Vehicles damaged by the tornado that struck Liberty, South Carolina, 
on 5 January 2007. Image courtesy of and copywright by The Pickens 
Sentinel, used by permission.

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

1.  Introduction

A line of strong to severe thunderstorms produced at least three 
confirmed tornadoes, and several more reports of damaging wind gusts, 
across upstate South Carolina and the Charlotte metro area during the 
afternoon of Friday, 5 January 2007.  The National Weather Service 
Office in Greer, South Carolina (GSP), issued five tornado warnings 
and 14 severe thunderstorm warnings between noon and 6:00 pm on that 
day.  The first tornado touched down briefly at 2:24 pm (1924 UTC) in 
Liberty, South Carolina, on the campus of Liberty Elementary School, 
tossing about several vehicles in the parking lot waiting for afternoon 
dismissal.  The second tornado struck an area northwest of Moore, South 
Carolina, around 3:10 pm (2010 UTC), destroying two sheds, damaging 
the roof of a mobile home, and snapping several large pine trees.  
The third tornado touched down briefly at 4:45 pm (2145 UTC) near 
Gastonia, North Carolina, damaging several roofs in the Autumn Acres 
subdivision.  [All times in this document from this point onward are 
referred to in Universal Time Coordinated (UTC), which is Eastern 
Standard Time plus five hours.]  The Liberty Tornado was rated F1, 
while the Moore Tornado and the Gastonia Tornado were rated F0 on 
the Fujita Scale.

(Click here to view a summary of severe weather reports for 
5 January 2007.)

Figure 1.  Wind damage, large hail, and tornado reports for 
5 January 2007.  Click on image to enlarge.  

The meteorology leading up to the events on 5 January 2007 was well 
understood and well anticipated by the GSP Weather Forecast Office and 
the Storm Prediction Center (SPC).  While the storm that produced the
Moore Tornado appeared to be a classic example of a "broken-S" type of
quasi-linear convective system (McAvoy et al. 2000), the storm that
produced the Liberty Tornado had more subtle features which made the
warning process particularly challenging.  The Gastonia storm showed 
few signs that a tornado was imminent, at least not according to our 
current understanding of tornadogenesis in high shear and weak 
instability environments.  

2.  Synoptic Features and Pre-Storm Environment

A dynamic closed upper low was located over the Mississippi Delta region
on the 500 mb analysis at 1200 UTC on 5 January (Fig. 2), and could also 
be seen on the GOES-12 water vapor imagery.  Although the upper low was 
expected to open and deamplify during the day, strong forcing at mid- 
levels was expected to continue with an 80-100 kt jet streak wrapping 
around the forward edge of the short wave trough.  Additional forcing 
aloft was anticipated by midday with the arrival of the left exit region 
of a jet streak at 300 mb, seen moving northward from the Gulf of Mexico 
at 1200 UTC (Fig. 3).  In fact, a linear convective system had already 
developed by 1200 UTC across eastern Alabama in this strongly forced 
environment.

Click here to view a 19 frame java loop of GOES-12 water vapor 
satellite imagery.

Figure 2.  SPC objective analysis of 500 mb geopotential height, 
temperature, and wind at 1200 UTC 5 January.  Click on image to 
enlarge.

Figure 3.  SPC objective analysis of 300 mb isotachs, streamlines, 
and wind divergence at 1200 UTC 5 January.  Click on image to enlarge.

A southerly low level jet of 40-45 kt at 850 mb (Fig 4) and winds of 
35-40 kt at 925 mb across Georgia and the western Carolinas were 
favorable for a continuation of organized severe thunderstorms.  The 
environment ahead of the squall line, as sampled by the upper air 
sounding at Peachtree City, Georgia (FFC), at 1200 UTC (Fig. 5), was 
characterized by strong deep layer shear on the order of 60 kt, surface 
to 1 km shear of 30-35 kt, and surface to 1 km storm relative helicity 
on the order of 200 m2/s2 were all favorable for the development of 
tornadoes.  In fact, the upper air sounding taken at Greensboro, North
Carolina (GSO), at 1200 UTC (Fig. 6) showed a surface to 3 km shear of 
40 kt, which is known to be conducive to the formation of tornadoes in 
quasi-linear convective systems.  In spite of extensive low clouds, 
daytime heating was expected to raise Convective Available Potential 
Energy to around 800 J/kg ahead of the line.  This measure of updraft
potential, combined with the strong shear, would be sufficient to 
maintain the squall line as it moved east. For that reason, the SPC 
placed the area roughly to the south of a line from Athens, Georgia, 
to McCormick, South Carolina, to Wadesboro, North Carolina, in a Slight 
Risk in the Day 1 Convective Outlook issued at 1229 UTC.

