Tornadoes · United States · Oklahoma · 2017

EF1 tornado, Stidham to Shady Grove, Oklahoma, May 18, 2017

Name: EF1 tornado, Stidham to Shady Grove, Oklahoma, May 18, 2017
Start: 2017-05-19T03:25:00.000Z
End: 2017-05-19T03:32:00.000Z
Location: Stidham to Shady Grove, Oklahoma

From Stidham to Shady Grove, this EF1 tornado ran 8.8 miles across McIntosh County on May 18, 2017, touching down at 10:25 PM CDT and reaching 600 yards wide. It killed nobody, and did $125,000 of property damage.

The rating scale

Tracks are drawn in the color of the rating. The Enhanced Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.

EF065 to 85 mph
Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.
EF186 to 110 mphthis tornado
Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.
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.
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.
EF4166 to 200 mph
Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.
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.
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.

The record

Rating: EF1
Date: May 18, 2017
Touchdown: 10:25 PM CDT (03:25 UTC)
Lifted: 10:32 PM CDT (03:32 UTC)
On the ground: 7 minutes
Path length: 8.8 miles (14.2 km)
Path width: 600 yards (549 m)
Deaths: 0
Injuries: 0
Property damage: $125,000
County: McIntosh County
Touchdown point: 35.466, -95.491
Lift-off point: 35.540, -95.364
Record number: 1705182125-01

The damage survey

96 damage points were recorded along this path by NWS TSA, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 110 mph.

adjacent tree blown down to the n
light pole also bent to the ground to the sw
garage door failure; roof structure torn up

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

What the Weather Service recorded

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 destroyed a mobile home, damaged the roofs of several other homes, destroyed outbuildings, snapped or uprooted numerous trees, and blew down power poles. Based on this damage, maximum estimated wind in the tornado was 95 to 105 mph.

This tornado destroyed an outbuilding, damaged a home, snapped or uprooted numerous trees, and blew down power poles. Based on this damage, maximum estimated wind in the tornado was 95 to 105 mph.

This tornado developed north of I-40 near the N 4230 Road where it snapped large tree limbs, damaged homes, and blew down privacy fences. It moved northeast snapping or uprooting trees and damaging outbuildings. A home was damaged, a large outbuilding was destroyed, power poles were blown down, and numerous trees were snapped or uprooted near the N 4270 Road. The tornado dissipated after crossing the N 4290 Road, to the north of the E 1020 Road. Based on this damage, maximum estimated wind in the tornado was 100 to 110 mph.

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

The forecast that day

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.

What forecasters said that day

The local office's own words before the tornado touched down, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Tulsa, OK wrote its last area forecast discussion before the tornado touched down at May 18, 9:19 PM CDT, 1 hour 6 minutes earlier.

Area forecast discussion, May 18, 9:19 PM CDT, 1 hour 6 minutes before

Area Forecast Discussion
National Weather Service Tulsa OK
919 PM CDT Thu May 18 2017

...UPDATE...

.DISCUSSION...
Strong to severe thunderstorms continue this evening with heavy
rainfall occurring in the stronger clusters. A marginal wind/hail
threat will likely persist into the overnight hours as storms
progress eastward into instability axis. In addition, given the
rainfall rates, the threat for localized flash flooding will also
be possible.

A quick look at the latest 00Z NAM indicates another round of
severe thunderstorms late Friday afternoon into Friday night.
Flash flooding could become a major concern, especially given the
rainfall that is ongoing. Update out shortly given latest radar
trends.

&&

.TSA WATCHES/WARNINGS/ADVISORIES...
OK...Flash Flood Watch through Saturday morning for OKZ054>067-070-
     071.

