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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 280857
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
357 AM EST Sun Feb 28 2021

.SYNOPSIS...
A warm front will lift northward across the region today. A cold
front will approach the southern Appalachians from the northwest
tonight and then cross the area on Monday. Dry high pressure will
build over from the north as the high center moves from the Great
Lakes to the Mid-Atlantic coast Monday night into Tuesday. Unsettled
weather returns from the west Tuesday night into Wednesday morning.
Another low pressure system may affect the southeast Friday into
Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
400 AM Update...Local ob trends have showed an improvement in vsby
across the Upstate and east toward CLT. Still anticipate patchy dense
fog from GSP toward the CLT area thru daybreak with some deterioration
in vsby around daybreak possible. The DFA has been reduced in coverage
to exclude the wrn Upstate zones and remains in effect elsewhere until
13z.

The main concern/challenge over the early part of the fcst will be
the persistence and possible extra development of dense fog across
the non/mtns. A llvl ridge is trapping moisture at the sfc over the
NC zones, but some improvement in vsby is noted arnd CLT. The
Upstate areas within the DFA are experiencing intermittent patchy
dense fog, which may become more widespread toward dawn. Wont make
any areal changes to the DFA at this time and keep the 13z expiration
time when sfc heating is expected to increase BL mixing.

The forecast area will remain in a sw/ly flow regime this afternoon
and evening ahead of an approaching cold front. Good mixing will
enable low-end gusts with moderate gusts likely across the higher
mtn elevations persisting thru the overnight period. A look at theta
charts indicate weak isent lift ahead of the front coupled with
low-end available moisture. So, think the best relative chance of
light rainshowers will occur across the srn NC mtns and BR escarpment
in mech lift throughout the day. The front will take it/s time
reaching the NC mtns, likely aft 08z, when stronger sfc forcing and a
llvl jet begin to generate higher precip rates over the wrn NC mtns.
Not anticipating any hydro threats thru the near term period, but
the lingering rainfall into the short range may create isol and
minor flooding over the far srn NC mtns, mainly in wrn Graham Co
thru late morning Mon.

Max temps will increase again today in moderate llvl WAA flow. Highs
should reach the mid to upper 70s over the far srn zones to the l70s
north. The mountain valleys will reach the u60s to arnd 70 F. Mins
tonight will also remain well abv normal with readings likely
ranging from the l50s over the mtn valleys to the u50s south of the
I-85 corridor.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
As of 235 am EST Sunday: A progressive northern stream trough will
cross the eastern U.S. on Monday, steadily pushing the passing
surface cold front south of the region through the day. Anticipate
mainly morning rainfall along the passing frontal zone, with
precipitation rates and coverage decreasing as the moisture exits
the lower Piedmont during the afternoon. Brief upslope showers could
also linger into the afternoon along the TN border counties, but
still anticipate that basins can handle the event without any
flooding of note, so no Flood Watches are expected at this time.
Temperature trends will be hard to pin down Monday with the fropa.
Expect falling mountains temperatures through the day there in the
post fropa cold advection, but with a modest Piedmont spike in
midday temps with downslope warming and drying east of the
mountains.

Deep-layer drying will continue from the northwest Monday night as
the surface boundary settles off to the south. A southern stream
closed upper low over the southern Plains Monday night will lift
eastward through the lower MS River Valley on Tuesday. Meanwhile,
surface high pressure moving from the Midwest to New England will
permit cooler and drier air to spill southward into the region on
Tuesday. Upglide moisture could begin to return to our region
through late Tuesday. As forcing and better moisture with the
southern stream system reach the southern Appalachians Tuesday
night, mixed precipitation types may develop over the mountains,
especially at onset of the steadier precipitation. Profiles over the
high terrain suggest that snow may develop along the ridges Tuesday
evening, with ptypes transitioning to more of a mixed bag overnight
into Wednesday morning. The forcing and moisture should move east of
the forecast area by early Wednesday as the associated surface low
passes through Midlands of SC toward the NC coast. An HWO mention
for the mixed ptypes could be needed for the NC mountains for
Tuesday night/Wed morning. Temps should rebound at least a category
on Wednesday afternoon with better insolation returning.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
As of 245 am EST Sunday: Deep-layer northwest flow and modestly
building heights will set up Wednesday night through Thursday ahead
of yet another southern tier closed low pressure system moving east
across Texas during the period. Temperatures will rebound again into
the 60s east of the mountain by Thursday afternoon.

The latest GFS solution has trended toward the ECMWF camp of opening
up the southern stream system across the lower MS River Valley and
Deep South and bringing more modest forcing through the southeast
Friday night. Recent runs of the GFS have trended drier with this
late week system, but will keep solid chance PoPs going in a nod to
the wetter, more consistent ECMWF solutions. The ECMWF 850 mb and
surface low center tracks would be interesting for northern tier
snow potential, but this remains a long way off so no HWO mention
will be made for now. Saturday will be the chilly day of the
extended forecast, but with other days within a category or so of
climatology.

&&

.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
At KCLT: Dense fog and VLIFR conds will persist at KCLT this morning
as a shallow llvl ridge has setup within highly moist sfc layer. Not
anticipating much improvement until after sunrise into mid morning
when the BL warms, but there shud be a quick transition to MVFR or
VFR arnd 16z when gusty conds and increasing llvl mixing commences.
Winds will remain locked in sw/ly ahead of an approaching wrn bndry
and the gusty conds will reduce aft 22z-23z.

Elsewhere: KHKY will have the best chance of locking in dense fog
and VLIFR restrictions this morning as other sites remain a little
better mixed and will likely see VSBYs in the IFR to LIFR range arnd
daybreak, except at KAVL where down-valley flow and lack of a
shallow inversion may keep conds in the VFR to MVFR range. Low-end
sw/ly gusts are likely this afternoon and will diminish after 23z.
KAVL will see the best chance of precip thru 06z with a moist
frontal bndry approaching the TN/NC line. Thus, a PROB30 with -shra
and possible IFR restrictions are mentioned aft 02z thru the
period.

Outlook: Periodic flight restrictions and chances for precip are
expected to linger Mon into Mon night. Drier high pressure will
build back into the area Tuesday.

Confidence Table...

            09-15Z        15-21Z        21-03Z        03-06Z
KCLT       Low   58%     High  85%     High 100%     High 100%
KGSP       Med   66%     High  88%     High  98%     High 100%
KAVL       Med   70%     High  95%     High  98%     High 100%
KHKY       Med   63%     High  80%     High  98%     High  94%
KGMU       Med   65%     Med   65%     High  98%     High 100%
KAND       Med   71%     Med   78%     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 are available at
the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Dense Fog Advisory until 8 AM EST this morning for NCZ035>037-
     056-057-068>072-082-502-504-506-508-510.
SC...Dense Fog Advisory until 8 AM EST this morning for SCZ003-
     006>009.

&&

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