Figure 4.  SPC objective analysis of 850 mb geopotential height, 
temperature, dewpoint, and wind barbs at 1200 UTC 5 January.  Click on 
image to enlarge.

Figure 5.  Skew-T log P diagram (upper left) and hodograph (upper right) 
for upper air sounding at FFC at 1200 UTC 5 January. The tables at the 
bottom summarize several objective parameters used by the SPC to determine 
severe weather potential.  Click on image to enlarge.

Figure 6.  As in Figure 5, except at GSO.  Click on image to enlarge.

At the surface, a cold front stretched along the Mississippi-Alabama 
border (Fig. 7), with the air mass ahead of the squall line characterized 
by temperatures in the middle to upper 60s with dewpoints in the lower 
to middle 60s.  Regional surface analyses at 1200 UTC and 1300 UTC 
indicated the presence of a weak warm front lifting north across extreme 
northeast Georgia and the western part of upstate South Carolina, with 
dewpoints behind the front climbing into the lower 60s and surface winds 
veering to the southeast (Fig. 8).  It was quickly surmised that the 
environment across the Lower Piedmont and the Lakelands would be at 
least as favorable as that across the central Savannah River valley 
and the Midlands of South Carolina.  As as result, a Severe Weather 
Outlook was issued at 1339 UTC for the area south of the North Carolina 
border, mentioning the possibility of damaging wind gusts and the 
potential for a brief, isolated tornado.  

Figure 7.  Hydrometeorological Prediction Center surface fronts and 
pressure analysis at 1200 UTC 5 January.  Click on image to enlarge.

Figure 8.  Regional surface observations plots at 1200 UTC (left) and 
1300 UTC (right), 5 January.  Note how the winds veer at AND and GSP 
and the increasing dewpoint at AND as the warm front passes between 
1200 UTC and 1300 UTC.  Click on images to enlarge.

The pre-storm environment was sufficient to re-intensify the northern 
end of the squall line as it crossed the Atlanta metro area through the 
middle part of the morning.  The SPC adjusted the Slight Risk area 
northward to include the area generally along and south of Interstate 85 
on the updated Day 1 Convective Outlook issued at 1629 UTC.  The Severe 
Weather Outlook was updated at 1647 UTC to follow suit, and continued 
to mention the potential for brief, isolated tornadoes.  As the squall 
line approached extreme northeast Georgia, the air mass to the south 
of the North Carolina border was weakly unstable with a CAPE of 
300-400 J/kg, but strongly sheared with surface to 1-km shear values 
of 30-35 kt, as noted by a Mesoscale Discussion issued by the SPC at 
1706 UTC.  After coordination with the SPC, a Tornado Watch was issued 
at 1740 UTC for most of northeast Georgia, upstate South Carolina, and 
the Charlotte metro area.  By that time, the leading edge of the squall 
line was poised to enter the WFO GSP County Warning Area.

Click here to view a 16 frame java loop of the 0.5 degree 
reflectivity mosaic centered on the KGSP radar.

3.  Radar observations

The squall line (otherwise known as a quasi-linear convective system,
or QLCS for short) had a history of producing strong wind gusts as it
moved across north central Georgia, including a gust of 54 mph in 
Gainesville (Hall County).  The GSP Weather Forecast Office issued a 
Severe Thunderstorm Warning for Rabun, Habersham, Stephens, and Franklin 
counties in Georgia, and for Oconee County in South Carolina, at 1737 UTC 
as the leading edge of the line was poised to move into Habersham 
County (Fig. 9).  Wind damage was reported across southern Habersham
County, Stephens County, and western Franklin County as the line of
thunderstorms passed.  Additional damage was reported in western 
Elbert County near Bowman.

