Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 180559

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
159 AM EDT Wed Oct 18 2017

Cool high pressure will move off the East Coast for the second half
of the week providing a light south to southwest flow of milder air.
Temperatures will warm a little to a few degrees above normal
through the weekend. A strong cold front will arrive early next week
which brings the coldest air so far this season.


As of 145 AM: High pressure is centered over the Mid-Atlantic
states and will force a light northeasterly flow into the area
today and tonight. The atmospheric column will remain quite dry
above the PBL so skies will be largely free of clouds. That said,
a shortwave trough is moving in from the west and will bring some
bands of cirrus across over the next few hours. This is expected to
have little impact on cooling. Sfc dewpoints are relatively high,
and temp trends are expected to be similar to last night, i.e., not
cratering. Nonetheless they eventually should cool enough for some
frost to form in the more sheltered portions of the advisory area.

The pattern changes little over the next 24 hours; the core
of the sfc high will push offshore tonight in response to the
advance of the aforementioned trough. Winds will continue to
be light and temperatures below normal, though modification of
the airmass will result in maxes/mins a little warmer than the
previous day. Nonetheless some frost is expected again tonight,
though we have not fully evaluated the possibility of an advisory. A
decision will be made by the issuance of the full morning package,
in collaboration with neighboring WFOs.


As of 135 AM EDT Wednesday: Upper ridging builds across the eastern
CONUS Thursday and Friday. Surface high pressure remains across the
area as well. Thicknesses rise each day leading to a warming trend.
There may be some cirrus from time to time, especially on Friday,
but mostly clear skies will prevail. Highs a couple of degrees above
normal Thursday rise to around 5 degrees above normal Friday. Should
be good radiational conditions each night leading to inverse lapse
rates across the mountains and colder conditions outside of the
normally warmer thermal belt and heat island areas. Lows will be a
couple of degrees above normal each day however, keeping any frost
chances to a minimum.


As of 130 pm EDT: A strong 500 mb ridge azis over the southeastern
U.S. Friday night will slide off the southeast coast on Saturday.
Meanwhile, the nose of a New England surface high pressure center
will remain over the forecast area - with dry profiles and above
climo temps in place for the early weekend.

The medium range models feature relatively good agreement on the
southern stream portion of a central CONUS trough axis cutting off,
or at least becoming out of phase with the northern stream, over
east Texas on Sunday. Return flow moisture ahead of this system, as
well as around the offshore Atlantic high pressure center, will
permit clouds to steadily return to the region Saturday night
through Sunday, with deeper moisture and better forcing developing
Sunday night through Monday. Instability will also be uncovered in
southeast sections by Monday afternoon, and a thunder mention will
be included. Any shear ahead of the lifting southern tier system
looks limited, as does severe potential at this point.

A trailing strong cold fropa will move through the southern
Appalachians on Tuesday, with much cooler thicknesses starting to
spill into the region. Subfreezing 850 mb temps along with better NW
flow moisture appear timed just beyond the current forecast period
next Tuesday night.


At KCLT and Elsewhere: Cool high pressure will remain the
dominant feature thru the period, leading to generally low-impact
weather. That said, dewpoints are not all that low, so some fog
is still expected in the mtn valleys, plus outlying areas of
the Piedmont. At KAVL guidance has backed off earlier consensus
on daybreak IFR, so the mention has been pulled back to MVFR in
TEMPO. Similarly, frost is a possibility at KAVL and across the
mtns and foothills. Winds are expected to prevail NE, when not
light and VRB.

Outlook: Seasonably cool and overall VFR conditions will persist
through the work week with the only possible exceptions being
mtn valley fog/stratus restrictions in the morning. Moisture will
begin to return to the area Saturday in advance of a cold front
early next week.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  88%     High  94%     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:


NC...Frost Advisory until 9 AM EDT this morning for NCZ033-035>037-


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