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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Thursday
• 
• High: 81 °
• Low: 57 °
• T-Storms

• Friday
• 
• High: 73 °
• Low: 48 °
• Partly Cloudy

• Saturday
• 
• High: 77 °
• Low: 46 °
• Partly Cloudy

• Sunday
• 
• High: 79 °
• Low: 50 °
• Clear

• Monday
• 
• High: 79 °
• Low: 59 °
• Partly Cloudy

Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
121 am EDT Thursday may 23 2013 


Synopsis... 
an approaching upper level trough will continue to influence the 
region through Thursday. A cold front moves through the area 
Thursday night...before a cooler and drier airmass settles in for 
the weekend and modifies through the early part of next week. 


&& 


Near term /through today/... 
0500 UTC update...probability of precipitation were realigned to concur with radar 
trends...moving a line of convection across Interstate 77 over the 
net few hours...another cluster of storms across the upper Savannah 
River valley...and a third group of storms from the Georgia mountains 
into SC. Winds were updated with a blend of the latest adjmav and 
NAM...favoring the later for higher winds in the mountains. 
Visibility was updated form observations and a blend of the adjmav 
and adjmet...lowered slightly toward the lamp guidance. 


As of 1045 PM...broken multicell line of thunderstorms continues to 
move to the east northeast across the upstate in association with 
convergence near frontal boundary. Elsewhere...discrete pulse 
showers and thunderstorms were present across portions of the North 
Carolina foothills/Piedmont. The main threats with any of these 
thunderstorms are brief heavy rainfall...large hail...damaging 
winds...and frequent cloud to ground lightning. As for the 
forecast...the activity currently extending across the western County warning forecast area 
should move eastward across the County warning forecast area gradually diminishing in 
intensity as instability wanes. Generally changed probability of precipitation to reflect 
this wave of activity being followed by much lower probability of precipitation in schc to 
low chance range due to continued presence of upstream activity. 
Adjusted temperature trends further by lowering temperatures across the 
North Carolina Piedmont due to outflow boundaries from earlier 
convection spreading across this region. 


Remainder of previous discussion... 


As of 800 PM...touched up evening temperature trends...which have been 
impacted greatly by thunderstorms and their cool outflow. Radar 
indicates several boundaries spreading across the Piedmont...where 
temperatures remain in the middle to upper 70s. Think these will be impacted 
by both diurnal cooling as well as the outflow. Lamp temperatures seem to 
reflect the current situation fairly well and these are in decent 
agreement with late evening temperatures...so no changes made other than to 
update first few hours. 


As of middle afternoon...a broken band of showers and thunderstorms was 
located just east of the Blue Ridge in NC from I-40 northeastward...with 
other storms popping up across the higher terrain aided by 
differential heating. Expect the storms to become more numerous 
across the mountains through late afternoon...with that convection moving 
east over the foothills and Piedmont into the evening. Pop has been 
adjusted accordingly. Some of these storms will produce large hail 
and damaging wind gusts. High temperatures still look okay. 


For tonight...the convection allowing models suggest that another 
round of storms will fire to the west and then move east into the 
forecast area in the early evening. The hrrr and 4km WRF paint a similar 
picture with numerous storms over the western half of the forecast area 
through middle to late evening. A short wave moving around the upper 
trough...combined with some upper divergence...should provide the 
necessary support for this convection to thrive. With that in 
mind...the pop was raised to likely over the western half. After 
some loss of heating...the storms should become a bit less numerous 
over the NC Piedmont. At that point...the pop was kept below 50 percent 
only because of some uncertainty given by the convection having not 
yet developed as of 18z. Min temperatures should remain mild. 


The cold front will move in from the west on Thursday...most likely 
over the mountains in the morning and then moving out over the foothills 
in the afternoon. New convection should develop along the front 
mainly over the Piedmont in the afternoon. This is tricky because of 
the likelihood of widespread debris cloudiness into the early 
afternoon that would limit convection. Think the mountains stand a chance 
because of the front early in the day. The upstate and NE Georgia 
has the least favorable environment...so a 20 percent pop was kept. The 
Piedmont has a better chance ahead of the front so a likely pop was 
carried over the eastern zones for a time. Severe storms are 
possible...but more likely to the east of I-77. High temperatures will be 
a few degrees cooler. 


&& 


Short term /tonight through Saturday/... 
as of 230 PM Wednesday...a surface cold front should be located near 
the edge of our western North Carolina Piedmont early Thursday 
evening. This lines up well with the short term suite of models... 
and lines up with with an axis of DPVA which should be crossing that 
region late in the day/early evening. Convective allowing models 
also depict this trend and is supported by instability lingering 
across that area. As a result we will have a corridor of lower 
chance probability of precipitation in our eastern forecast area (fa) until around dark or 
so. 