Click here to view a 16 frame java loop of composite reflectivity 
from the KGSP radar from 1734 UTC to 1839 UTC.

Figure 9.  Radar reflectivity on 0.5 degree scan from the KGSP WSR88-D 
radar at 1738 UTC.  The radar is located at the upper right edge of the 
image.  Click on image to enlarge.

a.  The Liberty Tornado

The leading edge of the QLCS stretched from central Oconee County 
just west of Seneca, south across the extreme western tip of Anderson 
County, to Hartwell, Georgia, at 1839 UTC (Fig. 10).  A notch of lower 
radar reflectivity developed in the rear flank of the QLCS near Fair 
Play at a height of 4.5 km above ground level between 1839 UTC and 
1843 UTC, seen on the 3.0 degree scan (Fig. 11).  A relative maximum 
in inbound radial velocity (i.e. toward the radar) of 50 knots or
greater was observed within the reflectivity notch.  This indicated 
the presence of a rear inflow jet.  Over the next four minutes, a 
similar low reflectivity notch developed at the back edge of the 
QLCS on the 0.5 degree scan.  This was seen as an indentation of lower
reflectivity at a height of approximately 1 km above ground level near 
Townville (Fig. 12).  By 1900 UTC, the notch was located along the 
Pickens-Anderson county line to the south of Clemson (Fig. 13).  The 
radial velocity increased from at least 26 kt to greater than 36 kt, 
indicative of strengthening rear-to-front flow.  The appearance of 
the notch on the 3.0 degree scan four to eight minutes prior to its 
appearance at the lowest elevation scan strongly suggests a subsident 
component to the rear-to-front flow in the storm.

Figure 10.  Radar reflectivity on the 0.5 degree scan from the KGSP 
radar at 1839 UTC.  The radar is located in the upper right corner to 
the right of the last 'e' in Greenville.  Click on image to enlarge.

Figure 11.  Radar reflectivity (top) and radial velocity (bottom) 
on the 3.0 degree scan from the KGSP radar at 1843 UTC.  Negative
values (green shades) indicate motion toward the radar and positive
values (red shades) indicate motion away from the radar.  The arrow 
points to the notch of lower reflectivity at the back edge of the 
QLCS corresponding to higher inbound velocity near the town of 
Fair Play (point FP).  Note the red colors near the tip of the 
arrow in the bottom figure represent velocities that have been 
improperly dealiased.  The actual velocity is a value greater than
50 kt toward the radar.  Click on images to enlarge.

Figure 12.  As in Fig. 10, except for 1847 UTC.  The arrow denotes 
the rear inflow notch.  Click on image to enlarge.

Figure 13.  Radar reflectivity (top) and radial velocity (bottom) 
on the 0.5 degree scan from the KGSP radar at 1900 UTC.  The arrow 
points to the notch of lower reflectivity at the back edge of the 
QLCS south of Clemson.  Click on images to enlarge.

Between 1847 UTC and 1909 UTC, the southern (or leading) segment of 
the QLCS accelerated east across Anderson County, leaving the 
northern (or trailing) segment behind across southwestern Pickens 
County (Fig. 14).  This evolution was similar to other QLCSs in high 
shear environments.  However, in this case a clean break in the line 
into southern (leading) and northern (trailing) segments was not 
readily apparent, at least not at the resolution of the data and the 
color table that was used.  A channel of weak reflectivity began to 
wrap cyclonically around the appendage of high reflectivity to the 
east of Clemson at 1909 UTC, which was even more apparent at 1913 UTC 
(Fig. 15).  A weak low-level mesocyclone appeared to form by 1913 UTC 
on the storm relative motion image as the rotational velocity at 
0.5 degrees strengthened to 30 kt by this time.  This was an increase 
of about one-third over the previous scan.  In a storm-relative sense, 
convergence is implied from the southeast corner of the reflectivity 
appendage, south along the back edge of the storm over Anderson 
County.  A Severe Thunderstorm Warning was issued for southern Pickens 
County at 1915 UTC.

