Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
500 PM EDT Tuesday Oct 13 2015
as a cold front moves southeast of the area tonight...drier high
pressure will gradually spread over the area from the west over the
next few days. Another cold front will arrive from the northwest on
Friday with stronger high pressure settling in the fronts wake over
Near term /through Wednesday/...
as of 430 PM EDT...several minor changes to update sky grids
/reduce them/ and adjust temperature trends through about midnight
or shortly thereafter...but no major changes.
As of 220 PM EDT...water vapor imagery shows the longwave eastern
trough axis stretched along the Appalachians this afternoon...with
deep layer drying working into the region on northwest flow from KY/TN. The
associated surface cold front extended from tri to near cha and
this boundary should move steadily southeast through the forecast
area this evening. A series of shortwaves will then move through
the longwave trough tonight and Wednesday...but with little to no
moisture to work with. The only scant moisture to be found will
be at low levels in the northwest upslope flow...which should lead to a
few more northern mountain clouds overnight than in the rest of the
area...but with no precipitation expected. Min temperatures will fall
back toward climatology values for middle October. Another round of Mountain
Valley fog will likely form and may become dense in places in the
French Broad and little Tennessee River valleys.
Sprawling surface high pressure will slowly build eastward from
the MS River Valley on Wednesday. Maximum temperatures should be within a category
of climatology...a little above in the Piedmont and a little below in
the mountains...Wednesday afternoon.
Short term /Wednesday night through Friday/...
as of 2 PM Tuesday...the center of surface high pressure will build
southeast from the northern plains to the southern Appalachians by
sunrise Thursday. At the middle levels...the axis of a longwave trough
will remain across the East Coast. Sky during the early morning
hours will remain mostly clear. However...model cross sections
indicate a thin layer of cirrus passing over the region late
Thursday into Thursday evening. The cirrus could be associated with
a weak orographic wave...by wave formation appears very shallow. Low
and high temperatures on Thursday will range very close to normal.
On Friday...a cold front associated with low pressure over east
Canada is expected to sweep northwest to southeast across the region. If the GFS
front was oriented a 10-20 degrees clockwise it would be considered a
back door front. Short range guidance is in good agreement that the
front will encounter little moisture across the forecast area...yielding no
convection. I will keep the forecast dry. Cold air advection is expected to hold
off until Friday evening...allowing high temperatures to range from the low
70s within the mountain valleys to middle 70s east.
Long term /Friday night through Tuesday/...
as of 200 PM EDT Tuesday...the medium range forecast period initializes
Friday evening amidst a broad upper longwave trough with its axis
centered over the southern Great Lakes...stretching southward toward
Gulf Coast. At the surface...a cold front will be pushing through
the region at forecast initialization...likely along or just south of
Interstate 85 by that time. Profiles look to dry to threaten any
precipitation with this frontal passage...thus the forecast reflects such.
Canadian high pressure will spill in across the Mississippi River
valley immediately behind the front...eventually pushing into
the northeast Georgia and the western Carolinas by Saturday morning.
A cooler/drier airmass will result leading to temperatures nearly
8-10 degrees below normal through the weekend. As a result we may
see the first frost/freeze conditions of the season on Sunday/Monday
morning. Latest guidance favors near freezing temperatures along
the higher peaks and ridgetops...especially in the northern NC mountains
further south and east into the central mountains as well and the i40
corridor...calm winds and temperatures in the middle/upper 30s will
present favorable conditions for patchy frost. Still too far out
to highlight in the severe weather potential statement as even minor changes in the temperature
guidance could affect the outcome. Otherwise...surface high pressure
will dominate through the first part of the new work week as
the upper longwave trough migrates out to sea allowing heights to
rise aloft. This will persist into middle week until heights fall
yet again ahead of another approaching system from the west.
Aviation /21z Tuesday through Sunday/...
at kclt...no significant changes for the 21z amend. Deep layer
drying is spilling in on northwest flow aloft...while surface winds remain
SW to west-southwest with the approaching cold front still west of the mountain
chain. Any gusts in the late afternoon mixing should abate quickly this
evening...with winds turning northwest with frontal passage. There is some potential
for lower restrictions toward daybreak given the moist ground...but
the MOS and model profiles do not depict any restrictions so will
omit them at present. Winds should remain west-northwest through 18z Wednesday with
continued VFR conditions.
Elsewhere...kavl will remain the primary concern going forward with
a likely repeat of daybreak fog/low stratus restrictions given
the moist ground in the mountain valleys. Brief daybreak fog is
also indicated at khky and kand as well...but light west-northwest downslope
should preclude restrictions elsewhere. Otherwise...expect little
more than few cumulus with heating through Wednesday.
Outlook...dry and mainly VFR conditions are expected through
21-03z 03-09z 09-15z 15-18z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 100% low 36% 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)