Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 261430
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
930 AM EST Sun Feb 26 2017

.SYNOPSIS...
Cool high pressure will be centered over our area today then move
off the Carolina coast tonight.  Expect warmer air to return
during the first half of the week. A warm front lifts north through
the area Tuesday then a cold front crosses our region from the
northwest Wednesday night. Cool high pressure brings temperatures a
little below normal at the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 930 AM: Under quiescent conditions, only small adjustments to
T/Td were made to the fcst today, these based on our short-term
model consensus product. Max temps near normal are still
anticipated.

Quasizonal flow overhead of building sfc high pressure highlights
the weather across Northeast GA and the Western Carolinas this
morning.  Said high pressure will continue to push atop the region
through the period leading to a relaxed pressure gradient and thus
weaker nwly flow leading into mid/late morning.  Weak lee troughing
across the Western Upstate will work to keep sites across the Upper
Savannah River valley a bit backed early on, before guidance favors
backed wswly flow nearly regionwide late in the day as the center of
the surface high moves across the Carolinas.  The airmass associated
with said surface ridge is cooler than days past, and drier as well.
Sunny skies, low dewpoints, and deep mixing still look to promote
very low RH values across nearly the entire region this afternoon,
with most sites likely to fall into the teens to upper 20s (not
much change from previous fcst). This will lead to enhanced fire
danger; please refer to the fire weather discussion for details.
A few high cirrus are fcst to stream in aloft late tonight into
Monday morning as convection gets going across the Arklatex/MidSouth
regions in association with a deepening upper shortwave.  Min temps
tonight are fcst to be around or just below normal levels.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
As of 315 AM EST Sunday: Heights will gradually rise across the
eastern Conus throughout the short term period, in response to a
deepening trough across the West. Resultant strengthening SW flow
across the southeast U.S. will allow for increasing moisture
beginning late Monday into Mon night and Tue, with a bit of warm
frontal activation anticipated as a cyclone organizes across the
Great Plains. The first order of business for this forecast cycle
was to refine Monday`s pops (i.e., lower them) across much of the
area, as a consensus of guidance is hinting at delaying moisture
advection until Mon night and early Tue. Even then, the moisture
remains fairly shallow and overall forcing profiles weak. Therefore,
while high chance to likely pops will be favored near the high
terrain, most areas will see a 20-40 percent chance for rain. If
anything, as the low levels moisten up late Mon night, forecast
soundings take on an advection fog/drizzly appearance, with near
saturation depicted from the surface to around H8.

A consensus of guidance would see the warm front passing through the
area by Tue afternoon, with much more of a warm sector profile shown
in forecast soundings by then. Of course, this will depend at least
partly upon how much rain and or/drizzle falls into the initially
dry air mass, which will undoubtedly force an ageostrophic response/
establishment of brief and shallow in-situ cold air damming.
Nevertheless, with the surface high positioned several hundred miles
off the Mid-Atlantic coast by 18Z Tue, it seems reasonable that the
warm sector will overtake much of the forecast area by Tue evening,
and temps will be forecast at more than 10 degrees above climo Tue
and Tue night. (Actually, Tue night has the look of one of those
"min temps that are close to normal max temps" kind of nights.) The
establishment of the warm sector will also lead to diminishing pops
during this time.

Another very warm spring-like day is in the offing for Wednesday, by
which time strong/deep layer SW flow will be well-established. I
suppose some weak diurnal convection cannot be entirely ruled out
Wed afternoon, as forecast soundings do indicate positive
surface-based buoyancy, while mechanical forcing near the high
terrain will be significant with a 40-50 kt LLJ expected through
much of the day. However, warm mid-level temps should keep any
activity isolated at best. Pops then ramp up quickly Wed evening
into the overnight hours, as a cold front is expected to move
quickly into the area from the TN Valley. While the better deep
layer forcing is expected to pass north of the area, a consensus of
guidance is suggestive of a decent frontal circulation, good
moisture profiles, and a strong pre-frontal low level jet. These
factors support maintenance of high pops (likely) Wed night, while
suggesting a severe weather potential (with buoyancy being the main
limiting factor as usual) that will require continued monitoring.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 145 AM EST Sunday:  On Thursday the cold front moves off the
Carolina coast with brief NW Flow Snow ending in the Northern NC
Mountains Thursday afternoon. The favorable NW Flow wind speeds and
direction at 12Z Thursday goes light and more west midday as rapid
drying occurs, thus ending all light snowfall by mid afternoon.
Another strong shortwave passes across the Great :ales Thursday
night and may generate some light snow in the northern NC Mountains
early Friday. If this happens, it will not be much as GFS barely
affects the Nrn Mtns and the EC is too far north with the shortwave
to do anything for our area.  Cool high pressure will be centered
over our area early Saturday bringing the coolest air in a while.
This high remains over our region through Sunday keeping it dry. A
low comes out of the Gulf early next week but that if after the end
of the current forecast.

Temperatures on Thursday will be near normal outside of the
mountains but a little below normal in the mountains. Temps on
Friday and Saturday will be a few degrees below normal overall with
Saturday around 5 degrees below normal as cool high pressure
overhead.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
At KCLT and Elsewhere:  VFR through the period at all sites as
surface high pressure shifts through the region.  Profiles remain
rather dry today/tonight leading to mostly SKC with a few mid/high
clouds streaming aloft late in the period.  Light nwly winds will
prevail through the morning hours as the pressure gradient continues
to relax, with some mid/late afternoon wswly backing expected at
all sites.  Guidance favors further backing to nearly ese/ene flow
near periods end as the transient high sets up over the Delmarva,
however opted to keep out of taf at this time given low confidence.

Outlook: Dry conditions with very low chances for restrictions
expected to start the work week, before another upper impulse
approaches on Monday afternoon leading to increased chances for
precipitation/restrictions for Tuesday and again on Wednesday as
cold front approaches from the west late in the evening/overnight.

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:

www.weather.gov/gsp/aviation

&&

.FIRE WEATHER...
Cool/dry high pressure to move across the region today.  Pressure
gradient forces are expected to relax leading to weaker surface
winds of generally around 5-10mph sustained, with gusts in the
15-20mph range possible across the high terrain.  The bigger
issue will be mixing of already low dewpoints which will lead to
critical RH levels across the entire region.  Said RH levels will
likely fall into the lower/mid 20s by midday, lowering further into
the teens through the afternoon as peak mixing occurs.  Given the
expectation of weaker surface winds, Fire Danger Statement criteria
is not fcst for NC/SC.  However, these RH levels are sufficient
for such across Northeast GA, therefore a statement will be issued
for Fire Danger between noon and 6PM.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Fire Danger Statement until 6 PM EST this evening for GAZ010-
     017-018-026-028-029.
NC...None.
SC...None.

&&

$$
SYNOPSIS...DEO
NEAR TERM...CDG/Wimberley
SHORT TERM...JDL
LONG TERM...DEO
AVIATION...CDG
FIRE WEATHER...CDG


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