Alert archive / California / Severe Thunderstorm Warnings
Severe Thunderstorm Warnings in California, 2018
71 severe thunderstorm warnings in 2018. 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 2018. Tap one for its archive.
- Severe Thunderstorm Warnings
- 71
- Busiest month
- July26 severe thunderstorm warnings
- Busiest day
- October 4, 20187 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.
7 of 71 severe thunderstorm warnings covering California in 2018 had a qualifying storm report inside them; 6 of 23 hail, wind and damage reports fell inside a warning, on average 18 minutes after it went out.
California, 2018
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| Severe thunderstorm warnings | 71 | 7 | 90% | 23 | 26% | 18 min |
Each office's whole area, 2018
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| NWS Sacramento, CA: severe thunderstorm warnings | 4 | 0 | 100% | 1 | 0% | |
| NWS Hanford, CA: severe thunderstorm warnings | 7 | 0 | 100% | 1 | 0% | |
| NWS Las Vegas, NV: severe thunderstorm warnings | 73 | 15 | 79% | 151 | 66% | 24 min |
| NWS Phoenix, AZ: severe thunderstorm warnings | 107 | 39 | 64% | 216 | 54% | 17 min |
| NWS San Diego, CA: severe thunderstorm warnings | 15 | 2 | 87% | 4 | 50% | 24 min |
| NWS Medford, OR: severe thunderstorm warnings | 13 | 3 | 77% | 5 | 60% | 16 min |
| NWS Reno, NV: severe thunderstorm warnings | 18 | 0 | 100% | 1 | 0% |
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 16, 5:24 PM PDT | Severe Thunderstorm Warning | STO | Butte, Tehama | 36 min |
| Mar 16, 6:02 PM PDT | Severe Thunderstorm Warning | STO | Butte, Tehama | 28 min |
| Mar 22, 2:12 PM PDT | Severe Thunderstorm Warning | HNX | Mariposa, Merced | 33 min |
| Mar 22, 3:56 PM PDT | Severe Thunderstorm Warning | HNX | Tulare | 34 min |
| Mar 22, 4:18 PM PDT | Severe Thunderstorm Warning | HNX | Kern, Kings, Tulare | 42 min |
| Mar 22, 4:31 PM PDT | Severe Thunderstorm Warning | HNX | Tulare | 29 min |
| May 1, 6:39 PM PDT | Severe Thunderstorm Warning | STO | Tuolumne | 36 min |
| May 1, 7:22 PM PDT | Severe Thunderstorm Warning | STO | El Dorado | 23 min |
| May 24, 2:07 PM PDT | Severe Thunderstorm Warning | REV | Alpine | 38 min |
| Jul 9, 1:56 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 49 min |
| Jul 9, 8:08 PM PDT | Severe Thunderstorm Warning | PSR | Imperial | 37 min |
| Jul 9, 8:44 PM PDT | Severe Thunderstorm Warning | PSR | Imperial | 31 min |
| Jul 11, 12:47 PM PDT | Severe Thunderstorm Warning | SGX | San Diego | 88 min |
| Jul 11, 6:40 PM PDT | Severe Thunderstorm Warning | SGX | Riverside | 65 min |
| Jul 12, 1:09 PM PDT | Severe Thunderstorm Warning | SGX | San Bernardino | 47 min |
| Jul 12, 1:53 PM PDT | Severe Thunderstorm Warning | SGX | San Diego | 67 min |
| Jul 14, 6:24 PM PDT | Severe Thunderstorm Warning | REV | El Dorado | 36 min |
| Jul 15, 2:36 PM PDT | Severe Thunderstorm Warning | MFR | Siskiyou | 24 min |
| Jul 15, 3:21 PM PDT | Severe Thunderstorm Warning | MFR | Modoc, Siskiyou | 24 min |
| Jul 18, 12:31 AM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 59 min |
| Jul 18, 12:39 AM PDT | Severe Thunderstorm Warning | PSR | Riverside | 36 min |
| Jul 19, 1:42 PM PDT | Severe Thunderstorm Warning | SGX | San Bernardino | 63 min |
| Jul 21, 7:05 AM PDT | Severe Thunderstorm Warning | PSR | Imperial, Riverside | 40 min |
| Jul 22, 6:06 PM PDT | Severe Thunderstorm Warning | REV | Alpine, El Dorado, Placer | 39 min |
| Jul 22, 6:08 PM PDT | Severe Thunderstorm Warning | REV | Lassen, Plumas | 37 min |
| Jul 22, 6:47 PM PDT | Severe Thunderstorm Warning | REV | Lassen, Plumas | 43 min |
| Jul 22, 7:31 PM PDT | Severe Thunderstorm Warning | MFR | Siskiyou | 29 min |
| Jul 22, 7:36 PM PDT | Severe Thunderstorm Warning | REV | Lassen, Plumas | 39 min |
| Jul 23, 5:06 PM PDT | Severe Thunderstorm Warning | REV | El Dorado, Placer | 39 min |
| Jul 23, 6:51 PM PDT | Severe Thunderstorm Warning | MFR | Siskiyou | 24 min |
| Jul 23, 6:55 PM PDT | Severe Thunderstorm Warning | MFR | Siskiyou | 20 min |
