Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 170247

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
947 PM EST Tue Jan 16 2018

A cold front will cross the area tonight. This front will usher in a
quick shot of cold air, with snow likely across the forecast area
later tonight into early Wednesday. High pressure will slide off the
East Coast by Friday, allowing a warming trend for the end of the


As of 930 PM EST Tuesday: Complicated forecast tonight. As mentioned
earlier, 18z guidance came in stronger/wetter, and 00z NAM trickling
in is following that trend, as did the 21z SREF. NWS Morristown
measured a 22:1 SLR at 00z which is a bit disturbing given the
uptick in QPF, but that SLR should modify as it crosses the
mountains with the deeper moisture that should form as the self-
development of the cyclone gets a little more geared up (nice little
baroclinic leaf suggested on 1000-500mb RH graphics by tomorrow
morning). This will help to lift moisture more into the dendritic
growth zone which will moderate the SLRs, but some mid-level
frontogenesis may help to destabilize, which would also help to lift
the moisture.

With the increasing QPFs that have been a trend for the last several
runs now, see no choice but to increase snowfall amounts across the
area. Ended up blending the previous WPC QPF as well as the new 21z
SREF together, and then used the more typical WPC SLRs of 12:1-14:1
to come up with new totals that give me warning criteria across a
good chunk of the Upstate and NC Piedmont Counties. Confidence in
the higher amounts along the I-77 corridor is moderate but generally
went with the mean so at this point in time, the forecast seems
reasonable. Expect a bit of a minimum across the foothills and
adjacent Blue Ridge, and the mountains have a 4" WSW criterion
anyway. This would include all of the CLT metro area and a good
chunk of the GSP area as well.


As of 315 PM EST Tuesday: The forecast period begins Wednesday night
with dry conditions in place across the entire forecast area,
persisting through the end of the week. Latest GFS/ECMWF remains in
agreement placing an eastward propagating upper trough over the
Carolinas Wednesday night, which will extend from the northeast,
down southward into FL. This feature will exit the eastern seaboard
late overnight into early Thursday morning, leaving dry conditions
to persist and NW flow in it`s wake as sfc high pressure builds in.

Though wintry precipitation will come to an end Wednesday afternoon,
temperatures Wednesday night through Thursday morning will dip into
the teens across the forecast area, with single digits across the
higher elevations. While increased NW winds during the day on
Wednesday will help to dry ground sfcs somewhat, any residual water
from snow melt on roadways/elevated surfaces will refreeze overnight
Wednesday into Thursday morning (while noting high temperatures on
Wednesday will have struggled to reach freezing to begin with). As
confidence increases with expected overnight low temperatures, do
expect areas of black ice on roadways/elevated surfaces, likely
causing slippery roads and hazardous travel conditions for Thursday
morning`s commute. Temperatures will fall below freezing again
overnight into Friday morning, thus again, any residual water will
likely refreeze.

For the rest of the day on Thursday, sfc high pressure will continue
expand into the Southeast, gradually moving overhead on Friday as
flow aloft becomes zonal and the pressure gradient relaxes. With
plenty of sunshine both days, temperatures will warm into the low to
mid 40s across the Upstate and Piedmont and upper 30s/lower 40s
across the mountains, warming even more and rising to near or just
above normal for Friday. With increased winds and temperatures, wind
chill values Thursday morning will again near dangerous values of
around - 5F to -10F across the higher elevations, single digits
across the mountains, into the teens across the Upstate and


As of 210 PM EST Tuesday: The ext range continues with good
confidence thru the weekend. The op models are showing a strong srn
stream sfc high dominating the pattern while overcoming a dry trof
axis east of the mtns Fri/Sat then centering offshore on Sun.
Soundings indicate a very dry atmos which will aide in allowing max
temps abv normal thru the period and increasing thicknesses helping
to hold min temps abv normal as well. The pattern becomes more
dynamic Sun as a 130 kt ulvl jet coincides with 300 K isent lift and
continued moist adv associated with an incoming cold front. With a
wide open GOM...a deep moist layer will encompasses the area Sun
night thru Mon. Heavy rain will be possible in this environ...esp
across the favored srn BR upslope regions. Expect diurnally driven
higher elev -snsh in NW flow as the frontsl system begins moving
east Mon night...however snowfall amounts shud remain low-end as
available moisture quickly wanes.


At KCLT and elsewhere: Still VFR out there this evening, but -SN
is moving into the mountains and should start at KAVL soon,
spreading E across the area through the overnight hours (beginning
likely as -RASN before transitioning to -SN at other terminals), and
with it will come MVFR cigs/vsby and the possibility of brief IFR
cigs/vsby. Any bursts of heavy snow may bring with it LIFR to VLIFR,
but these bursts should be short-lived. New guidance is lingering
-SN later in the day on Wednesday, but should improve to VFR
everywhere by the end of the period with -SN moving out. SW winds to
start the period will be briefly lgt/vrb before transitioning to NW
and picking up behind the front, with low-end gusts possible as
well. KAVL as usual should have stronger gusts, over 25kt by the end
of the period.

Outlook: Dry/VFR condition are expected to continue through the week
and into the weekend.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High  83%     High  87%     High  87%
KGSP       High  98%     High  86%     Med   75%     High  97%
KAVL       Low   45%     Med   73%     High  98%     High 100%
KHKY       High 100%     Med   70%     Med   78%     High  98%
KGMU       High  98%     High  82%     High  84%     High  98%
KAND       High 100%     High  80%     High  94%     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:


GA...Winter Weather Advisory until noon EST Wednesday for GAZ018-
     Winter Weather Advisory until 10 AM EST Wednesday for GAZ010-
NC...Winter Weather Advisory until noon EST Wednesday for NCZ035-
     Winter Storm Warning until noon EST Wednesday for NCZ068.
     Winter Weather Advisory until 7 AM EST Wednesday for NCZ051-
     Winter Weather Advisory until 10 AM EST Wednesday for NCZ033-
     Winter Storm Warning until 2 PM EST Wednesday for NCZ036-037-
SC...Winter Weather Advisory until noon EST Wednesday for SCZ001-
     Winter Storm Warning until noon EST Wednesday for SCZ003-
     Winter Storm Warning until 2 PM EST Wednesday for SCZ009-014.


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