A supercell thunderstorm moves through Abbeville, South Carolina, on Saturday 15 March 2008. Numerous reports of hail and wind damage were received from Abbeville County and a tornado touched down near Due West. Image courtesy of GwdToday.com, photographer unknown.

Author's Note: The following report has not been subjected to the scientific peer review process.

1.  Introduction

On 15 March 2008, a series of supercell thunderstorms produced a 
significant outbreak of severe weather across Upstate South Carolina 
and northeast Georgia (Fig. 1).  Numerous reports of large hail were 
received, including one report of softball size hail in Anderson 
County, South Carolina.  In addition, three tornadoes were confirmed, 
the strongest being the EF2 tornado that tracked over southeast 
Elbert County, Georgia.  The other two tornadoes affected Franklin
and Hart counties in Georgia, and northeast Abbeville County in South 
Carolina, and were rated at EF0 intensity.  This was an unusual event 
for the region, as the atmospheric ingredients necessary for supercell 
thunderstorms rarely coexist across northeast Georgia and the western
Carolinas.  Nevertheless, the severe weather episode was well-forecast 
several days in advance by the National Weather Service (NWS) Weather 
Forecast Office (WFO) at Greenville-Spartanburg (GSP) and by the NWS 
Storm Prediction Center (SPC).

Click here for a list of storm reports from this event

Figure 1.  Preliminary SPC storm reports for 15 March 2008.  Tornado reports 
are shown in red, large hail reports are shown in green, and damaging wind
reports are shown in blue.  Black squares represent reports of wind gusts
of 65 knots or greater, while black triangles are reports of hail 2 inches
in diameter or larger.

Note that all times in this report are referenced to Coordinated Univeral 
Time (UTC), which is four hours ahead of Eastern Daylight Time (EDT).  
To convert to EDT, subtract four hours from the UTC time.

2.  Background

The possibility of a significant outbreak of severe weather occurring 
on 15 March 2008 within the GSP County Warning and Forecast Area (CWFA) 
was first identified by GSP forecasters on 11 March.  The Area Forecast 
Discussion issued by GSP at 1800 UTC mentioned the resemblance of 
forecast soundings from the National Centers for Environmental 
Prediction’s (NCEP) Global Forecasting System (GFS) model to the 
"loaded gun" sounding (Fig. 2) often associated with Great Plains 
supercell outbreaks.  

Figure 2.  An example of a "loaded gun" sounding.

One of the important characteristics of this sounding that contributes 
to its strong potential instability is the layer of steep, nearly 
dry-adiabatic lapse rates that exists above the moist boundary layer.  
This layer is referred to as the "elevated mixed layer."  Originating 
from the warm and dry high-elevation regions of northern Mexico, strong 
southwest flow in the 5,000 to 10,000 feet layer often advects this 
airmass north and east over the southern Great Plains and lower 
Mississippi Valley during Spring.  As this warm, dry air overspreads 
relatively cool, moist maritime air originating from the Gulf of Mexico, 
a strong inversion becomes established at the top of the marine layer.  
This inversion inhibits or "caps" convective development.  Due to the 
high degree of potential instability in the sounding, removal of the 
cap often results in explosive convective development, hence the term 
"loaded gun."  It is quite rare for the elevated mixed layer to advect 
much further east than the lower Mississippi Valley (Lanicci and Warner, 
1991).  This is due to the fact that convection often significantly 
modifies (moistens and warms) this layer before it reaches Georgia and 
the Carolinas.  This results in significant weakening of mid-level lapse 
rates, and therefore weaker potential instability.

Subsequent model runs of the GFS continued to indicate the potential 
for an outbreak of severe weather on 15 March, increasing forecasters’ 
confidence that a significant event would occur.  The Hazardous Weather 
Outlook (HWO) issued by GSP at 0925 UTC on 12 March specified that the 
Piedmont and Foothills of the western Carolinas and northeast Georgia 
were the most likely areas to receive severe weather on Saturday, 
15 March.

