Alert archive / California / Severe Thunderstorm Warnings

Severe Thunderstorm Warnings in California, 2020

67 severe thunderstorm warnings in 2020. An alert counts here when it covered any part of the state, so the counties below add up to more than the state. The archive of severe thunderstorm warnings reaches back to 1986.

Severe Thunderstorm Warnings by county

Each county as a circle sized by its count in 2020. Tap one for its archive.

Severe Thunderstorm Warnings: 67
Busiest month: July29 severe thunderstorm warnings
Busiest day: July 22, 202011 severe thunderstorm warnings

Over time

By month

Warning verification

How often warnings here had a storm report inside them, and how much warning the reports had.

5 of 67 severe thunderstorm warnings covering California in 2020 had a qualifying storm report inside them; 6 of 29 hail, wind and damage reports fell inside a warning, on average 8 minutes after it went out.

California, 2020

	Warnings	With a report	False alarm ratio	Reports	Inside a warning	Mean lead time
Severe thunderstorm warnings	67	5	93%	29	21%	8 min

Each office's whole area, 2020

	Warnings	With a report	False alarm ratio	Reports	Inside a warning	Mean lead time
NWS Medford, OR: severe thunderstorm warnings	25	4	84%	8	63%	21 min
NWS San Francisco Bay Area, CA: severe thunderstorm warnings	4	0	100%	0
NWS Hanford, CA: severe thunderstorm warnings	7	0	100%	2	0%
NWS Los Angeles, CA: severe thunderstorm warnings	1	0	100%	7	0%
NWS Reno, NV: severe thunderstorm warnings	34	1	97%	8	13%	7 min
NWS Sacramento, CA: severe thunderstorm warnings	5	2	60%	5	60%	9 min
NWS Eureka, CA: severe thunderstorm warnings	2	1	50%	2	50%	2 min
NWS San Diego, CA: severe thunderstorm warnings	9	0	100%	4	0%
NWS Las Vegas, NV: severe thunderstorm warnings	15	1	93%	13	8%	15 min
NWS Phoenix, AZ: severe thunderstorm warnings	43	13	70%	41	71%	15 min

An office's figures cover every county it serves, including across state lines.

Verified by the Iowa Environmental Mesonet's Cow, which matches each storm-based warning with the local storm reports inside its polygon while it was in force, within 15 km of its edge: a tornado warning counts as verified on a tornado report, a severe thunderstorm warning on hail of 1 inch or more, a gust of 58 mph or more, or wind damage, a flash flood warning on a flash flood report. The false alarm ratio is the share of warnings with no such report; "inside a warning" is the probability of detection, the share of reports that fell inside one; lead time runs from the warning's issue to each report inside it, counting zero for a report that came first. A warning with no report is not proof nothing happened: reports come from spotters, the public and damage surveys, and are thin where few people live.

The alerts

Every alert, in the order issued. Times are local, Pacific Time. Each opens its own page with the text, the map, the radar and the sounding.

