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Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
655 AM EDT SAT JUL 23 2016

Broad deep layered high pressure will remain across the region 
through early next week, with a general weakness developing over the
east coast on Monday. Moisture levels will gradually increase across
the western Carolinas and northeast Georgia by the middle of next
week as a weak cold front settles south into the area.


As of 650 AM, fog and low stratus have expanded across the mtn 
valleys this morning, so have beefed up sky cover and lowered visby 
in those areas for the next couple of hours. Otherwise, Little 
change in the overall pattern is expected during the near term, as 
the forecast area will remain parked between the subtropical high 
centered over the Four Corners, and a weakness in the S.T. ridge off 
the Southeast Coast. While this pattern is not obviously supportive 
of substantial precip chances, it's not entirely hostile to 
development of deep convection. In fact, plenty of heat and some 
humidity will be realized once again this afternoon, with NAM 
soundings somewhat impressive on the buoyancy front. Max temps will 
be a couple of degrees warmer than on Friday in most areas, with 
much of the SC/GA and southwest NC Piedmont expected to see heat 
indices of 100-104. 

Meanwhile, much as they were yesterday, the GFS and the RAP are 
quite aggressive in mixing drier air to the surface within a lee 
trough this afternoon, such that there is very little CAPE depicted 
in these models' forecast soundings. This did not work out well at 
all yesterday. In fact, some of the best convective coverage 
yesterday occurred across the northern foothills and northwest 
Piedmont, where the GFS/RAP were depicting the weakest instability. 
In that same vein, none of the mesoscale/convection-allowing models 
were excited about convection in those areas yesterday, and they are 
painting a pretty similar picture for today. 

If anything, the mid-level flow is expected to be more NE today, so 
it would stand to reason that any convection developing within lee 
trough and across the higher terrain would tend to drop south as 
opposed to SE, sparing much of the Piedmont of the solid scattered 
coverage that was observed yesterday. Have therefore opted to 
forecast a slight chance across the Piedmont this afternoon, with 
30-40 pops across the foothills, and 40-60 pops across the mtns. 
Mid-level dry air and a well-mixed/deep boundary layer will result 
in impressive downdraft CAPE once again this afternoon, thus 
microbursts will be a concern with the stronger cells. 

Convection should wind down this evening, with another warm 
overnight expected.


As 250 AM Saturday: On Sunday, the axis of the H5 ridge will build 
over the forecast area, increasing to 594 dm by the afternoon. At 
the sfc, little to no pressure gradient will exist across the 
western Carolinas and NE GA during the day. In fact, model guidance 
indicates that wind speeds are forecast to remain below 5 kts from 
the sfc up to H7. High thicknesses and good insolation should 
support high temperatures from around 90 degrees within the mtn 
valleys to upper 90s to around 100 across the I-85 corridor. 
Forecast soundings show the mixed layer deepening slightly above H8 
during the heat of the afternoon. The mixing may lower sfc dewpoints 
from around 70 in the morning to the upper 60s during the afternoon. 
Heat Index values may peak between 101 to 106. In addition, forecast 
soundings indicate that llvl CIN will linger east of the mtns 
through most, if not all, of Sunday afternoon. Thermal profiles 
appear supportive of mtn ridge convection as early as mid day. 
Storms may propagate by developing along outflow boundaries. This 
process should support sct coverage across the mtns and isolated 
coverage east. Convection should ash out shortly after sunset, with 
debris gradually clearing into the late night hours. Low 
temperatures Sunday night are forecast to range for the 60s across 
the mtns to the low to mid 70s east.

On Monday, a sfc front is forecast to slowly slide across the Ohio 
River Valley, with a lee trof across the foothills and Piedmont. 
light south winds should result in a one to two degree rise in 
afternoon dewpoint temperatures. As a result, llvl CIN appears 
weaker than Sunday across the foothills and Piedmont. NAM forecast 
soundings for KGSP indicates CAPE above 2500 J/kg and PW rising to 
1.8 inches. Winds are forecast to remain less than 10 kts from the 
sfc to H4. I will time chc PoPs across the CWA by mid day, rising 
very quickly across the mtns around lunch, then spreading east across 
all of the Piedmont. A few areas may see high Heat Index values 
between 100 to 106 degrees during the mid to late afternoon.


As of 3 AM Saturday: Tuesday through Thursday, the center of the H5
ridge will shift over the Deep South. Models indicate that a series
of weak mid level S/W will ripple across the forecast area. Each
day, moderate instability and weak CIN will exist across the region
during the afternoon and early evening. I will continue to indicate
diurnal chc to ridge top likely PoPs each day, schc east. I would
expect that PW values will remain above normal as a front becomes
stationary to our north. Temperatures should range within a couple
of degrees of normal, cooler than Sunday and Monday.


At KCLT and elsewhere (except KAVL), VFR conditions are expected 
through the period at most terminals. Generally expect light S/SW 
winds to persist through the period. Isolated to scattered 
convection is expected to develop once again this afternoon, esp 
near the Upstate SC terminals and KHKY, and VCTS and/or PROB30s are 
advertised at these sites from late afternoon into the evening. 
Cannot at all rule out convection near KCLT, but coverage should be 
a bit more sparse in the Piedmont, and due to the inherent 
uncertainty, will omit any mention of convection there for the time 

At KAVL, fog and low stratus have finally developed, and this should 
burn off by around 14Z. Otherwise, scattered convection is expected 
to develop once again this afternoon, and VCTS is advertised 
beginning at 17Z, with PROB30s carried from late afternoon into the 
early evening. Another round of fog and/or low stratus is possible 
late tonight, but timing and magnitude of this is completely 
uncertain attm, and restrictions are limited to MVFR fog around 

Outlook: Scattered/isolated afternoon and evening showers and 
thunderstorms will continue across the mountains/piedmont through 
early next week. Morning fog and low stratus will be possible each 
day in the mountain valleys and also in locations that receive heavy 
rainfall the preceding afternoon/evening.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z 
KCLT       High 100%     High 100%     High 100%     High 100%     
KGSP       High 100%     High 100%     High 100%     High 100%     
KAVL       Med   61%     High 100%     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:



  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      96 1983     68 1985     71 1934     52 1966    
   KCLT     100 1983     73 1938     78 2010     59 1947    
                1952                    1883                
   KGSP     101 1952     70 1985     79 2010     59 1904    


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      92 2010     68 2000     70 2012     51 1895    
                2005                    2011                
                1987                    2010                
   KCLT     101 2010     69 2000     79 2010     62 1947    
   KGSP     100 1995     72 2000     77 2010     57 1911    





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