EF1 Tornado near Bolton, NC: May 21, 2015

A tornado touched down east of Bolton in Columbus County, NC during the afternoon of May 21, 2015. No fatalities or serious injuries occurred, however one mobile home was heavily damaged. The tornado created a damage path which crossed US Highway 74/76 and continued for almost five miles. An NWS storm survey found evidence for winds up to 105 mph, making this an EF1 tornado on the Enhanced Fujita Scale.

Surface low pressure across interior North Carolina moved eastward toward the coast during the afternoon of May 21st. Ahead of this low southerly winds brought heat and humidity northward with air temperatures rising to near 90 degrees with dewpoints around 70. This generated a strongly unstable atmosphere with CAPE (Convective Available Potential Energy) rising to 2000 to 3000 J/kg. A belt of stronger west winds 2-3 miles above ground created sufficient wind shear to help support severe thunderstorms, and the NWS Storm Prediction Center issued a Severe Thunderstorm Watch for eastern North Carolina beginning around 1:00 pm.

Thunderstorms began in the Sandhills before 2:00 pm from the state line north to almost Raleigh. This line of storms moved steadily eastward across Lumberton between 2:30 and 3:00 pm and Elizabethtown between 3:00 and 3:30 pm. Around 3:30 pm the first of two thunderstorm cell mergers occurred across southern Bladen County. This changed the dynamics of the convective line, and the southernmost thunderstorm cell north of Lake Waccamaw began to display supercellular characteristics on radar imagery. The cell's direction of movement also changed, veering southeastward toward Columbus County. A severe thunderstorm warning which had been in effect for Bladen County since 3:20 pm was extended southward into Columbus county just before 4:00 pm.

A second cell merger occurred near the town of Bolton in Columbus County between 4:05 and 4:13 pm. This event appears to be what ultimately set the stage for the tornado; radar velocity products showed a rapid increase in the magnitude and area covered by rear-flank downdraft winds on the back side of the thunderstorm cell. Radar imagery also displayed an increasingly well-defined inflow notch in reflectivity imagery along the front edge of the supercell thunderstorm. This feature is typically associated with strong winds feeding into the storm's updraft. Increasing radar-indicated convergent shear along the interface between the inflow and rear-flank downdraft led forecasters to issue a tornado warning at 4:12 pm.

This two-dimensional cross section through the severe thunderstorm near Bolton, NC at 4:11 pm on May 21, 2015 shows a Bounded-weak Echo Region (BWER) at the center of the image. This hole in the precipitation is created when powerful updraft winds physically prevent precipitation from reaching the ground by lofting rain and hail back up into the cloud. The developing tornado was located on the southwestern edge of the BWER within a hook echo in low-level radar reflectivity. Image generated by GR2Analyst software.

This is a three-dimensional visualization of the severe thunderstorm near Bolton, NC, at 4:11 pm on May 21, 2015 looking toward the northwest. In this image inflow winds would be blowing directly away from the viewer into the storm, then ascending vertically producing the BWER feature. An overhang of high reflectivity can be observed, with the hook echo and developing tornado tucked in behind. Image generated by GR2Analyst software.

This is the radar reflectivity loop showing the thunderstorm that produced the tornado. At the beginning of the loop there were two discrete thunderstorm cells: one dropping southeastward across the Bladen-Columbus county line and a second cell south of Highway 74/76 moving eastward. These two cells merged just minutes before the tornado developed.

The hook echo associated with the tornado is visible between 4:13 pm and 4:22 pm as a counter-clockwise swirl of red (high reflectivity) echoes just south of Highway 74/76. This feature dissipated as the tornado lifted, and the storm weakened as it moved eastward into northern Brunswick County.

County lines are in black, while highways are in light gray.

Here is the radial velocity loop showing wind directions and speeds relative to the doppler radar site in Shallotte, NC. Green colors indicate winds blowing toward the radar, and red is away from the radar.

An expanding area of inbound winds (green) developed across northern Columbus County as the rear-flank downdraft strengthened between 4:00 and 4:08 pm. The storm's inflow (red) intensified between 4:08 and 4:13 pm. The tornado developed along the interface between these two opposing wind regimes, then moved southeastward across Highway 74/76.

The circulation noticably weakened between 4:22 and 4:28 pm as the storm moved into northern Brunswick County.

Correlation Coefficient (CC) is a new doppler radar product only available since the installation of dual-polarization radar technology back in 2012. It compares differences in how the vertical and horizontal pulses are reflected back to the radar antenna. In uniform precipitation where all the raindrops have the same shape this CC value is typically 0.98 or 0.99. In rain-hail mixtures or when sleet-snow mixtures occur CC often drops to 0.65 to 0.90.

In the case of debris lofted by a tornado, the CC signature is very unique and can range as low as 0.25 to 0.50. This is what we see here between 4:14 and 4:22 pm, as a region of very low CC values follows the tornadic circulation southeastward across Columbus County.

