EF1 tornado, Porter to Locust Grove, Oklahoma, May 18, 2017

1. EF065 to 85 mph

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. EF186 to 110 mphthis tornado

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. EF2111 to 135 mph

   Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.

4. EF3136 to 165 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. EF4166 to 200 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. EF5over 200 mph

   Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.

7. Unrated

   The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.

Rating

EF1

Date

May 18, 2017

Touchdown

10:48 PM CDT (03:48 UTC)

Lifted

11:05 PM CDT (04:05 UTC)

On the ground

17 minutes

Path length

12.7 miles (20.4 km)

Path width

650 yards (594 m)

Deaths

0

Injuries

0

Property damage

$200,000

Counties

Wagoner and Mayes counties

Touchdown point

35.915, -95.330

Lift-off point

36.081, -95.237

Record number

1705182148-01

169 damage points were recorded along this path by NWS TSA, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF2. The highest wind the damage implies is 120 mph.

• four poles snapped here and n
• northern-most pole that was snapped
• trees uprooted convergently
• adjacent tree blown down to the n

Survey points are preliminary and are the raw material the published rating was built from. Source: NWS Damage Assessment Toolkit.

A slow-moving, strong upper level storm system moved from the Central Rockies into the Central Plains on the 18th and 19th. A dry line sharpened ahead of this system across western Oklahoma by early afternoon on the 18th, as a frontal boundary over northern Oklahoma shifted north into Kansas as a warm front. Warm, very moist, and very unstable air was in place east of the dry line and south of the warm front, and thunderstorms erupted across western Oklahoma during the early afternoon near the dry line. These storms evolved into a line by the time they moved into and across eastern Oklahoma during the evening hours. The storms produced multiple tornadoes, damaging wind, and hail up to half dollar size as they moved across eastern Oklahoma.||Another round of thunderstorms developed and moved across eastern Oklahoma during the morning hours of the 19th. No severe weather occurred with these storms but locally heavy rainfall did occur. As a cold front pushed into the area during the afternoon hours, another round of strong to severe thunderstorms developed. Hail up to half dollar size and damaging wind occurred with the strongest storms. Several widespread rainfall events over the past couple days set the stage for this event to evolve into flash flooding during the evening of the 19th through the morning hours of the 20th.

This tornado developed south of Porter where it uprooted trees and destroyed an outbuilding. It moved northeast damaging homes, destroying outbuildings, uprooting or snapping numerous trees, and blowing down power poles. The tornado dissipated on the northwestern side of Wagoner, north of Highway 51. Based on this damage, maximum estimated wind in the tornado was 95 to 105 mph.

This is the second segment of a three segment tornado. In Wagoner County, this tornado snapped and uprooted numerous trees. The tornado continued into Cherokee County. Based on this damage, maximum estimated wind in this segment of the tornado was 95 to 105 mph.

This is the first segment of a two segment tornado. In Wagoner County, this tornado developed southeast of Wagoner in the lowlands of Fort Gibson Lake. It moved northeast uprooting numerous trees, damaging homes, and destroying outbuildings north of Highway 51. The tornado then moved over Fort Gibson Lake and back onshore northeast of Wagoner where trees were uprooted and snapped, several boat docks were destroyed, and homes were damaged. It moved back over Fort Gibson Lake and then across the far northeastern portion of Wagoner County where trees were uprooted and snapped. The tornado continued into Mayes County. Based on this damage, maximum estimated wind in this segment of the tornado was 90 to 100 mph.

This is the second segment of a two segment tornado. In Mayes County, this tornado snapped large tree limbs and then dissipated north of Ear Bob Road. Based on this damage, maximum estimated wind in this segment of the tornado was 80 to 85 mph.

This is the second segment of a two segment tornado. In Mayes County, this tornado uprooted trees and snapped large tree limbs. Based on this damage, maximum estimated wind in this segment of the tornado was 90 to 100 mph.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

25 minutes of warning. NWS TSA issued a tornado warning for this county at 03:23 UTC, 25 minutes before the tornado touched down, in force until 04:00 UTC.

The county was under a tornado watch, issued at 23:02 UTC and running to 06:00 UTC.

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The Storm Prediction Center had this point in a Enhanced Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 00:58 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.

Tahlequah Municipal (TQH), 27 km from the path, in the two hours either side.

From the Iowa Environmental Mesonet's archive of airport observations.

The Tulsa radar (KINX), 32 km away, was scanning. The volume nearest the touchdown began at 03:44 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

Local storm reports within 60 km of the path, in the three hours either side.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

The live radar over the trackEvery 2017 tornado in OklahomaEvery tornado in Oklahoma since 1950Warnings in force in Oklahoma nowThe forecast where you are

47 more were confirmed in the United States that day.

Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.