Scientific Forecaster Discussion
fxus62 kgsp 201039
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
639 am EDT sun Aug 20 2017
relatively dry high pressure will give way to a warming and
moistening airmass early in the new work week, bringing hot and
humid afternoons Monday through Wednesday. A cold front is expected
to pass through Wednesday night and usher in cooler and drier air
that will last into next weekend.
Near term /through tonight/...
as of 630 am: fog/low stratus has settled into most mountain valleys
this morning, and will burn off/lift before 10 am. Otherwise,
heights will rise through the near term, as upper trough progresses
off the East Coast and the subtropical ridge increases its influence
on the southeast. Resultant warmer temperatures as well as
increasing boundary layer moisture due to a transition to more of a
southeast flow should yield improved instability across our area this
afternoon. However, mid-level lapse rates will remain very poor,
owing in part to a pronounced stable layer based at around 700mb as
depicted in forecast soundings. Nevertheless, the improved
instability does allow some spotty convection to develop along the
ridge tops in most high resolution guidance, so slight chances for
deep convection will be advertised there. Max temps will generally
be a solid category above climo. Warm and increasingly muggy
conditions will be felt tonight, as low level moisture continues
increasing on southeast flow.
Short term /Monday through Tuesday/...
as of 3:00am EDT sunday: short-term forecast is dominated by
presence of a Bermuda high extending westward across the southeast.
On Monday, surface anticyclone with this high over the Atlantic
produces a little southeasterly flow than will help moisture with
the GFS indicating some showers in upslope areas of the southern
Appalachia Monday afternoon. Winds will continue generally light,
and this anticyclone will only advance dewpoints a few degrees,
but flow into the mountains may help initiate some showers.
Cloudiness on Monday for eclipse time are still not too bad at 30 to
40% (near climo). Mountainous areas look to have a greater chance
for clouds given the weak upslope moisture flow. MLCAPE does
increase to the marginal level on Monday and Tuesday afternoons,
with lower amounts over the mountains where initiation is more
On Tuesday, situation does not change a whole lot with 500mb heights
declining a slight 2 dam as eastern Continental U.S. Pattern becomes slightly
more trough-oriented, and Bermuda high moves a little eastward,
making surface winds more southwesterly and keeping some chance for
Tuesday afternoon showers, primarily over the mountains.
With only subtle changes to the airmass, conditions will remain hot
and sticky through Tuesday.
Long term /Tuesday night through Saturday/...
as of 3:30am EDT sunday: ec and GFS models maintain some agreement
through the extended forecast as they both have an eastern Continental U.S.
Upper trough with a cold front and enhanced chances for rain by
Wednesday evening, followed by cold frontal passage on Thursday and drier
subsequent conditions; though details differ quite a bit with the ec
having a somewhat deeper trough. Models generally agree on higher
pops with a frontal passage in the Wed.-Thu. Time frame, with a substantial
drop-off in dewpoints and highs dropping below climo thurs. Through
Per the GFS, MLCAPE levels remain subdued to moderate in the 400 to
1200 j/kg range through Thursday with moisture being scoured behind
the front and much reduced chances for thunder Friday and Saturday.
Aviation /12z Sunday through Thursday/...
at kclt and elsewhere: have been watching fog/low stratus creep
toward kavl on GOES-16 imagery early this morning. However, it's
still debatable as to whether it will make it to the terminal before
it begins to erode/lift. A tempo for sct003 has been included there
for the first hour of the forecast period. Would not rule out a
brief visby restriction developing at any of the other sites, but
this is not looking likely attm. Otherwise, VFR conditions are
expected to persist through at least the evening hours. Chances for
high terrain convection will be slightly improved today vs.
Yesterday, but coverage will be very sparse and no mention of
convection is warranted at any of the terminals this afternoon/
evening. Otherwise, light north to NE winds should turn south of due
east this afternoon. Improved chances for fog/low stratus are
anticipated tonight, particularly in the mtn valleys, and MVFR visby
is forecast at kavl by 09z, although conditions certainly could
prove to be more restrictive.
Outlook: chances for diurnal convection and morning mtn valley
fog/low stratus gradually increase during early-to-mid week, with
the best chances expected Wednesday, as a cold front pushes into the
area. Chances for restrictions and diurnal convection may diminish
again during late week.
10-16z 16-22z 22-04z 04-06z
kclt high 91% high 100% high 100% high 100%
kgsp high 91% high 100% high 100% high 100%
kavl high 83% high 100% high 100% high 100%
khky high 83% high 100% high 100% high 100%
kgmu high 100% high 100% high 100% high 100%
kand high 83% 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: