Rare Wintertime Tornadoes
Across the North Carolina Foothills on January 11, 2012
Patrick D. Moore
NOAA/National Weather Service
A tornado struck near Ellenboro, North Carolina, on 11 January 2012. Image taken by Dustin Wiser and reprinted from the NWS Facebook page.
Author's Note: The following report has not been subjected to the scientific peer review process.
During the early part of the evening on Wednesday, 11 January 2012,
a series of severe thunderstorms produced three tornadoes across the
eastern part of Rutherford, Burke, and Caldwell counties in North
Carolina. The first tornado touched down in Rutherford County
northwest of Ellenboro at approximately 522 pm EST (Eastern Standard
Time), or 2222 UTC (Universal Time Coordinated). The tornado briefly
made contact with the ground at two locations before leaving a 2.3 mile
long path of destruction. Six to ten homes were damaged and some mobile
homes were completely destroyed. Ten people were injured as a result.
The damage was estimated at EF-2 intensity on the Enhanced Fujita Scale.
The next tornado touched down at 604 pm EST (2304 UTC) about five miles
south southwest of Icard in Burke County. After a short period of
intermittent contact with the ground, a more continuous trail of damage
was produced along a 3.6 mile long path. At least 75 homes were damaged
near Icard, with several mobile homes totally destroyed, and eight people
were injured. The damage was also estimated at EF-2 intensity. The
final tornado briefly struck the northern shore of Lake Hickory in
extreme southeast Caldwell County at 618 pm EST (2318 UTC). The damage
was limited to the area near the Lake Hickory Marina and was rated at
EF-0 intensity. No other reports of severe weather were received across
the entire United States on that day (Fig. 1).
[Note: Times in this report from this point forward are referenced to
UTC, which is Eastern Standard Time plus five hours.]
Figure 1. Preliminary severe wind, large hail, and tornado reports
received at the Storm Prediction Center for the 24 hour period ending at
1200 UTC on 12 January 2012. Click on image to enlarge.
The events of 11 January were noteworthy because no tornadoes had been
verified in the months of December, January, or February over the North
Carolina foothills within the NWS Greenville-Spartanburg (GSP) County
Warning Area (CWA) since detailed records began in 1950 (Fig. 2). The
lack of tornadic activity over the North Carolina foothills should come
as no surprise as this area often experiences cold air damming with the
passage of low pressure in the cool season. Historically speaking, the
only other tornado of record over the North Carolina foothills in the
winter months occurred on 21 January 1959 over Surry County. The last
significant tornado in western North Carolina during "Meteorological
Winter" occurred in Cleveland County on 10 February 1990 (an F2). Thus,
it would be fair to consider the tornadoes on 11 January 2012 to be a
Figure 2. Tornadoes confirmed across western North Carolina during the
months of December, January, and February for the period from 1950 to 2011.
Click on image to enlarge.
2. Synoptic Features and Pre-Storm Environment
The pre-storm environment on 11 January 2012 was characterized by deep
forcing for upward vertical motion and high values of wind shear, but
low values of Convective Available Potential Energy (CAPE). In the
morning of 11 January, an upper low at 500 mb centered over Mississippi
at 1200 UTC (Fig. 3) was forecast to open up across the Cumberland
Plateau and Tennessee Valley during the day, while a large area of upper
difluence at 300 mb was expected to spread across the region ahead of
the low. Strong wind shear was forecast to translate across the western
Carolinas during the middle of the day as the mid-level jet of 50-70 kt
wrapped around the southern extent of the upper low and a southerly 850 mb
jet of at least 50 kt (Fig. 4) moved overhead. At the surface, a warm
front was oriented west to east across central Georgia and coastal South
Carolina (Fig. 5). The warm front intersected a cold front over east
central Alabama, from which point a cold front trailed down to the Florida
Panhandle and an occluded front extended north to a center of low pressure
over southwest Kentucky. Although the upper air observation at Peachtree
City, Georgia (FFC, Fig. 6), at 1200 UTC was taken in the more stable air
mass to the north of the warm front, the modified convective parameters
compared favorably with values computed in the warm sector later in the day.
Figure 3. Objective analysis of 500 mb geopotential height (black
contours), temperature (red dashed contours), and wind barbs at 1200 UTC
on 11 January 2012. Click on image to enlarge.
Figure 4. Objective analysis of 850 mb geopotential height (black
contours), temperature (red and blue dashed contours), dewpoint (green
contours), and wind barbs at 1200 UTC on 11 January 2012. Click on image
Figure 5. Surface fronts and pressure analysis from the Hydrometeorological
Prediction Center at 1200 UTC on 11 January 2012. Click on image to enlarge.
Figure 6. Skew-T, log P, diagram of the upper air sounding taken at FFC
(Peachtree City, Georgia) at 1200 UTC on 11 January. The temperature
sounding is shown in red and the dewpoint sounding is shown in green.
A hodograph is shown in the upper right. A table showing convective
parameters is provided at the bottom. Click on image to enlarge.
The best combination of shear and instability were forecast to occur along
the Carolina coast, where a Slight Risk was included in the Day 1 Convective
Outlooks issued by the Storm Prediction Center (SPC) at 1630 UTC and 2000 UTC.
Convection the previous night and during the morning left behind a cool pool
of relatively stable air across the western Piedmont and foothills of North
Carolina. A relative lack of instability was thought to be a limiting factor
across the GSP forecast area as it was still unclear how far inland the warm
front would penetrate during the afternoon.
In fact, the warm front lifted to the vicinity of the South Carolina –
North Carolina border by 2100 UTC with a triple-point located over the
North Carolina Mountains (Fig. 7). Within a narrow warm sector over
northern South Carolina, dew point temperatures surged into the mid-50s
with a southerly wind of 10 kts. The movement of the upper low to eastern
Tennessee, seen on water vapor imagery at 2145 UTC (Fig. 8), and the
northward movement of the warm front into North Carolina, had a pronounced
effect on the environment ahead of shallow convection moving across
Upstate South Carolina. Differential positive vorticity advection at mid
and upper levels combined with strong low level convergence along the
South and North Carolina border in the vicinity of the surface triple-
point (Fig. 9) to produce strong upward vertical motion. Colder air
aloft associated with the upper low contributed to a steeper lapse rate
in the 700-500 mb layer. The northwestern extent of the effective bulk
shear greater than 40 kt and the effective Storm Relative Helicity (SRH)
of at least 200 m2s-2 reached into northern South Carolina and the southern
Foothills of North Carolina, indicating that storms moving into that region
would have a favorable environment to acquire rotation. Superimposed on
the strong shear, most unstable CAPE (MUCAPE) reached 500 J kg-1 within
the warm sector. The most unstable lifted index (MULI) reached its lowest
negative number over the same region, while the core of the mid-level jet
streak moved overhead.
Click here to view a 25 frame Java loop of GOES-13 water vapor satellite
imagery from 0245 UTC on 11 January to 0245 UTC on 12 January.
Figure 7. Surface fronts and pressure analysis from the Hydrometeorological
Prediction Center at 2100 UTC on 11 January 2012. Click on image to enlarge.
Figure 8. GOES-13 water vapor imagery at 2145 UTC on 11 January 2012.
Brightness temperatures are given by the color table at the bottom. Click
on image to enlarge.
Figure 9. SPC objective mesoanalysis of (a) boundary layer wind (kt; barbs),
streamlines (black vectors), and convergence (red contours), (b) 700-500 mb
lapse rate (oC km-1; green contours, (c) effective bulk shear (kt; blue
contours, (d) effective SRH (m2s-2; blue contours, inflow base (m AGL,
color fill) , and storm motion (kt, barbs), (e) MUCAPE (J kg-1; orange
contours), MUCIN, and effective bulk shear (kt; barbs), and (f) 850 and
500 mb wind crossover (kt; barbs) and MULI (index; yellow contours) at
2200 UTC on 11 January. Click on image to enlarge.
3. Radar observations
Thunderstorms developed close to the triple point over extreme northeast
Georgia between 1800 UTC and 1900 UTC, then moved east and northeast
across the northwestern part of Upstate South Carolina through 2100 UTC.
Penny-sized hail was reported as a cell moved over Six Mile (Pickens County),
South Carolina, at 2025 UTC.
Click here to view a 35 frame Java loop of KGSP Composite Reflectivity from
1901 UTC to 2059 UTC on 11 January.
A persistent thunderstorm cell moved northeast across the middle of
Greenville County, South Carolina, between 2100 UTC and 2130 UTC. This
storm gained strength for the next ten minutes. The KGSP radar showed
the vertical extent of the 55 dBZ reflectivity core reaching a maximum
of 20,500 feet above Mean Sea Level near Lake Bowen at 2140 UTC (Fig. 10).
The apparent echo overhang between Inman and Lake Bowen was probably the
result of a new updraft developing on the southeastern (inflow) flank of
the storm, and not a tilted updraft in the same storm. The vertically-
integrated liquid product also peaked at 42 kg m-2 at that time. A
Tornado Vortex Signature (TVS) alarm was generated at 2144 UTC, but was
thought to be false because of spurious low level radial velocity data.
Penny-sized hail fell across the northern part of Spartanburg County
between Fingerville and the state line. A Severe Thunderstorm Warning
was issued for this storm at 2155 UTC, including eastern Rutherford
County, North Carolina, valid until 2300 UTC (Fig. 11).
Click here to view a 16 frame Java loop of KGSP Composite Reflectivity from
2059 UTC to 2200 UTC on 11 January.
Figure 10. Base reflectivity (dBZ) from the KGSP radar on the (a) 0.5 degree,
(b) 5.1 degree, and (c) 12.5 degree scans, and (d) vertically integrated
liquid (kg m-2) at 2140 UTC. Click on image to enlarge.
Figure 11. KGSP composite reflectivity at 2152 UTC with polygon for Severe
Thunderstorm Warning #0001 (outlined in yellow) issued at 2155 UTC and
valid until 2300 UTC. Click on image to enlarge.
After 2140 UTC, the storm moved down-radial from the KGSP radar. Between
2144 UTC and 2204 UTC, the base velocity on the lowest four elevation
scans on the KGSP radar showed evidence of developing rear to front flow
across the upshear (southern) flank of the storm as it crossed southeastern
Polk County, North Carolina, and into southwestern Rutherford County. An
expanding area of reflectors moving away from the radar at 45-50 kt was
noted behind a bow in the higher reflectivity, while the targets ahead of
the higher reflectivity were only moving away at 15-25 kt (Fig. 12). By
2204 UTC, the radar showed evidence of the rear to front flow moving
around the eastern flank of the storm. The leading edge of the stronger
outbound velocity coincided with the southern extent of the reflectivity
wrapping around the southeastern side of the storm at that time. After
2207 UTC, this began to manifest itself as broad rotation on the inflow
side of the storm.
Figure 12. Base reflectivity and base velocity from the KGSP radar on
the (a, b) 1.8 degree scan at 2144 UTC, (c, d) 1.3 degree scan at 2156 UTC,
and (e, f) 0.9 degree scan at 2204 UTC. An alternate color scale was used
for the base velocity which highlights outbound winds greater than 45 kt
in pink. The white arrow in (a), (c), and (e) is used as a tracer for
the leading edge of the higher reflectivity. The small black ‘x’ in (b),
(d), and (f) is at the same height relative to MSL in each image. Click
on image to enlarge.
The storm moved into the range of the Terminal Doppler Weather Radar (TDWR)
located north of the Charlotte airport (the TCLT radar) around 2213 UTC.
Rotational velocity and shear remained relatively weak until 2217 UTC and
steadily increased thereafter on both radars (Figs. 13 and 14). Although
an inbound-outbound velocity couplet tightened on the KGSP radar through
2224 UTC, values of rotational shear remained below values normally
associated with tornadic activity. The TCLT radar showed a more rapid
increase in rotational shear to the point where it exceeded 0.02 s-1 on
the 0.2 degree scan at 2221 UTC. Other than some modest echo overhang as
the storm was developing, reflectivity clues that a tornado was imminent
were limited to evidence of an inflow notch on the southeastern flank of
the storm (Fig. 15). A gate-to-gate velocity couplet had formed on the
TDWR storm relative velocity product, but rotation kept a broad appearance
on the KGSP radar. Tornadogenesis occurred at 2222 UTC. Neither of the
radars detected a mesocyclone or TVS during this phase of the event.