Figure 14.  As in Fig. 10, except for 1909 UTC.  The gray arrow 
denotes the developing weak echo channel.  White lines indicate 
the leading and trailing segments of the quasi-linear convective 
system.  Click on image to enlarge.

Figure 15.  Radar reflectivity (top) and storm relative motion 
(bottom) on the 0.5 degree scan from the KGSP radar at 1913 UTC.  
The arrow points to the channel of weak reflectivity.  Click on 
images to enlarge.

Some portion of the rear-to-front flow appeared to wrap completely 
around the reflectivity appendage to the west-southwest of Liberty 
by 1917 UTC, as evidenced by the development of an area of outbound 
radial velocity (i.e. away from the radar) northeast of the 
reflectivity appendage (Fig. 16).  It is interesting to note the 
developing outbound radial velocity appeared directly beneath a new 
area of higher reflectivity aloft on the 1.8 degree scan, which 
suggests either a developing updraft in the storm or a strongly tilted 
one.  The mesocyclone remained broad but cyclonically convergent on 
the 0.5 degree scan.  At this time, the rotational velocity on the 
1.2 degree scan jumped by 50 percent over the previous scan (from 
21 kt to 31 kt) and was also cyclonically convergent, suggestive of 
an upward development of the mesocyclone (Fig. 17).

Click here to view a 14 frame java loop of 0.5 degree reflectivity 
from the KGSP radar from 1847 UTC to 1943 UTC.

Click here to view a 14 frame java loop of 0.5 degree storm relative 
motion from the KGSP radar from 1847 UTC to 1943 UTC.

Figure 16.  Radar reflectivity on the 1.8 degree scan (upper left) 
and the 0.5 degree scan (lower left), storm relative motion on the 
0.5 degree scan (upper right), and radial velocity on the 0.5 degree 
scan (lower right) from the KGSP radar at 1917 UTC.  Click on 
images to enlarge.

Figure 17.  As in Figure 15, except for the 1.3 degree scan at 
1917 UTC.  Click on images to enlarge.

The mesocyclone reached its peak intensity at 1922 UTC in a purely 
rotational sense at a height of 1.2 km above the ground (Fig. 18).  
The mesocyclone continued to grow upward as suggested by a plot of 
rotational velocity on the 0.5 degree, 1.2 degree, and 2.4 degree 
scans (Fig. 19), and the WSR-88D mesocyclone algorithm.  The distance 
between the maximum outbound and inbound storm relative velocity was 
nearly 3 nautical miles at a range of 24 nautical miles from the radar, 
which is considered broad and weak by the mesocyclone nomogram.  
Nevertheless, a tornado developed and touched down on the campus of 
Liberty Elementary School at 1924 UTC, as reported by several 
eyewitnesses.

Figure 18.  Storm relative motion on the 0.5 degree scan from the KGSP 
radar at 1922 UTC.  Click on image to enlarge.

Figure 19.  Rotational velocity in the Liberty storm.  Click on 
image to enlarge.

The storm that produced the Liberty tornado moved quickly northeast
across the eastern part of Pickens County over the next 30 minutes.  
The low level rotation in the mesocyclone showed signs of strengthening 
as it passed to the north and northeast of Easley after 1939 UTC, but
by that time the storm was collapsing.  No other reports of damage were
received along the storm's path.

b.  The Moore Tornado

Shortly after the Liberty Tornado, the QLCS gained strength as it 
moved across Greenville County.  By 1947 UTC, a line of very high 
reflectivity was oriented from north to south across southern 
Greenville County (Fig. 20), moving rapidly to the east.  The 
evolution of the reflectivity pattern in the severe storm that 
produced the tornado to the northwest of Moore exhibited a classic 
"Broken-S" radar presentation as it moved into western Spartanburg 
County.  The "Broken-S" radar reflectivity signature has been linked 
to the occurrence of non-supercell tornadoes in QLCSs in similar 
environments over the western Carolinas in the past (Lane and Moore 
2006, McAvoy et al. 2003).

Click here to view a 22 frame java loop of 0.5 degree reflectivity 
from the KGSP radar from 1922 UTC to 2051 UTC.