A second area of precipitation for Thursday night will be in the NC 
mountains where another lobe of energy...embedded in a sharpening 500 mb 
trough...crosses the area. We will carry chance probability of precipitation in the NC 
mountains Thursday night and Friday morning...in a continually 
deepening forced upper air pattern. Although the sharpening trough 
crosses all of our region Friday...the atmosphere looks to dry for 
any precipitation. 


Meanwhile the 850 mb isallobaric pattern was indicating significant 
cross contours of thermal structure and heights Friday. This 
suggests at least significant cold air advection (especially just 
above the surface) and mixing down. We have followed BUFKIT 
information for wind gusts Friday...and in all likelihood we will 
need some type of wind headline Friday for part of our FAA... 
particularly in the afternoon. 


High pressure will edge toward the region Friday night...which will 
bring a cool/cold night around the area. Some mountain locations to 
dip into the 30s...but believe enough mixing should prevent frost 
due to the lingering gradient of high pressure off to the northwest 
and low pressure moving up the eastern Seaboard. However we will 
have to monitor trends. 


High pressure to hold sway Saturday with a pleasant day on 
tap. 


&& 


Long term /Saturday night through Wednesday/... 
as of 225 PM Wednesday...rather good agreement is had in the upper 
level Omega pattern over the ext range. The 12z GFS is a bit of an 
outlier and sharpens the East Coast trough and subsequent deep northwest/ly 
flow gradient moreso than the other op models...but not enough for a 
sigfnt low level response. At the surface...there are major differences 
evolving with the synoptic pattern...thus a less than average 
confidence is had as the ext range progresses. 


High pressure continues to build in from the north sun and keeps 
things dry. High temperatures will be a little below normal with a 
reinforcing cp airmass mixing in. The low level flow becomes defined 
SW/ly Monday as the atl high nudges in. This will also enable a warm 
front or stationary to perhaps impinge upon the region Monday night 
into Tuesday. There is low confidence in this feature...however...as the 
GFS keeps any frontogenesis well to the north of the region with a 
weak trough building into the surface Southeast Ridge...while the European model (ecmwf) has the 
warm front stalling out across the County warning forecast area during the day Tuesday into Wednesday. 
Right now...probability of precipitation have been continued in the low end chance range Monday 
through Tuesday...and a drier HPC blend was maintained for Wednesday. 
Soundings show very little SBCAPE developing Monday as the upper flow 
keeps a subsidence inversion in place...however a relative weakening 
aloft Tuesday should enable the development of some enhance convection 
and thunderstorms. Maximum temperatures will warm each day Monday through the period to a 
little above normal in good SW/ly flow and insolation. 


&& 


Aviation /06z Thursday through Monday/... 
at kclt...another line of thunderstorms will cross the field 
shortly...then activity will diminish. A damp air mass and prior 
rainfall amounts support visibility and ceiling restrictions toward dawn...and 
MVFR will be carried. SW winds will mix out restrictions after in 
the morning. Another round of convection with possible restrictions 
is expected on Thursday as a cold front moves through from the 
west...and another approaches from the northwest. Convection will move off to 
the east by Thursday evening....while SW winds veer to northwest and become 
gusty. 


Elsewhere...convection will move east our of the foothills shortly. 
Earlier rainfall has moistened the atmosphere and ground to the 
point that at least MVFR restrictions are expected by daybreak...and 
temporary IFR at kavl. By middle morning restrictions will end as the 
winds comes up from the SW in the foothills ND northwest in the mountains. 
Additional convection and restrictions are expected by midday 
between a departing cold front...and another stronger front arriving 
from the northwest. Winds will veer to the west during the day in the 
foothills and become gusty...veering further to become northwest in the 
evening. Precipitation will be mainly confined to the mountains 
Thursday evening in northwest upslope flow. 


Outlook...restrictions possible with lingering moisture overnight 
Thursday night and Friday morning. Generally VFR weather Friday and Saturday. 


Confidence table... 


05-11z 11-17z 17-23z 23-05z 
kclt high 84% high 90% high 100% high 100% 
kgsp medium 79% high 88% high 100% high 100% 
kavl medium 70% high 88% high 100% high 97% 
khky low 56% high 83% high 100% high 100% 
kgmu medium 73% high 83% high 100% high 100% 
kand medium 69% high 94% 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...sbk 
near term...cdg/jat/PM/Wimberley 
short term...ts 
long term...sbk 
aviation...jat