The SPC Day 3 Convective Outlook, issued at 0722 UTC on 13 March 
(Fig. 3) featured a slight risk for severe weather across much of the 
Southeast.  Meanwhile, GSP continued to highlight the potential for a 
severe weather outbreak in the HWO issued at 0936 UTC on 13 March and 
specifically mentioned areas south of Interstate 85 as being the highest 
threat area.  With confidence increasing that a significant event was 
likely, GSP began making plans to augment staffing for 15 March.

Figure 3.  SPC graphical Day 3 Convective Outlook issued 0722 UTC 
13 March 2008.

The SPC Day 2 convective outlook issued at 0541 UTC on 14 March (Fig. 4a) 
continued to indicate a slight chance for severe weather across much of 
the Southeast.  The probabilistic Day 2 outlook (Fig. 4b) featured an area 
of 30% or greater probability of severe weather that covered the southern 
half of the GSP CWFA.  The updated probabilistic Day 2 outlook, issued at 
1729 UTC on 14 March (Fig. 4d), featured an area of 10% or greater chance
of significant severe weather across much of northern Georgia and the 
lower Piedmont and northern Midlands of South Carolina.

Figure 4.  Categorical Day 2 Convective Outlook (a.) and Probabilistic
Outlook (b.) issued by SPC at 0541 UTC 14 March 2008.  Categorical Outlook
(c.) and Probabilistic Outlook (d.) issued at 1729 UTC on 14 March.  The
light blue hatched area in (d.) indicates the greater than 10% probability
of significant severe weather. 

Finally, the Day 1 Convective Outlook issued by SPC at 0559 UTC on 
15 March (Fig. 5) indicated a moderate risk for severe weather for much 
of north Georgia, and the Upstate and Midlands of South Carolina.  The 
probabilistic outlook issued at this time featured a large area of 30% 
or greater probability of large hail and damaging wind, along with a 
15% or greater probability of tornadoes across much of South Carolina, 
as well as central and north Georgia.  The threat for severe weather 
was considered significant enough for the SPC to issue a Public Severe 
Weather Outlook at 1004 UTC.

Figure 5.(a.) Categorical Day 1 Convective Outlook issued by SPC at 
0559 UTC 15 March 2008. Probabilistic forecasts are shown for (b.) 
large hail, (c.) tornadoes, and (d.) damaging wind gusts.

3.  Synoptic Characteristics

On the 500 hPa analysis at 1200 UTC on 15 March, a low amplitude, 
fast, quasi-zonal flow was observed across much of the southern half 
of the country (Fig. 6).  A weak short wave trough was moving off the 
East Coast, while another weak short wave trough was moving out of 
the Great Plains and into the Mississippi Valley.  Short wave ridging 
was noted between these two features over the Appalachian Mountains.

Figure 6.  SPC 500 hPa objective analysis of geopotential height, 
temperature, and wind barbs at 1200 UTC 15 March.

The 300 mb analysis (Fig. 7) at 1200 UTC on 15 March indicated the 
upper-level reflection of the short wave trough over the Mississippi 
Valley, with a strong jet streak (125 - 150 knots) upstream of the 
trough over the southern Plains.  This resulted in strong upper 
divergence over much of the Mississippi Valley and western Ohio 
Valley.  The rear entrance region of a weaker jet associated with the 
short wave trough over the east coast produced a second area of upper 
divergence over Georgia and the Carolinas.  This area of forcing was 
responsible for isolated, marginally severe thunderstorms over the 
lower Piedmont of South Carolina during the late morning hours.

Figure 7.  SPC 300 hPa objective analysis of isotachs, streamlines, and 
divergence at 1200 UTC 15 March.

