Area Forecast Discussion
Issued by NWS Greer, SC

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373
FXUS62 KGSP 270855
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
455 AM EDT Mon Mar 27 2017

.SYNOPSIS...
Moist southerly flow will linger over the southeast through Tuesday,
with several rounds of showers and thunderstorms possible. Drier air
will briefly return by the middle of the week as a cold front
settles south of the area. Another low pressure system will bring
moisture back to the southeast Thursday, increasing rain chances
through late Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 445 AM EDT: Forecast PoPs were cleaned up a bit - focusing
mainly on much higher shower chances east of I-77 early this
morning, and then fanning isolated to scattered convective chances
back southwest to northeast Gerogia in the moist southwesterly flow.

Otherwise, water vapor imagery reveals a cyclonic mid/upper level
circulation moving over Missouri early this morning. Low level flow
east of this system is generally south to southwest and this
persistent fetch of Gulf moisture across the southeastern states
will yield continued morning clouds and lingering isolated to
scattered showers for our region. This flow regime will continue
across the southeast through the day. The combination of
temperatures warming quickly through the 70s, despite the mostly
cloudy conditions, and dewpoints solidly in the 50s will likely
produce SBCAPE values in the 1000 to 2000 J/kg range this afternoon.
Narrow lobes of vorticity lifting east ahead of the main trough this
afternoon will provide a triggering mechanism for deep convection.
Although thunderstorm coverage will be in the solid scattered range,
several of the storms could be strong to severe as CAPE improves in
the minus 10 to minus 30 C hail growth zone. Relatively modest
Spring freezing levels should permit 55 dBZ cores reaching the lower
20kft range this afternoon and early evening to yield some
marginally large hail and briefly gusty winds. Fortunately, 850 mb
flow and associated deep layer shear will be less than observed on
Sunday, so cells should not persist as long and a bit less storm
organization is indicated. Will mention the severe potential in the
HWO.

The deeper forcing will occur with the trough as it crosses the
southern Appalachians overnight with better upper jet divergence and
deep layer Q vector convergence indicated. However, instability
should be waning a bit overnight and low level flow will start
veering, so this may limit the strong to severe potential somewhat
for the early morning hours. The real question mark will be how well
the more robust convection from the upstream Slight to Enhanced
severe thunderstorm risk areas is able to survive as it approaches
the mountains. All in all, expect a mild and increasingly wet night.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 225 AM EDT Monday: An ulvl s/w will continue to cross the area
Tue and drag a broad cold front east throughout the day. The atmos
will remain unsettled during this time and isol/sct tstms are
probable early on thru the afternoon. The main focusing area for
stronger storms will be east of the mtns as pre-frontal lift
coincides with destabilizing warm sector by 21z. The op models have
varying ideas with the placement of convec and the degree of
instability...but the ern zones with better sfc td pooling
associated with increased sfc convg shud be the favored area for
deep convection...possibly producing a few svr storms. This activity
will wane rather quickly aft fropa arnd 00z with little if any
showery activity lingering thru the overnight period.

Heights actually begin to rise quickly during the afternoon Tue and
by 12z Wed a deep layered ridge axis will be situated just west of
the FA. A strong subs inversion will engulf the area and prevent
deep convec activity from developing thru the day. There may be some
-shra late and overnight across the nrn zones as a moist wedge
begins to build in. Max temps will reach 10-12 degrees above normal
in good downslope flow...however td/s will be about 10 degrees
cooler than Tue`s values. Thus...no good chance will be had to break
the h7 cap in a non/triggered environ. Min temps will remain 8-10
degrees above normal both Tue and Wed nights.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 305 AM EDT Monday: A strong ulvl ridge will cross the ern
CONUS early Thu thru Fri morning. This will force a cP sfc high off
the mid-Atl coast which will ridge south across the FA. This ridge
will bring some Glakes moisture which will combine with advecting
llvl Atl moisture. Isent lift and increasing precip coverage will
thereby strengthen and hold a wedge in during this time. This will
make for a tricky temp forecast Thu and also the amount of thunder
activity possibly developing across the wedge bndry to the south and
west. For now...have tstms developing across the far sw/rn zones and
max temps ranging from the u50s nrn piedmont to m70s over the far
srn zones. This could change over the next few fcst packages.

Meanwhile...a strong low pressure system will develop across the
srn Plains early Thu and advance toward the OH Valley by Fri
morning. This feature will bring yet another frontal system to the
area Fri. The models agree well with breaking down the sfc wedge
arnd 12z Fri leaving plenty of time for the atmos to destabilize in
a highly dynamic environ....possibly producing stg/svr storms along
a retreating TMB. This scenario has a good amount of uncertainty
however as the speed of the cold front or upper s/w could change and
the inherent complexities and uncertainty involved with
frontal/wedge interactions. The front looks to cross east of the
area late Fri and a dry airmass shud build in over the weekend. Max
temps Fri could be tricky as well...but for now have highs reaching
near normal levels. Over the weekend...highs will likely increase to
about 5 degrees above normal in good insol within a drying column.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
At KCLT: Passing early morning showers have generally moved east of
I-77, but additional isold to scattered activity developing back
over the I-85 corridor in SC will warrant continued VCSH chances.
Profiles are fairly moist and there is considerable uncertainty over
where ceilings will form as temperatures cool through daybreak, but
the best consensus indicates a fairly extended period of MVFR
ceilings continuing until early afternoon before lifting and
scattering occurs. Thunderstorm chances will improve once again
after 19Z and continue into the early evening hours. Expect SW winds
around 10 kt or less throughout, with a few low end gusts possible
this afternoon.

Elsewhere: Isolated shower chances will continue through the morning
hours in persistent, moist southwest flow. Anticipate MVFR level
clouds developing all across the mountains and foothills, with tempo
daybreak IFR ceilings possible at times. MVFR cigs will slowly lift
and scatter late morning into early afternoon, with the thunderstorm
potential increasing again after 18Z. Expect south to southwest
winds throughout at 10 kt or less, with a few low end afternoon
gusts possible.

Outlook: Another round of thunderstorms will be possible on Tuesday,
especially near KCLT. Continued low level moisture will provide a
good chances of restrictions throughout. Drier conditions should
briefly return during mid-week before another storm system begins
affecting the region Thursday and Friday.

Confidence Table...

            09-15Z        15-21Z        21-03Z        03-06Z
KCLT       High  83%     High  90%     High 100%     High  80%
KGSP       Med   70%     High  89%     High 100%     High  92%
KAVL       Med   68%     High  94%     High 100%     Low   53%
KHKY       Med   61%     High  83%     High 100%     Med   74%
KGMU       Med   64%     High  96%     High 100%     High  90%
KAND       Med   66%     High  90%     High  98%     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...None.
SC...None.

&&

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



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