Tornadoes · United States · Nebraska · 2017

EF0 tornado, Cortland, Nebraska, April 9, 2017

This EF0 tornado ran 0.1 miles across Gage County on April 9, 2017, touching down at 8:51 PM CDT and reaching 10 yards wide. It killed nobody.

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.

  1. EF065 to 85 mphthis tornado

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

  2. EF186 to 110 mph

    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.

The record

Rating
EF0
Date
April 9, 2017
Touchdown
8:51 PM CDT (01:51 UTC)
Lifted
8:52 PM CDT (01:52 UTC)
On the ground
1 minutes
Path length
0.1 miles (0.2 km)
Path width
10 yards (9 m)
Deaths
0
Injuries
0
County
Gage County
Touchdown point
40.510, -96.760
Lift-off point
40.510, -96.757
Record number
1704091951-01

What the Weather Service recorded

Thunderstorms developed during the afternoon over the high Plains of northeast Colorado and southwest Nebraska ahead of a cold front. These thunderstorms tracked to the east through the evening entering southeast Nebraska. Although instability was limited, strong shear allowed for a couple of supercells to track across the area producing one short-lived tornado, and numerous reports of large hail. The thunderstorms exited the area by early morning.

A storm chaser captured photographic images of a short-lived weak tornado that occurred as a supercell crossed the surface boundary. No damage was observed in the area and the tornado quickly dissipated.

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 Slight Risk, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 00:56 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 Omaha, NE wrote its last area forecast discussion before the tornado touched down at Apr 9, 6:29 PM CDT, 2 hours 22 minutes earlier.

Area forecast discussion, Apr 9, 6:29 PM CDT, 2 hours 22 minutes before
Area Forecast Discussion
National Weather Service Omaha/Valley NE
629 PM CDT Sun Apr 9 2017

.SHORT TERM...(Tonight through Wednesday)
Issued at 341 PM CDT Sun Apr 9 2017

Large scale flow via WV imagery this aftn was depicting a
shortwave trof situated over the nrn high plains beginning to push
into the wrn Dakotas. Meanwhile...88D regional mosaic was showing
a narrow line of convection forming in the panhandle along a
dryline/20deg sfc dew point depressions.

At this point...HIRES models indicate the environment will become
less supportive for severe storm early this evening.  Deep layer
shear will remain relatively strong...but CAPE drop off dramatically.
Cannot totally rule out the possibility for one or two severe/near
severe storms though with hail possible over the nrn CWA.  Toward
mid/late evening...the RAP13 advertises a narrow line convection
forming along increasing bndry lyr threat-E convergence
along/south of the I-80 corridor associated with a cold front
dropping into the cntrl Plains. With DCAPES around 1200J/kg
coupled with increasing lyr Theta-E diff...seems possible a few
storms may produce severe/near-severe winds gusts over the srn
CWA.

Monday aftn...NAM12/GFS20/CMC all prog secondary shot of cold air
advection into the CWA with another round of pcpn activity mainly
over the nrn CWA being driven by rather strong 305-310k isentropic
upglide. More pcpn possible on Wednesday with the passage of a
shortwave trof coupled with warm front lifting thru the region.

.LONG TERM...(Wednesday night through Sunday)
Issued at 341 PM CDT Sun Apr 9 2017

GFS20/ECM/CMC all advertise a progressive pattern during the
extended pds with pcpn chances from Thursday night into Saturday
evening.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 627 PM CDT Sun Apr 9 2017

Thunderstorms across central NE appear to have enough support to
possibly hold together to affect the TAF sites within a few hours,
by 01-02z at KOFK/KLNK and 02-03z at KOMA. Have put in about 2-3
hour window of thunder at all TAF sites. Otherwise, VFR initially,
but becoming MVFR at KOFK through the night. Gusty northwest winds
developing tomorrow morning, with a few showers in the vicinity of
KOFK.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

SHORT TERM...DEE
LONG TERM...DEE
AVIATION...
Hazardous weather outlook, Apr 9, 4:52 PM CDT, 3 hours 59 minutes before
Hazardous Weather Outlook
National Weather Service Omaha/Valley NE
452 PM CDT Sun Apr 9 2017