The 1200 UTC surface analysis from the Hydrometeorological Prediction
Center (HPC)(Fig. 8) indicated an area of low pressure across southern 
Arkansas, with a quasi-stationary frontal boundary extending from the 
surface low across Mississippi and Alabama and into north Georgia and 
the Midlands of South Carolina.  The frontal boundary was clearly seen 
in the observations shown on the regional surface plot at the same 
time (Fig. 9).  An airmass characterized by temperatures and dewpoint 
temperatures in the 60s was observed along the Coastal Plain.  Meanwhile, 
temperatures and dewpoints were in the 40s across the Piedmont and 
Foothills of the Carolinas.

Figure 8.  HPC analysis of surface fronts and pressure at 1200 UTC 
15 March.

Figure 9.  Regional surface plot at 1243 UTC 15 March, including surface 
observations taken at 1150 UTC.  Data are plotted according to the 
traditional station model.

The similarity between the observed sounding from Birmingham, Alabama 
(BMX), at 1200 UTC on 15 March (Fig. 10) and the sounding in Figure 2 
was notable.  A very moist layer of air was indicated from the surface 
to around 850 hPa.  This layer was capped by a strong temperature 
inversion.  Very steep lapse rates were observed above the inversion. 
Although this sounding featured very little instability (106 J/kg), 
the potential instability in the sounding was quite high, owing to the 
steep mid-level lapse and the moist boundary layer.  Modifying this 
sounding for a surface temperature of around 70 degrees F, and a 
dewpoint of around 65 degrees F, produced convective available 
potential energy (CAPE) in excess of 2000 J/kg, a relatively large 
CAPE value for the Southeast in March.

Figure 10.  Observed sounding from Birmingham, Alabama (BMX), at 1200 UTC 
15 March.  The red line is the temperature sounding and the green line
is the dewpoint sounding.  Wind barbs are shown in the column on the 
right.  A hodograph is indicated in the upper left corner.  Image 
created using RAOB v.5.8 for Windows.

The southeast regional radar composite image at 1200 UTC on 15 March 
indicated two areas of elevated convection north of the frontal boundary
over the region (Fig. 11).  One was located over Upstate South Carolina,
but a larger area was over northern Mississippi.  Meanwhile, the capping 
inversion appeared to be inhibiting convective development over the warm 
sector.  Based on this information, only minor changes were made to the 
Day 1 Convective Outlook when it was updated at 1227 UTC.

Figure 11.  Southeast regional radar image at 1200 UTC on 
15 March 2008.  Image obtained from the Iowa Environmental Mesonet.

During the middle part of the morning, all signs pointed to the rapid
development of severe thunderstorms in the favorable environment ahead
of convection moving from north Alabama into north Georgia.  As a
result, the SPC issued a Tornado Watch for much of north Georgia and 
the Upstate and Midlands of South Carolina at 1500 UTC (Fig. 12).  
The moderate risk area was expanded on the updated Day 1 Convective
Outlook issued at 1614 UTC and as of late morning, a severe weather 
outbreak appeared to be likely.

Figure 12.  Outline of Tornado Watch number 119 issued by the SPC 
at 1500 UTC on 15 March 2008.

The absence of convection in the warm sector during the morning of 
15 March and resultant lack of overturning allowed the plume of steep 
mid-level lapse rates sampled by the 1200 UTC BMX sounding to advect 
over the western Carolinas and northeast Georgia during the afternoon. 
Increasing south to southeast flow responding to the surface low caused 
the frontal boundary to move slightly to the north during the afternoon.  
Meanwhile, dewpoint temperatures in the 60s were being drawn northward 
to the boundary (Fig. 13).  As the upper jet streak continued to dig 
into the Southeast, increasing upper divergence within the left exit 
region lifted and cooled the capping inversion, allowing for explosive 
release of the potential instability over much of South Carolina and 
north and central Georgia.

Figure 13.  As in Fig. 9, except at 1643 UTC.