Issued	Product	Office	Counties	Lasted
Mar 10, 6:12 PM PDT	Severe Thunderstorm Warning	HNX	Kern	48 min
Mar 10, 7:01 PM PDT	Severe Thunderstorm Warning	HNX	Kern, Tulare	29 min
Mar 10, 7:58 PM PDT	Severe Thunderstorm Warning	HNX	Kern	47 min
Mar 12, 3:19 PM PDT	Severe Thunderstorm Warning	PSR	Imperial	26 min
May 10, 4:06 PM PDT	Severe Thunderstorm Warning	VEF	San Bernardino	39 min
May 28, 8:43 PM PDT	Severe Thunderstorm Warning	MFR	Siskiyou	32 min
May 28, 9:12 PM PDT	Severe Thunderstorm Warning	MFR	Siskiyou	33 min
May 28, 9:46 PM PDT	Severe Thunderstorm Warning	MFR	Siskiyou	29 min
May 29, 5:40 PM PDT	Severe Thunderstorm Warning	REV	Alpine, El Dorado	35 min
Jun 3, 3:06 PM PDT	Severe Thunderstorm Warning	LOX	Santa Barbara	37 min
Jun 4, 6:28 PM PDT	Severe Thunderstorm Warning	REV	Lassen, Modoc	32 min
Jun 23, 3:22 PM PDT	Severe Thunderstorm Warning	STO	Alpine, Amador, El Dorado	23 min
Jun 23, 6:27 PM PDT	Severe Thunderstorm Warning	REV	Lassen	33 min
Jun 24, 4:19 PM PDT	Severe Thunderstorm Warning	REV	Mono	41 min
Jun 24, 4:44 PM PDT	Severe Thunderstorm Warning	MFR	Modoc	31 min
Jun 25, 4:56 PM PDT	Severe Thunderstorm Warning	STO	Alpine, Tuolumne	49 min
Jun 25, 4:57 PM PDT	Severe Thunderstorm Warning	VEF	Inyo	48 min
Jun 25, 6:06 PM PDT	Severe Thunderstorm Warning	HNX	Madera	24 min
Jul 16, 3:00 PM PDT	Severe Thunderstorm Warning	REV	El Dorado	45 min
Jul 16, 5:02 PM PDT	Severe Thunderstorm Warning	HNX	Madera, Mariposa, Tuolumne	28 min
Jul 20, 2:05 PM PDT	Severe Thunderstorm Warning	STO	Alpine, Tuolumne	25 min
Jul 20, 3:40 PM PDT	Severe Thunderstorm Warning	REV	Nevada, Placer	35 min
Jul 20, 4:43 PM PDT	Severe Thunderstorm Warning	REV	Placer	32 min
Jul 20, 5:15 PM PDT	Severe Thunderstorm Warning	REV	Placer	30 min
Jul 20, 7:20 PM PDT	Severe Thunderstorm Warning	REV	Plumas	25 min
Jul 20, 7:41 PM PDT	Severe Thunderstorm Warning	REV	Lassen, Plumas	34 min
Jul 21, 3:33 PM PDT	Severe Thunderstorm Warning	REV	Plumas	42 min
Jul 21, 3:52 PM PDT	Severe Thunderstorm Warning	REV	Alpine	38 min
Jul 21, 4:07 PM PDT	Severe Thunderstorm Warning	REV	Lassen, Plumas	53 min
Jul 21, 4:39 PM PDT	Severe Thunderstorm Warning	REV	Lassen	51 min
Jul 22, 2:08 PM PDT	Severe Thunderstorm Warning	REV	Lassen	37 min
Jul 22, 2:36 PM PDT	Severe Thunderstorm Warning	MFR	Siskiyou	39 min
Jul 22, 2:44 PM PDT	Severe Thunderstorm Warning	REV	Plumas	31 min
Jul 22, 2:55 PM PDT	Severe Thunderstorm Warning	REV	Alpine	35 min
Jul 22, 3:30 PM PDT	Severe Thunderstorm Warning	EKA	Trinity	15 min
Jul 22, 3:44 PM PDT	Severe Thunderstorm Warning	REV	Sierra	46 min
Jul 22, 3:49 PM PDT	Severe Thunderstorm Warning	MFR	Siskiyou	26 min
Jul 22, 3:58 PM PDT	Severe Thunderstorm Warning	REV	Nevada, Placer	32 min
Jul 22, 4:01 PM PDT	Severe Thunderstorm Warning	REV	Sierra	29 min
Jul 22, 4:12 PM PDT	Severe Thunderstorm Warning	MFR	Siskiyou	33 min
