Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 271743
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
143 PM 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 140 PM EDT: Radar currently showing showers over the mountains
and over the Lakelands. Still expect coverage to increase through
the afternoon and continue into the evening. Basically no change
from going forecast.

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 /18Z MONDAY THROUGH SATURDAY/...
At KCLT: MVFR cigs have scattered out. However, low VFR and the
potential for convection return during the afternoon. Guidance has
backed off on the potential for TSRA at the airfield, but chance is
high enough to change the TEMPO to VCTS. Decreasing nocturnal
instability should lead to mainly showers overnight. Guidance has
been consistent bringing in MVFR VSBY and IFR cigs overnight, so
have added these to the TAF. Should be a quick VSBY recover Tuesday
but a slow cig recovery. Winds will be S to SSW through the period.

Elsewhere: Similar conditions to KCLT except with an earlier onset
of convection. Wind will shift after daybreak to NW at KAVL and will
go more westerly elsewhere.

Outlook: Another round of thunderstorms will be possible on Tuesday
afternoon, 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...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       Med   78%     High 100%     High 100%     High  81%
KGSP       Med   71%     High 100%     High 100%     High  81%
KAVL       High 100%     High 100%     Med   61%     Low   41%
KHKY       Med   78%     High  94%     High  83%     Low   35%
KGMU       Med   71%     High 100%     High 100%     Med   65%
KAND       Med   71%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

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



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