May 6, 2007 Tornadoes in
Oklahoma and Seminole Counties Both Rated As EF0

The following is from a public information statement issued by the Norman Forecast Office at 340 pm CDT on Tuesday, May 8, 2007.

The National Weather Service oversaw a damage survey in Seminole, Pottawatomie, Lincoln, and Oklahoma counties to investigate storm damage that occurred on Sunday, May 6, 2007.

Here are the preliminary results of that survey.

Seminole County:

Straight Line Winds/ Weak Tornado

Enhanced Fujita (EF) Scale Rating - EF0

Max winds around 80 mph

Damage to a few trees, two single-wide mobile homes and a garage was noted along Oklahoma State Highway 9 two miles east of the intersection U.S. Highway 377 and Oklahoma State Highway 99. Damage to most of the trees consisted of large branches being broken off or small trees in wet soil being pushed over. One large tree fell onto one of the trailers and a car, apparently pushing the trailer off its foundation.

The majority of damage to the mobile home appeared to be due to the falling tree. The other mobile home was immediately adjacent (north) of the garage and east of the first mobile home. The garage was used for storage and was not anchored to its foundation. It consisted of particle board walls and a sheet metal roof that was straight-nailed down into the walls. The garage roof got flipped northward and up against the east-west oriented mobile home, while the outer walls of the garage collapsed.

Damage to the mobile home appeared to be mostly due to flying debris from the garage,  though it appeared the home was shifted slightly north off its foundation. All of the debris at this damage site appeared to be blown toward the north. Trees: damage indicator (DI) 27, degree of damage (DOD) high 2 or low 3, estimated wind speeds of 80 mph. Mobile homes DI 3, DOD 3, estimated wind speeds of 80 mph.

Two small metal barns sustained roof damage on Oklahoma State Highway 99A 1.3 miles east of the intersection of U.S. Highway 377 and Oklahoma State Highway 99. One barn lost its entire roof but it was noted that this very small metal storage building had an open doorway with a gate, so it was not a completely closed building. Small trees and a home immediately adjacent to this structure showed no damage. Pieces of sheet metal were blown northward across the highway.

About 100 yards to the north, a slightly larger metal east-west oriented barn or free-standing garage had several peeled-back metal sections from the southern side of it roof. Between 25-50 percent of the sheet metal was peeled back. Again, surrounding trees and structures showed no visible damage, though some branches were broken off trees. As at the other site, most of the debris was blown south to north with not enough damage indicators to determine the type of wind that caused the damage. Trees: DI 27, DOD 2, wind speeds estimated 80 mph. Small metal barns/garages: DI 1, DOD 4, wind speeds estimated 80 mph.

Other than very minor tree damage no other significant damage was found along this storm path in Seminole, Pottawatomie or southeast Lincoln counties.

Oklahoma County:

Straight Line Winds/ Weak Tornado

Enhanced Fujita (EF) Scale Rating - EF0

Max winds around 80 mph

An auto repair garage at NW 8th Street and Western Avenue was significantly damaged by straight line winds.  The failure point appeared to be a south-facing garage door that was blown inward. Some uplift of the lip of the metal roof was also noted on the southwest corner. It was noted the interior frame of the garage was charred indicating a previous fire. Further, there was some dry rot noted in the base of the failed garage door. The resulting upward pressure on the free-span flat metal roof along with outward pressure on the west-facing wall caused the west wall to collapse outward onto the street. It was also noted the garage doors on the west wall were blown outward. There was little damage to surrounding buildings, sheds, trees, utility poles, and signs.  One large tree to the north of the building (behind another building) was blown over, and a couple of large trees one block south had significant damage.

However, the lack of damage to other nearby damage indicators, including vulnerable structures such as awnings and garage doors, indicate much of the damage to the auto repair garage was due to structural faults. There were not enough damage indicators to determine whether this event was due to a vortex or general high winds. Auto repair garage: DI 14, DOD 7 technically, but we believe wind speeds were considerably lower, likely closer to 70 mph, than this DI/DOD pair would indicate because of the surrounding lack of damage.

A small, weak tornado developed just northwest of the intersection of NE 36th and MLK Drive and ended just northeast of the intersection of U.S. Interstate Highway I-35 and NE 50th Street. A narrow path of considerable tree damage was found from just northwest of the intersection of NE 36th Street and MLK Drive in Oklahoma City to just east of the intersection of I-35 and NE 50th Street, including a swath about 30 yards wide across Lincoln Park golf course. Damage consisted of numerous small to medium branches broken off trees, as well as numerous large rotted branches. A number of small trees in wet soil were also pushed over along this path.

It was noted along MLK Drive, just north of 36th Street, some confluence in the direction of tree falls, with east- to northeast-facing tree falls along the left side of the path and north-facing falls on the right side of the path. Minor shingle damage was noted to a home just east of I-35 and NE 50th Street, and minor gutter damage was noted to a large metal building just to the southwest of the house. A couple of wooden fences were pushed over and a small canopy was torn near the start of the path. 

However, other structures in or near the path showed little discernible damage. The distinct and confluent path of concentrated tree damage is consistent with a weak tornado at the start of the damage path. By the time the feature reached NE 50th Street and I-35 there was not enough damage to determine confluence or diffluence. Trees: DI 27, DOD low 3, wind speeds estimated 80 mph. House shingles:  DI 2, DOD 1, wind speeds estimated 75 mph. Gutter damage to metal building: DI 21, DOD 1, wind speeds estimated 65 mph.

Special thanks to Kevin Scharfenberg and Kevin Manross with NSSL/CIMMS for their work and expertise in gathering the data for this survey report.

Rick Smith, WCM