Rotational shear remained on the transition between the "probable" and
"likely" areas of the rotational shear nomogram (Falk and Parker 1988)
through about 2232 UTC, although the Ellenboro tornado lifted around
2227 UTC. A Tornado Warning (#0001) was issued for northeastern Rutherford,
northwestern Cleveland, northwestern Lincoln, southeastern Burke, and
southwestern Catawba counties at 2235 UTC, valid until 2315 UTC (Fig. 16).
Click here to view a 13 frame Java loop of TCLT 1.0 Degree base reflectivity
and storm relative motion from 2213 UTC to 2325 UTC on 11 January.
Figure 13. Maximum rotational velocity (kt) and rotational shear (10-3 s-1)
on the lowest three scans from the KGSP radar from 2207 UTC to 2331 UTC on
11 January 2012. The yellow bar indicates the time of the Ellenboro tornado.
The pink bars represent the times of the Icard and Lake Hickory tornadoes.
Click on image to enlarge.
Figure 14. Maximum rotational velocity (kt) and rotational shear (10-3 s-1)
for the two lowest scans from the TCLT radar from 2213 UTC to 2331 UTC on
11 January. The 0.2 degree data was not available from 2301 UTC to 2316 UTC.
The time of the Ellendale tornado is shown by the yellow bar and the times
for the Icard and Lake Hickory tornadoes are shown by the pink bars. Click
on image to enlarge.
Figure 15. Base reflectivity (a) and Storm Relative Motion (b) on the
0.5 degree scan from the KGSP radar and base reflectivity (c) and storm
relative motion (d) on the 0.2 degree scan from the TCLT radar at 2221 UTC
on 11 January. The KGSP radar is located off the bottom left corner of
the top two images, while the TCLT radar is located off the right edge of
the bottom two images. The pink arrow points to the weak inflow notch on
the eastern flank of the storm. Click on image to enlarge.
Figure 16. Composite reflectivity from the KGSP radar at 2233 UTC with the
polygon outline (in red) for Tornado Warning #0001, issued at 2235 UTC
and valid until 2315 UTC. Click on image to enlarge.
A new, detached updraft formed around 2227 UTC along the Rutherford and
Cleveland County line, off the eastern flank of the old storm (Fig. 17).
The new cell quickly acquired low level rotation after 2237 UTC. Another
surge in rotational shear was analyzed in the 0.2 degree scans from TCLT
after 2241 UTC (Fig. 14) as the new cell moved past Casar in northern
Cleveland County. Values climbed back into the "tornado probable" range
after 2245 UTC and peaked at 0.04 s-1 at 2252 UTC over southeastern Burke
County. Although a weather watch was contemplated by the SPC, one was
not issued because of the small extent and downward trend of weak
instability at that time of day.
Figure 17. KGSP radar scans at 2237 UTC of base reflectivity (a) and
storm relative motion (b) at 0.5 degrees, and base reflectivity (c) and
storm relative motion (d) at 0.9 degrees. The "E" corresponds to the
remnant of the Ellenboro storm, while the "I" indicates the development
of the storm that would eventually produce the tornado near Icard. Click
on image to enlarge.
A weak echo channel developed behind the higher reflectivity associated
with the main cell over eastern Burke County, perhaps associated with a
rear flank downdraft (Fig. 18). A cusp formed in the reflectivity where
the weak echo channel began to wrap around the southeast flank of the
storm. This cusp was co-located with a prominent velocity couplet on the
0.2 degree scan from TCLT at 2300 UTC. Rotational shear on the lowest two
elevation angles remained strong through 2304 UTC, when the second tornado
touched down in eastern Burke County to the south southwest of Icard. A
new Tornado Warning (#0002) was issued at 2305 UTC to extend the warning
area into Alexander County and more of Caldwell County (Fig. 19). While
the Icard tornado was on the ground, the weak echo channel continued to
wrap around the eastern side of the main part of the cell and forced a
split between the main cell and an arc of higher reflectivity that
extended to the south (Fig. 20). The resemblance to the "Broken-S"
reflectivity evolution (e.g. Lane and Moore 2006) was noteworthy. By the
time the Icard tornado lifted at 2310 UTC near Hildebran, the fracture
between the main cell and the flanking arc of reflectivity was complete.