Figure 20.  Radar reflectivity on the 0.5 degree scan from the KGSP 
radar at 1947 UTC.  The radar is located near the center of the 
image, just to the right of the e in Greenville.  Click on image to 
enlarge.

An examination of the reflectivity on the 1.2 degree scan from the 
KGSP WSR-88D radar (approximately 300 to 500 meters above ground level 
at that range) revealed a break in the line segment between 2000 UTC 
and 2008 UTC (Fig. 21).  The line segment showed broad curvature in 
the form of an S in the high reflectivity (35 dBZ and greater) over 
western Spartanburg County at 2000 UTC, which wrapped tighter to the 
west of Moore by 2004 UTC.  A fracture in the high reflectivity line 
segment occurred over the area to the northwest of Moore and west of 
Roebuck at 2008 UTC, just two minutes before the tornado touched down.  
The fracture appeared as a north to south oriented minimum in 
reflectivity (30 dBZ and less) west of Moore (Fig. 21, bottom).

A short loop of the 1.2 degree reflectivity shows the break in
the line segment to the west of Moore.

Figure 21.  Radar reflectivity on the 1.2 degree scan from the KGSP
WSR-88D at 2000 UTC (top), 2004 UTC (middle), and 2008 UTC (bottom), 
on 5 January.  The point labeled KGSP is the location of the radar 
and the point labeled T is the approximate location of the tornado 
damage.  Click on images to enlarge.

The radial velocity showed the rapid development of the mesocyclone 
associated with the Moore Tornado between 2000 UTC and 2008 UTC (Fig. 22).
The rotation in the developing mesocyclone can be inferred from the 
couplet of inbound velocity (green shades) and outbound velocity (red
shades) to the west of Moore at 2000 UTC.  The couplet strengthened 
through 2004 UTC, to the point where the maximum inbound velocity was
on the order of 20 kt and the maximum outbound velocity was greater 
than 64 kt to the northwest of Moore at 2008 UTC.  The storm relative
velocity showed the rotational couplet with even greater clarity at 
2008 UTC (Fig. 23).  Interpretation of these images allowed the warning
forecaster to issue a Tornado Warning before the tornado touched 
down northwest of Moore.

A short loop of the 1.2 degree radial velocity shows the development 
of the rotational couplet associated with the mesocyclone to the west 
of Moore.

Figure 22.  Radial velocity on the 1.2 degree scan from the KGSP
WSR-88D at 2000 UTC (top), 2004 UTC (middle), and 2008 UTC (bottom), 
on 5 January.  Targets moving toward the radar are indicated by
green shades and targets moving away from the radar are shown by
red shades.  The point T is the approximate location of the 
tornado damage.  Click on images to enlarge.

Figure 23.  Storm relative motion on the 1.2 degree scan from the 
KGSP radar at 2008 UTC.  Click on image to enlarge.

Shortly after the Moore Tornado lifted, the severe thunderstorm produced 
a microburst near the town of Roebuck at 2015 UTC.  Several trees were 
uprooted and snapped.  A few trees fell across roadways and on top of 
at least one house.  Reports of funnel clouds were received as the storm
tracked over eastern Spartanburg County and into Cherokee County, but
apparently no other damage occurred.

c.  The Gastonia Tornado

The QLCS crossed the line between Cherokee County and York County, 
South Carolina, around 2100 UTC.  A fracture in the convective line 
occurred over northwestern York County between 2108 UTC and 2112 UTC, 
prompting the issuance of a Tornado Warning. A second-hand report of 
a tornado was received from the area near Clover, South Carolina, but 
the report has not been substantiated.

The system continued to move east northeast as two distinct segments 
over the next half hour.  The southern (or leading) segment moved 
along the North and South Carolina line and the northern (or trailing)
segment moved over Gaston County, North Carolina.  As the system moved 
past Gastonia between 2129 UTC and 2138 UTC, the two segments became 
more separated as lower reflectivity moved around the southern end 
of the trailing line segment to the southeast of Gastonia.  The KGSP 
radar showed the trailing segment of the QLCS extending to the south 
of Gastonia at 2133 UTC, but only weak rotation was seen in the storm 
relative motion on the lowest elevation scan (Fig. 24).  However, it 
should be noted that the center point of the radar beam was 1.6 km 
above ground level in the vicinity of Gastonia.  This put the KGSP 
radar at a disadvantage when attempting to detect low level features.  
The radar signatures associated with the Liberty Tornado were confined 
to levels below 1.5 km.  This suggested the KGSP radar was too far 
away from the storm to be able to detect the important low level 
features that were associated with a developing tornado.

