Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 121857

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
257 PM EDT Mon Mar 12 2018

Colder and drier high pressure will build to our west and persist
through midweek. A period of mountain snow showers will
persist along the Tennessee border into mid week. Expect
a warming trend late this week to near normal temperatures.
A front and low pressure will bring showers over the weekend
and early next week.


Latest water vapor imagery indicates upper low wobbling east/
southeast across the heart of the Upstate this afternoon. We are
still seeing some flurries/light snow (with perhaps a band of
moderate snow weakening along the TN border) across the area this
afternoon, but little to no additional accumulation appears likely
east of the TN border counties. Speaking of which, moisture will
briefly deplete across the entire area late this afternoon into the
evening before northwest flow moisture begins increasing again
around midnight-ish. Forecast thermo profiles and magnitude of the
northwest flow appear to be pretty decent for about a 6-hour window
late tonight/early Tues, with the primary limiting factor being not-
great upstream lapse rates/low Froude number (always an issue with
nocturnal northwest flow events) and a tenuous Great Lakes
connection. In terms of headlines, will transition the high
elevation warning to an advisory while canceling the low elevation
advisory for Swain/Haywood. All other headlines will remain

Temperatures tonight are expected to be well-below climo, and in
fact, most locations should experience a freeze. This will create
black ice concerns, at least on a patchy basis, but allow time for
some more products to expire for the next shift to further evaluate
things. Northwest flow snow showers will diminish through the
morning hours, giving way to mostly sunny skies in all locations by
Tue afternoon. Temps will remain quite a bit below climo, around 10
degrees in most areas.


As of 200 PM Mon: From Tuesday night through early Thursday we
will continue to see the effects of a deep upper trough over the
East, and cold high pressure accordingly centered over the Gulf
states. Northwest flow will continue across the area during this
time. Min temps will be around 10 degrees below normal, with maxes
more like 15 degrees below normal.

1000-850mb RH will increase late Tuesday on the upslope side of
the Appalachians, so another snow event is expected to develop
there Tuesday night. Conditions look most ideal around dawn
Wednesday, when moisture is deepest and lapse rates will be
enhanced by a passing shortwave, producing a wee amount of SBCAPE
along the ridges. Current expectations are for 1 to 2 inches of
new accumulation between 00z-18z Wed, which is below advisory
criteria. However, gradient winds will be moderately strong and
high-elevation wind chills are expected to dip below zero. We can`t
rule out a Winter Weather Advisory for the combined impacts along
the TN/NC border. The moisture diminishes toward midday Wednesday
which looks to bring accumulating snowfall to an end.

The upper low will begin to depart to the east by early Thursday,
but brisk winds will continue. Temperatures won`t be quite as
cold Thursday morning, and subzero wind chills are not expected at
those high elevations. Continued height rises Thursday will permit
temperatures to rise back close to normal. We will remain under a
moderately tight gradient flow Thursday, and during diurnal mixing
frequent gusts are likely in all zones.


As of 250 PM EDT Monday: After a fairly dry period during the middle
part of the week, the medium range forecast period begins Thursday
night as latest guidance continues to highlight a developing
unsettled weather pattern for the end of the week through into the

With sfc high pressure situated across the GOM/FL panhandle Thursday
night, latest guidance places an upper ridge across the central
plains in between a low pressure system well off to the northeast
and another system coming out of the Rockies. This wave moving out
of the Rockies is progged to develop into a sfc low across the
central plains with the aid of an upper level disturbance as the
aforementioned upper ridge to the east continues to propagate
eastward. Anticipate a warm front associated with this system to
extend eastward, remaining just north of the FA through the early
part of the weekend, placing our area in the warm sector. Tapping
into GOM moisture with the gradual return of SW flow, this along
with isentropic lift will increase shower activity beginning as
early as Friday morning, mainly across the TN border. Would not
entirely rule out an initial rain/snow mix across the northern
mountains early Friday morning, before warming temperatures allow
for a transition to all rain as coverage expands eastward. Attm, do
not anticipate any snow accumulations. Saturday night into Sunday,
upper troughing across the NE will push the warm front back through
the FA as a back door cold front, allowing for a lull in the precip
during the day on Saturday as Canadian sfc high pressure builds in
behind the boundary. As the sfc high moves off the Carolina coast
Sunday, unsettled weather returns for the end of the weekend, and
per latest guidance could potentially continue into the early part
of next week, just beyond the forecast period. Temperatures
throughout the forecast period are expected to remain at or just
above normal.


AT KCLT and elsewhere: Any lingering IFR cigs should improve to MVFR
no later than 20Z, with all areas likely becoming VFR by early
evening, as drier air overspreads the area from the west. May see
additional flurries or -SN at KHKY and perhaps KCLT, but the
intensity should not be sufficient to reduce visibility below
5-6sm. Otherwise, skies should continue to clear through the
evening, with VFR conditions expected through the end of the period.
Generally N/NW winds are expected through much of the period, around
10 kts (with gusts to near 20) expected over much of the foothills
and piedmont (as usual, a good 10 kts higher at KAVL), diminishing
by late evening, before increasing again after sunrise Tuesday.

Outlook: Northwest flow moisture could keep some clouds in at KAVL
from time to time through mid week. Otherwise, VFR conditions are
expected to persist through the end of the work week.

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       High  85%     High 100%     High 100%     High 100%
KGSP       High  93%     High 100%     High 100%     High 100%
KAVL       High  94%     High 100%     High  96%     High 100%
KHKY       High  94%     High 100%     High 100%     High 100%
KGMU       High  93%     High 100%     High 100%     High 100%
KAND       High  93%     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...Winter Storm Warning until 8 AM EDT Tuesday for NCZ033-048>050.
     Winter Weather Advisory until 5 PM EDT this afternoon for
     Winter Weather Advisory until 8 AM EDT Tuesday for NCZ048>052.


SHORT TERM...Wimberley
AVIATION...JDL is the U.S. government's official web portal to all federal, state and local government web resources and services.