| Jul 23, 8:31 PM PDT | Severe Thunderstorm Warning | MFR | Siskiyou | 29 min |
| Jul 23, 8:55 PM PDT | Severe Thunderstorm Warning | MFR | Siskiyou | 35 min |
| Jul 24, 4:10 PM PDT | Severe Thunderstorm Warning | MFR | Siskiyou | 24 min |
| Jul 29, 2:59 PM PDT | Severe Thunderstorm Warning | SGX | San Diego | 61 min |
| Aug 2, 2:58 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 47 min |
| Aug 2, 3:07 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 38 min |
| Aug 2, 3:29 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 26 min |
| Aug 8, 3:25 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 50 min |
| Aug 8, 5:29 PM PDT | Severe Thunderstorm Warning | VEF | Inyo | 46 min |
| Aug 9, 2:46 PM PDT | Severe Thunderstorm Warning | SGX | San Bernardino | 59 min |
| Aug 9, 3:42 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 33 min |
| Aug 9, 5:44 PM PDT | Severe Thunderstorm Warning | HNX | Kern | 29 min |
| Aug 9, 10:03 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 27 min |
| Aug 9, 10:26 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 39 min |
| Aug 9, 10:52 PM PDT | Severe Thunderstorm Warning | PSR | Riverside | 23 min |
| Aug 11, 8:03 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 42 min |
| Aug 11, 9:25 PM PDT | Severe Thunderstorm Warning | VEF | Inyo, San Bernardino | 65 min |
| Aug 15, 1:59 PM PDT | Severe Thunderstorm Warning | SGX | San Diego | 61 min |
| Aug 15, 2:09 PM PDT | Severe Thunderstorm Warning | SGX | Riverside, San Diego | 44 min |
| Aug 15, 2:59 PM PDT | Severe Thunderstorm Warning | SGX | Riverside | 61 min |
| Aug 15, 3:30 PM PDT | Severe Thunderstorm Warning | SGX | San Diego | 75 min |
| Aug 15, 3:37 PM PDT | Severe Thunderstorm Warning | SGX | Riverside, San Diego | 27 min |
| Aug 16, 12:27 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 48 min |
| Aug 16, 1:58 PM PDT | Severe Thunderstorm Warning | SGX | Riverside | 62 min |
| Aug 16, 2:34 PM PDT | Severe Thunderstorm Warning | SGX | Riverside | 56 min |
| Aug 16, 3:09 PM PDT | Severe Thunderstorm Warning | SGX | San Bernardino | 53 min |
| Sep 30, 12:58 PM PDT | Severe Thunderstorm Warning | PSR | Imperial | 32 min |
| Sep 30, 5:02 PM PDT | Severe Thunderstorm Warning | PSR | Imperial | 28 min |
| Oct 3, 3:20 PM PDT | Severe Thunderstorm Warning | HNX | Fresno | 40 min |
| Oct 3, 5:47 PM PDT | Severe Thunderstorm Warning | PSR | Riverside, San Bernardino | 28 min |
| Oct 3, 6:18 PM PDT | Severe Thunderstorm Warning | PSR | Imperial, Riverside | 27 min |
| Oct 3, 6:18 PM PDT | Severe Thunderstorm Warning | VEF | Inyo, San Bernardino | 42 min |
| Oct 3, 6:39 PM PDT | Severe Thunderstorm Warning | PSR | Imperial, Riverside | 36 min |
| Oct 3, 7:15 PM PDT | Severe Thunderstorm Warning | PSR | Riverside, San Bernardino | 30 min |
| Oct 3, 7:47 PM PDT | Severe Thunderstorm Warning | PSR | Riverside | 28 min |
| Oct 3, 8:18 PM PDT | Severe Thunderstorm Warning | VEF | San Bernardino | 24 min |
| Oct 12, 11:26 PM PDT | Severe Thunderstorm Warning | PSR | Imperial, Riverside | 49 min |
| Oct 13, 12:48 AM PDT | Severe Thunderstorm Warning | PSR | Riverside | 42 min |
| Oct 13, 1:48 AM PDT | Severe Thunderstorm Warning | PSR | Riverside, San Bernardino | 42 min |
| Nov 29, 5:28 PM PST | Severe Thunderstorm Warning | HNX | Madera | 32 min |
By county
Every county with at least one alert. A county page lists each alert that covered it.
- San Bernardino County21
- Riverside County17
- Imperial County8
- Siskiyou County8
- San Diego County7
- El Dorado County4
- Tulare County3
- Lassen County3
- Plumas County3
- Inyo County3
- Butte County2
- Tehama County2
- Kern County2
- Alpine County2
- Placer County2
- Mariposa County1
- Merced County1
- Kings County1
- Tuolumne County1
- Modoc County1
- Fresno County1
- Madera County1
The busiest days
Days with the most alerts issued, by UTC date.
Nearby
Alerts in force nowTornadoes on recordThe radar archive20172019
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.