Click here to view a 16 frame java loop of 0.5 degree reflectivity 
from the KGSP radar from 2055 UTC to 2159 UTC.

Figure 24.  Reflectivity and radial velocity on the 0.5 degree 
scan from the KGSP radar at 2133 UTC.  Click on images to enlarge.

This was not the case with the Terminal Doppler Weather Radar (TDWR)
located north of the Charlotte - Douglas International Airport.  
Whereas the KGSP radar was located about 100 km to the west of the 
QLCS, the Charlotte TDWR (TCLT radar) was only 30 km distant.  The 
favorable location and the smaller beamwidth of the TCLT radar allowed 
for a more detailed view of the storm.  A comparison between the 0.5 
degree scan from the KGSP radar (beam center point about 1700 m AGL) 
with the 2.4 degree scan from the TCLT radar (beam center point about 
1200 m AGL) at 2134 UTC showed the difference in resolution (Fig. 25).  
Note the appearance of the channel of lower reflectivity that extended 
to the north of the Gastonia airport (KAKH) on the TCLT scan.  The 
poorer resolution of the KGSP radar at that distance smeared out the 
appearance of the low reflectivity channel.

Figure 25.  Radar reflectivity from the KGSP radar on the 0.5 degree 
scan at 2133 UTC (top) and from the TCLT radar on the 2.4 degree scan 
at 2134 UTC (bottom).  The location of TCLT is shown in the upper 
right.  Click on images to enlarge.

The favorable location of the TCLT radar allowed it to see more of the 
low level structure of the QLCS as well.  A loop of the 1.0 degree 
reflectivity from TCLT showed the initial break in the QLCS over 
northwestern York County, South Carolina.  By 2133 UTC, the QLCS had 
evolved to where the break in the two segments was well defined, with 
a channel of weak reflectivity having wrapped around the southern end 
of the northern (or trailing) segment (Fig. 26).  The only significant 
rotation observed by the TCLT radar prior to the tornado occurred on 
the 1.0 degree scan at this time.  It is interesting to note that the
rotational couplet was not even directly associated with the southern
end of the trailing reflectivity segment, but was embedded within a
notch in the rear flank of the southern (or leading) reflectivity 
mass.  The 0.2 degree scans from TCLT were even more revealing.  
Between 2130 UTC and 2135 UTC, a small mass of reflectivity peeled
away from the rear flank of the larger reflectivity mass over the
southeast corner of Gaston County.  This smaller mass moved on a
more northeasterly track and merged with the trailing reflectivity
segment to the east of Gastonia around 2139 UTC.  The tornado touched
down at approximately 2141 UTC about four miles east of Gastonia.
The tornado appeared to be associated with the southern end of the 
trailing line segment (Fig. 27), but the storm relative motion was
contaminated with improperly dealiased velocities.

Click here to view a 17 frame java loop of 0.2 degree reflectivity 
from the TCLT radar from 2128 UTC to 2144 UTC.

Figure 26.  Radar reflectivity (top) and storm relative motion (bottom) 
from the TCLT radar on the 1.0 degree scan at 2134 UTC.  The location 
of TCLT is shown in the upper right.  Click on images to enlarge.

Figure 27.  As in Figure 26, except for 2140 UTC.  The approximate 
location of the Autumn Acres subdivision, where the tornado struck, 
is shown by point A. Click on images to enlarge.

