Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 220153

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
953 PM EDT Tue Mar 21 2017

A cold front will move through the area later tonight, increasing
the chances for widespread showers and thunderstorms. A few of the
thunderstorms could be severe. Cooler air will return behind the
front to end the work week before another frontal system approaches
the area next weekend.


Evening Update...Widespread storms continue across the FA with the
stg/svr cells beginning to exit to the south and east. Most of the
svr reports were large hail...up to 2 inches. Hover the s/w moving
in from the west has created wind damage across the SW NC mtns. The
bulk of the s/w activity has shifted south and west of the CWFA and
MUCAPE values have dropped sigfnt/ly...but there is still enuf
unstable air to generate thunder and small hail...which will likely
require SPS statements over the next few hrs. A broad area of
stratiform precip will cross the area and exit to the east by 06z or
so. Min temps will be tricky outside the mtns thanks to pockets of
rain/hail cooled air. Will adj the hr/ly temps and attempt to create
a new diurnal curve.

730 PM EDT Update...Strong/severe storms with big hail arnd the GSP
area tonight. Reports of car windows smashed and golf ball size or
greater hail. These storms have trained down from the escarpment of
nrn G-ville Co and there are some concerns with high water levels
across local streams as well. Will investigate for possible flood
advisories or SPSs. Strong h5 s/w noted crossing into nrn GA and ern
TN attm will track across the CWFA late tonight thru the early
morning hrs. More strong to severe storms are probable with this
feature producing damaging winds and large hail once again.

500 PM EDT Update...A couple Upstate svr storms are beginning to
break the thermal cap and slowly advance south ahead of a sfc bndry.
Expect isol stg/svr activity to remain across NE GA and the Upstate
through 00z. An advancing acute h5 s/w will enhance activity from
the west and cross the watch area into the late evening. The watch
may need to be expanded east later on.

As of 215 PM: A nearly stationary front remains across the northern
tier of NC and TN attm; it is difficult to pinpoint the front in
many areas, but it is clear VA and KY are north of the front. At any
rate, an amplified upper ridge will move into the Plains states this
evening, and in response high pressure will shift into the Great
Lakes region, driving the front south through our area tonight.

This afternoon, south of the front, warm and seasonably humid
conditions will be present. Mid-level lapse rates are rather strong,
and accordingly forecast CAPE values range from 750-1000 J/kg over
the NE CWFA to nearly 2000 J/kg over parts of SW NC and NE GA. Most
prog soundings continue to feature at least a small cap until around
21z, and this is reflected in reflectivity/QPF output from the CAMs,
which is minimal until then. 0-6km bulk shear values will be on the
order of 30-35 kt around peak heating, and we continue to expect
storms to organize to some degree. SPC has outlined an Enhanced
Risk centered to our west, but extending into a small portion
of our northeast GA territory; this is surrounded by a narrow
Slight Risk region. At least the Enhanced area will receive the
effects of a compact shortwave during the late afternoon hours,
and models are a bit more aggressive in pushing the front south
thru TN than they are over our area. Also of note, meso model runs
have tended to show a forward-propagating cluster developing in the
Tennessee Valley and tracking east this evening. This may present
a secondary threat to our western areas in addition to that posed
by the greater afternoon instability. Our entire CWFA continues
to be included in a Marginal Risk where the threats appear largely
the same, but the coverage will be lower.

Remnant stratiform precip associated with the decayed MCS is
expected to cross the area overnight, perhaps with a few isolated
rumbles of thunder but otherwise just light rainfall. With any
broad frontal boundary progged to push through in the early morning
hours, I am somewhat cautious about advertising a total "scouring"
of low-level moisture. However, essentially all guidance sources,
including MOS, depict the low clouds pushing out by daybreak, and
cooler and drier conditions lasting thru Wednesday. GFS still tries
to develop a little instability over NE GA, but currently this looks
to be an outlier. All precip mention has been dropped. Sunshine
and gradual downsloping should permit high temps near normal.


As of 2pm EDT Tuesday:  GFS and EC models in good agreement on
synoptic pattern transitioning Wednesday evening to Friday from
northwesterly flow with dry, cool low-level advection to a ridge
centered over the CWA by Friday afternoon.  Dewpoints begin to
improve Friday afternoon as surface high pressure center moves
eastward off the coast and low-level flow veers from easterly to
southeasterly, beginning the southeasterly advection of
moisture into the area.

With a dry boundary layer and ridging aloft, there will be little
chance for precipitation Wednesday night through Friday, with only
an outside chance for some orographic-related showers in far western
parts of the CWA.  Main issue will be chances for frost/freeze
Thursday and Friday mornings.  Current lows show freeze possible
with frost likely for western parts of North Carolina, with less
potential for Piedmont areas.  Drier air and few clouds northeast of GSP
leads to lower forecast lows to the northeast with CLT possibly
reaching low to mid 30s Thursday morning and mid to upper 30s Friday


As of 205 PM EDT Tuesday: the medium range fcst picks up at 00z on
Saturday with upper ridging centered over the SE CONUS and a
southern stream closed upper low moving across the southern plains.
Over the next 24 to 48 hrs, the low will approach the fcst area and
as it does, it will lift northward and up over the ridge. As it
does, it`s also expected to deamplify and open up as it rides up the
ridge. As we move into early next week, another H5 shortwave will
approach the CWFA from the west. It also appears to deamplify as it
approaches the CWFA.

At the sfc, broad high pressure will be centered well offshore with
moist SLY flow over the region. By early Sunday, a vigorous low will
lift NE towards the Great Lakes and push a moist warm front over the
CWFA. The cold front associated with the low, looks like it will
largely washout as it lays across our northern fringe early Monday.
As we move into Tuesday, another sfc low follows a similar track
towards the Great Lakes and brings another cold front to our
doorstep by the end of the period. As for the sensible wx, POPs
steadily ramp up from the west on Sat with likely POPs over half of
the CWFA by Sunday morning. Some drying is expected on Monday,
however POPs increase again on Tuesday with the approach of the next
frontal system. Temps start out above normal and remain above normal
thru the period.


At KCLT and elsewhere: Showers and strong to severe thunderstorms will cross
the SC sites as well as KCLT thru the overnight. Large hail and
damaging winds could occur at any site thru 09z. CIGS and VSBY are
generally remaining in the VFR range outside of the storms...with
MVFR/IFR conds and erratic gusty winds underneath the individual
cells. The mtn sites should remain out of the strong activity with
isol general tstms possible overnight. Skies clear up around
daybreak with winds shifting n/ly to nne/ly.

Outlook: Low level moisture starts to lift back north and deepen by
Thursday, keeping chances of showers and low cigs into the weekend.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High  98%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  97%     High  97%     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:




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