Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 171805

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
105 PM EST Sat Feb 17 2018

Cool high pressure to our north today combined with low pressure
approaching from the west will make for a cool, wet day.  Cool and
dry high pressure will give our region one dry day on Sunday. Expect
a warm up through mid week as another cold front arrives from
Tennessee by Thursday. This front is expected to move north as a
warm front at the end of the week as our temperatures remain well
above normal.


As of 1255 pm: E/W-oriented front/wedge boundary has stalled just
north of the I-20 corridor, with NE winds and cool temps (i.e.,
25-30 degrees cooler than at this time yesterday!)/hybrid cold air
damming noted across all non-mountain locations. Meanwhile, -RA and
drizzle continues to expand in response to isentropic lift/upslope
flow atop the shallow cool air. This trend should continue over the
next couple of hours, with at least likely pops warranted in most
areas along/north of I-85. Today`s highest pops (categorical) will
be reserved for later this afternoon across the far western mtns, as
precip associated with weak surface wave riding northeast along the
baroclinic zone across the TN Valley brushes the southern
Appalachians. Rainfall totals should be very light across the vast
majority of the area, generally less than .25 inch, although some
localized amounts of around a half inch will be possible across the
southwest NC mtns this afternoon.

While temps across the Blue Ridge/foothills and northern/far western
Piedmont have cooled further due to falling precip/wet bulb effects,
temps have begun slowly warming across the (mostly) precip-free
areas of the southern Piedmont and far western mountains. These
areas will likely see the upper 50s/lower 60s before the day is
done, while other locations will see steady temps that may rise
slightly as precip begins to taper off late.

Any lingering precip tapers off during the evening as the synoptic
forcing moves northeast out of the area, and the low level flow
turns west then northwest ending the isentropic lift. There will be
some lingering moisture across the mountains which could keep a
brief period of NW flow showers across the northern mountains. Even
with weak cold advection developing, temps do not fall very quickly
and precip ends before any wintry precip can develop. Low clouds may
diminish outside of the mountains after midnight as the strong
damming inversion erodes. Should this occur, patchy dense fog would
be possible toward morning. Lows will be 5 to 10 degrees above


As of 300 AM EST Saturday: The short term will feature an upper
ridge building over the western Atlantic, with deep-layer
southwesterly flow setting up atop the region. At the surface, a
transient high will cross the southern and central Appalachians
during the day on Sunday, exiting off the Mid-Atlantic coast Sunday
night. This will result in a mostly sunny day with pleasant, above
normal temps. Moisture returns quickly Sunday evening, however, as a
deep low in the lee of the Colorado Rockies activates a warm front
across the Gulf states. This front will lift north thru the area
Sunday night, bringing a round of clouds and light showers
overnight. The best chances will be in the southwesterly upslope
areas. Temps will remain elevated under the overcast skies and
low-level WAA flow.

Monday`s forecast looks a bit tricky, as the guidance hints at a
weak in-situ CAD holding on thru the day. This would need to be
anchored by precip, but forecast soundings show mid levels dry out
with a subsidence inversion. So precip should pretty much taper off
during the day, except for lingering chances in the upslope areas.
If low clouds can hold thru the day, temps should be held back, but
still above normal. If clouds break out, temps may bust by a couple
categories from the current forecast. Will go with mostly cloudy
skies thru the day and into Monday night. Temps mainly in the 60s
for highs, and 50s for lows (well above normal).


As of 130 AM EST Saturday.  The medium range period begins Tuesday
morning with 500mb pattern having the center of high pressure just
south of Bermuda with the axis of a trough over the Rockies. The
cold front from Texas to the Great Lakes will approach our region
from the NW in mid week. The low level southerly flow ahead of this
front will result in upslope enhancement of showers from NE GA to the
Caesars Head area.  The GFS is faster in bringing the front and bulk
of the rain into our area while the ECMWF holds the front from east
Texas to KY Wednesday evening.  Instability increases and it appears
Wednesday afternoon has the best CAPE values of 600 to 900 from
Elberton to Rock Hill. After the front stalls out over east
Tennessee to VA Wed night into Thursday, the front will drift north
as a warm front Friday becoming stationary well north of our area
over the weekend. Models vary during this time on afternoon CAPE
values depending on smaller scale vort maxes and amount of moisture.
Interesting that the surface high over northern New England late
Friday may push the front south as a backdoor cold front. The
current official front display keeps the front near Maryland.
Regardless...still going with above normal temperatures through the


At KCLT and elsewhere: IFR cigs have been filling in rather quickly
in response to -RA and DZ across the mountains and foothills early
this afternoon. Once these settle in, they are expected to continue
through at least the afternoon. Meanwhile, IFR/MVFR visby can be
expected to accompany the periods of precip. Meanwhile, KCLT
stubbornly remains  at the high end of MVFR, but as light precip
continues to overspread the NC Piedmont from the southwest, KCLT
should see cigs lower to IFR no later than 21Z. While the precip is
expected to taper off this evening, lingering low level moisture
within cool wedge will continue to pose the potential for BR, while
cigs should remain IFR, if not lower to LIFR. A cold front will push
across the area this evening into the overnight. Winds will shift to
light NW at most terminals (except for the usual up-valley gustiness
at KAVL), with some improvement in flt conditions forecast. However,
the introduction of drier air behind the front will be somewhat
slow, and winds will not be strong enough to strongly mix the
atmosphere. Therefore, restrictions in BR and perhaps low stratus
will remain possible, especially across the foothills and Piedmont
through at least sunrise Sunday. (Confidence in the forecast is
lower than normal from about 06Z-12Z or so Sunday.)

Outlook: VFR conditions expected for the bulk of the day Sunday.
Moisture returns early next week, and the weather will remain
periodically unsettled, with occasional restrictions likely through
much of next week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       Med   71%     Low   57%     Med   67%     High  94%
KGSP       Med   78%     Low   57%     High  85%     High 100%
KAVL       Med   75%     Med   75%     Med   76%     High 100%
KHKY       Med   77%     Low   53%     Med   74%     High  94%
KGMU       Med   74%     Med   72%     High 100%     High 100%
KAND       High  85%     High  81%     High  88%     High  85%

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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