At the surface...ridging from the Bermuda
high weakens allowing a low level southerly to southwesterly flow to develop as
well. This will help create a deep plume of Gulf moisture which
moves into the area...especially the western County warning forecast area during this period.
Therefore...expect scattered convection to develop over the western County warning forecast area
Monday diminishing to no convection over the I-77 corridor. Precipitation
chance increases across the board on Tuesday as moisture and forcing
increase. Although there will be a diurnal trend to the convective
coverage...expect at least some rain showers to linger through the night given
the copious low level moisture and general upslope flow. The threat
of severe weather will be mitigated by poor lapse rates and
relatively weak instability. Above normal temperatures Monday will remain
nearly steady or rise a couple of degrees Tuesday depending on location.
Long term /Wednesday through Saturday/...
as of 315 am Sunday...the upper ridge axis over the East Coast
weakens and allows a series of short waves to move over or near the
area through the period. At the surface...a Bermuda high remains in place
over the area in a pattern more typical of Summer. This keeps a
moist southwesterly flow over the area. This pattern will lead to mainly
diurnal convection each day...possibly lingering through the night Wednesday
night. Coverage will likely be higher Wednesday and Thursday then on Friday and
Sat...due to greater moisture early in the period. Temperatures will remain
above normal through the period.
Aviation /15z Sunday through Thursday/...
at kclt...no major changes to the thinking for the 12z tafs. As high
pressure slides east...southeasterly flow will increase a bit today
compared to yesterday. Winds will start out calm or light southeast...then
increase to the 8-12 knots range with a few low-end gusts possible this
afternoon. There will be a few wisps of thin cirrus through the day...with a
few fair weather cumulus with bases around 5000 feet. Some low level moisture
will increase off the Atlantic...with guidance showing low ceilings
developing to the west of kclt before daybreak. Guidance in good
agreement that it should remain west of the terminal through 12z...so no
low ceilings will be shown in the 12z taf.
Elsewhere...southeast winds will pick up to the 8-12 knots range under a few
fair weather. A few fair weather cumulus clouds with bases in the 4500 to 6000
feet range are expected this afternoon. Models in good agreement that IFR
or low MVFR ceilings will develop before daybreak Monday...as the
southeasterly low level flow transports Atlantic moisture into the area.
The stratus may or may not make it to khky. So will leave out of the
12z taf there.
Outlook...moisture will gradually return out of the south through the
middle of the week. So increased morning stratus...and a return of
isolated to scattered afternoon/evening rain showers/thunderstorms and rain can be expected by Tuesday-
14-20z 20-02z 02-08z 08-12z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% medium 66%
kavl high 100% high 100% high 100% high 83%
khky high 100% high 100% high 100% high 98%
kgmu high 100% high 100% high 100% low 58%
kand high 100% 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)