Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 150829

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
329 AM EST Mon Jan 15 2018

Cold and dry high pressure will linger across the region ahead of an
approaching cold front crossing the Plains through tonight. The cold front
will cross the area late Tuesday thru Wednesday morning. This front
will usher in a quick shot of cold air Wednesday into Thursday. High
pressure will slide off the East Coast by Friday, allowing a warming
trend for the end of the week.


As of 230 AM: Looks like a relatively quiet but cool 24 hrs as sfc
high pressure ridges all the way down from eastern Canada today,
and then a cold front approaches from the west tonight. Altho we
should see plenty of sun, temps will remain on the order of 10 deg
below normal. An upper trof will sharpen to the west tonight as an
upper low moves over the Great Lakes region, and that should tilt
our flow aloft to the SW. Increasing clouds and some weak warm
advection should help to keep low temps tonight from bottoming
out so cold, but will still be on the order of five degrees below
normal. At this point, there seems to be little chance that any
precip will reach the fcst area before sunrise on Tuesday, as all
the guidance has the leading edge out over the Cumberland Plateau
region at 12Z Tuesday.


As of 230 AM EST Monday: Models are coming into pretty good
agreement on overall timing and QPF with the next system, with still
slight differences. The GFS is on the quicker side, while the
NAM is slower.

An upper low will open up into a positively tilted trough on
Tuesday over the Great Lakes to the Mid-South. The trough will
remain very sharp and start to pivot toward neutral tilt Tuesday
night thru Wednesday. This will provide strong deep-layer Q-vector
convergence along a frontal zone as it crosses the area. Low-level
forcing looks to be confined mainly to southwesterly upslope and
isentropic lift within a fairly narrow frontal band of moisture. The
band may be enhanced by frontogenesis, but INSTBY will be lacking so
intense banding is not expected. With all that said, guidance
generally shows a tenth of an inch of QPF or less for most of the
area, except locally higher amounts possible near the TN border. As
for precip type, guidance shows cold air in place aloft, with just a
sfc-based warm layer southeast of I-85 on Tuesday that may result in
rain or rain/snow mix at the onset. So most of this precip should
fall as snow. Snow-to-liquid ratios of 10:1 to 15:1 should support
1-2" along the TN line, but generally a trace to up to 1" elsewhere.
The current consensus on the timing is for the band to enter the
western NC mountains late Tue aftn or early evening, then cross into
the piedmont during the pre-dawn hours Wednesday, before tapering
off in the I-77 corridor by early Wed aftn. Temps will be able to
drop into the teens across the mountains, so expect whatever falls
to stick on the roads. Across the Piedmont, it`s a little iffy, but
temps in the 20s may allow for messy roads, even with a half inch of
snow (as long as snow rates get heavy enough). Plan to expand
mention of snow impacts in the HWO. Temps then only manage to rise
into the mid to upper 30s in the piedmont, and stay below freezing
across the mountains and foothills.

Wednesday night thru Thursday, the cold front quickly exits to the
east, while arctic high pressure builds in from the west. Gusty winds
will linger in the mountains while temps drop, resulting in wind
chills -5 to -15 F above 3500 ft. Temps will fall into the teens
across pretty much the entire area, with some single digit lows in
the highest elevations. From there, temps rebound into the 30s to
mid 40s, as high pressure quickly slides into the deep south and
brings flow out of the west-southwest. This results in the piedmont
not quite reaching the 48-hour cold wave criteria, but probably will
in the mountains.


As of 330 AM EST Monday: Surface high pressure will dominate over
the Southeast on Friday, then start to shift east off the coast as a
low pressure system starts to organize over the Plains on Saturday.
This pattern change should result in a nice warm up of temps back to
above normal Saturday and Sunday. Return flow around the high will
start to advect some Gulf moisture into the region late Saturday
thru Sunday, but the deeper moisture will still be back off to the
west. So there should be an increase in cloud cover, but PoPs only
gradually creep up into the slight CHC to low-end CHC, mainly in the
usual southwesterly upslope areas. Temps should be sufficiently
moderated such that any precip that develops will be rain.


At KCLT and Elsewhere: VFR through the period. Mostly clear with a
light N/NE wind overnight, but some mid-level clouds will encroach
before daybreak. This could bring a mid-level ceiling overhead
for the rest of the morning. Guidance suggests a wind shift to SW
from midday through mid-afternoon, but speed will continue to be
5kt or less. Clouds should thin out again by late afternoon.

Outlook: VFR conditions are expected to prevail at least through
Tuesday. A fast-moving system may bring a brief shot of moisture
and possible restrictions Tuesday night into Wednesday. The main
concern is that temps will be cold enough that any precip that
falls would most likely be in the form of light snow. Conditions
will improve to VFR by late Wednesday.

Confidence Table...

            08-14Z        14-20Z        20-02Z        02-06Z
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%     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:




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