Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 141126

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
626 AM EST Sat Jan 14 2017

Cool high pressure ridges down from New England today as a
stationary front remains over Georgia. This high pressure moves out
over the Atlantic tonight and Sunday as the front moves north over
North Carolina on Sunday. Another cool high pressure over New
England on Monday will force the front south over Georgia again. A
cold front will approach our region from the west through mid week
as well above normal temperatures prevail ahead of the front.


600 AM EST Update...Once again chasing warm temps over most of the
CWFA as low cloud cover has made for rather steady state conds, even
with weak sfc wedging CAA. The lowering pop trends are aligned well
and need no sigfnt adjs.

400 AM EST Update...made some upward adjs to hr/ly temps as mixing
has kept max cooling limited. Moist adv remains weak to nil across
incoming wedge the low-end pop trends still look good.

A llvl wedge continues to build in slowly across the CWFA with
little fanfare outside of a few brief weak showers and gradually
lowering cigs. Not anticipating much in the way of coverage nor
precip amounts with this setup since the llvl flow atop the wedge
remains unorganized and relatively dry. The moisture is shallow and
mainly confined within the wedge layer. Thus...pops have been cut
back following this trend and a hires model consensus.

Opaque cloud cover outside the mtns will remain in place through mid
afternoon before w/ly downsloping begins to break things up before
sunset. This will have some consequence on temps...although in a
relative sense. Expect little heating today....with about a 10
degree warm-up over the sw/rn zones and only a few degrees over the
NW Piedmont. The mtn valleys should remain mostly cloudy today with
the better precip chances across the wrn facing ridgetops.

A fast moving ulvl disturbance rounding the subtrop ridge will bring
a shot of moisture and light precip to the wrn NC mtn zones late
this evening and overnight. No concerns with p/type as temps should
remain well above freezing even across the higher peaks. Bkn/ovc
layered clouds will persist across the non/mtns with a weak llvl
bndry bisecting the CWFA and w/ly moist adv. This will create
another period of low diurnal temperature change with mins dropping
about 10 degrees to the SW and only 3-5 degrees over the ne/rn


As of 320 AM Saturday, a highly amplified/split flow upper air
pattern will remain in place into early next week, with a
slowly-evolving southern stream, and a rather progressive northern
stream anticipated. Early in the period, this pattern will support
maintenance of a quasi-stationary frontal zone that will extend from
the southern Great Plains into the Ohio Valley and Mid-Atlantic,
with erosion of a surface wedge either complete or well underway
across our area on Sunday. This will allow temps to return to above
or well-above climo levels by Sunday afternoon, with maxes likely
reaching or exceeding 70 across far southern Piedmont areas. Pops on
Sunday will be confined to the mtns, and largely limited to token
slight/low chances as westerly H8 flow yields mechanical lift near
the TN border.

By Sunday night, yet another area of strong surface high pressure
will be building into New England, in the wake of another
fast-moving northern stream short wave trough. Associated inverted
surface ridge building south along the Eastern Seaboard will send
the frontal boundary back into our forecast area beginning Sunday
evening, with increasing isentropic lift supporting an uptick in
pops, especially across the NC foothills and northern Piedmont.
However, forcing will be such that nothing over 40-50 percent
chances appear warranted attm. Much of the forecast area will see
another cool day on Monday as another transient cold air damming
scenario unfolds, although locations across the upper Savannah River
Valley and the SC Lakelands may see temps remain well into the 60s.
Pops slowly dwindle throughout Monday as low level flow becomes
increasingly neutral with respect to isentropic surfaces. However,
pops begin to increase again across western areas by daybreak Tue,
as mechanical lift increases near the high terrain with southerly
flow responding to height falls spreading into the eastern Conus.


As of 215 AM Saturday, The medium range begins Tuesday with cool
high pressure ridging down from eastern Canada moves east with low
pressure crossing the Great Lakes in mid week and its associated
cold front slowly approaching our area from the west. As the high
moves east, the CAD breaks down and the result will be max temps
going from about 10 degrees above normal Tuesday to about 15 degrees
above normal on Wednesday. Average 925mb wind on Tuesday from the
south at 10kts becomes SW and west increasing to 20 to 30kts Tuesday
night into Wednesday. The cold front then lays down nearly
stationary roughly west to east across our region Thursday into
Friday. This front becomes a warm front on Friday as another low
moves NE from east Texas bringing our region widespread showers on
Friday. Models show day to day CAPE values rather low during our
current forecast period through Friday then the GFS has 500 to 800
CAPEs across our foothills and piedmont late Saturday which again is
just beyond the current forecast. by the way, the old EC does not
have such instability. The concern for likely T Storms on Thursday
from last nights forecast has faded away as the models evolved. The
new ECMWF just came out and it has wave after wave of low pressure
passing from the Gulf coast region to the Carolinas from mid week
through next weekend. Comparing this to the GFS however has a Ohio
Valley low bringing good coverage of showers to the NC mtns Tuesday
night and another Ohio Valley low doing about the same on Friday.
Therefore, quite a bit of model differences and thus low confidence
in the overall timing of the areas of showers. Only thing confident
is that we are in an active weather pattern with above normal temps.


At KCLT/KHKY: A llvl wedge will build in and slowly breakdown late
in the TAF period. There wont be much isent lift over the cold
dome...however enuf prevailing moisture will be available to produce
isol/sct -shra over the fthills and piedmont regions. The hires
models agree on a very limited qpf response. Thus...pops were cut
back and went with vcsh thru the morning hrs at both locales. Cigs
shud remain in the MFVR range at KCLT til 04z when a drop to IFR is
possible with bndry settling over the area. Similar outlook for
KHKY...with also a drop to IFR vsby late in the period.

Elsewhere:  KAVL will remain locked in with VLIFR fog/cigs til 16z
as slow sfc heating occurs. Don/t see much chance for precip across
these sites with limited lift...but perhaps very brief -shra or vcsh
across KGSP/KGMU this morning. MVFR to IFR cigs will persist thru
most the taf period with downsloping flow developing arnd 22z
scattering out clouds over the Upstate. With a weak moist bndry
remaining over the area as a sfc wedge retreats...all sites are
expected to drop back to MFVR/IFR cigs arnd or shortly aft midnight.

Outlook: Cool high pressure ridges down the East Coast over the
weekend, bringing chances for precipitation and restrictions.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High 100%     High 100%     Med   63%     Med   75%
KGSP       High  83%     Med   75%     Med   73%     Med   62%
KAVL       Med   72%     High 100%     Med   68%     Med   62%
KHKY       High 100%     High 100%     Med   68%     Med   62%
KGMU       High  89%     Med   75%     Med   73%     Med   75%
KAND       Med   75%     High  83%     Med   63%     Med   69%

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:




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