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Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
349 AM EDT SAT AUG 27 2016

.SYNOPSIS...
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 into 
the Gulf of Mexico. Forecast uncertainty is very high with this 
system.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 330 AM: The center of 595 DM ridge will lift over the DELMARVA 
region as a western Atlantic mid level low drifts slowly toward the 
Carolina coast today. Broad high pressure will remain across the 
Great Lakes region, ridging south across the forecast area. This 
pattern should provide SKC to FEW sky cover through the morning 
hours. Winds are forecast to rise to 6 to 8 kts from the ESE during 
the daylight hours. The forecast for SHRA and TSRA will be a 
challenge this afternoon and evening. It appears that a region of 
mid level Q-Vector convergence will develop between the H5 ridge and 
western Atlantic low, generally over the I-85 corridor. The llvl ESE 
flow should transport an old sea breeze inland across the Midlands 
to eastern Piedmont this morning. CAPE values west of the sea breeze should 
generally range in the moderate range with low values of CIN. The 
combination of the weak mid level forcing and weak llvl boundary 
should trigger SCT SHRA/TSRA this afternoon, tracking from NE to SW. 
Supported by the HRRR and 4km WRF, I will forecast the greatest 
coverage of convection across the I-77 corridor this afternoon. It 
is possible that a few damaging wet microbursts will occur within a 
field of 1300-1500 J/kg DCAPE, we will highlight in the HWO. Using a 
blend of warmer MOS, I will forecast highs near 90 within the mtn 
valleys to low to mid 90s across the foothills and Piedmont.

Tonight, convection is expected to dissipate by late evening across 
the western Carolinas and NE GA. Debris clouds and convective CU 
should thin out by midnight. H85 winds will remain out of the ENE as 
the sfc ridge becomes slightly deeper during the overnight hours. 
Upslope flow and lingering moisture from wet ground could support cloud 
cover along and east of the Blue Ridge overnight. Low temperatures 
are forecast to range from the mid to upper 60s across the mtns to 
low to mid 70s east.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
As of 315 AM Saturday: Heights are expected to fall ever so slightly 
across the Mid-Atlantic and Southeast during the short term, but 
subtropical ridging will nevertheless dominate across much of the 
southern 2/3 of the country. Short term guidance remains consistent 
in establishing more of a NE low level flow on Sunday, as 1020+ 
surface high pressure builds into New England, resulting in a 
sharpening of the inverted ridge axis down the Eastern Seaboard. 
This results in lower theta-E air filtering into the area by Sunday 
afternoon, such that there isn't a whole lot of sbCAPE forecast 
across the northeast quarter or so of the forecast area. There should 
be enough instability to support widely scattered convection across 
the western half of the area, but pops of only 10-20 percent will be 
forecast across our eastern zones. 

If anything, Monday's forecast ingredients appear even less 
supportive of deep convection, with the NAM and GFS indicating that 
a substantial portion of the area will see sbCAPE values < 500 J/kg 
Monday afternoon, especially across the heart of the forecast area. 
Only slight chance pops will be carried across our far southern and 
western areas Mon afternoon into evening. A bit of a potential fly 
in the ointment concerns the fate of a weak tropical disturbance, 
currently located near Bermuda, that short term guidance tends to 
agree will push onto the Carolina coast in the Mon night/early Tue 
time frame. The NAM is by far the most aggressive model in advecting 
the plume of deep moisture into the western Carolinas, but even it 
does not do a whole lot in terms of QPF response in our area. Opted 
to just linger a small pop across the southern and eastern zones 
Monday night into Tue as a nod to this possibility.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
As of 335 AM: The tropics in the vicinity of eastern North America 
will be pretty active during the medium range, but primarily in 
terms of quantity instead of quality (i.e., intensity). The global 
models depict multiple weak disturbances across the Gulf of 
Mexico/Caribbean/western Atlantic during this time, so much so that 
it's difficult to determine where one ends and another begins. The 
Canadian is the only model that wants to do something of note with 
any of these disturbances, developing a significant tropical cyclone 
across the eastern gulf by mid-week (it's been fairly consistent in 
doing this), but it's difficult to put much stock in this 
considering the "meh" response among other (more reliable) guidance 
sources. 

The general consensus is that heights over the eastern conus will 
fall sufficiently by mid/late week such that a frontal boundary will 
push across the Southeast, sweeping away these various disturbances 
from the Conus before they would have a chance of having much of an 
impact on sensible weather in our area. It therefore does not appear 
the medium range will be particularly active, even in terms of 
diurnal convective activity, as low level NE flow acts to keep 
relatively low theta-E air over the forecast area through the period. 
In fact, the models are not even that enthused with the potential 
for convection associated with the passage of the front. Pops will 
therefore remain at or a little below climo through the period. 
Temps will generally remain a couple of degrees above normal until 
the end of the week.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: The center of 595 DM ridge will lift over the DELMARVA 
region as a western Atlantic mid level low drifts slowly toward the 
Carolina coast today. Broad high pressure will remain across the 
Great Lakes region, ridging south across the forecast area. This 
pattern should provide SKC to FEW sky cover through the morning 
hours. Winds are forecast to rise to 6 to 8 kts from the ESE during 
the daylight hours. The forecast for SHRA and TSRA will be a 
challenge this afternoon and evening. It appears that a region of 
mid level Q-Vector convergence will develop between the H5 ridge and 
low, generally over the I-85 corridor. The llvl ESE flow should 
transport a weak sea breeze inland across the Midlands to eastern 
Piedmont. CAPE values west of the sea breeze should generally range 
in the moderate range with low values of CIN. The combination of the 
weak mid level forcing and weak llvl boundary should trigger SCT 
SHRA/TSRA this afternoon, tracking from NE to SW. I will highlight 
the most likely period of convection with a PROB30. Otherwise, sky 
conditions should favor SCT045-050 CU. However, KAVL could see a 
period of LIFR ceiling this morning around sunrise, KAND may see 
MVFR fog between 11z to 13z. 

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 within two hours following sunset.
Patchy fog will be possible any morning following a late afternoon
to early evening shower or thunderstorm.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z 
KCLT       High 100%     High 100%     High 100%     High 100%     
KGSP       High 100%     High 100%     High 100%     High 100%     
KAVL       High  86%     High  96%     High 100%     Med   76%     
KHKY       High  86%     High 100%     High 100%     High  96%     
KGMU       High 100%     High 100%     High 100%     High 100%     
KAND       High 100%     High  92%     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:

www.weather.gov/gsp/aviation

&&

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

&&

$$
SYNOPSIS...HG
NEAR TERM...NED
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...NED

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