Shortly after the tornado occurred, reports from emergency management in Columbus County indicated significant damage occurred east of Bolton. A subsequent NWS Storm Survey found a five-mile long damage path beginning about 2 miles east of Bolton, extending across U.S. Highway 74/76, and ending well south of the highway about 3 miles southwest of Delco. Evidence for wind speeds as high as 105 mph was found in multiple locations along the damage path, giving support to the tornado's EF1 classification. The tornado appears to have touched down around 4:13 pm, remaining on the ground until 4:21 pm. Numerous areas of straight-line thunderstorm wind damage (likely produced by strong winds within the storm's rear-flank downdraft) occurred near and south of the tornado's path.

Here are some photos taken by the NWS Storm Survey Team.

This mobile home along US Highway 74/76 was heavy damaged by the tornado about one minute after touchdown.	Another view of the mobile home heavily damaged by the tornado.
Most of the area the tornado traveled was heavily forested with Loblolly pines.	More tornado wind damage to pines.

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE WILMINGTON NC
1234 PM EDT FRI MAY 22 2015

...TORNADO CONFIRMED NEAR BOLTON 3 E IN COLUMBUS COUNTY NORTH
CAROLINA...

LOCATION...BOLTON 3 E IN COLUMBUS COUNTY NORTH CAROLINA
DATE...05/21/2015
ESTIMATED TIME...4:13 PM EDT TO 4:21 PM EDT
MAXIMUM EF-SCALE RATING...EF-1 
ESTIMATED MAXIMUM WIND SPEED...105 MPH 
MAXIMUM PATH WIDTH...100 YARDS 
PATH LENGTH...5.0 MILES 
BEGINNING LAT/LON...34.3227N / -78.3549W 
ENDING LAT/LON...34.2852N / -78.2764W
* FATALITIES...0
* INJURIES...0

* THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO
CHANGE PENDING FINAL REVIEW OF THE EVENT(S) AND PUBLICATION IN
NWS STORM DATA.

...SUMMARY...
THIS INFORMATION HAS BEEN UPDATED AS A RESULT OF ADDITIONAL 
SURVEYING COMPLETED ON THE MORNING OF 5/22/2015.

THE NATIONAL WEATHER SERVICE IN WILMINGTON NC HAS CONFIRMED A
TORNADO APPROXIMATELY 3 MILES EAST OF BOLTON IN COLUMBUS COUNTY
NORTH CAROLINA ON 05/21/2015.

THE TORNADO TOUCHED DOWN ON THE NORTH SIDE OF HIGHWAY 74 AND 
SNAPPED APPROXIMATELY 100 PINE TREES. THE TORNADO MOVED SOUTHEAST
AND CROSSED HIGHWAY 74 CAUSING SIGNIFICANT STRUCTURAL DAMAGE TO 
A SINGLE WIDE MOBILE HOME AND ADJACENT BUILDINGS. NUMEROUS LARGE
PINE TREES WERE SNAPPED IN THE VICINITY OF THE RESIDENCE. THE 
TORNADO CONTINUED SOUTHEAST THROUGH FOREST AND SNAPPED LARGE PINE
TREES THAT BLOCKED ROBINSON ROAD. ADDITIONAL TREES WERE SNAPPED 
AND LARGE LIMBS BROKEN AS THE TORNADO CROSSED SPEARMAN ROAD. SEVERAL
POWER LINES WERE DOWN IN THE AREA DUE TO TREE DAMAGE.

DAMAGE BECAME LESS SEVERE AS THE TORNADO APPROACHED BYRDVILLE-FREEMAN
ROAD...AND IT APPEARS THE TORNADO LIFTED BRIEFLY BEFORE TOUCHING DOWN 
AGAIN ALONG SWIMMING HOLE ROAD. SEVERAL LARGE PINE AND CEDAR TREES 
WERE SNAPPED...AND A FEW LARGE HARDWOODS WERE UPROOTED BEFORE THE
TORNADO LIFTED NEAR THE INTERSECTION OF DOGWOOD STAND ROAD AND JM 
BORDEAUX LANE.

SPOTTY MINOR TO MODERATE DAMAGE...MAINLY IN THE FORM OF BROKEN LARGE 
TREE LIMBS...WAS OBSERVED SOUTH OF THE TORNADO TRACK FROM WEST OF 
BYRDVILLE-FREEMAN ROAD TO LENNON ROAD NEAR THE INTERSECTION OF WATER
TANK ROAD. THIS DAMAGE WAS UNIDIRECTIONAL IN NATURE AND WAS THE RESULT
OF STRAIGHTLINE WINDS UP TO AROUND 70 MPH.

THIS INFORMATION CAN ALSO BE FOUND ON OUR WEBSITE AT
WEATHER.GOV/ILM.

FOR REFERENCE...THE ENHANCED FUJITA SCALE CLASSIFIES TORNADOES
INTO THE FOLLOWING CATEGORIES:

EF0...WIND SPEEDS 65 TO 85 MPH.
EF1...WIND SPEEDS 86 TO 110 MPH.
EF2...WIND SPEEDS 111 TO 135 MPH.
EF3...WIND SPEEDS 136 TO 165 MPH.
EF4...WIND SPEEDS 166 TO 200 MPH.
EF5...WIND SPEEDS GREATER THAN 200 MPH.

$$

CRM/SRP

Page Author: Tim Armstrong
Date Created: May 30, 2015
Last Updated: June 4, 2015