Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 160809

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
409 AM EDT Fri Mar 16 2018

A front will stall over western North Carolina today, but with
dry conditions continuing. Moisture will return from the west late
tonight, well east of a low pressure system lifting from the plains
to the Midwest. This low will dive southeast across the southern
Appalachians through Saturday night to keep conditions unsettled.
Brief high pressure will return to the area Sunday before stronger
low pressure arrives from the west Monday into Tuesday.


As of 408 AM: The latest RAP has come in with 50 to 55 kt of 850 mb
winds persisting along the northern Blue Ridge past 12Z. In
addition, it features slightly improving cold advection which should
permit better mixing down of the winds. A Wind Advisory has thus
been posted through 14Z across the northern NC mountains.

Otherwise, the upper ridge axis to the west of the area will
steadily flatten today through tonight as closed low pressure lifts
northeast from the plains to the midwest. Closer to home, a backdoor
surface boundary will remain draped over western NC today, but with
little to no attendant forcing or better moisture. This will permit
good insolation with temperatures warming back into the 70s over the
southern tier, except mid 60s near the I-40 corridor closer to the
front. Dewpoints should moderate from the extremely dry values
yesterday as some rebounding occurs under southwesterly flow.

Meanwhile, the closed low pressure evolving over the plains will
generate convection over the lower MS River Valley today. This
activity may make a run eastward toward or through the southern
Appalachians during the early morning hours Saturday. The hi-res
models mostly have showers arriving after 06Z Saturday morning.
Surface-based instability should be quite limited tonight, but there
is potential for elevated instability in the upstream warm sector,
and 850 to 500 mb lapse rates will steepen a bit through the period
as well. Will thus introduce slight chances of thunder in southwest
sections for the pre-dawn hours, though nothing severe is expected.


As of 300 AM EST Friday: The short term forecast period kicks off
Saturday morning as latest guidance continues to prog a somewhat
northward progression of an eastward extending warm front across the
FA (the previous backdoor cold front/stationary boundary from
Friday) as it`s weakening parent sfc low moves out of the central
Plains and through across the OH Valley, into the Carolinas/VA
Saturday night as a S/W trough (along with it`s accompanying cold
front). With a warmer airmass in place and increased available
moisture with WSW flow, suggestion of weak instability/steeper lapse
rates from latest guidance may help spark isolated thunderstorms
Saturday afternoon and evening, especially across the mountains,
which coincides nicely with the latest SPC Day 2 Convective Outlook.
Otherwise, expect plenty of clouds across the area with scattered
showers throughout the day. Latest GFS has precip tapering off
across the area with the exception of the NC mountains Saturday
night as the system gradually moves offshore, while the ECMWF holds
onto the precip longer through into Sunday. For now have kept with
the trend of the GFS, with conditions drying out late Sunday morning
as sfc high pressure builds down in across the area and upper ridge
sets up to the west behind the exiting system. Will note, with
warmer temperatures, expect any precipitation that falls this
weekend to fall as rain.

The brief period of sunshine across the FA on Sunday will be short-
lived as clouds return later in the day ahead of the next
approaching system moving out of the Plains, with increasing rain
chances into Sunday night. High temperatures will range in the low
to mid 60s across the NW Piedmont, to near 70 across portions of
northeast GA and the Upstate, and slightly cooler across the NC
mountains. Overnight lows will remain above normal.


As of 350 AM EST Friday: The extended forecast period begins
on Monday as attention is turned towards a potent system approaching
from the west out of the central Plains. With it`s eastward
extending warm front south of the FA Monday morning, a return to SW
flow just before the start of the forecast period will continue to
allow for the infiltration of Gulf moisture into the Southeast, with
plenty of cloud cover in place for the beginning of the work week.
Isentropic lift will aid in the decent coverage of precip already
occurring Monday morning, which will continue well into the evening
hours. Do expect available instability to remain south of the area
with the warm front, though would not entirely rule out an isolated
thunderstorm across the extreme southern portions of the FA on

As the sfc low propagates eastward through the Carolinas/VA on
Tuesday (Miller B characteristics), the upper closed low is progged
to move into the OH Valley where it`ll open up into a wave and
quickly become a part of the upper longwave trough across the
northeast. Precip is expected to continue through the day on Tuesday
as the warm front moves northward before the sfc low pushes through.
With increasing (weak) instability, anticipate slightly higher
chances for isolated thunderstorms on Tuesday than am currently
anticipating for Monday.

Into Tuesday night, disagreement across the models grows, but
overall have kept with the suggestion of a secondary sfc low
developing off the Carolina coast and quickly moving off to the
northeast. With colder air infiltrating in on the backside of the
system, rain will gradually taper off, but it seems with wrap around
moisture and cold temperatures, another northwest flow event could
bring a rain/snow mix and/or light snow showers to the NC mountains
along the TN border Tuesday night, lingering potentially through
into Wednesday night. On Thursday, conditions quiet down for the end
of the forecast period as high pressure builds in. Temperatures will
remain around or just above normal Monday and Tuesday, dropping to
below normal by midweek.


At KCLT and elsewhere: VFR conditions should continue through the
period as a backdoor front settles through western NC, but with very
limited forcing and moisture. The main concern early in the period
will be LLWS at KAVL and at KCLT as a 40 to 50 kt low level jet in
the westerly flow rides in atop lighter lower elevation winds before
daybreak. Otherwise, expect some flavor of SW to WNW flow through
the day, with winds diminishing steadily as the gradient weakens.
KAVL will be the main exception, with continued gusty NW winds.

A band of showers arriving along a diminishing convective cold pool
may impact the area from the west overnight. Any showers surviving
into the region should arrive mainly after 06Z, but PROB30 for SHRA
is warranted late in the period at KAVL and then overnight at KCLT
with the 30-hour TAF. Thunder currently appears unlikely overnight.

Outlook: Chances for scattered precipitation and restrictions
continue over the weekend. Chance look much better for next Monday
and Tuesday, with a stronger low pressure system arriving from the

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:


NC...Wind Advisory until 10 AM EDT this morning for NCZ033-049-050-


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