The 1800 UTC sounding from BMX (Fig. 14) revealed the evolution of the 
atmosphere during the morning and early afternoon.  An inversion remained, 
but had been lifted to around 700 hPa.  Despite the presence of this 
inversion, the atmosphere was no longer capped, as heating and moistening 
of the boundary layer had increased instability sufficiently so that an 
air parcel lifted from the surface experienced positive buoyancy from 
the lifted condensation level (LCL) through the depth of the troposphere. 
The sounding yielded almost 1500 J/kg of CAPE. Storm Relative Helicity 
(SRH) in the sounding was 375 m2/s2 in the 0-3 km layer, and 309 m2/s2 
in the 0-1 km layer. These values of CAPE and SRH were well within the 
range of values found by Lane (2008) to be characteristic of significant 
tornado environments over the western Carolinas and northeast Georgia. 

Figure 14.  As in Fig. 10, except at 1800 UTC 15 March.

4.  Convective Evolution

By 1700 UTC, scattered supercell thunderstorms developed along the 
stationary front across northern Alabama and north Georgia.  These 
storms produced widespread severe weather across these areas as 
they moved along the stationary front toward the Carolinas.  GSP 
forecasters, recognizing the threat that these storms posed to the 
GSP CWFA, issued a Special Weather Statement (SPS) at 1706 UTC to 
alert customers and partners of the increasing potential for 
dangerous thunderstorms.  The growing threat was also noted by the 
SPC at 1722 UTC.  The first warning issued by WFO GSP during the 
afternoon of 15 March was a Tornado Warning at 1818 UTC for portions 
of Elbert, Hart, and Franklin Counties in Georgia, as a well-organized
supercell moved across northeast Georgia.  The composite reflectivity 
from the Greer (KGSP) Weather Service Radar - 1988 Doppler (WSR-88D) 
at 1840 UTC and 1848 UTC (Fig. 15) showed the initial supercell moving 
into Franklin County.  A sequence of storm relative velocity (SRV) 
images from KGSP (Fig. 16) indicated a deep, but relatively broad 
mesocyclone at 1840 UTC.  However, by 1848 UTC, a smaller, more 
intense circulation was observed near the center of the mesocyclonic 
circulation on the Franklin and Hart county border (Fig. 17).  A 
gate-to-gate velocity couplet of around 80 knots (35 knots outbound + 
45 knots inbound) was observed at 0.5 degrees.  This velocity 
differential qualified this circulation as a Tornado Vortex Signature 
(TVS).  However, the radar algorithm did not identify this feature as 
a TVS until the next volume scan.  Incidentally, an EF0 tornado was 
in progress in association with this rotational signature across 
southeast Franklin and extreme southwest Hart County (Fig. 18).  
However, the tornado was near the end of its life cycle when the 
gate-to-gate shear became evident in radar data.  By the time the 
radar algorithm identified the circulation as a TVS, the tornado 
had dissipated.

Figure 15.  Composite reflectivity from KGSP radar at (a.) 1840 UTC and 
(b.) 1848 UTC.

Figure 16.  Storm relative velocity images from KGSP at 1840 UTC at 
(a.) 0.5 degrees, (b.) 1.3 degrees, (c.) 2.4 degrees, and (d.) 3.1 degrees.
The white arrows in (b.) indicate the motion associated with a couplet
of inbound and outbound targets that identify a low level mesocyclone.
The speed is given by the color table at the lower right, where negative
values represent motion toward the radar and positive values represent 
motion away from the radar, by convention.

Figure 17.  As in Fig. 16, except at 1848 UTC.  The white arrow shows
the strongest gate-to-gate shear on the 0.5 degree scan.

Figure 18.  Track of tornado across parts of Franklin County and Hart 
County, Georgia, on 15 March 2008.  The tornado track is delineated by 
the heavy black line below Franklin Springs and Royston.  The background 
map is from Delorme Street Atlas USA.

The environment across northeast Georgia remained highly favorable for 
additional supercell thunderstorms and tornadoes during the early 
afternoon.  In fact, the SPC upgraded the Day 1 Convective Outlook at
1940 UTC to a high risk of severe weather across part of northeast 
Georgia and the lower Piedmont of South Carolina.  