AR...None.
&&

SHORT TERM...12

Hazardous weather outlook, May 18, 4:55 PM CDT, 5 hours 30 minutes before

Hazardous Weather Outlook
National Weather Service Tulsa OK
455 PM CDT Thu May 18 2017

ARZ001-002-010-011-019-020-029-OKZ049-053>076-191145-
Adair OK-Benton AR-Carroll AR-Cherokee OK-Choctaw OK-Craig OK-
Crawford AR-Creek OK-Delaware OK-Franklin AR-Haskell OK-Latimer OK-
Le Flore OK-Madison AR-Mayes OK-McIntosh OK-Muskogee OK-Nowata OK-
Okfuskee OK-Okmulgee OK-Osage OK-Ottawa OK-Pawnee OK-Pittsburg OK-
Pushmataha OK-Rogers OK-Sebastian AR-Sequoyah OK-Tulsa OK-Wagoner OK-
Washington OK-Washington AR-
455 PM CDT Thu May 18 2017

...SEVERE STORM POTENTIAL INCREASES THIS EVENING AND CONTINUES
INTO FRIDAY...

This Outlook is for Northwest and West Central Arkansas as well as
much of Eastern Oklahoma.

.DAY ONE...This evening through Tonight.

TORNADO.
	RISK...Limited.
 	AREA...West of highway 75.
    ONSET...after 6 PM.

SEVERE THUNDERSTORM.
	RISK...Elevated.
	AREA...Eastern Oklahoma and to a lesser extent Northwest Arkansas.
	ONSET...after 6 PM.

FLASH FLOOD.
	RISK...Limited.
	AREA...Northeast Oklahoma.
	ONSET...after midnight.

HEAVY RAIN.
	RISK...Elevated.
	AREA...Northeast Oklahoma.
	ONSET...after 6 PM.

SIGNIFICANT WINDS.
	RISK...Limited.
	AREA...Eastern Oklahoma and Western Arkansas.
	ONSET...ongoing.

DISCUSSION...

An enhanced to moderate risk of severe storms is forecast by early
evening into tonight across Eastern Oklahoma. Very large hail, in
excess of 2 inches in diameter, damaging winds and isolated
tornadoes are possible, with the greatest risk northwest of Tulsa. A
slight risk of severe storms is forecast for Western Arkansas late
tonight. Damaging winds and marginally severe hail would be the main
threats, mainly after midnight.

Strong to severe storms have develop this afternoon over western and
central Oklahoma.  These storms are expected to move east into the
region early this evening. The best chance for discrete surface
based cells, and thus the highest tornado and largest hail threat,
will be to the west of highway 75 this evening.

Storms are expected to gradually grow into clusters or lines this
evening as they move deeper into Eastern Oklahoma. Damaging winds
and large hail would be the main threats. An isolated tornado could
occur with any bowing line segments.

SPOTTER AND EMERGENCY MANAGEMENT ACTION STATEMENT...
Activation of the Regional Spotter Network Expected.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY.
FRIDAY and SATURDAY...Severe Thunderstorm Potential...High Wind
                        Potential...Heavy Rain Potential.
SUNDAY...No Hazards.
MONDAY...Severe Thunderstorm Potential.
TUESDAY...Thunderstorm Potential.
WEDNESDAY...No Hazards.

EXTENDED DISCUSSION...

Another round of strong to severe storms are expected Friday into
early Saturday as upper level system approaches the region.
Storms will fire along the dryline and cold front, becoming more
numerous with time. All modes of severe will be possible,
especially early when storms are more discrete, with storms again
merging into a line as they move east. Severe threat will
transition to more of a wind and heavy rain/flooding threat as
the night goes on. Convection will linger into Saturday while
gradually weakening, across northwest Arkansas and southeast
Oklahoma.

A system dropping through the region in northwest flow will bring
another round of storm potential Monday and Tuesday. A limited
risk for severe weather can be expected with this system.

weather.gov/tulsa Contains additional information.