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-101200-
Monona-Harrison-Shelby-Pottawattamie-Mills-Montgomery-Fremont-
Page-Knox-Cedar-Thurston-Antelope-Pierce-Wayne-Boone-Madison-
Stanton-Cuming-Burt-Platte-Colfax-Dodge-Washington-Butler-
Saunders-Douglas-Sarpy-Seward-Lancaster-Cass-Otoe-Saline-
Jefferson-Gage-Johnson-Nemaha-Pawnee-Richardson-
452 PM CDT Sun Apr 9 2017

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST
IOWA...WEST CENTRAL IOWA...EAST CENTRAL NEBRASKA...NORTHEAST
NEBRASKA AND SOUTHEAST NEBRASKA.

.DAY ONE...TONIGHT AND MONDAY

Scattered thunderstorms are possible this evening. A few of these
storms may become strong to severe, with large hail and damaging
winds the main threats. The potential is highest from
southeasternmost Nebraska into southwest Iowa.

.DAYS TWO THROUGH SEVEN...MONDAY NIGHT THROUGH SUNDAY

There will be a chance for thunderstorms Wednesday and Wednesday
night, and again from Friday into Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated tonight or Monday.

In the hours before

Special weather statement, Apr 9, 8:26 PM CDT, 25 minutes before
Special Weather Statement
National Weather Service Omaha/Valley Nebraska
826 PM CDT SUN APR 9 2017

NEZ043-050-051-100200-
Saunders NE-Butler NE-Colfax NE-
826 PM CDT SUN APR 9 2017

...Significant Weather Advisory for SOUTHERN COLFAX...EASTERN BUTLER
AND NORTHWESTERN SAUNDERS COUNTIES UNTIL 900 PM CDT...

At 825 PM CDT, Doppler radar was tracking a strong thunderstorm near
David City, or 18 miles southeast of Columbus, moving east at 35 mph.

Pea size hail will be possible with this storm.

Locations impacted include...
Wahoo, David City, Brainard, Weston, Prague, Octavia, Malmo, Bruno,
Linwood and Abie.

This includes Highway 92 IN Nebraska between mile markers 419 and
446.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4109 9713 4137 9722 4144 9678 4120 9662
TIME...MOT...LOC 0125Z 250DEG 38KT 4127 9707

KERN
Special weather statement, Apr 9, 8:44 PM CDT, 7 minutes before
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Local storm report, Apr 9, 8:49 PM CDT, 2 minutes before
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
849 PM CDT SUN APR 09 2017

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

0835 PM     HAIL             3 W DAYKIN              40.32N 97.35W
04/09/2017  E1.50 INCH       JEFFERSON          NE   EMERGENCY MNGR

            TIME ESTIMATED BASED ON RADAR.

&&

VDEWALD

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.

Omaha, NE (KOAX), 00:00Z

1.9 hours before the tornado, 96 km from the path. April 10, 2017.

Skew-T log-pSkew-T log-p diagram, Omaha, NE at 00:00Z on 2017-04-10Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 863 joules per kilogram, CIN -169, lifted condensation level 1606 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
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.
HodographHodograph, Omaha, NE at 00:00Z on 2017-04-10The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity 133 square meters per square second, 0 to 6 km bulk shear 55 knots.19395878Sfc1 km3 km6 km9 kmRMLM
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
863 J/kg
Mixed-layer CIN
-169 J/kg
Surface CAPE
1811 J/kg
Mixed-layer LCL
1606 m above ground
0-6 km bulk shear
55 kt
0-1 km bulk shear
16 kt
0-1 km storm-relative helicity
133 m²/s²
0-3 km storm-relative helicity
265 m²/s²
Significant tornado parameter
0.1
Supercell composite
5.0
0-3 km lapse rate
7.0 K/km

Open this sounding in Storm Lab

The surface observations

Beatrice Municip (BIE), 23 km from the path, in the two hours either side.

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

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

The radar

The Omaha radar (KOAX), 96 km away, was scanning. The volume nearest the touchdown began at 01:50 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 trackEvery 2017 tornado in NebraskaEvery tornado in Nebraska since 1950Warnings in force in Nebraska nowThe forecast where you are

The other tornadoes of April 9, 2017

1 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
April 912:54 AM CDTEF1Marathon, WI0.4100

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.