Jul 22, 4:13 PM PDT	Severe Thunderstorm Warning	EKA	Trinity	32 min
Jul 26, 3:23 PM PDT	Severe Thunderstorm Warning	REV	Alpine	52 min
Jul 26, 6:32 PM PDT	Severe Thunderstorm Warning	REV	Lassen, Plumas	58 min
Jul 26, 7:19 PM PDT	Severe Thunderstorm Warning	MFR	Siskiyou	26 min
Jul 26, 7:29 PM PDT	Severe Thunderstorm Warning	MFR	Siskiyou	31 min
Jul 27, 3:21 PM PDT	Severe Thunderstorm Warning	STO	Lassen, Plumas, Shasta	24 min
Jul 27, 3:44 PM PDT	Severe Thunderstorm Warning	STO	Lassen, Plumas	31 min
Aug 5, 2:59 PM PDT	Severe Thunderstorm Warning	MFR	Siskiyou	31 min
Aug 11, 12:50 PM PDT	Severe Thunderstorm Warning	REV	Lassen	55 min
Aug 15, 2:24 PM PDT	Severe Thunderstorm Warning	SGX	Riverside, San Diego	55 min
Aug 15, 4:08 PM PDT	Severe Thunderstorm Warning	PSR	Riverside	37 min
Aug 16, 2:41 AM PDT	Severe Thunderstorm Warning	MTR	Alameda, Monterey, San Benito, City and County of San Francisco, San Mateo, Santa Clara and 1 more	94 min
Aug 16, 3:55 AM PDT	Severe Thunderstorm Warning	MTR	Alameda, Contra Costa, Marin, Monterey, Napa, City and County of San Francisco and 4 more	80 min
Aug 16, 5:14 AM PDT	Severe Thunderstorm Warning	MTR	Alameda, Contra Costa, Marin, Napa, City and County of San Francisco, San Mateo and 3 more	91 min
Aug 16, 6:37 AM PDT	Severe Thunderstorm Warning	MTR	Alameda, Contra Costa, Marin, Monterey, Napa, City and County of San Francisco and 4 more	83 min
Aug 17, 5:05 PM PDT	Severe Thunderstorm Warning	HNX	Fresno, Madera, Mariposa, Tuolumne	55 min
Aug 17, 6:11 PM PDT	Severe Thunderstorm Warning	HNX	Mariposa, Tuolumne	34 min
Aug 18, 12:28 PM PDT	Severe Thunderstorm Warning	SGX	Riverside	46 min
Aug 18, 12:54 PM PDT	Severe Thunderstorm Warning	SGX	San Bernardino	66 min
Aug 18, 1:57 PM PDT	Severe Thunderstorm Warning	SGX	San Bernardino	39 min
Aug 18, 3:12 PM PDT	Severe Thunderstorm Warning	SGX	Riverside	21 min
Aug 18, 3:45 PM PDT	Severe Thunderstorm Warning	REV	Lassen	45 min
Aug 21, 1:21 PM PDT	Severe Thunderstorm Warning	SGX	Riverside	26 min
Aug 21, 1:37 PM PDT	Severe Thunderstorm Warning	SGX	San Bernardino	25 min
Aug 22, 2:00 PM PDT	Severe Thunderstorm Warning	VEF	San Bernardino	45 min
Aug 22, 2:21 PM PDT	Severe Thunderstorm Warning	SGX	San Diego	54 min
Aug 22, 4:13 PM PDT	Severe Thunderstorm Warning	SGX	San Bernardino	47 min

The busiest days

Days with the most alerts issued, by UTC date.

Nearby

Alerts in force now Tornadoes on record The radar archive 2019 2021

Sources

National Weather Service watches, warnings, advisories and statements from the Iowa Environmental Mesonet's VTEC archive, which reconstructs tornado, severe thunderstorm, flash flood and marine warnings back to 1986 from the NWS text archive. Storm Prediction Center watches and mesoscale discussions from SPC's archive through the Mesonet. County centers from the US Census Bureau. Warning verification from the Mesonet's Cow. Rebuilt daily.