In the hours before

Local storm report, May 18, 9:47 PM CDT, 38 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TULSA OK
947 PM CDT THU MAY 18 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0939 PM     TSTM WND GST     4 NE TULSA              36.17N 95.87W
05/18/2017  M65 MPH          TULSA              OK   MESONET

&&

JDS

Local storm report, May 18, 10:02 PM CDT, 23 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TULSA OK
1002 PM CDT THU MAY 18 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0945 PM     HAIL             4 NE PRYOR              36.35N 95.27W
05/18/2017  E0.75 INCH       MAYES              OK   EMERGENCY MNGR

&&

JDS

Local storm report, May 18, 10:12 PM CDT, 13 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TULSA OK
1012 PM CDT THU MAY 18 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1005 PM     TSTM WND GST     2 S WYNONA              36.52N 96.33W
05/18/2017  M59 MPH          OSAGE              OK   MESONET

&&

JDS

Local storm report, May 18, 10:14 PM CDT, 11 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TULSA OK
1014 PM CDT THU MAY 18 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1010 PM     HAIL             OOLOGAH                 36.45N 95.71W
05/18/2017  E0.75 INCH       ROGERS             OK   PUBLIC

1009 PM     TSTM WND DMG     HANNA                   35.21N 95.89W
05/18/2017                   MCINTOSH           OK   BROADCAST MEDIA

            POWER LINES DOWN.

0953 PM     TSTM WND DMG     4 S SPERRY              36.24N 95.99W
05/18/2017                   TULSA              OK   PUBLIC

            TREE UPROOTED IN TURLEY.

0933 PM     TSTM WND GST     1 NW JENKS              36.03N 95.98W
05/18/2017  M62 MPH          TULSA              OK   ASOS

            MEASURED AT RIVERSIDE AIRPORT.

&&

KAH

Local storm report, May 18, 10:22 PM CDT, 3 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TULSA OK
1022 PM CDT THU MAY 18 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1015 PM     TSTM WND GST     4 WNW EUFAULA           35.31N 95.65W
05/18/2017  M66 MPH          MCINTOSH           OK   MESONET

&&

JDS

Local storm report, May 18, 10:24 PM CDT, 1 minute before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TULSA OK
1024 PM CDT THU MAY 18 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1020 PM     TSTM WND GST     BIXBY                   35.94N 95.88W
05/18/2017  E60 MPH          TULSA              OK   TRAINED SPOTTER

&&

JDS

The air that afternoon

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.

Norman, OK (KOUN), 12:00Z

8.6 hours after it, 182 km from the path. May 19, 2017.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.

Mixed-layer CAPE: 525 J/kg
Mixed-layer CIN: -227 J/kg
Surface CAPE: 120 J/kg
Mixed-layer LCL: 813 m above ground
0-6 km bulk shear: 46 kt
0-1 km bulk shear: 33 kt
0-1 km storm-relative helicity: 295 m²/s²
0-3 km storm-relative helicity: 318 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.8
0-3 km lapse rate: 3.7 K/km

Open this sounding in Storm Lab

The surface observations

Muskogee/Davis Field (MKO), 18 km from the path, in the two hours either side.

Time (UTC)	Temp (°F)	Dew point (°F)	Wind	Gust (kt)	Pressure (mb)	Weather
00:00 UTC

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

The radar

The Tulsa radar (KINX), 76 km away, was scanning. The volume nearest the touchdown began at 03:24 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.

This ground now

The live radar over the track Every 2017 tornado in Oklahoma Every tornado in Oklahoma since 1950 Warnings in force in Oklahoma now The forecast where you are

The other tornadoes of May 18, 2017

47 more were confirmed in the United States that day.