A Tornado Warning was issued for Elbert County, Georgia, at 1954 UTC 
for another supercell thunderstorm moving out of north central Georgia.  
A series of reflectivity images from KGSP (Fig. 19) showed the low-level 
structure of this storm, including an impressive hook echo, as it was 
producing an EF2 tornado across extreme southern Elbert County.  The 
three-dimensional cross section from KGSP at 2016 UTC depicted in 
Figure 20 indicated classic supercell structure, including a strongly 
tilted updraft, bounded weak echo region (BWER), and a high reflectivity 
core suspended aloft.  These features were indicative of a very strong, 
rotating updraft.

Figure 19.  Radar reflectivity from KGSP at 0.5 degrees at (a.) 2016 UTC, 
(b.) 2021 UTC, (c.) 2025 UTC, and (d.) 2029 UTC on 15 March.  The white 
arrow in (b.) indicates the location of a well-defined hook echo.  The 
reflectivity scale is shown by the color bar on the left of each image.

Figure 20.  Radar volumetric cross-section of the Elbert County storm 
at 2016 UTC.  The white arrows indicate the location of a BWER, tilted 
updraft, and an elevated hail core.  The color scale is the same as in
Figure 19.  Image made with GR2Analyst software.

A sequence of SRV images from KGSP corresponding to the reflectivity 
images in Figure 19 indicated a rapidly strengthening low-level 
circulation (Fig. 21).  Note that the 2012 UTC SRV image is shown in 
place of the 2016 UTC image due to velocity dealiasing errors.  A gate-
to-gate rotational couplet of around 85 knots was evident at 2012 UTC.  
By 2020 UTC, this couplet strengthened to greater than 100 knots.  The 
EF2 tornado developed at 2015 UTC and dissipated over the extreme 
southeast corner of the county at 2030 UTC (Fig. 22).  Although an 
operator-defined TVS was identified prior to tornado development, the 
radar algorithm did not identify this feature as a TVS until near the 
end of this tornado’s life cycle.

Figure 21.  Images of 0.5 degree storm relative velocity from KGSP at  
(a.) 2012 UTC, (b.) 2021 UTC, (c.) 2025 UTC, and (d.) 2029 UTC on 
15 March.  The white arrow in (b.) denotes the gate-to-gate shear of 
greater than 100 knots.  The speed values are given by the color table
in the lower right corner of the figure.  By convention, negative
values represent motion toward from the radar while positive values
represent motion away from the radar.

Figure 22.  Track of tornado across the southern part of Elbert County, 
Georgia, on 15 March 2008.  The tornado track is delineated by the heavy 
black line.  The background map is from Delorme Street Atlas USA.

As the tornadic supercell thunderstorms moved out of the eastern end 
of the original Tornado Watch and into the eastern Piedmont of South 
Carolina, a new Tornado Watch was issued by the SPC at 2035 UTC.  The 
Elbert supercell thunderstorm continued to produce periodic tornadoes as 
it moved over the South Carolina Midlands during the late afternoon 
and early evening.  In addition, very large hail from this storm caused 
millions of dollars in property damage as the core of the storm moved 
over southern Greenwood County (Fig. 23).

Figure 23.  This manufactured home was damaged by wind driven hail near 
Callison, South Carolina, on 15 March 2008.  Image courtesy of Greenwood 
County Emergency Management.

