Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 150806

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
306 AM EST Thu Feb 15 2018

Warmer high pressure will linger to our southeast through the end of
the work week, bringing well above normal temperatures. A cold front
will approach from the northwest 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 245 AM EST: Regional radars show the coverage of scattered
showers slowly diminishing across the area as any deeper moisture
moves east and forcing wanes. The main lingering forcing mechanism
will be southwesterly to westerly low-level upslope flow into the NC
mountains, where we will maintain low likely PoP early this morning
and then chancy PoPs through the day.

Otherwise, relatively zonal flow will continue atop the region
throughout the near-term, and any forcing will remain rather weak.
850 mb flow will ratchet up to about 40 kt today, with windy
conditions likely across the higher ridges of the mountains, and
breezy conditions with mixing east of the mountains. Abundant
moisture below an inversion in profiles should keep more clouds than
not in place through the day. If locations receive any significant
insolation, temperatures will soar. Even with the clouds, plenty of
70s are currently expected for afternoon maxes.

Better low level moisture will fill back in across the mountains
tonight into Friday morning. PoPs will improve especially across the
western mountains in westerly upslope flow tonight. Moisture will
likely get trapped under the persistent 850 mb temperature
inversion, keeping plenty of clouds in place along with very mild
minimum temperatures.


As of 230 AM EST Thursday: Another unsettled weather pattern will
consume the short term forecast period, which begins Friday morning.

General consensus among latest guidance highlights a sfc low
pressure moving off the New England coast Friday morning as a cold
front extends southwestward through the OH Valley, back into the
southern plains. Initially situated just northwest of the FA, expect
this system to slowly drop down through the FA throughout the day on
Friday, allowing for increasing rain chances and potentially a few
embedded thunderstorms along the leading edge of the front with
limited instability.

Slightly different scenarios begin to evolve between guidance as
this boundary pushes through the FA into Friday night. The GFS
suggests a slower progression of the system through the FA where it
is then progged to become stationary across the Carolinas on
Saturday, keeping overall lower end PoPs Friday afternoon and
Saturday. At the same time, sfc high pressure behind the front will
move through the Midwest and off the eastern seaboard as it wedges
back in across the Carolinas Saturday night, with a series of weak
impulses aloft riding along the boundary allowing for upglide to
hold onto lingering precip into the overnight hours ahead of another
approaching cold front from the west. The ECMWF differs in that it
propagates the front slightly faster as it is progged to stall just
south of the FA, allowing for a period of dry conditions Saturday
morning before an upper wave to the northwest amidst zonal flow
aloft aids in moist upglide over the boundary, increasing PoPs again
Saturday night and holding onto moisture longer than the GFS into
early Sunday morning ahead of the next approaching cold front.

Overall, have only made minor tweaks to inherited PoPs through the
forecast period, with expected QPF of a half of an inch up to an
inch possible, with higher amounts along the TN border. Despite
expected cloud cover on Friday, warm advection will allow for high
temperatures to remain above normal as both Greenville SC and
Charlotte NC will near record highs for the day (See Climate section
below). Into Saturday, a significant cool down is expected behind
the front with temperatures dropping to just below normal.


As of 130 AM EST Thursday: The medium range period begins
Sunday morning in between systems giving a brief break. Models
show a transient high pressure moving from west to east passing
just north of our area. This will create a brief wedge pattern
but then low level wind flow shifts from NE during the day
Sunday to a southerly direction as the high moves off the East
Coast. Moisture will be on the increase again. A cold front that
is forecast to be from Kansas to the Great Lakes early Monday
should be crossing Tennessee in mid week and stalling out just
north and west of our area. Low pressure may form on the front
near the Mississippi Delta late Wednesday moving NE toward our
area. Instability could be a factor in the forecast Wednesday
afternoon with CAPE values 300 to 400 across the forecast area
with higher values just south and west. Max temps are forecast
to be around 70 along and south of I-85 Wed afternoon. That will
be around 13 degrees above normal. So max temps going from near
normal Sunday and Monday to much above Tuesday and especially
Wednesday. Expect some thunder in Day 7.


At KCLT and elsewhere: Scattered showers will continue around the
terminal forecast area through the early morning hours before the
deeper moisture moves east. Anticipate mainly MVFR cigs before 09Z,
but with many locations exhibiting IFR at times until just beyond
daybreak. Low level moisture will persist today, with gradual
improvement through MVFR to afternoon VFR. Expect SW flow to
increase, with gusts near 20kt possible at the peak of mixing. Lower
clouds will return tonight as moisture stays trapped under the 850
mb inversion.

Outlook: Unsettled weather, and associated restrictions, will return
Friday through the weekend as a cold front arrives from the
northwest and then stalls in or near the area.

Confidence Table...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       Med   61%     Med   78%     High  92%     High  97%
KGSP       High  90%     High  89%     High  94%     High  90%
KAVL       High  87%     High 100%     High 100%     High 100%
KHKY       Low   56%     High  81%     High 100%     High 100%
KGMU       High  87%     High  86%     High  84%     High  84%
KAND       High  90%     High  95%     High  98%     High  89%

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





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