Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 191449

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
949 AM EST Fri Jan 19 2018

Dry high pressure will build over the region today before gradually
moving offshore over the weekend. Temperatures will rapidly increase
to above normal values. Another cold front arriving from the west
will bring precipitation to the Carolinas and northeast Georgia
early next week, with drying following through mid-week.


As of 930 AM EST: Temperatures are running slightly ahead of
forecast values in full sun and maxes at most locations have been
boosted at least one degree for the afternoon. The Winter Weather
Advisories and SPS products are scheduled to expire at Noon and that
seems fine given the warming. Any new products going forward for
tonight appear to be SPS level at worst.

Otherwise, high pressure will remain centered just south of the area
through the period as a strong convergence zone is maintained
associated with a split h5 flow. A srn stream h5 low will work
toward the area, however moisture flux will be shunted west due to
stg llvl ridging. Thus, any good precip chances will remain west of
the area through the period. Soundings remain quite dry with PWAT
values less than 0.25 inches so insolation will be high-end allowing
temps to reach a few degrees abv normal levels this afternoon.

With the increase in heating and dry air mixed to the sfc, the
remaining snow will continue to melt and evaporate. Another night
with patchy black ice concerns is possible after midnight as temps
drop below freezing, especially in the NC piedmont. A Special
Weather Statement could be needed.


As of 200 AM EST Friday: Dry surface high pressure will remain
centered over the Gulf Coast states Saturday with broad upper
ridging in place over the eastern 2/3 of the CONUS and a weak
embedded upper low propagating through the mean flow over the
southeast. The surface high will shift off the east coast Sunday,
with the upper level low pinching off and generally drifting over
the Carolinas. The low is too weak to have developed a surface
reflection by this point...and surface flow will be so weak and
variable Saturday that very little in the form of moisture return,
and therefore QPF, materializes near our area. The system appears
unimpressive at the moment, though an occasional model run that
develops a small amount of QPF  in the NC mountains keeps popping
from time to time. Pops were kept dry for now, but there remains
some uncertainty surrounding the system. Warm southeasterly return
flow sets up over the Carolinas Sunday and Sunday night and
transient upper ridging will propagate off the east coast by Monday
morning ahead of an approaching cold front. For the past few model
cycles, guidance has been trending later on precip onset time
associated with the cold front, so pops were held out of the forecast
through 12Z Monday morning.

Despite numerous small disturbances propagating through the mean
flow, in general, our area will be under the influence of upper
ridging through the weekend, resulting in temperatures climbing to
almost 10 degrees above average across the forecast area.


As of 230 AM EST Friday: The medium range begins with a strong
upper/surface low swinging across the central CONUS with a cold
front trailing off of it. The system has slowed down even more with
the new model guidance, and agreement on precip onset time is
generally better, closer to 18Z Monday or possibly even later. The
onset of pops were therefore delayed slightly from the last forecast
package. though dramatic changes weren`t necessary. The bulk of the
pre-frontal precipitation will move in overnight Monday, resulting
in a quick inch or so of QPF across much of the area. Precip end
time is proving a bit more tricky for the models to resolve, though
there is agreement that the system will be progressive, and the
front will have passed by 18Z Tuesday. Above normal temperatures
will keep precip types all liquid to start the event Monday, with a
transition to snow expected across the high terrain of the NC
mountains very early Tuesday morning just before the system departs
to the east. QPF does not appear to be a problem at the moment,
though any slowing of the system could make it possible for a few
isolated hydro issues to develop.

The system is also quite dynamic, and shear profiles (particularly
in the low levels) are very impressive ahead of the surface cold
front. The main precip shield and system will be moving through the
area overnight though, a diurnally unfavorable time for instability.
Guidance continues to show virtually no surface-based instability
and extremely meager elevated instability, so a severe threat looks
unlikely at the moment given current guidance. Shear is so
impressive, however, that this system will need to be watched
closely over the next couple of days.

After the front passes, much drier air will arrive in the forecast
area, with a sprawling surface high moving through the OH River
Valley through the end of the work week. Temperatures will return to
near normal as the progressive upper flow moderates to a more zonal
pattern through the end of the week.


At KCLT and Elsewhere: No restrictions are expected at all TAF sites
thru the period with mostly clear conditions given the dry profiles.
The hires models are hinting at some VSBY issues near CLT Sat
morning, however there is not enuf confidence to include a mention
in the TAF as soundings show a sigfnt negative hydrolapse. Winds
will remain generally sw/ly and weak thru the period.

Outlook: Dry/VFR conditions are expected to continue through the
weekend, with moisture returning ahead of a strong cold front early
next week.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
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...Winter Weather Advisory until noon EST today for NCZ033-


SHORT TERM...Carroll
LONG TERM...Carroll
AVIATION...HG/SBK is the U.S. government's official web portal to all federal, state and local government web resources and services.