Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 230745
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
245 AM EST Thu Feb 23 2017

.SYNOPSIS...
Brief drying develops today into early Friday before a significant
cold front brings chances for rain and thunderstorms Friday night
and Saturday. Overall, daytime temperatures will remain well above
normal through Saturday, with a return to normal for Sunday. Above
normal temperatures and chances for rain return for early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Areas of lowering vsby are setting up across the nrn zones with
localized dense fg noted across the nrn NC ftills. Hi-res modeled sfc
cpd/s indicate areas underneath the llvl ridge axis area most
susceptible to dense fg formation...which includes the NC piedmont
and ne/rn Upstate. Will continue to monitor this situation and issue
a sps/dfa as/if needed.

The public fcst for today should be rather straightforward compared
to the past couple days. The upper level slow moving Col will be
replaced by increasing h5 ridging which will aide in keeping a broad
sfc ridge across the fcst area while generating decent subsidence.
Thus...expect cloud cover to decrease sigfnt/ly fairly early this
morning across most locales...except in the mtns where se/ly moist
Atl flow will maintain mech lift sct/bkn cloud cover and perhaps
some isol -shra. There could also be enuf llvl lift and mtn top
convg to spawn a couple tstms over the higher terrain. These tstms
would be short lived and relatively weak. Max temps will be pleasant
and should have no problem reaching the lower to mid 70s non/mtns
and upper 60s mtn valleys. Mins shud also remain a few cats above
normal as the synoptic pattern favors the development of llvl stcu
invading most of the FA.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 230 AM EST Thursday: A closed low pressure system will move
east over Iowa on Friday while a downstream ridge axis persists over
the southeastern U.S. Under the ridge, moist southerly flow will
continue at low levels, providing some weak upslope triggering along
and near the Blue Ridge. However, profiles appear rather warm and
capped aloft so little to no thunder is expected Friday afternoon.
Very warm temperatures are expected throughout the region as the
lingering nose of surface high pressure dissipates and south to
southwest winds predominate along with warming low level thicknesses.

The low pressure system will lift over the Great lakes through
Friday night and send a cold front into the southern Appalachians.
Breezy to windy conditions will ramp up over the higher terrain of
the NC mountains ahead of the front Friday night as 850 mb southerly
flow increases to around 40 kt. Wind gusts are expected to remain
sub-advisory across all but the very highest peaks in the warm
advection flow regime. The strength of the approaching convection
will be the primary issue, as upstream locations from Kentucky to
central/eastern TN are now in the Day 2 convective slight risk. The
feeling is that the pre-frontal convection will largely run out of
steam as it enters the southern Appalachians and encounters lower
instability, but some gustiness along the TN border counties is
quite possible. The passing surface cold front should cross the
mountains by mid morning on Saturday and move east of the Interstate
77 corridor circa 18z. Any stronger areas of 500 to 1000+ SBCAPE
ahead of the cold front should only briefly intersect with our far
eastern piedmont. 850 to 500 mb lapse rates do briefly surge to
about 6.5 deg C/km there and surface to 3 km bulk shear values may
reach 35 to 40 kt in the unidirectional southwesterly flow early
Saturday afternoon. Severe thunderstorms are not currently expected,
however, as the instability should be greatest off to the east.

Deep layer westerly flow will develop over the region behind the
departing cold front late Saturday through Saturday night as snow
levels fall across the higher terrain of the NC mountains. Upslope
moisture, however, appears rather shallow and winds will be more
westerly in the boundary layer over eastern Tennessee. Any high
elevation snow accumulations overnight Saturday night will be quite
light.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 205 AM EST Thursday...starting Sunday morning with cool high
pressure over Tennessee transiting east. This high will be moving
off the Carolina coast late Sunday with southerly return flow
moisture beginning over east Texas to Missouri shifting east into
Monday. There should be a surface low pressure over Arkansas early
Monday.  Some models have around a 10kt 925mb South to SSE flow
across GA and SC which would enhance upslope against our mountains
producing some showers out ahead of the approaching system.  Weak
lows will continue to develop and move NE from the lower Mississippi
Valley through Wed night with some instability late Tues and Wed.
The GFS shows 700 to 900 CAPE along and south of I-85 at both 18Z
Tuesday and 18Z Wednesday with mainly speed shear. At 18Z Wed the
925mb wind is forecast to be SW at 30 to 35kts and 700mb wind
slightly more west at speeds near 50kts. Strong to a few severe
possible. Of course, that is nearly a week away and much can change.
At least some areas should get good rain out of this 3 day event.
The cold front moves through late Wed night with dry high pressure
building into our region from the west going into Thursday.

Temperatures near normal Sunday, rising to around 5 degrees above
Monday then 10 to 15 degrees above Tuesday and warmest on Wednesday.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
At KCLT...Expect lowering of cigs overnight as back end of cloud
shield works east. Vsby will also lower as hires cpd/s show max
saturation in the sfc layer around daybreak. A drop to IFR conds by
10z and possible LiFR vsby by 12z. A lifting and scattering out will
occur quickly aft 15z with drier air mixing in underneath a building
mlvl ridge allowing for good sfc heating.

Elsewhere: KHKY will be the trouble spot wrt to IFR/LIFR conds thru
daybreak. Previous rainfall and calm conds under a sfc ridge will
enable a highly moist sfc layer to persist thru mid morning. KAVL
will also be under the gun for IFR vsby/cigs a few hrs before
daybreak. Across the Upstate...VFR dropping to MFVR conds with
perhaps IFR vsby...esp at KGSP/KGMU where tdd/s are running lower
and cpd/s drop the most. A quick return to VFR conds will occur arnd
14z with relatively drier air mixing in and sfc heating commencing.

Outlook: Moist southerly to easterly low-level flow will persist
across the area until a cold front pushes thru on Saturday. This
will keep high chances of morning stratus and possibly fog each day
thru Saturday morning. Drier conditions set up on Sunday.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High  88%     High  84%     High 100%     High 100%
KGSP       Med   73%     High  93%     High 100%     High 100%
KAVL       Med   77%     High  83%     High 100%     High  96%
KHKY       Low   58%     High  83%     High  99%     High  96%
KGMU       Med   71%     High  82%     High 100%     High 100%
KAND       Med   71%     High  80%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Dense Fog Advisory until 10 AM EST this morning for NCZ033-
     035>037-048>050-053-056-057-501>506.
SC...None.

&&

$$
SYNOPSIS...DEO
NEAR TERM...SBK
SHORT TERM...HG
LONG TERM...DEO
AVIATION...SBK


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