Unrated tornado, Coyoteville to Plumas, California, August 15, 2020

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.

Rating

Unrated

Date

August 15, 2020

Touchdown

2:41 PM PDT (21:41 UTC)

Lifted

3:10 PM PDT (22:10 UTC)

On the ground

29 minutes

Path length

3.2 miles (5.1 km)

Path width

156 yards (143 m)

Deaths

0

Injuries

0

County

Lassen County

Touchdown point

39.731, -120.101

Lift-off point

39.761, -120.056

Record number

2008151541-01

Dry conditions and anomalously low fuel moisture, in combination with an unstable low-to-mid-level atmosphere, allowed the Loyalton wildfire to develop extreme fire behavior on the afternoon of 15 August 2020. Robust heat and moisture fluxes from the wildfire caused rapid smoke plume deepening and lofting of pyrometeors above the lifting condensation level, which led to the formation of two vertically extensive pyrocumulonimbi and three tornadoes.

A mesoanticyclone embedded within a deep pyrocumulonimbus updraft inside the Loyalton wildfire perimeter generated an EF1 rated anticyclonic tornado that snapped several quaking aspen trees (DI 27, DOD 4) along a 0.09-mile path on the northeast facing slope of Roberts Canyon. The tornado spun up 0.37 miles south-southwest of the intersection of Forest Service Road 182 and Forest Service Road 31182 and dissipated 0.46 miles south-southwest of the aforementioned intersection. The damage path had a maximum width of 20 yards. No injuries or deaths occurred with this tornado.

Bystanders along CA 70 and US 395 near Hallelujah Junction captured multiple videos and photographs of an anticyclonically rotating tornado pendant to the base of a pyrocumulonimbus cloud. The tornado caused no damage from which the NWS could assign an EF-scale rating as it traversed across an area of burned sagebrush. From photographs and video evidence, the approximate path of the tornado was calculated. The tornado traveled along a 3.16-mile path from the head of Roberts Canyon to 1.33 miles southwest of Hallelujah Junction. The maximum path width was approximately 156 yards. No injuries or deaths occurred with this tornado.

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

6 minutes of warning. NWS REV issued a tornado warning for this county at 21:35 UTC, 6 minutes before the tornado touched down, in force until 22:30 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 General Thunderstorms 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 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.

The Reno radar (KRGX), 53 km away, was scanning. The volume nearest the touchdown began at 21:41 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 2020 tornado in CaliforniaEvery tornado in California since 1950Warnings in force in California nowThe forecast where you are

6 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.