Date	Time	Rating	Where	Path (mi)	Width (yd)	Damage
May 18	2:02 PM CDT	Unrated	Jackson, OK	0.7	50
May 18	2:11 PM CDT	EF0	Jackson, OK	1.2	75	$5,000
May 18	3:29 PM CDT	EF1	Washita, OK	6.0	100	$5,000
May 18	2:29 PM MDT	Unrated	Otero, CO	2.9	75
May 18	3:40 PM CDT	Unrated	Washita, OK	0.5	100
May 18	4:03 PM CDT	EF0	Stafford, KS	0.6	50
May 18	4:04 PM CDT	Unrated	Wilbarger, TX	0.2	50
May 18	4:11 PM CDT	Unrated	Dewey, OK	0.2	50
May 18	4:14 PM CDT	EF0	Ford, KS	0.5	50
May 18	4:18 PM CDT	EF0	Ford, KS	0.3	50
May 18	4:20 PM CDT	Unrated	Custer, OK	0.2	30
May 18	4:23 PM CDT	EF0	Woodward, OK	8.6	200	$10,000
May 18	4:30 PM CDT	EF0	Barton, KS	0.1	50
May 18	4:33 PM CDT	EF0	Stafford, KS	0.6	50
May 18	4:33 PM CDT	EF0	Blaine, OK	0.2	50	$5,000
May 18	4:37 PM CDT	Unrated	Major, OK	0.2	30
May 18	4:40 PM CDT	Unrated	Washita, OK	0.3	50
May 18	4:48 PM CDT	Unrated	Wichita, TX	1.2	50
May 18	4:49 PM CDT	EF1	Woods, OK	9.0	200	$2,000
May 18	4:54 PM CDT	EF2	Wichita, TX	2.0	100	$100,000
May 18	4:57 PM CDT	Unrated	Woods, OK	0.2	50
May 18	5:05 PM CDT	EF0	Blaine, OK	3.4	50	$12,000
May 18	5:23 PM CDT	EF0	Barton, KS	0.2	50
May 18	5:49 PM CDT	EF0	Barton, KS	0.6	50
May 18	5:52 PM CDT	EF0	Wabaunsee, KS	0.0	25
May 18	6:31 PM CDT	EF0	Saline, KS	0.3	50
May 18	7:00 PM CDT	EF0	Stephens, OK	0.2	50	$2,000
May 18	7:41 PM CDT	EF1	Brown, TX	3.3	450
May 18	8:04 PM CDT	EF0	Brown, TX	0.4	50
May 18	8:38 PM CDT	EF1	Brown, TX	4.4	880
May 18	9:13 PM CDT	EF0	Pontotoc, OK	0.6	75	$5,000
May 18	9:46 PM CDT	EF1	Pittsburg, OK	8.2	1,000	$30,000
May 18	9:56 PM CDT	EF1	Pittsburg, OK	4.6	1,000	$15,000
May 18	9:57 PM CDT	EF2	McIntosh, OK	13.7	850	$175,000
May 18	10:11 PM CDT	EF1	McIntosh, OK	4.7	500	$75,000
May 18	10:15 PM CDT	EF1	McIntosh, OK	3.8	450	$25,000
May 18	10:30 PM CDT	EF1	Wagoner, OK	5.0	500	$25,000
May 18	10:35 PM CDT	EF1	Muskogee, OK	5.3	900	$20,000
May 18	10:37 PM CDT	EF1	Muskogee, OK	2.0	400	$25,000
May 18	10:39 PM CDT	EF1	Wagoner, OK	10.3	700	$120,000
May 18	10:40 PM CDT	EF2	Muskogee, OK	2.8	400	$350,000
May 18	10:41 PM CDT	EF1	Muskogee, OK	3.7	350	$20,000
May 18	10:45 PM CDT	EF1	Muskogee, OK	16.6	650
May 18	10:48 PM CDT	EF1	Wagoner, OK	12.7	650	$200,000
May 18	11:01 PM CDT	EF1	Cherokee, OK	5.8	800
May 18	12:07 AM CDT	EF0	Benton, AR	2.0	225	$40,000
May 18	12:23 AM CDT	EF1	McDonald, MO	1.0	100	$100,000

What this means

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.

Sources

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