Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 171843

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
243 PM EDT Tue Oct 17 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 200 PM EDT Tuesday: Upper trough is pushing out of the area
but weak NW flow continues as surface high pressure settles over the
Mid-Atlantic. As we move through the near term, a shortwave ridge
will develop ahead of a deepening wiggle over the MS Valley, which
allows the surface high to remain in place over the VAs and
Carolinas. The deepening trough over the MS Valley will push east
toward the Appalachians late in the period but with no attendant
moisture, should see at best maybe a slight increase in high clouds
across the mountains, but that might be pushing it. The bigger
concern will be frost development tonight. Guidance in fairly good
agreement, but a degree or two difference in temps might result in a
larger difference in frost formation. Winds should go calm or very
near it with the surface high in place, and though the airmass is
dry, dewpoint depressions should be enough to allow at least some
dew, or for the concern in question, frost to form. Mixing in the
mountains might actually mean that some of the NW Piedmont sees more
frost than the mountains, but getting a little nitpicky there. Have
opted to expand the Frost Advisory east to include more of the NW NC
Piedmont, with a little wiggle down into Lincoln county to catch the
climatologically cooler areas there (as per COOP MOS). Though note
the overnight low temp forecast might end up being a tad warm in
some areas. With ideal radiational cooling across the SC Piedmont,
could see some patchy frost in southern zones away from the mixing
influence of the mountains/foothill, but at this time not enough to
warrant an advisory in those areas.

Continued cool (below normal) tomorrow but a few degrees warmer than
what we`ll end up seeing today, with a slight NE breeze picking up
especially across the Piedmont during the afternoon.


As of 100 PM EDT Tuesday: Llvl ridging lingers atop the region
Wednesday night. Under another night of clear skies and light wind,
Thu am mtn valley min temps will flirt within the frost range.
With weak but veering flow at 85h, mins in the higher elevations are
expected to be milder than the valleys. Upper heights atop the SE
Conus start to rise on Thursday. With another day of sunshine, max
temps will rise back to above climo. Upper ridging is progged to
build atop the region on Friday with perhaps some high clouds
topping the upper ridge and spilling in. The warming trend is slated
to continue, with solid middle 70s progged for the Piedmont.


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: Dry high pressure north of the region will
maintain clear skies at all TAF sites today. Winds will be mainly
NE. A few low-end gusts are likely in the late morning but these
should mix out quickly. Tonight, the center of the high nears,
and guidance suggests winds will become light and VRB. Despite
temps well below normal within a dry continental airmass, sfc
dewpoint depressions are expected to be fairly small. Some frost
formation is possible in the mountains and foothills, including
at KAVL. Also, similar to what happened this morning, mountain
valley fog/stratus is likely. At KAVL this has prompted mention
of IFR vsby near daybreak.

Outlook: Seasonably cool and overall VFR conditions will persist
through the work week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     Low   47%     High  87%
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 from 2 AM to 9 AM EDT Wednesday for NCZ033-


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