Area Forecast Discussion
Issued by NWS Greer, SC

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040
FXUS62 KGSP 191103
AFDGSP

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

.SYNOPSIS...
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.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
600 AM EST Update...no major changes needed to the going fcst. Made
some upward tweaks to hr/ly temps and td/s where mixing has been
consistent. No area fog issues anticipated with sfc layer remaining
too dry...yet isol locales have RH values hovering in the 90 percent
range.

High pressure will remain centered just south of the FA  thru the
period as a strong convg 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.
Soundings remain quite dry with PWAT values less than 0.25 inches so
insol 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. Will probably
have decent snow pack left over this evening across the NC zones
where amounts were the greatest...so another night with black ice
concerns is likely aft midnight as temps drop below freezing. Will
let the WSW for black ice ride and let the day shift reassess the
need for another WSW/SPS for the overnight period.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
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.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
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.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
At KCLT and Elsewhere: No restrictions expected all TAF sites thru
the period. Some increasing low clouds and perhaps isol precip
across the NC mtns late Sat...but besides that the column will
remain quite dry. The hires models are hinting at some VSBY issues
near CLT Sat morning...however there is not enuf confidence to
include mention in TAF as soundings show a sigfnt neg 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...

            11-17Z        17-23Z        23-05Z        05-06Z
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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Winter Weather Advisory until noon EST today for NCZ033-
     035>037-048>050-053-056-057-065-068>072-082-501>510.
SC...None.

&&

$$
SYNOPSIS...SBK
NEAR TERM...SBK
SHORT TERM...Carroll
LONG TERM...Carroll
AVIATION...SBK



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