Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 141604

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1104 AM EST Wed Feb 14 2018

Warmer high pressure will build to our southeast through the end of
the work week, bringing well above normal temperatures. A cold front
will approach from the northwest later on Friday, bringing increased
rain chances. This unsettled pattern will keep some chance of rain
through the weekend and into early next week.


As of 1030 AM EST Wednesday: Light rain continues to move across the
area, though some of it isn`t quite reaching the ground. Have
increased extent of slight chance pops across a good chunk of the
Piedmont, but otherwise very few changes to the forecast, just
updates for observational trends.

Otherwise, surface high pressure persists in a weak cold air damming
position early this morning, but the high center will steadily
migrate to the southeast coastline today to permit southwesterly
return flow to develop and temperatures to warm. Maximum
temperatures should rise to some 5 to 10 degrees above climo this
afternoon. Meanwhile, zonal upper flow will continue through the
near-term period, with moisture starting to cross the southern
Appalachians around 12Z this morning before spreading east. The
deeper moisture and weak forcing will struggle eastward across the
forecast area today, with a relatively sharp PoP gradient of likely
across the TN/NC border area to dry but mostly cloudy conditions
over the southeast piedmont.

The next round of deeper moisture will arrive from the west tonight,
along with an increase in westerly 850 mb flow to 35 to 40 kt late
tonight. This will contribute to breezy to windy ridgetop
conditions, and PoPs will rise to the likely to low end categorical
range for rain across the TN border area and the higher peaks, but
with a continued sharp PoP gradient to the southeast. Very warm
minimum temperatures will run some 20 degrees above climo.


As of 230 AM EST Wednesday: The two warmest days expected over the
next seven days will fall within the short term forecast period
which begins on Thursday.

As flow aloft remains nearly zonal, sfc high pressure over the
Carolinas will continue to weaken and move southeastward offshore
Thursday morning as a recently passed warm front continues to
propagate northward towards the OH Valley. With deep moisture in
place from SW flow (moreso across the western fringes of the FA)
along with a few weak impulses moving within upper flow (before
shifting northward as well) and the aid of upslope flow, expect
showers to persist mainly across the mountains into the early
afternoon hours, as the already in place lower PoPs across the
Upstate and Piedmont are expected to decrease even more, giving way
to a drier day into Thursday afternoon. Despite anticipated cloud
cover, high temperatures are expected to climb into the low to mid
70s across the Upstate and Piedmont, back into the mid to upper
60s/around 70 degrees across the mountains. If clouds should
decrease in opacity moreso than currently forecasted, insolation
could allow temperatures to be a bit warmer than expected. This will
be something to watch as high temperatures on both Thursday and
Friday will near record highs for both Greenville (SC) and Charlotte
(NC). See the Climate section in the forecast discussion below for
more information. Overnight lows both nights will remain above

Latest guidance continues to be in good agreement with the initial
placement of an approaching upper wave and it`s associated cold
front off to the northwest Friday morning. It`s the progression of
the cold front through the forecast area on Friday where the models
begin to differ temporally. With plenty of moisture return and
enhanced lift, expect precipitation to begin ahead of the front late
overnight Thursday into early Friday morning along the TN line,
expanding southeastward as the system is progged to move across the
forecast area throughout the day. Thus, have kept the inherited
trend of increasing PoPs from NW to SE. Overall, expect the front to
be southeast or just exiting the southeastern fringe of the FA
(depending on which model run is followed) ahead of the
aforementioned approaching upper wave, which will keep mentionable
PoPs going just beyond the short term forecast period.


As of 230 PM EST Wednesday: The medium range remains a bit of a
mess, with a progressive and unsettled pattern expected to continue.
By 12Z Saturday, the remnants of a frontal boundary will have sagged
south of our area with surface high pressure beginning to wedge in.
The respite in rain chances will be short-lived, however, as an
upper shortwave quickly passes over our area amidst fast and zonal
flow aloft. This shortwave will be accompanied by an influx of Gulf
moisture, and aided by isentropic upglide over the wedge, will
produce a healthy QPF response over our area Saturday evening and
into the overnight hours. By Sunday, the progressive flow will clear
the upper impulse from the area, allowing some drying (and maybe
even some sun!) as surface high pressure builds in again.

Monday, rain chances ramp up again as another wedge of high pressure
sets up against the spine of the Appalachians and some weak upper
vort streamers round the strong upper ridge sitting just off the east
coast of Florida. Both major global models have QPF response Monday
and Tuesday, though there is discrepancy on exactly how much precip
to expect early in the work week. Another more robust cold front
will approach our area by the middle of next week, though exactly
when any precip might arrive is complicated by the building upper
Atlantic ridge arresting flow over the central CONUS. Temperatures
on Saturday will be near average due to the cloud cover/precip from
the wedge, and will increase to 10-15 degrees above average for the
rest of the medium range as the strong upper high builds over the
Atlantic off the east coast of Florida.


At KCLT and elsewhere: Adjustments for the KCLT 16z AMD include
adding VCSH while reducing SCT MVFR to FEW. Otherwise, surface high
pressure center is slipping southward and will soon low-level return
flow to develop. MVFR stratus returning from the southeast should
provide solid ceilings at KAND, but MVFR cigs may be more TEMPO in
nature from KGMU to KGSP to KCLT through late morning, with mainly
VFR at KHKY. KAVL will be the primary exception, where river valley
fog and low stratus should keep LIFR conditions socked in through
15Z, with slow improvement through IFR into early afternoon. Shower
chances will be best, and occur earliest, from KAVL to KHKY. Cigs
will lower back through MVFR this evening, with spotty shower
chances picking up east of the mountains overnight, along with
occasional IFR cigs at times. Light and variable winds will become
more S to SW today, but remain less than 10 kt.

Outlook: Unsettled weather, and associated restrictions, may return
later this week into the weekend with a cold front approaching from
the northwest.

Confidence Table...

            16-22Z        22-04Z        04-10Z        10-12Z
KCLT       High 100%     High 100%     High  84%     High  85%
KGSP       Med   64%     High  84%     High  97%     High  85%
KAVL       High  82%     High  84%     Med   65%     Med   78%
KHKY       High 100%     High 100%     Med   78%     Med   75%
KGMU       Med   78%     High  84%     High 100%     High  85%
KAND       High 100%     Med   75%     High  87%     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:



  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      74 1989     18 1905     55 2001      5 1943
   KCLT      80 1989     32 1943     60 1909     12 1943
   KGSP      75 1989     30 2016     57 2001     -3 1899


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      72 2001     18 1958     51 1990      2 1905
   KCLT      76 1976     28 1969     60 1990     11 1905
   KGSP      80 1911     32 1958     59 1990      9 1958




LONG TERM...Carroll
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