Tornadoes · United States · Illinois · 2017

EF0 tornado, Bolton to Damascus, Illinois, August 16, 2017

From Bolton to Damascus, this EF0 tornado ran 3.3 miles across Stephenson County on August 16, 2017, touching down at 7:28 PM CDT and reaching 20 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
August 16, 2017
Touchdown
7:28 PM CDT (00:28 UTC)
Lifted
7:38 PM CDT (00:38 UTC)
On the ground
10 minutes
Path length
3.3 miles (5.2 km)
Path width
20 yards (18 m)
Deaths
0
Injuries
0
County
Stephenson County
Touchdown point
42.322, -89.712
Lift-off point
42.367, -89.691
Record number
1708161828-01

The damage survey

8 damage points were recorded along this path by NWS DVN, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 95 mph.

  • Crop damage, possible tornado beginning.

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

Scattered showers with some embedded thunderstorms moved northeastward across northwest Illinois during the evening of August 16 where a warm front was draped across the region. Thunderstorms moving across the warm front produced a brief EF-0 tornado in Jo Daviess County and an EF-1 and EF-0 tornadoes in Stephenson County.

A weak EF-1 tornado tracked north/northeast, damaging numerous trees. Two homes also suffered minor damage. The tornado was on the ground for around 2.8 miles with a maximum width of 75 yards. The peak winds were estimated to be around 90 MPH.

An EF-0 tornado developed at the same time a tornado just to the south and damaged trees on its north/northeast path. The peak winds were estimated to be around 80 MPH. The tornado was on the ground for about 3.3 miles and was 20 yards wide.

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

The warnings

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down.

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 forecast that day

The Storm Prediction Center had this point in a Marginal Risk. The outlook in force was issued at 19:51 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 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.

Davenport, (KDVN), 00:00Z

0.5 hours before the tornado, 104 km from the path. August 17, 2017.

Skew-T log-pSkew-T log-p diagram, Davenport, at 00:00Z on 2017-08-17Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 662 joules per kilogram, CIN -5, lifted condensation level 897 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, Davenport, at 00:00Z on 2017-08-17The 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 118 square meters per square second, 0 to 6 km bulk shear 27 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
662 J/kg
Mixed-layer CIN
-5 J/kg
Surface CAPE
1106 J/kg
Mixed-layer LCL
897 m above ground
0-6 km bulk shear
27 kt
0-1 km bulk shear
18 kt
0-1 km storm-relative helicity
118 m²/s²
0-3 km storm-relative helicity
144 m²/s²
Significant tornado parameter
0.3
Supercell composite
2.0
0-3 km lapse rate
6.2 K/km

Open this sounding in Storm Lab

Davenport, (KDVN), 12:00Z

11.5 hours after it, 104 km from the path. August 17, 2017.

Skew-T log-pSkew-T log-p diagram, Davenport, at 12:00Z on 2017-08-17Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 85 joules per kilogram, CIN -119, lifted condensation level 854 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, Davenport, at 12:00Z on 2017-08-17The 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 21 square meters per square second, 0 to 6 km bulk shear 28 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
85 J/kg
Mixed-layer CIN
-119 J/kg
Surface CAPE
340 J/kg
Mixed-layer LCL
854 m above ground
0-6 km bulk shear
28 kt
0-1 km bulk shear
21 kt
0-1 km storm-relative helicity
21 m²/s²
0-3 km storm-relative helicity
18 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.1
0-3 km lapse rate
5.0 K/km

Open this sounding in Storm Lab

The radar

The Quad Cities radar (KDVN), 109 km away, was scanning. The volume nearest the touchdown began at 00:26 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.

What was reported nearby

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

Time (UTC)ReportWhereCountyRemark
00:21 UTCTORNADO5 Wsw FreeportStephenson, ILA WEAK EF1 TORNADO TRACKED NORTH/NORTHEAST, DAMAGING NUMEROUS TREES. TWO HOMES ALSO SUFFERED MINOR DAMAGE. MAX WINDS ESTIMATED AROUND 90 MPH. MAXIMUM PATH WIDTH AROUND 75 YEARDS. PATH LENGTH AROUND 2.8 MILES. TORNADO END
00:22 UTCTORNADO5 Wnw ElizabethJo Daviess, ILAN EF1 TORNADO TRACKED NORTHEAST, CAUSING EXTENSIVE TREE DAMAGE. LARGE WALNUT TREES WERE UPROOTED AND SNAPPED OFF AROUND 10 FEET FROM THE BASE. MAXIMUM PATH WIDTH WAS AROUND 60 YARDS, AND PATH LENGTH WAS AROUND A HALF MI
00:28 UTCTORNADO5 Wnw FreeportStephenson, ILAN EF0 TORNADO DEVELOPED AT THE SAME TIME AS A TORNADO JUST TO THE SOUTH, AND DAMAGED TREES ON ITS NORTH/NORTHEAST PATH. MAXIMUM WINDS ESTIMATED AROUND 80 MPH. MAXIMUM PATH WIDTH AROUND 20 YARDS. PATH LENGTH AROUND 3.3 M
00:38 UTCTORNADO3 W FreeportStephenson, ILBRIEF TOUCHDOWN...SLIGHT DAMAGE TO A HOUSE...CORN DOWN...2 TREES DOWN...OTHER TREES HAVE TOPS MISSING.

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

This ground now

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

The other tornadoes of August 16, 2017

13 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 164:46 PM CDTEF0Nicollet, MN3.975
August 165:03 PM CDTEF0Nicollet, MN1.925
August 165:32 PM CDTEF0Nicollet, MN1.320
August 165:33 PM CDTEF1Nicollet, MN5.275
August 166:15 PM CDTEF0Sibley, MN1.460
August 166:26 PM CDTEF0Sibley, MN4.175
August 167:05 PM CDTEF0Scott, MN1.310
August 167:21 PM CDTEF0Sibley, MN0.625
August 167:21 PM CDTEF1Stephenson, IL2.875
August 167:22 PM CDTEF1Jo Daviess, IL0.560
August 167:46 PM CDTEF0Scott, MN1.275
August 168:05 PM CDTEF0McLeod, MN0.850
August 168:08 PM CDTEF0McLeod, MN0.130

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.