Figure 18. TCLT radar base reflectivity (a) and storm relative motion (b)
at 0.2 degrees on the 2300 UTC scan, and base reflectivity (c) and storm
relative motion (d) at 1.0 degrees on the 2301 UTC scan. The white curved
arrow denotes the weak echo channel. The TCLT radar is situated off the
bottom right corner of each graphic. Click on image to enlarge.
Figure 19. KGSP composite reflectivity at 2304 UTC with outline of polygon
for Tornado Warning #0002 (in red), issued at 2305 UTC and valid until
2345 UTC on 11 January. Click on image to enlarge.
Figure 20. KGSP base reflectivity on the 0.5 degree scan at (a) 2301 UTC,
(b) 2307 UTC, (c) 2313 UTC, and (d) 2319 UTC. The curved white arrow
denotes the weak echo channel wrapping around the southern and eastern
flank of the main reflectivity core moving from eastern Burke into
southeastern Caldwell counties. Click on image to enlarge.
One final increase in rotational shear was analyzed on the 1.0 degree
scan between 2313 and 2319 UTC as the main thunderstorm moved into extreme
southeast Caldwell County. The final tornado touched down briefly on the
north shore of Lake Hickory at the Lake Hickory Marina at about 2318 UTC.
No other severe weather was reported.
In spite of a lack of reflectivity features commonly associated with
miniature supercells, the storms on 11 January met the most basic
definition of a supercell. The environment had sufficient shear,
helicity, and buoyancy to support supercell development. While the
cell had some low level characteristics of a mini-supercell, such as
a low level pendant on the upshear flank, observed rotation was
categorized as weak. The rotation failed to trigger a mesocyclone
or TVS alarm. The WSR-88D at Columbia did not show any significant
rotation, but was too far away to scan below approximately 8000 feet
above ground level. The Ellenboro storm appeared to have a quasi-steady
updraft for over an hour before it acquired significant rotation.
The supercell that produced the Icard tornado was not the same cell as
the one that produced the Ellenboro tornado. In addition to the
reflectivity evidence of a new and separate updraft core developing to
the east of the cell that produced the Ellenboro tornado, the rotation
track map (Fig. 21) obtained from the National Severe Storms Laboratory
clearly showed two corridors of rotation across eastern Rutherford and
northwest Cleveland counties.
Figure 21. Rotation tracks for 11 January 2012 obtained from the KGSP and
TCLT radars. Image created by the National Severe Storms Laboratory.
Click on image to enlarge.
Low-level rotation developed very quickly in the Ellenboro storm about
five minutes before tornadogenesis. There was a two minute lag in the
increase of rotational velocity between the 0.2 degree scan and the
1.0 degree scan, suggesting that rotation developed upward in the storm.
Rotational shear jumped from ambient levels at 2217 UTC to a level above
what has been observed in tornadic storms at 2221 UTC. There were no
hooks or appendages in the lowest reflectivity scans. Thus, the issuance
of a Tornado Warning was not supported by a preponderance of the evidence
until about one minute before tornadogenesis.
Pictures of the Ellenboro Tornado Damage
Pictures of the Icard Tornado Damage
Pictures of the Lake Hickory Tornado Damage
Falk, K., and W. Parker, 1998: Rotational shear nomogram for tornadoes.
Preprints, 19th Conf. on Severe Local Storms, Minneapolis, MN, Amer.
Meteor. Soc., 733-735.
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.
The upper air maps, soundings, mesoscale analysis, and storm report
plots were obtained from the Storm Prediction Center. The surface
analysis was obtained from the Hydrometeorological Prediction Center.
Satellite imagery and surface observation plots were provided by
the University Corporation for Atmospheric Research. The radar
images with warning polygon graphics were obtained from the Iowa
Environmental Mesonet web page, maintained by the Iowa State
University Department of Agronomy. Tornado track maps were created
using Google Earth and Google Maps. The damage survey for the
Ellenboro tornado was conducted by Tony Sturey and Larry Gabric.
The damage surveys for the Icard tornado and Lake Hickory tornado were
conducted by Harry Gerapetritis and John Tomko. The map of rotation
tracks was obtained from the National Severe Storms Laboratory.