Tornadoes · United States · Colorado · 2020

Unrated tornado, Granada to Holly, Colorado, May 21, 2020

From Granada to Holly, this Unrated tornado ran 2.0 miles across Prowers County on May 21, 2020, touching down at 3:47 PM MDT and reaching 25 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 mph

    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. Unratedthis tornado

    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
Unrated
Date
May 21, 2020
Touchdown
3:47 PM MDT (21:47 UTC)
Lifted
3:58 PM MDT (21:58 UTC)
On the ground
11 minutes
Path length
2.0 miles (3.2 km)
Path width
25 yards (23 m)
Deaths
0
Injuries
0
County
Prowers County
Touchdown point
37.920, -102.310
Lift-off point
37.920, -102.310
Record number
2005211547-01

What the Weather Service recorded

A very active afternoon over the far eastern Colorado plains spawned a few large supercell thunderstorms with very heavy rainfall, very large hail, and a few tornadoes. Far eastern Prowers County was hit especially hard by baseball sized hail and a few tornadoes south of Garanda, CO.

Chaser reported a tornado south of Granada. Tornado was on the ground for a few minutes before lifting. No reports of damage as the tornado was over open fields.

Trained spotters reported a tornado south of Holly, CO. The tornado lasted 5-7 minutes before lifting near the town of Holly. No damage reported as the tornado moved through open fields.

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. One was issued for the county at another hour that day.

Issued (UTC)ExpiredProductOffice
21:30 UTC22:00 UTCSevere Thunderstorm WarningPUB
21:48 UTC22:15 UTCTornado WarningPUB
21:59 UTC22:30 UTCSevere Thunderstorm WarningPUB
22:18 UTC22:45 UTCTornado WarningPUB
22:30 UTC23:00 UTCSevere Thunderstorm WarningPUB
22:32 UTC22:45 UTCTornado WarningPUB
22:34 UTC23:00 UTCSevere Thunderstorm WarningPUB
22:49 UTC23:15 UTCSevere Thunderstorm WarningPUB

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 19:56 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.

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.

Dodge City, (KDDC), 12:00Z

9.8 hours before the tornado, 212 km from the path. May 21, 2020.

Skew-T log-pSkew-T log-p diagram, Dodge City, at 12:00Z on 2020-05-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 275 joules per kilogram, CIN -409, lifted condensation level 690 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, Dodge City, at 12:00Z on 2020-05-21The 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 -64 square meters per square second, 0 to 6 km bulk shear 9 knots.193958Sfc1 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
275 J/kg
Mixed-layer CIN
-409 J/kg
Surface CAPE
32 J/kg
Mixed-layer LCL
690 m above ground
0-6 km bulk shear
9 kt
0-1 km bulk shear
47 kt
0-1 km storm-relative helicity
-64 m²/s²
0-3 km storm-relative helicity
186 m²/s²
Significant tornado parameter
0.0
Supercell composite
-0.0
0-3 km lapse rate
3.6 K/km

Open this sounding in Storm Lab

Dodge City, (KDDC), 00:00Z

2.2 hours after it, 212 km from the path. May 22, 2020.

Skew-T log-pSkew-T log-p diagram, Dodge City, at 00:00Z on 2020-05-22Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 1349 joules per kilogram, CIN -21, lifted condensation level 1147 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, Dodge City, at 00:00Z on 2020-05-22The 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 83 square meters per square second, 0 to 6 km bulk shear 37 knots.193958Sfc1 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
1349 J/kg
Mixed-layer CIN
-21 J/kg
Surface CAPE
2321 J/kg
Mixed-layer LCL
1147 m above ground
0-6 km bulk shear
37 kt
0-1 km bulk shear
9 kt
0-1 km storm-relative helicity
83 m²/s²
0-3 km storm-relative helicity
173 m²/s²
Significant tornado parameter
0.9
Supercell composite
8.0
0-3 km lapse rate
7.2 K/km

Open this sounding in Storm Lab

The surface observations

Lamar (LAA), 37 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
20:40 UTC40° 5 kt1009.1

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

The radar

The Goodland radar (KGLD), 169 km away, was scanning. The volume nearest the touchdown began at 21:47 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
21:47 UTCHAIL 1.55 S GranadaProwers, CO
21:47 UTCTORNADO10 S GranadaProwers, CO
22:17 UTCTORNADO2 S HollyProwers, COMULTIPLE TORNADOES REPORTED SOUTH OF HOLLY.
22:18 UTCHAIL 2.751 W HollyProwers, CO
22:28 UTCHAIL 2.75HollyProwers, COMOSTLY 1/2 INCH TO PING PONG BALL SIZED, WITH A FEW UP TO BASEBALL SIZED.
22:47 UTCHAIL 1.251 E BristolProwers, COREPORT FROM MPING: HALF DOLLAR (1.25 IN.).
22:50 UTCHAIL 12 N GranadaProwers, CO

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

This ground now

The live radar over the trackEvery 2020 tornado in ColoradoEvery tornado in Colorado since 1950Warnings in force in Colorado nowThe forecast where you are

The other tornadoes of May 21, 2020

9 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
May 212:45 PM EDTEF0Palm Beach, FL0.325
May 211:33 PM MDTUnratedGreeley, KS0.050
May 213:56 PM EDTEF1Hoke, NC0.2200$50,000
May 213:41 PM CDTEF0Stanton, KS0.130
May 213:15 PM MDTEF0Hamilton, KS0.650
May 213:15 PM MDTEF0Hamilton, KS0.350
May 214:17 PM MDTUnratedProwers, CO1.025
May 215:06 PM MDTEF0Hamilton, KS0.150
May 217:11 PM CDTUnratedKearny, KS1.8150

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.