Both radars showed a low reflectivity notch in the rear flank of 
the QLCS as it moved into York County, South Carolina.  However, 
the radial velocity data from KGSP did not show higher wind speeds 
associated with the notch and the data from TCLT was contaminated 
by range folding.  The QLCS fracture occurred about 30 minutes before 
the tornado touched down, similar to the Bessemer City storm nearly a
year ago to the day.  The KGSP radar gave little indication that a 
tornado was imminent on the 2138 UTC scan, with broad and weak
rotation indistinguishable from other parts of the scan.  Although 
the TCLT radar was much closer, and therefore able to see the low 
level features in the storm, it also gave little indication that a 
tornado was imminent on the scans leading up to tornado formation.  
Only one elevation scan in the 2134 UTC volume indicated significant 
rotation.  The role played by the weak cell merger in the minutes 
prior to tornado formation is unknown.  The parent storm weakened 
rapidly through 2200 UTC and no additional severe weather was 
reported.

4.  Discussion and Summary 

The forecasters at GSP had a relatively high degree of situational
awareness leading up to the event and expected a few tornadoes as 
the squall line moved across the Upstate and Piedmont.  However, 
that knowledge did not make the warning process any less challenging.
With the benefit of hindsight, an examination of the radar data 
yields several subtle clues in the minutes leading up to each 
tornado.  What is not known is the relative significance of any of
the subtle radar signatures, or if similar signatures could be 
detected in any of the storms that did not produce a tornado on 
this day.  The fact that hindsight magnifies the apparent importance
of any radar clues should not be lost by the casual reader.

In the case of the Liberty Tornado, confidence was not high that
a tornado was about to form.  The QLCS did not exhibit the distinct
break in the line that forecasters have observed in other cases.
While some rotation was noted in the storm at low levels, it was
thought to be too broad and too weak to be indicative of an 
impending tornado.  This suggests that the threshold for issuing
tornado warnings based on low level rotation might need to be 
lowered for similar high shear, low instability environments.
The radar observations of the descending rear inflow jet support
conclusions about low level vorticity generation drawn by earlier 
modeling work on QLCSs.  The detection of rear inflow jets in
similar systems warrants further study.

The Moore Tornado followed the classic radar evolution of a 
tornado-producing QLCS in this type of environment.  This allowed
the forecaster to issue an effective Tornado Warning.  The close
proximity to the KGSP radar yielded a high quality data set, which
makes this case very valuable for future study.

As for the Gastonia Tornado, the radar signatures were the
most subtle and thus the least understood.  The poor representation
on the KGSP radar suggests that early detection of important low-level 
signatures might be nearly impossible at ranges beyond 100 km.
Fortunately, the TCLT radar greatly improves the capability to see 
the low level structure of similar storms across the North Carolina 
Piedmont.

More images of damage produced by the Liberty Tornado.  The concession 
stand at the Liberty High School football field was ripped from its 
mooring and overturned.  Part of a fence was also knocked down.  
Relatively little tree damage was noted owing to the location of the 
very narrow and short tornado path.  Click on images to enlarge.

More images of the damage produced by the Liberty Tornado in the parking 
lot of Liberty Elementary School.  Images are courtesy of the Pickens 
Sentinel and are subject to copywright.

Damage to outbuildings and a barn caused by the Moore Tornado.

Damage to a home and a tree in the Autumn Acres subdivision east of 
Gastonia, caused by the Gastonia Tornado.  Click on image to enlarge.

Acknowledgements

Sandy Foster, editor of The Pickens Sentinel, provided the images of 
the damaged vehicles in Liberty, South Carolina.  The upper air 
analysis and sounding graphics were obtained from the Storm 
Prediction Center.  The surface analysis graphic was obtained from 
the Hydrometeorological Prediction Center. The regional surface plots, 
satellite imagery, and radar mosaic images were obtained from the 
University Corporation for Atmospheric Research.  The images from
the KGSP radar were made using the Java NEXRAD Viewer from the 
National Climatic Data Center.

References

Lane, J. D., and P. D. Moore, 2006: Observations of a non-supercell 
     tornadic thunderstorm from a Terminal Doppler Weather Radar. 
     Preprints, 23rd Conf. on Severe Local Storms, St. Louis, MO, Amer. 
     Meteor. Soc. 

	 
McAvoy, B. P., W. A. Jones, and P. D. Moore, 2000: Investigation of an 
     unusual storm structure associated with weak to occasionally strong 
     tornadoes over the Eastern United States. Preprints, 20th Conf. on 
     Severe Local Storms, Orlando, FL, Amer. Meteor. Soc., 182-185.