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Area forecast discussion 
National Weather Service Greenville-Spartanburg SC
1013 PM EDT Friday Jul 11 2014

Synopsis...
a weak frontal boundary will gradually weaken and dissipate
overnight with weak high pressure returning for the weekend. An
unseasonably strong cold front is then expected to reach the western
Carolinas by Tuesday increasing the possibility of widespread
thunderstorms.

&&

Near term /through Saturday/...
as of 1010 PM...an interesting convective cluster has remained
across NE Georgia...just west of the forecast area...for several hours
this evening. Latest radar images indicate that a conveyor belt of
feeder cell have develop across the upper Savannah River
valley...tracking into the nearly stationary storm cluster. Area of
50 dbz and lightning trends are down over the past half hour. I will
anticipate that the cluster will steadily weaken and dissipate short
after the latest rounds of feeder cells merge. To the north...sky clear
remains clear with calm wind. I will update the probability of precipitation to adjust probability of precipitation
and timing according to latest thinking. Update severe weather potential statement will be issued
soon.

As of 745 PM...cumulus has become limited to extreme NE Georgia and the NC
mountains radar image indicate a cluster of outflow associated rain showers/thunderstorms and rain
across northern Georgia. These cells are slow moving and would likely
encounter more low level inhibition by the time any boundary reaches the
western edge of the County Warning Area. The combination of weak flow and diurnal
decrease of instability...I will keep schc to chance probability of precipitation around area
of current activity for the next 1-3 hours...then drop mention of
convection. I will update the forecast to increase mention of fog
within the mountain valleys.

As of 525 PM...latest satellite images continue to indicate
enhanced cumulus across the mountains and adjacent foothills. The cumulus along and
east of I-85 and I-77 appeared to be small cells with shallow
vertical development. Kgsp radar indicated a few showers and
isolated thunderstorms across the east facing slopes...the greatest
coverage was near the NC/GA/SC state line intersection. I will
update the forecast to adjust probability of precipitation and align temperatures to
observations.

As of 230 PM EDT Friday...quasi stationary surface frontal boundary
remains in place across the midlands of SC..eastward into the
sandhills and coastal plains of NC. Despite the weak frontal passage...not
much has changed thermodynamically across the County warning forecast area today. Dewpoints
remain in the upper 60s to lower 70s with modest heating allowing
for conditional destabilization. Upper ridge building in over the
Southern Plains continues to stretch eastward allowing for heights
to rise over the southeast. Thus...forecast soundings indicate
improving middle level subsidence leading to a partially capped
environment. Kept probability of precipitation at solid chance levels across the Blue Ridge
this afternoon tapering to no mentionable probability of precipitation eastward into the
NC/SC Piedmont regions where capping should hold. Not expecting any
of the mountain showers/thunderstorms to develop any deep updrafts which
will limit longevity and intensity. That said...abundant dcape in
the region could yield a modest microburst threat along with
frequent cloud to ground lightning with the stronger cells.

Things will quiet down overnight as heating is lost and weak upslope
flow subsides. Guidance indicates the moist boundary layer will
decouple allowing for low stratus and/or fog to develop in and
around the mountain valleys...and potentially to a lesser degree
across the NC Piedmont. Typical summertime pattern returns on
Saturday as high pressure across the northeast gives way to the
Bermuda high. In response...strong southeasterly flow will return
leading to a diurnal pop/temperature trend. Forecast will feature
chances probability of precipitation in the climatology favored regions of the high terrain where
upslope enhancement occurs...along with slight chance probability of precipitation along the
southern tier of the County warning forecast area where surface convergence along old
stationary front could initiate showers/thunderstorms as above
mentioned southeasterly flow migrates the front north. Temperatures
through the period will remain at or just above normal levels.

&&

Short term /Saturday night through Monday/...
as of 145 PM Friday...latest guidance still suggests that the short
term will feature rather typical July weather for the western
Carolinas and NE Georgia. High pressure will remain ridged over the area
Saturday through Sunday as a westward extension of the Bermuda high.
The high will begin to break down over the area on Monday as heights
begin to fall across the eastern U.S. In response to a strong upper
low dropping southeast out of Canada toward the Great Lakes.
Hence...a more prominent Lee trough is showing up in the model
guidance for Monday...which should serve as a trigger for more
convection over the Piedmont than on previous days. To
summarize...on Sunday afternoon convection should be mostly confined
to the upslope areas in the mountains...while on Monday all areas
should see scattered convection during the afternoon. Maximum temperatures
Sunday and Monday will be at or a degree or two above climatology normals.

