Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201537
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1137 AM EDT Fri Apr 20 2018

.SYNOPSIS...
Dry and cool high pressure will linger over the region into Saturday.
Ahead of developing low pressure, deeper moisture will return to the
area on Sunday, with unsettled weather continuing into early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
1130 AM Update...No sigfnt changes needed to the fcst grids. Hourly
temps are running a little behind the curve and have adj/d localized
areas outside the mtns.

As of 635 AM Friday...conditions remain quiet this morning with clear
skies and light NLY flow. Some sites have gone calm over the past few hours
and we are still seeing some 20+ kt gusts over some of the higher terrain.
These should subside over the next few hours as the pressure gradient
weakens. I had to lower temps a few degrees over the NC Piedmont as
some sites are now reporting freezing temps. Temps will rebound quickly
when the sun comes up and heating commences.

Otherwise, heights will steadily increase across the region today and
tonight as upper ridging builds in from the west. At the sfc, very broad
Canadian high pressure will overspread the region from the NW bringing
dry and stable air to the area. Winds will remain light and out of the
N to NE thru the day before becoming light and vrb later tonight and
into the overnight. With weaker winds anticipated for today, fire-wx
concerns are diminished outside of NE Georgia where low RH is the only
criteria needed for a Fire Danger Statement. As for high temps, non-mtn
areas should remain a bit cooler than yesterday owing to the NLY flow.
The higher terrain is fcst to be 1 to 2 categories warmer than yesterday
owing to increased low-lvl thicknesses and less vigorous cold air
advection.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 330 AM EDT Friday: Quiet conditions are expected to prevail on
Saturday as sfc high pressure continues to build in from the Great
Lakes region/OH Valley, with a piece of it breaking off and settling
along the Carolina/VA coast Saturday afternoon as the next
approaching system slowly tracks across the southern Plains. Aside
from passing clouds throughout the day, overall expect Saturday to
be a pleasant Spring day, with high temperatures in the mid to upper
60s to around 70 degrees across much of the area, though cooler in
spots across the mountains. Overnight lows will trend just a few
degrees below normal. While the seasonal weather would be welcome to
stay longer, it seems latest guidance continues to trend towards a
period of increasing clouds, slightly cooler temperatures and
increasing rain chances, extending into the middle part of next week.

As the upper low to the west is progged to propagate across the
southern plains and eastward across the Deep South within split
flow, moisture from the GOM and isentropic lift will aid in the
development and gradual expansion of rainfall throughout the day on
Sunday, SW to NE across the FA. The onset of precip may be a tad
early in the going forecast per the latest trends of the notable
disagreement both temporally and spatially in regards to the system,
but overall suggestion of precip beginning on Sunday stands. The
aforementioned sfc high pressure is expected to move offshore and
wedge back in across the Carolinas, but with latest trends,
anticipate cooler temperatures to hold off until Monday, as for now
have kept with high temperatures on Sunday to be a bit cooler than
that on Saturday as cloud cover increases. Overnight lows Sunday
night into Monday morning will range in the mid to upper 40s/low 50s
across the Upstate and NW Piedmont, and cooler across the mountains.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 350 AM EDT Friday: The medium range forecast begins Monday
morning where guidance continues to place a sfc high near New
England wedging back in across the Carolinas, while to the SW of the
FA, a 500 mb low is progged to be pushing across MS/AL as plenty of
moisture continues to stream in across the FA. This along with the
aid of isentropic lift, do anticipate rain to already be falling
across most of the area at the start of the medium range forecast
period, likely lingering through midweek. This with high
temperatures expected to only reach into the mid to upper 50s/around
60 degrees on Monday (into the 40s across the mountains) - it`ll be
a dreary start to the work week to say the least.

As the system slowly propagates into TN/GA and the Carolinas
throughout the day on Monday, the suggestion of a secondary low
developing off the FL/GA/SC coast Monday night by some of the
guidance continues. Details from latest guidance become a bit foggy
through the end of the medium range, but overall, anticipate this
system will linger across the Carolinas Tuesday into early Wednesday
morning as another upper low is projected to sweep across the Upper
Midwest and combine with the exiting system - allowing for both
systems to join within the main upper trough across the eastern US.
While previous guidance suggested the potential for some
thunderstorm activity Tuesday afternoon, it seems latest guidance
keeps the best instability well south and east of the FA, thus have
kept with only rain (showers) attm. As the aforementioned next
system approaches, guidance remains in disagreement in regards to
the amount of moisture and forcing in place as flow becomes
northwest. Thus, for now have kept with the trend of precipitation
tapering off across the area on Thursday. Will mention, am expecting
higher QPF at the beginning of the week, with a downward trend
through into Thursday. Temperatures will begin to rebound on
Wednesday as the wedge breaks down, with temperatures nearing normal
towards the end of the week.

&&

.AVIATION /16Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: expect VFR conditions to persist thru the 12z
taf period. With dry high pressure in place, cloud cover will be limited
to only a few high clouds. Winds have weakened more since the last update
with KAVL still hanging on prevailing NWLY winds in the 12 to 15kt range.
The speeds should come down there over the next few hours and remain out
of the NW until late tonight, at which point they go light and vrb. Other
sites will see N to NNE winds in the 4 to 7 kt range today. KGSP, KGMU,
KAND, and KHKY will likely become light and vrb this afternoon with KCLT
doing so later tonight, similar to KAVL. No significant gusts are expected
thru the period.

Outlook: Broad and dry high pressure will linger through Saturday.
Restrictions may develop late Sunday into Monday as a warm front
lifts northward over the area, bringing deeper moisture up from the
Gulf of Mexico.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
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:

www.weather.gov/gsp/aviation

&&

.FIRE WEATHER...
Cooler and much drier conditions are expected today. Low RH values
combined with dry fuels across northeast Georgia will create
increased fire danger conditions for this afternoon and evening,
thus a Fire Danger Statement has been issued. Elsewhere, while winds
will be below critical thresholds today and tonight, RH values are
expected to remain very low, falling to below 30 percent across
Upstate SC and the NW Piedmont and mountains of NC this afternoon.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Fire Danger Statement until 8 PM EDT this evening for GAZ010-
     017-018-026-028-029.
NC...None.
SC...None.

&&

$$
SYNOPSIS...JPT/SBK
NEAR TERM...JPT
SHORT TERM...SGL
LONG TERM...SGL
AVIATION...JPT
FIRE WEATHER...SGL


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