Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 281521

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1021 AM EST Tue Feb 28 2017

A warm front will lift north across our area today warming
temperatures further and then a cold front crosses the area
Wednesday night preceded by showers and thunderstorms.  Cool high
pressure will drop temperatures to near normal for the second half
of the week. As the high moves off the Carolina coast, a warm
southerly flow brings temperatures above normal again Sunday and


As of 945 AM EST: Weak shortwaves embedded in the deep layer
southwest flow aloft along with low level isentropic lift continue
to trigger convection from northern AL to central TN this morning,
and this activity should move northeast toward the southern
Appalachians through the afternoon hours. PoP trends have been
ramped up a bit in western mountain and southwest sections in line
with the consensus of the convection allowing models, but
instability for anything strong still looks very limited this
afternoon and evening. A thunder and lightning mention is now
included for occasional cloud to ground strikes in SW sections.
Temperatures appear on track as south to southwest winds start to
modify the airmass.

Otherwise, the thunderstorm activity should struggle to make
significant inroads across our forecast area this evening. Typical
warm sector conditions (anomalously high dewpoints, persistent
surface flow, clouds) will thus be predominant, resulting in
Wednesday morning min temps pretty close to where our highs should
be this time of year.


As of 230 AM EST Tuesday:  The short range fcst period kicks
off on Wednesday morning amidst falling heights aloft as a deep
upper trough slides east out of the Plains.  At the surface, a
subtropical high will be anchored over the Western Atlantic while
a cold front pushes into the MS/OH River Valleys.  Llv flow around
the aforementioned high, combined with improving swly H85 flow ahead
of the front will work to enhance waa across the region through the
day leading to modest destabilization as guidance has trended toward
steeper lapse rates.  With that, profiles will exhibit uncapped pos
CAPE fairly early in the afternoon, however lack of any triggering
is expected to keep any convection at bay until later as the front
approaches, therefore pops will remain rather low.

Guidance seems to have converged a bit better with latest runs
regarding any prefrontal late day precipitation, as well as any
frontal forced convection into the evening as the front itself looks
to move into the high terrain by around 8-9PM.  Instability fields
have improved somewhat with ample pooling of nearly 1-1.5k j/kg
sbcape westward across Middle TN, upwards of 5-7 hundred joules
east into Northeast GA and the Western Carolinas, all mainly due
to the slightly increased speed of the system negating a mostly
nocturnal fropa.  Overall, given that shear fields continue to
look impressive, think chances for strong/severe convection have
improved a bit.  Still to early to tell some of the details, but
given the overall synoptic pattern and the placement of features,
think convection will likely fire to the west across MS/AL ahead
of the front in the moist/unstable warm sector before sliding
east into North Georgia, possibly moving into the Upper Savannah
River Valley by late afternoon, all while frontal convection gets
going to the west.  Evolution of diurnally favored instability
fields would suggest some weakening of the earlier convection
after dark before the primary frontal MCS arrives.  The front
will slide across the region into early morning Thursday, likely
at a fast pace, especially if any cold pooling gets established.
Given relatively veered llv flow, and no backing of surface flow
at all, think the tornado threat is rather low, thus the primary
threats will be damaging winds and possibly some large hail.

Beyond the fropa into Thursday, high pressure will build across
the region from the west leading to drier and cooler conditions yet
again.  Winds could be a bit gusty early on Thursday across the mtns
as the pressure gradient remains enhanced, however should weaken
through the day.  Skies are expected to clear out in response to
the drying conditions and ample downslope flow across the Piedmont.
Temperatures on Wednesday will be well above normal, likely topping
out in the mid/upper 70s across the Piedmont, generally 5-7 degrees
cooler in the mtns.  Expecting temperatures to fall behind the front
for Thursday, however likely hovering at or just above normal for
highs, but cooling substantially into Friday morning as the cool
high settles in.


As of 145 AM EST Tuesday:  On Friday a shortwave passes through the
trough north of our area with the ECMWF having all energy
sufficiently north of our region with no precip for our northern
mountains. The GFS on the other hand has a deeper shortwave
resulting in NW Flow precip reaching the northern NC mountains
around 18Z Friday. Since this shortwave passage would be up in the
daytime, precip would be less snow and more rain than if it were
nighttime. Not a significant event either way.  The shortwave moves
quickly off the East Coast with the center of surface high pressure
centered over NC at 12Z Saturday.  As the high moves offshore late
in the weekend, a southerly flow will result increasing clouds ahead
of the next cold front.

The wind field models are not showing any upslope low level flow
ahead of this front as wind shifts quickly SW early Sunday and stays
that way until frontal passage on Tuesday. Little if any instability
with the front before our forecast ends at 12Z Tuesday. Chances of
precip begin in the mountains late Monday then the bulk of the
frontal precip arrives late Monday night.

Temperatures slightly below normal Friday and Saturday then several
degrees above normal again by Monday.


At KCLT and the foothills TAF sites: Lower MVFR clouds have
generally lifted and scattered late this morning and now anticipate
mainly SCT to BKN VFR clouds going forward in the southwesterly flow
today. Winds have toggled southerly this morning and should pick up
from the SW through the afternoon (but less than 10 kt). Any
precipitation going forward should focus on the mountains this
evening and generally stay well west of KCLT.

Elsewhere, scattering and lifting low clouds should keep bases SCT
to BKN at lower VFR levels through the rest of the day, with thicker
cirrus aloft. Convection arriving from the southwest should bring
showers, and possibly isolated thunder, to KAVL late day. A return
to MVFR is likely later tonight in continued moist
southerly/southwest upslope and upglide flow.

Outlook: A cold front will approach from the west late Wednesday and
bring additional chances of showers and restrictions, as well as
some thunderstorms. Drier conditions end the week following the

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High 100%     High 100%     High 100%     Med   74%
KGSP       Med   70%     High 100%     High  98%     Low   58%
KAVL       High 100%     High  91%     Med   71%     High  92%
KHKY       Med   60%     High 100%     Med   75%     High  85%
KGMU       Med   70%     High  86%     High 100%     Med   66%
KAND       Med   78%     High 100%     High 100%     Med   65%

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:




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