Tornadoes · United States · Iowa · 1999

F3 tornado, Missouri Vly, Iowa, May 16, 1999

This F3 tornado ran 6.2 miles across Harrison County on May 16, 1999, touching down at 3:45 PM CDT and reaching 200 yards wide. It killed nobody, and did $100,000 of property damage.

The rating scale

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

  1. F040 to 72 mph

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

  2. F173 to 112 mph

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

  3. F2113 to 157 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. F3158 to 206 mphthis tornado

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

  5. F4207 to 260 mph

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

  6. F5261 to 318 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
F3
Date
May 16, 1999
Touchdown
3:45 PM CDT (20:45 UTC)
Path length
6.2 miles (10.0 km)
Path width
200 yards (183 m)
Deaths
0
Injuries
0
Property damage
$100,000
County
Harrison County
Touchdown point
41.630, -95.900
Lift-off point
41.630, -95.800
Record number
393

What the Weather Service recorded

The smaller of 2 strong tornadoes that hit Harrison county the afternoon of 5/16/99. This one destroyed a home west of Logan before it weakened, it then made a loop back to the northwest before dissipating.

The stronger of the 2 tornadoes that ripped through Harrison county the afternoon of 5/16/99 killed 2 people and destroyed 6 homes and a bridge before it dissipated a couple of miles east of Logan. A family of 5 leaving a high school graduation party encountered the tornado on a road around 6 miles northeast of Missouri Valley and took cover in a ditch about the time the path of the tornado widened to a quarter mile. Two of them were killed after their car and a 3-ton combine head were thrown on them. There were also numerous flipped or smashed vehicles in this area.

The deaths

2 direct deaths are recorded for this tornado, each with what Storm Data knows of it.

AgeSexWhereKind
15FOutside/Open AreasDirect
37FOutside/Open AreasDirect

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

The warnings

8 minutes of warning. NWS OAX issued a tornado warning for this county at 20:37 UTC, 8 minutes before the tornado touched down, in force until 21:25 UTC.

Issued (UTC)ExpiredProductOffice
06:05 UTC06:35 UTCSevere Thunderstorm WarningOAX
19:57 UTC20:45 UTCSevere Thunderstorm WarningOAX
20:07 UTC20:40 UTCTornado WarningOAX
20:37 UTC21:25 UTCTornado WarningOAX
21:22 UTC22:10 UTCTornado WarningOAX
22:11 UTC22:45 UTCTornado WarningOAX

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 Moderate Risk. The outlook in force was issued at 19:54 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.

Omaha, NE (KOAX), 00:00Z

3.2 hours after it, 55 km from the path. May 17, 1999.

Skew-T log-pSkew-T log-p diagram, Omaha, NE at 00:00Z on 1999-05-17Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 996 joules per kilogram, CIN -19, lifted condensation level 781 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 1999-05-17The 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 -12 square meters per square second, 0 to 6 km bulk shear 56 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
996 J/kg
Mixed-layer CIN
-19 J/kg
Surface CAPE
2278 J/kg
Mixed-layer LCL
781 m above ground
0-6 km bulk shear
56 kt
0-1 km bulk shear
7 kt
0-1 km storm-relative helicity
-12 m²/s²
0-3 km storm-relative helicity
261 m²/s²
Significant tornado parameter
1.3
Supercell composite
10.2
0-3 km lapse rate
6.3 K/km

Open this sounding in Storm Lab

The radar

The Omaha radar (KOAX), 55 km away, was scanning. The volume nearest the touchdown began at 20:46 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 1999 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

The other tornadoes of May 16, 1999

24 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
May 163:03 PM CDTF0Cass, NE to IA2.060$10,000
May 163:33 PM CDTF2Monona, IA22.590$620,000
May 164:04 PM CDTF0Crawford, IA0.10
May 164:15 PM CDTF1Crawford, IA2.050$50,000
May 164:16 PM CDTF3Harrison, IA7.5440216$1.9 million
May 164:30 PM CDTF0Crawford, IA0.20
May 165:07 PM CDTF0Pottawattamie, IA1.080$10,000
May 165:14 PM CDTF2Pottawattamie, IA5.0120$690,000
May 165:33 PM CDTF0Audubon, IA0.120
May 166:10 PM CDTF1Dickinson, KS2.5100$60,000
May 166:28 PM CDTF0Marion, KS0.00
May 165:50 PM MDTF0Lincoln, CO0.10
May 166:50 PM CDTF0Kent, TX0.130
May 167:00 PM CDTF1Marion, KS2.0440$70,000
May 167:10 PM CDTF0Kingman, KS0.00
May 167:20 PM CDTF0Kingman, KS4.0110
May 166:25 PM MDTF0Kit Carson, CO0.220
May 167:34 PM CDTF0Dickens, TX0.550
May 167:36 PM CDTF0Dallas, IA0.30$2,000
May 167:41 PM CDTF0Marion, KS10.0110
May 168:13 PM CDTF1Taylor, IA1.240$50,000
May 168:39 PM CDTF1Foard, TX0.550$10,000
May 168:52 PM CDTF0Story, IA0.230$10,000
May 169:00 PM CDTF0Jo Daviess, IL0.110

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.