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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Tuesday
• 
• High: 81 °
• Low: 64 °
• T-Storms

• Wednesday
• 
• High: 79 °
• Low: 66 °
• Chance of T-Storms

• Thursday
• 
• High: 82 °
• Low: 55 °
• Chance of T-Storms

• Friday
• 
• High: 75 °
• Low: 46 °
• Clear

• Saturday
• 
• High: 72 °
• Low: 48 °
• Clear

Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
114 am EDT Tuesday may 21 2013 


Synopsis... 
an approaching upper level trough will continue to influence the 
region for most of this week. Southerly flow will keep the area in a 
moist and generally unsettled airmass with storm chances each 
afternoon. Rain chances diminish after a cold front crosses through 
by the end of the week. 


&& 


Near term /through today/... 
0515 UTC update...winds were updated to incorporate the latest NAM 
data. Probability of precipitation were lowered based on radar trends. Visibility was 
updated from a blend of the adjmav and adjmet...placing patchy fog 
across most of the area toward daybreak. 


As of 1030 PM...for the 0230 UTC update...have cut back probability of precipitation for the 
night...to just a slight chance in the eastern zones. A fair amount of 
cloudiness expected...with patchy fog developing overnight. Temperatures 
were bumped up a hair...given the high dewpoints. 


For Tuesday...a look at the 12z convective allowing models...it 
appears shower and thunderstorm coverage may not be quite as high as expected. 
So I cut back probability of precipitation a little bit...especially in the Piedmont. Still 
expecting scattered storms...with a higher microburst threat (cape 
2500-3500 j/kg in forecast soundings with very weak flow sfc-350mb). Highs 
will be above normal under building ridge aloft. 


&& 


Short term /tonight through Thursday/... 
as of 230 PM Monday...looks as if not much has changed with regards 
to model guidance in the short term. Remnants of upper trough 
responsible for the weather across the region over the last few days 
will finally begin to push of the East Coast Tuesday evening. An 
upper level ridge will build in across the region during the 
overnight hours of Wednesday morning. Model soundings continue to 
indicate weak capping and moderate instability through the profile 
Wednesday. Expecting convection to get going across the mountains 
early on Wednesday as mechanical forcing will overcome any weak 
inversions. Convective activity will spread southeast across 
the i85 corridor by middle to late afternoon as diurnal heating 
destabilizes the boundary layer further. Shear profiles look rather 
weak across northeast Georgia and the Carolinas during this 
period so expecting any convection to be somewhat disorganized 
leading to more of a pulse/cluster type storm Mode threat. With 
that...the main threats with any of these storms will be brief heavy 
rainfall and gusty winds. Temperatures on Wednesday will depend 
somewhat on overall coverage of shower and thunderstorm activity in 
the area. However...went with slightly above normal lows...and near 
normal highs. 


Meanwhile...deep upper level trough and its associated surface low 
will continue to slowly move to the east across the Great Lakes 
region. A surface cold front extending to the southeast across the 
Mississippi River valley will continue its eastward progression 
towards the Appalachians. Forecast models seem to show slightly 
weaker instability across the region on Thursday...however shear 
profiles look stronger as the upper level wave passes by and the 
surface cold front approaches. As the front moves into the area on 
Thursday afternoon...heights will fall allowing showers and 
thunderstorms to initiate across the higher terrains first...then 
spread to the southeast across the piedmonts of the Carolinas. Some 
of these thunderstorms could be strong to severe as upper level 
support could allow for some organization. Thus...the main threats 
on Thursday will be heavy rainfall...and the potential for damaging 
wind gusts and small hail. Overall temperatures on Thursday will be 
slightly above normal. 


&& 


Long term /Thursday night through Monday/... 
as of 100 PM Monday...the large scale pattern is well agreed upon 
through the period. A strong...yet moisture limited short wave will cross 
over the forecast area Friday...while a strong mean ridge axis develops to 
the west and dominates the sensible weather through Monday. 


There are enough varying ideas by the way the op models with respect to the airmass 
change and possibility of a back door cold front sun to keep probability of precipitation on 
the low end sun/Mon. Before that...Friday should see the best chance for 
showers and deeper convection...but the upper short wave will be battling a 
800 mb/700 mb layer of cold air advection and a drying NE/ly surface flow. So...will keep probability of precipitation 
low end chance and mainly across the higher terrain due to good mech 
lift enhancement and low level moisture remaining relatively high. Model 
soundings are showing some weak afternoon instability and probably 
enough to spawn a few convective showers with the deep 
Omega...however thunderstorms should be hard to develop within a deeply dry 
atmos in place. 


Things will remain dry through the weekend with a low confidence 
back door cold front building in from the north sun. The ecwmf is 
more pronounced with this feature but the GFS also has a low level 
Theta/east boundary in the area which looks to linger into Monday. The 
models diverge once again Monday with the amount of short wave energy rounding 
the upstream ridge...with the GFS more definitive on enough upper 
support to generate at least scattered -shra and thunderstorms across the high 
terrain and along the aforementioned surface boundary. The European model (ecmwf) on the 
otherhand...keeps the best ulvl dynamics well to the north and thus 
no good chance of precipitation in the County warning forecast area. Thus...probability of precipitation late sun through 
Monday have been maintained in the slight range and limited to mainly 
the western zones. Maximum temperatures will begin the period right around 
normal...and probably adjacent down a couple degrees sun and Monday with the 
cp airmass and weak cad config. 


&& 


Aviation /05z Tuesday through Saturday/... 
at kclt...no precipitation will be carried overnight as heating has 
abated and the atmosphere has stabilized. A blend of model guidance 
supports only low VFR visibility in fog toward dawn...despite moist low 
levels. Confidence on ceilings is quite low due to model variance. 
Clouds heights will generally be based on current observations... 
with a daybreak dip to MVFR...which is supported by the middle of 
the Road met guidance. Instability will support robust convection on 
Tuesday...mainly in the afternoon...but coverage will be rather 
limited as upper level support drifts to the east. Light south winds 
will persist. 


Elsewhere...radar trends support leaving precipitation out of the 
tafs overnight in a stabilizing atmosphere. A guidance blend 
supports a daybreak IFR ceiling at kavl...low VFR at kgsp...and MVFR at 
all other sites. Confidence is low on ceilings...especially at 
daybreak...as model guidance varies considerably...and there is 
still some doubt cloud coverage will increase enough by dawn in the 
wake of a departing upper system. MVFR ceilings will be carried toward 
daybreak at kgmu...kgsp and khky...which is supported by less 
extreme met guidance. Although convective coverage will be limited 
Tuesday as upper forcing departs to the east...instability will 
support vigorous updrafts. Light south winds are expected. 


Outlook... ceiling and visibility restrictions in scattered showers 
and thunderstorms again Wednesday and Thursday aftn/eve. Generally 
VFR weather Friday and Saturday. 


Confidence table... 


05-11z 11-17z 17-23z 23-05z 
kclt high 83% medium 78% high 100% high 100% 
kgsp high 85% medium 74% high 100% high 100% 
kavl low 57% low 56% low 57% low 58% 
khky medium 72% high 84% high 100% high 100% 
kgmu high 85% high 87% high 100% high 100% 
kand medium 70% high 87% 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: (must be lower case) 


Www.Weather.Gov/gsp/aviation_tables 


&& 


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


&& 


$$ 
Synopsis...level 
near term...Ark/jat 
short term...cdg 
long term...sbk 
aviation...jat