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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Wednesday
• 
• High: 83 °
• Low: 64 °
• T-Storms

• Thursday
• 
• High: 81 °
• Low: 59 °
• Chance of T-Storms

• Friday
• 
• High: 72 °
• Low: 50 °
• Partly Cloudy

• Saturday
• 
• High: 75 °
• Low: 50 °
• Partly Cloudy

• Sunday
• 
• High: 75 °
• Low: 54 °
• Partly Cloudy

Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
245 PM EDT Wednesday may 22 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 Thursday/... 
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 
afew degrees cooler. 


&& 


Short term /Thursday night 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 /19z Wednesday through Monday/... 
at kclt...think conditions will remain VFR into the early 
evening...with scattered cloud bases around the 035 to 045 range. The 
latest guidance...including the convective models...is focusing more 
on the middle to late evening across the NC Piedmont for when a broken 
band of storms will move through. Will carry a prob30 for this in 
the 03z to 06z time frame. Expect adjustments to the probability and might 
have to include a tempo later in the day. With cooling...the cloud 
bases should fall into MVFR range late this evening and stay there 
through early afternoon on Thursday. Fog could become a problem 
around daybreak if significant rain happens late tonight. 
Otherwise...the visibility was kept above 5 miles. The front should stay 
west of the terminal through early afternoon and will serve as a 
trigger for new development by late morning Thursday...thus another 
prob30 group toward the end of the period. As a result...wind 
direction should remain S to SW. 


Elsewhere...VFR for the time being. Convective cloud bases should 
remain in the 035 to 050 range...mainly few to scattered...and then should 
drop into the MVFR range this evening as convection becomes more 
numerous. The front will probably make it into the mountains Thursday 
morning so the wind at kavl was shifted to northwest. Another round of 
showers and storms is possible over NC Thursday late in the period. 


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


Confidence table... 


18-24z 00-06z 06-12z 12-18z 
kclt high 86% high 100% high 86% high 90% 
kgsp high 100% medium 79% high 87% high 97% 
kavl high 93% medium 77% high 81% high 97% 
khky high 93% medium 73% low 54% high 80% 
kgmu high 100% medium 79% high 83% high 94% 
kand high 100% high 80% high 82% high 95% 


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...PM 
short term...ts 
long term...sbk 
aviation...PM