EF1 tornado, Alleman to Huxley, Iowa, May 19, 2013

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 19, 2013

Touchdown

7:07 PM CDT (00:07 UTC)

Lifted

7:12 PM CDT (00:12 UTC)

On the ground

5 minutes

Path length

4.7 miles (7.6 km)

Path width

150 yards (137 m)

Deaths

0

Injuries

0

Property damage

$90,000

Counties

Polk and Story counties

Touchdown point

41.846, -93.669

Lift-off point

41.865, -93.581

Record number

1305191807-01

4 damage points were recorded along this path by NWS DMX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 90 mph.

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

The seasons first major severe weather event took place as a strong upper level low pressure lifted north into the central U.S. This was ahead of a strong upper level low pressure system over the southwest U.S. A warm front lifted north across the Des Moines CWA with moist and unstable air pushing into the state. There were several rounds of convection. The first developed over northern Iowa during the mid afternoon hours and moved north into Minnesota. A break in the thunderstorm activity took place before the next round moved into southwest Iowa and spread north and east during the evening. The atmosphere became unstable with highs in the 80s and dewpoints in the low to mid 60s by afternoon. CAPE, though not excessive, was sufficient with 1000 to 3000 J/kg available. CAPE in the -10 to -30 C layer of the atmosphere was between 300 and 600 J/kg. In the late afternoon hours around 500 J/kg of downdraft CAPE was present, and it increased to around 900 to 1100 J/kg during the evening hours. The shear increased as well with 25 to 40 kts available at the beginning of the event, and 50 to 60 kts by the end. Precipitable water values increased to 1.2 to 1.5 inches. The LCL was relatively low, around 1000 meters. The freezing level was relatively low, around 11,900 feet. The storms produced heavy rain and large hail initially. Flash flooding occurred first in Crawford County in western Iowa with over two inches of rainfall in about an hour, causing water to flow over Highway 141. The event became a wind and hail event for the most part with winds gusting to 60 to 80 MPH across a large part of the CWA and hail up to 3 inches in diameter in Adams County. The largest hail was northwest of Carbon in Adams County, where 2 to 3 inch diameter hail fell. Reports indicated enough hail fell to completely cover the ground. Numerous reports of 1.5 inch hail were received. Three tornadoes touched down in central Iowa. Numerous reports of winds of 60 to 80 MPH were received all along the line of thunderstorms. High winds blew a semi truck off the highway and blew it over west of Earlham in Madison County. There was considerable tree damage reported with some damage to outbuilding, barns, and a few houses.

Tornado exhibited an intermittent track as it moved across northern Polk County into Story County. Peak damage included garage and a living room roof removed from a manufactured home. Tornado continued into Story County.

Tornado exhibited an intermittent track as it moved across northern Polk County into Story County. Peak damage included garage and a living room roof removed from a manufactured home. Tornado moved in from Polk County.

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

18 minutes of warning. NWS DMX issued a tornado warning for this county at 23:49 UTC, 18 minutes before the tornado touched down, in force until 00:15 UTC.

The county was under a tornado watch, issued at 20:00 UTC and running to 02:00 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 Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:40 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.

Ames (AMW), 15 km from the path, in the two hours either side.

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

The Des Moines radar (KDMX), 16 km away, was scanning. The volume nearest the touchdown began at 00:06 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 2013 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

26 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.