Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 261308

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
908 AM EDT FRI AUG 26 2016

Surface high pressure will build over the region through the
weekend. Tropical low pressure will slowly strengthen off the
southern tip of Florida early next week and then possibly move
toward the Gulf Coast through the week.


1310 UTC Update: Sky cover was lowered based on satellite trends.

As of 7 AM: I will issue a quick update to indicate mtn valley
stratus and fog around KAND. Otherwise, the current forecast appears
in good shape.

As of 510 AM: Water vapor loop indicates that band of vorticity has
not drift south and east as earlier numerical solutions indicated. I
will update the forecast to increase sky cover and raise PoP to schc
over the greater area this afternoon.

As of 305 AM: Restrictive fog and low clouds will be the primary
challenge early this morning. Based on forecast calm winds and thin
sky cover, NC mtn valleys should be the most likely area to see fog
this morning. I will forecast fog to develop near KAVL by 10z,
highlighting 10z to 13z for low ceilings. East of the  mtns, it
appears that H925 winds will remain out of the NW and may provide
weak downslope winds across the foothills. KAND and KHKY will be
limited to patchy fog. KGSP/KGMU/KCLT are expected to remain clear.

Latest satellite W/V images indicated a band of deeper moisture
along the I-85 corridor of the Carolinas. In addition, a well
develop circulation was drifting west across Jacksonville, FL. The
0Z runs of the near term guidance had a better handle on the band of
h5 vorticity across the western Carolinas. Based on a blend of the
guidance, this feature should gradually shear and pivot west over
the upper Savannah River Valley and extreme western NC this
afternoon and evening. This mid level feature will exist south of
the center of a 595 DM ridge centered over the NC/VA line. The
combination of widespread weak to moderate CAPE and the passage of
the mid level vort max should result in isolated to scattered
showers and thunderstorms this afternoon and early evening. The
greatest coverage of convection should occur across the western NC
mtns and over the upper Savannah River Valley.

Sfc high pressure will shift over the western Atlantic this
afternoon. A weak sfc trof is expected to develop over the central
Carolinas this morning and remain through the day. This pattern
should support calm winds during the early morning, light NE winds
after sunrise, then light SE winds during the afternoon. High
temperatures are forecast to range from the low to mid 90s east of
the mtns, with upper 80s common within the mtn valleys.

Tonight, showers/thunderstorms/Cu should dissipate two hours
following sunset. Decreasing sky cover, light winds, and dewpoints
in the upper 60s to low 70s should favor patchy fog during the
predawn hours. Using a blend of MOS, I will forecast upper 60s
within the mtn valleys to low to mid 70s east.


As of 315 AM Friday: Upper level high pressure will remain centered
over the Mid-Atlantic through the weekend, with deep/weak easterly
flow across the forecast area. On Saturday, this easterly flow
should keep dewpoints seasonably elevated, while not-terrible lapse
rates south of the center of the upper high should yield moderately
strong levels of instability. This should allow scattered convection
to fire near the Blue Ridge Sat afternoon and drift toward the west.
Therefore, chance pops will be advertised across the mtns Sat
afternoon into the evening, tapering to slight chance south of the
I-85 corridor. Although coverage should begin diminishing Sat
evening, isolated Blue Ridge convection could persist through the
night in the easterly flow regime.

Short term guidance is in fairly good agreement in expanding the
center of surface high pressure into North Carolina on Sunday,
shoving lower theta-E air into the forecast area by afternoon. In
fact, the GFS and the NAM depict sbCAPE of around 0 across much of
the NC Piedmont and foothills during this time. While solid chance
pops for diurnal convection will be advertised across the mtns
again, especially across southwest NC, pops taper to less than 20
percent along the I-77 corridor Sunday afternoon. It would appear
that heavy rainfall would be the main convective threat during the
short term, as weak cloud-bearing flow could allow for some
anchoring along the escarpment, although ingredients do not appear
to be in place for anything more than a highly localized threat.
Sufficient CAPE and dCAPE should also be available to support a
threat for isolated pulse severe storms.

Under the influence of the upper ridge, temps will be about 5
degrees above climo Saturday/Sat night, but may dip closer to normal
during the latter part of the period as the surface high ushers in
drier and slightly cooler air.


As of 340 AM Friday...The early part of the week should generally
see below-climo pops, as the global models agree in maintaining a
relatively dry NE surface flow which should preclude substantial
diurnal destabilization. Of course, the elephant in the room is the
tropics, but the evolution of the area of disturbed weather
currently in the vicinity of the Bahamas remains about as clear as
mud. Each model has its own "opinion" about the fate of this
disturbance, and they are literally all over the place in terms of
the eventual intensity and track of this feature. However, a clear
consensus of global model guidance does suggest that our area will
remain relatively inactive convection-wise through at least Day 6,
so pops were lowered a little closer to climo toward the end of the
period. Temps will also remain close to normal through this time.


At KCLT: Sfc high pressure across the southeast U.S. will weaken
this afternoon, resulting in a weak trof to develop over the
east-central Carolinas this afternoon. The region will remain under
the center of a H594 DM ridge. This pattern should yield calm to
light winds, direction favoring the NE this morning to SE this
afternoon. Winds speeds should remain 6kts or less. Based on
forecast soundings, I will indicate the CU will remain FEW to SCT at
045 through the daylight hours.

Elsewhere: Restrictive fog and low clouds will be the primary
challenge overnight and early this morning around KAND. East of the
mtns, it appears that h925 winds will remain out of the NW and may
provide weak downslope winds across the foothills. KGSP and KGMU are
expected to remain VFR. Winds of 5kts or less will vary from SE to S
through much of the day. KAVL could see a VCTS between 20z to 0z.
Based on forecast calm winds and thin sky cover tonight, KAVL should
be the most likely terminal to see fog during the pre dawn hours.

Outlook: A deep ridge of high pressure will persist across the
region through early next week. The environment should support mid
to late afternoon thunderstorms each day, primarily over the mtns and
adjacent foothills. Weak steering flow should favor iso to sct
coverage, with storms dissipating with two hours following sunset.
Patchy fog will be possible any morning following a late afternoon
to early evening shower or thunderstorm.

Confidence Table...

            13-19Z        19-01Z        01-07Z        07-12Z
KCLT       High 100%     High 100%     High  91%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High  82%
KHKY       High  91%     High 100%     High 100%     High  82%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High  99%     High 100%     High 100%     High  83%

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:


At 910 AM Friday: Mixing heights were lowered based on the latest
model soundings. Smoke management paramaters were updated




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