&&

Long term /Monday night through Friday/...
as of 200 PM Friday...one thing that the medium range guidance
continues to agree upon is the distinct upper level pattern change
that is forecast to occur in the early to middle week period across the
eastern part of the nation. A deep upper low is still forecast to
swing south out of northern Canada and establish an anomalous upper
trough over the east by midweek. However...the details are becoming
a little more murky in our region as the 12z GFS has gone out on its
own in regard to frontal timing, position and frontal wave
development. The 12z GFS is faster than its previous runs and with
the CMC/ecf in moving the upper low into the Great Lakes...and it
does not move the low as far south. In fact...it keeps the upper low
center across the northern lakes. This of course ultimately affects
how far south the surface cold front can be driven. The 12z GFS
moves the cold front into the NC mountains Monday night...then
stalls the boundary somewhere across the Piedmont on Tuesday. Then it
develops a series of frontal waves Tuesday-Thursday with widespread precipitation
each day. Wpc on the other hand has gone with a more ec/CMC solution
which brings the front into the area on Tuesday and moves the front far
enough south of the area to allow drier air to work into the region
Wednesday into Thursday. Although the 00z GFS ensemble is also farther north
with the frontal boundary...it is not as far north as the 12z
operational postiion. At this juncture...we prefer to trend
toward the wpc solution which is more consistent with previous
forecasts. We will linger some probability of precipitation over most of the area on Wednesday due
to the uncertainty involved...but will allow for a dry day on Thursday.
Will probalby feature climatology probability of precipitation on Friday as the front may begin to
return northward.

In regard to impacts...the front will be well forced for July and
convective available potential energy could pool ahead of the front to perhaps 1500-2000j/kg
depending on timing...so there is a possibility for an organized
severe storm event with the frontal passage. Wind shear will be
rather good for July with forecast soundings featuring up to 30-40kt
of 0-6km bulk shear. Also...temperatures are still expected to be at least 2
Standard deviations below average Wednesday and Thursday. For instance...the
12z consraw guidance for Wednesday has maximum temperatures close to 10 degrees below
climatology.

To summarize...a strong cold front is forecast to arrive on Tuesday
bringing the potential for severe thunderstorms. Much cooler weather
is expected Wednesday and Thursday with a lingering chance for showers on Wednesday.
Thursday may be a dry day...then a chance for showers/storms will return
for Friday.

&&

Aviation /02z Saturday through Wednesday/...
at kclt...a weak pressure gradient will remain across the region
this evening and tonight. Light southeast winds will continue through most
of tonight...possibly with periods of calm late. Recent observations
indicate that clt dewpoint has fallen to 61 degrees...while
kakh...kuza...and keqy remains in the upper 60s. I will assume that
clt dewpoint will increase after sunset. Model soundings and
condensation pressure deficits Show Low level/bl moisture increasing
during the pre dawn hours. I will indicate MVFR fog between 10-13z
with sct015 during the rest of the morning. Scattered cumulus bases will likely
form around 050kft around 18z...little to no chance for convection.

Elsewhere...conditions will be similar to clt. However...all near
term model guidance and x-over temperature support a mention of
fog/low clouds at kavl tonight. I will following the timing observed
last night...peaking visible at 1/2sm 8z-12z and bkn003 12z-15z. Scattered cumulus
bases will likely form around 050kft around 18z...little to no chance
for convection.

Outlook...high pressure will slowly settle over the area this
weekend. Any restrictions should mainly be confined to diurnal thunderstorms
and morning valley fog each day.

Confidence table...

02-08z 08-14z 14-20z 20-02z
kclt high 88% high 83% high 92% high 100%
kgsp high 99% high 90% high 85% high 100%
kavl high 86% medium 63% high 84% high 100%
khky high 97% high 88% high 85% high 100%
kgmu high 87% medium 76% high 85% high 100%
kand high 87% high 92% high 85% 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: (must be lower case)

Www.Weather.Gov/gsp/aviation_tables

&&

Gsp watches/warnings/advisories...
Georgia...none.
NC...none.
SC...none.

&&

$$
Synopsis...deo
near term...cdg/Ned
short term...lg
long term...lg
aviation...Ned

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