Scientific Forecaster Discussion
fxus62 kgsp 261432
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1032 am EDT Tue Sep 26 2017
dry and warm high pressure will remain across the region through the
middle of week...while Hurricane Maria is forecast to remain off the
East Coast. A fairly dry cold front will cross the area Thursday
while pushing Maria out to sea. A secondary cold front crosses
Friday night bringing much cooler and drier air for the weekend into
early next week.
Near term /through tonight/...
as of 1030 am: no significant changes with this update; the
fcst appears on track. A stagnant weather pattern will persist
through the near term, as upper ridging continues to yield
subsidence/weak mid-level lapse rates, while low level ridging
and the broad pressure pattern around Hurricane Maria supports a
relatively dry north/NE flow. However, surface dewpoints are expected
to be sufficiently high to support some weak/shallow buoyancy
this afternoon. This should allow for a healthy cu field across
much of the area, and we would not be surprised to see a brief
shower or two pop across the high terrain this afternoon, but
not enough to warrant a mentionable pop--latest hrrr runs are
dry to boot. Meanwhile, cirrus outflow circulating around Maria
is expected to shift east of the forecast area today, while
thicknesses should see a slight increase. This should spell an
across-the-board increase of 1-2 degrees above yesterday's Max
temps, with mid/upper 80s expected across all of the foothills
and Piedmont, and lower/mid 80s in the mountain valleys. Min temps
tonight will remain 5-8 degrees above climo in most locations.
Short term /Wednesday through Thursday night/...
as of 250 am EDT tuesday: the forecast area will remain quite dry and warm thru
the short range period. Ulvl ridging will be enhanced somewhat by
the departing tc Maria which will make for a convectively
suppressive atmos. The 00z guidance has actually come in drier for
Thu evening/night and this trend was applied to the grids as the
pre-frontal upstream moisture looks very shallow...not to mention
highly uncertain as to how much will make across the Tennessee/NC spine.
Well above normal temps looks pretty certain however as soundings
show very good insol conds with perhaps just few/sct fair-wx cu Wed
and a little more cloud coverage across the NC mtns Thu afternoon.
Expect Max temps pushing 90 f both days across the non/mtns and low
to mid 80s mtn valleys. Mins will be remain about 10 degrees abv
normal Wed night and a few degrees cooler Thu night as drier/cooler
air begins to work in from the northwest.
Long term /Friday through Monday/...
as of 310 am EDT tuesday: no sigfnt changes were made to the going
fcst. The op models and ensembles agree well with the synoptic
pattern evolution which features a cold front crossing the forecast area Fri
then strong cp high pressure building south over the Midwest. Not
expecting much fanfare in our area ahead of the frontal passage late Fri. Very
little to no ulvl dynamic support will be had and the llvl wind
fields are non/conducive for moist flux or mech lift. Believe the NC
mtns will see the best chance of -shra during the afternoon which
will be short-lived pulse type and thermally driven in nature.
Other than that...the sensible wx fcst will focus on temps and
dewpoints thru the period. With the first real cp airmass of the
season...noticeably cooler air will move in Fri and become reinforced
over the weekend as the Canadian high centers east and ridges into
the forecast area. Expect Max temps held 5-8 degrees below normal. Dewpoints
will also drop off sigfnt/ly with values ranging in the mid 50s Fri
to the m40s by sun. Thus...very pleasant conds are in store Fri-sun.
A strong dry-onset wedge develops Mon and some measure of moist E/ly
flow will adv into the area. This combo of llft/moisture will likely
result in more cloudiness and a perhaps a shot of some low-end
precip across the srn Escarpment. Most areas should remain dry
Aviation /15z Tuesday through Saturday/...
at kclt and elsewhere: VFR is forecast through the next 24 hours at
the main taf sites. Some fog/low stratus has formed in the French
Broad valley up and down-valley of kavl, but it now appears unlikely
to impact the terminal this morning. Otherwise, an area of IFR/low
MVFR stratocu will make a run toward the western NC Piedmont this
morning, but it should stall/scatter/lift before reaching kclt. NE
winds will increase to around 10 kts at most terminals this morning,
then diminish again this evening. Scattered cumulus in the 040-050 range
expected to develop this afternoon near kclt, possibly expanding as
stratocu and lingering through the evening.
Outlook: dry conditions are expected most of the week. Under mostly
clear skies and calm conditions, fog and/or low stratus are possible
in the mountain river valleys each of the next few mornings. A
mostly dry cold front will cross the region late in the week.
14-20z 20-02z 02-08z 08-12z
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% Med 71%
khky high 100% high 100% high 100% high 95%
kgmu high 100% high 100% high 100% high 100%
kand high 100% high 100% high 100% high 95%
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: