The Belton Hail Storm of 21 April 2006
Patrick D. Moore
NOAA/National Weather Service
Hail to the size of golf balls litters the ground near Belton, South
Carolina, on Friday evening, 21 April 2006. Image courtesy of David
Rogers, Anderson Independent-Mail. Used by permission.
Several severe thunderstorms developed across northeast Georgia and
the upstate of South Carolina on Friday evening, 21 April 2006. The
thunderstorm activity continued into the early morning hours of Saturday,
22 April. In all, the National Weather Service (NWS) Weather Forecast
Office (WFO) in Greer, South Carolina, located at the Greenville -
Spartanburg Airport (GSP), issued 26 Severe Thunderstorm Warnings and
2 tornado warnings during the period from 8 am Friday to 8 am Saturday.
[Note: All times in this document from this point on are referred to
in Universal Time Coordinated (UTC), which is Eastern Daylight Time
plus four hours.] Most of the severe weather produced by the storms
Friday evening came in the form of large hail, while several reports
of wind damage were received early Saturday morning (Fig. 1). The most
intense severe thunderstorm of the evening produced a swath of large hail
up to the size of golf balls across the area from Belton, South Carolina,
to the southwest corner of Greenville County near Fork Shoals.
Click here to see a list of all Local Storm Reports for this event.
Figure 1. Severe weather reports for the 24-hour period ending 1207 UTC
22 April 2006. The map may not reflect all the storm reports received at
WFO GSP post-event.
The Belton hail storm was interesting from a radar perspective in that
it displayed many of the classic characteristics of a large-hail-producing
severe thunderstorm, as we shall see in later sections.
2. Synoptic Pattern and Pre-Storm Environment
The upper air analysis from Friday morning indicated the environment
would be favorable for deep convection later in the day across northeast
Georgia and Upstate South Carolina. The 500 mb objective analysis from
the Storm Prediction Center (SPC) indicated a pool of slightly cooler
temperatures aloft just upstream over the Mississippi Delta region along
with a mid-level jet streak (Fig. 2). A weak short wave seen as the
inflection in the 576 dm height contour over Arkansas and Louisiana was
expected to lift northeast across Tennessee later in the day with the
upper ridge holding over the Carolinas. The 300 mb analysis showed a
region of upper diffluence moving over the western Carolinas. Meanwhile,
the 850 mb analysis showed a weak thermal ridge immediately upstream with
moisture transport implied by a southerly flow from the Gulf of Mexico.
The surface analysis at 1200 UTC from the Hydrometeorological Prediction
Center (HPC) showed a cold front extending from low pressure over northern
Wisconsin, through the mid-Mississippi Valley, to the Ozarks (Fig. 3).
Figure 2. SPC objective analysis of 500 mb geopotential height,
temperature, and wind for 1200 UTC 21 April 2006. Click on image to enlarge.
Figure 3. HPC surface pressure and fronts analysis for 1200 UTC 21 April.
Click on image to enlarge.
The upper air sounding observed at Peachtree City, Georgia (FFC), at
1200 UTC on 21 April (Fig. 4) gave further support to the idea that
severe thunderstorms were possible later in the day over northeast
Georgia and the western part of South Carolina. The sounding showed a
steep lapse rate in the 700-500 mb layer and a surface-based Convective
Available Potential Energy (CAPE) of greater than 2100 J/kg modified for
expected conditions in the afternoon. Wind shear was expected to be
sufficient to support the development of a few supercell thunderstorms.
However, the environment farther to the north and east was not expected
to be as favorable, as seen in the Greensboro, North Carolina, sounding.
The favorable environment for severe thunderstorms was reflected in the
Day 1 Convective Outlook, updated at 2000 UTC, which included northeast
Georgia and the western tip of South Carolina in a Slight Risk.
Figure 4. Skew-T log P diagram of the upper air sounding (left) and
hodograph (right) for FFC at 1200 UTC 21 April. The table at the bottom
shows many of the severe weather indices used by the SPC. Click on image
What transpired during the day was a general lack of deep convection
across most of the western Carolinas. Extensive debris cloudiness left
over from widespread convection in the morning over the Great Valley of
east Tennessee effectively cut down on solar heating across western North
Carolina and most of the Upstate of South Carolina. A severe thunderstorm
produced half-dollar sized hail near Marble in Cherokee County, North
Carolina, around 1500 UTC, while a similar storm produced marble to penny
sized hail over Rabun County, Georgia, around 1530 UTC. However, both
storms quickly diminished as they moved northeast into more stable air.
Middle and high level clouds remained across the western Carolinas through
at least 1900 UTC, as seen in Aqua MODIS imagery. The SPC objective
analysis of CAPE and convective inhibition at 1900 UTC was indicative of
marginal instability across most of the western Carolinas. It was not
until after 2100 UTC that some measure of destabilization occurred over
the upper Savannah River Valley. Surface observations around 2200 UTC
showed dewpoints pooling in the lower 60s in the area from Anderson to
Athens and Gainesville, Georgia, with winds backing to the southeast at
Anderson and Greenwood (Fig. 5). The higher dewpoints combined with
surface heating allowed by thinning cloud cover resulted in a CAPE above
1000 J/kg and eliminated the remaining convective inhibition (Fig. 6).
Figure 5. Surface observations plot at 2200 UTC 21 April. Click on
image to enlarge.
Figure 6. SPC objective analysis of surface based CAPE and CINH at
2200 UTC 21 April 2006. Click on image to enlarge.
In response to the increasing instability, thunderstorms developed
quickly over northeast Georgia by 2200 UTC.
3. Radar Observations of the Belton Storm
The convective cell that would become the severe thunderstorm over
Anderson County had its genesis over northeast Georgia around 2130 UTC.
The shower moved northeast over Elbert and Hart counties to a position
near Hartwell Dam through about 2215 UTC, at which time a new updraft
formed on its southern flank to the southeast of Hartwell, Georgia. Over
the next ten minutes, the updraft quickly developed into a thunderstorm
over the Hart and Anderson county line below Hartwell Dam, which is also
located about 45 miles to the southwest of the Weather Surveillance Radar-
88 Doppler (WSR-88D) at GSP. At 2236 UTC, the radar reflectivity in the
core of the thunderstorm, now located about 7 miles west of Iva, South
Carolina, exceeded 65 dBz above the freezing level (Fig. 7). Radar
reflectivity values this large are usually associated with large hail
stones, which are generally more reflective than a similar number of large
rain drops in a radar sampling volume. A Severe Thunderstorm Warning was
issued for Anderson County at 2237 UTC, with the expectation that hail of
at least the size of a penny size would fall in the area from Starr to
Anderson and Belton.
Figure 7. Radar reflectivity at 2.9 degree scan from KGSP radar at
2236 UTC. Note the core of greater than 65 dBz west of Iva. The KGSP
radar is located off the upper right corner of the image. Click on
image to enlarge.
Click here to view a 27 frame java loop of KGSP 0.5 degree base reflectivity.
The severe thunderstorm continued to move northeast at 25 mph across
the middle of Anderson county over the next 25 minutes. A new and more
vigorous updraft developed on the southeast flank of the storm about
6 miles south of Anderson at 2305 UTC, with a tremendous upward surge
in radar echo top and reflectivity values in the storm core. On the
2309 UTC volume scan, reflectivity surpassed 70 dBz and a three-body
scatter spike (Zrnic 1987, Lemon 1998) was observed on radar at about
17,000 feet above ground level, both of which are indicative of very
large hail (Fig. 8).
Figure 8. Radar reflectivity at 5.0 degree scan from KGSP radar at
2309 UTC. Note the very high reflectivity (greater than 70 dBz) between
Anderson and Homeland Park and the three-body scatter spike which appears
as weaker reflectivity extending along the radial to the southwest of
Homeland Park. The KGSP radar is located off the upper right corner of
the image. Click on image to enlarge.
A three-body scatter spike (TBSS) occurs when hydrometeors inside the
thunderstorm cell, typically large water-coated hail stones when viewed
with a 10-cm wavelength radar such as the WSR-88D, reflect some of the
energy within the radar beam down to the ground. A portion of this
energy scatters back upward into the thunderstorm, and then scatters a
third time back toward the radar antenna. The radar detects the main
energy scattered back from the hail stones, plus a smaller amount of
energy which the radar perceives to be at a greater distance because
of the triple reflection (hail stone-ground-hail stone) that adds
extra time between the initial radar pulse and the subsequent return
of energy. Thus, the TBSS appears as a “flare echo” (Wilson and Reum
1986, 1988) of weaker reflectivity at mid-levels of the storm on the
back side of the reflectivity core when viewed along a radial (Fig. 9).
A TBSS is typically seen down range from a high reflectivity core (65 dBz
and greater) in the presence of large hail stones (2.5 cm diameter or
greater) between 10 and 30 minutes before the hail reaches the ground
Figure 9. Schematic diagram showing the path of the radar beam during
three-body scattering by large hail stones in a thunderstorm core.
Adapted from Wilson and Reum (1988).
The thunderstorm continued to intensify as it moved across the area
between Anderson and Belton through 2325 UTC, perhaps as the result
of enhanced low level convergence and moisture as suggested by the
Mesoscale Discussion issued by the Storm Prediction Center. At mid-
levels of the storm, a mesocyclone was evident, which is typical for
a severe thunderstorm with a very strong updraft. With the original
Severe Thunderstorm Warning set to expire at 2330 UTC, the warning was
re-issued and upgraded to a Tornado Warning for Anderson County at
2327 UTC, due to the presence of rotation developing on the lowest
scan of the KGSP radar. A few minutes later, at 2330 UTC, a Severe
Thunderstorm Warning was issued for southern Greenville County based
on the movement of the storm to the northeast.
Figure 10. Base velocity at 0.4 degree scan from KGSP radar at
2331 UTC. Note the couplet of inbound targets (green) and outbound
targets (red) near Belton, indicative of cyclonic rotation in the
storm cloud. Click on image to enlarge.
Large hail probably began falling at the ground a few miles west of Belton
between 2327 and 2331 UTC, judging by the high reflectivity (65 dBz) on
the lowest elevation scan from the KGSP radar (Fig. 11). Between 2331
and 2335 UTC, the severe thunderstorm reached its peak intensity as it
moved over the north side of Belton. Radar scans at mid levels of the
storm showed a pronounced TBSS, weak echo region, and mesocyclone.
Numerous reports of large hail were received from the Belton area as the
storm passed, with sizes ranging from penny to golf ball (Fig. 12).
Click here to view a 14 frame java loop of reflectivity from the 2331 UTC
volume scan from the KGSP WSR-88D radar.
Figure 11. Radar reflectivity at 0.4 degree scan from KGSP radar at
2331 UTC. Note the high reflectivity (greater than 65 dBz) on the west
side of Belton. Large hail is most likely reaching the ground at this
time. Click on image to enlarge.
Figure 12. Large hail typically falls in a range of sizes. Note the
large stone near the bottom of the railing which appears to be approximately
1.5 inches wide, compared to the brick step. When reporting hail to the
National Weather Service, always remember to include an estimate of the
largest stones. Image courtesy of Cynthia Ownbey.
The severe thunderstorm crossed the Saluda River into southern Greenville
County between 2340 and 2345 UTC in a somewhat weakened state. Hail up
to the size of quarters continued to fall across the area from Belton to
Fork Shoals. Although strong mid-level rotation continued, low-level
rotation remained weak. An apparent funnel cloud was sighted along
Dunklin Bridge Road in southern Greenville County (Fig. 13), but no
tornadoes were actually sighted nor were any reports of wind damage
received from either Anderson or Greenville counties.
Figure 13. Funnel cloud sighted off Dunklin Bridge Road in southern
Greenville County, South Carolina. Quarter-sized hail stopped falling
moments before. Image captured by Mike & Christy Countryman.
Across the north side of Belton, hail accumulated to a depth of several
inches in some spots. In the aftermath of the severe thunderstorm,
large hail remained on the ground across the Belton area for an hour or
more as it gradually melted. The hail resulted in dangerous driving
conditions along Highway 20 north of Belton (Fig. 14). Driving on a
hail covered road is akin to driving on small ball bearings. Hail fog
formed when the accumulated hail lowered the temperature near the ground
to the point where the air became saturated (Fig. 15). The hail fog
locally reduced the visibility, making driving conditions even more
Figure 14. A significant accumulation of smaller sized hail stones resembles
a snowfall and can be just as difficult to drive through. This was the
case along State Highway 20 between Belton and Cheddar after the hail ended.
Images courtesy of David Rogers of the Anderson Independent-Mail.
Figure 15. Significant amounts of hail will also locally affect the
temperature and visibility. Large hail remains on the ground an hour
after it fell on the north side of Belton at intersection of Highway 20
and Calhoun Road. Note the poor visibility along Highway 20. Image
courtesy of David Rogers of the Anderson Independent-Mail.
Additional severe thunderstorms developed Friday night and early Saturday
morning across the northern part of the Upstate and the Piedmont of North
Carolina, but none were as intense as the Belton storm.
A severe thunderstorm produced a swath of penny to golf ball sized hail
from just south of Anderson, across Belton, to the southern part of
Greenville County near Fork Shoals during the early evening of 21 April
2006. The initial occurrence of large hail in the Belton area was
preceded by a Severe Thunderstorm Warning issued by the National Weather
Service Office in Greer with 50 minutes of lead time. Radar observations
of the storm showed a distinct three-body scatter spike approximately
16 minutes prior to the occurrence of golf ball sized hail on the north
side of Belton. Although strong mid-level rotation was also observed,
a tornado did not occur.
Thanks to John Cessarich at WYFF-TV for providing the images captured by
Cynthia Ownbey and Mike and Christy Countryman. The Anderson Independent-
Mail provided the contact to David Rogers, who captured the images of the
hail on the north side of Belton. The upper air and mesoscale analysis
graphics were obtained from the Storm Prediction Center. The surface
analysis was obtained from the Hydrometeorological Prediction Center.
Radar images were created using the Java NEXRAD Viewer and Data Exporter,
obtained from the National Climatic Data Center. The Aqua MODIS imagery
was obtained from the Space Science and Engineering Center at the
University of Wisconsin at Madison.
Lemon, L. R., 1998: The radar “three-body scatter spike”: An operational
large-hail signature. Wea. Forecasting., 13, 327–340.
Wilson, J. W., and D. Reum, 1986: “The hail spike”: Reflectivity and velocity
signature. Preprints, 23d Conf. on Radar Meteorology, Snowmass, CO, Amer.
Meteor. Soc., 62–65.
Wilson, J. W., and D. Reum, 1988: The flare echo: Reflectivity and velocity
signature. J. Atmos. Oceanic Technol., 5, 197–205.
Zrnic, D. S., 1987: Three-body scattering produces precipitation signature of
special diagnostic value. Radio Sci., 22, 76–86.