The final supercell of the day that affected the GSP CWA was not 
tornadic, but produced extremely large hail (tennis ball to soft ball 
size) across southern Anderson, northern Abbeville, and northern 
Greenwood counties.  A series of reflectivity scans from KGSP at 
2109 UTC is presented in Figure 24.  This was around the time that 
softball size hail was reported by a trained spotter located 7 miles 
northeast of Iva in southern Anderson County.  The images indicated 
an approximately 10,000 foot layer (between 10,000 feet and 20,000 feet 
AGL) in which a three-body scatter spike (TBSS) was evident extending 
southwest from the high reflectivity core.  This was an indication of 
very large hail.  The three-dimensional cross section in Figure 25 
from 2109 UTC indicated a large area of greater than 60 dBz reflectivity 
from the low levels of the storm to about 20,000 feet. There was an area 
of greater than 70 dBz reflectivity at around 16,000 feet.  This was 
well above the freezing level of about 10,000 feet as depicted on 
regional soundings at 1200 UTC and 1800 UTC.  The 50 dBz reflectivity 
core extended to around 30,000 feet, which was around 10,000 feet higher 
than the -20 degrees C level as indicated on regional soundings.  These 
factors all point to a thunderstorm that was producing very large hail. 

Figure 24.  Reflectivity images from KGSP at 2109 UTC at 
(a.) 1.8 degrees, (b.) 2.4 degrees, (c.) 3.1 degrees, and (d.) 4.0 degrees.
The white arrow in (a.) indicates a three-body scatter spike indicative
of large hail in the storm core.

Figure 25.  As in Figure 20, except at 2109 UTC 15 March.

Strong to severe thunderstorms continued across the western part of 
South Carolina and northeast Georgia through the late afternoon hours.  
The passage of a cold front during the early part of the evening pushed 
the severe thunderstorms to the east of the GSP CWFA ending the threat 
for severe weather.

5.  Summary 

A rare outbreak of classic supercell thunderstorms affected portions 
of northeast Georgia and the Upstate of South Carolina on 15 March 2008. 
The outbreak was the result of the coexistence of strong vertical wind 
shear and moderate levels of instability, which was an unusual situation 
in this part of the country.  The moderate levels of instability were 
largely the result of an atypical eastward advection of the elevated 
mixed layer (steep mid-level lapse rates).  The superimposition of the 
left exit region of a sub-tropical jet streak and the right entrance 
region of a maximum in the polar jet resulted in sufficient synoptic-
scale lift to remove the cap, allowing for explosive convective 
development on the warm sector side of the quasi-stationary front by 
early afternoon.  Scattered supercell thunderstorms affected the GSP CWA 
from about 1830 UTC to 2130 UTC before moving into the South Carolina 
Midlands.  Although large hail, and in some cases destructive hail, were 
the main impacts in the GSP CWA, two EF0 tornadoes and an EF2 tornado 
were also reported.

More images of large hail damage near Callison, South Carolina, on 
15 March 2008.  Images courtesy of Greenwood County Emergency Management.

References

Lane, Justin D., 2008:  A Comprehensive Climatology of Significant 
     Tornadoes in the Greenville-Spartanburg, South Carolina County 
     Warning Area (1880 - 2006).  Eastern Region Tech. Attachment
     2008-01, 35 pp. 

Lanicci, John M., and T. T. Warner, 1991: A Synoptic Climatology of 
     the Elevated Mixed-Layer Inversion over the Southern Great Plains 
     in Spring. Part I: Structure, Dynamics, and Seasonal Evolution.  
     Wea. Forecasting, 6, 198 - 213.

Acknowledgements

Pat Moore was responsible for conversion of the manuscript to html code. 
The convective outlooks, Tornado Watch products, and upper air analyses
were obtained from the Storm Prediction Center.  The surface fronts
analyses were obtained from the Hydrometeorological Prediction Center.
The surface observation plots, satellite imagery, and radar mosaics were
obtained from the University Corporation for Atmospheric Research.  The
composite reflectivity mosaic was obtained from the Iowa Environmental
Mesonet.  Tornado track maps were created using Delorme Street Atlas 
USA 2006.  Radar reflectivity cross sections were created using GR2Analyst 
version 1.22, by Gibson Ridge Software.  The upper air sounding images 
were made using RAOB version 5.8 for Windows, by Environmental Research 
Services, LLC.  Other radar images were created using the Java NEXRAD 
viewer from the National Climatic Data Center.  Greenwood County (SC)
Emergency Management provided most of the damage pictures.