Alert archive / California / San Mateo County
Weather alerts in San Mateo County, California, 2021
77 weather alerts in 2021, from the National Weather Service and the Storm Prediction Center. An alert counts here when it covered this county.
San Mateo County and its neighbors
Each county as a circle sized by its count in 2021. Tap one for its archive.
- Alerts
- 77
- Warnings
- 10
- Watches
- 7
- Advisories
- 53
- Busiest month
- December23 alerts
- Busiest day
- December 13, 20216 alerts
Over time
By month
Warning verification
How often warnings here had a storm report inside them, and how much warning the reports had.
San Mateo County, 2021
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| Tornado warnings | 0 | 0 | ||||
| Severe thunderstorm warnings | 0 | 0 | ||||
| Flash flood warnings | 3 | 1 | 67% | 2 | 0% |
Each office's whole area, 2021
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| NWS San Francisco Bay Area, CA: flash flood warnings | 16 | 2 | 88% | 30 | 7% | 354 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 | Lasted |
|---|---|---|---|
| Jan 1, 8:02 AM PST | High Surf Advisory | MTR | 49 hr |
| Jan 3, 8:38 AM PST | High Surf Advisory | MTR | 62 hr |
| Jan 5, 4:02 AM PST | Dense Fog Advisory | MTR | 7 hr |
| Jan 7, 12:46 AM PST | High Surf Advisory | MTR | 53 hr |
| Jan 9, 8:18 AM PST | High Surf Warning | MTR | 37 hr |
| Jan 10, 1:09 AM PST | Coastal Flood Advisory | MTR | 36 hr |
| Jan 11, 2:35 PM PST | Coastal Flood Advisory | MTR | 22 hr |
| Jan 11, 2:35 PM PST | High Surf Advisory | MTR | 54 hr |
| Jan 14, 8:04 PM PST | High Surf Advisory | MTR | 47 hr |
| Jan 16, 2:29 AM PST | Wind Advisory | MTR | 4 days |
| Jan 16, 7:08 PM PST | High Surf Advisory | MTR | 47 hr |
| Jan 17, 1:39 PM PST | High Wind Warning | MTR | 44 hr |
| Jan 23, 12:53 PM PST | Wind Advisory | MTR | 45 hr |
| Jan 24, 2:14 PM PST | Beach Hazards Statement | MTR | 5 hr |
| Jan 24, 5:19 PM PST | Flash Flood Watch | MTR | 4 days |
| Jan 25, 2:55 AM PST | High Wind Watch | MTR | 12 hr |
| Jan 25, 2:42 PM PST | High Wind Warning | MTR | 45 hr |
| Jan 25, 2:42 PM PST | Wind Advisory | MTR | 61 hr |
| Jan 26, 10:56 PM PST | Flash Flood Warning | MTR | 4 hr |
| Jan 26, 11:18 PM PST | Areal Flood Advisory | MTR | 4 hr |
| Jan 27, 12:33 PM PST | Flash Flood Warning | MTR | 6 hr |
| Jan 27, 2:11 PM PST | Areal Flood Advisory | MTR | 5 hr |
| Feb 23, 2:36 AM PST | Wind Advisory | MTR | 49 hr |
| Mar 3, 2:10 PM PST | Beach Hazards Statement | MTR | 37 hr |
| Mar 8, 8:17 AM PST | Beach Hazards Statement | MTR | 13 hr |
| Mar 14, 1:04 PM PDT | Wind Advisory | MTR | 25 hr |
| Mar 19, 3:38 AM PDT | Beach Hazards Statement | MTR | 18 hr |
| Mar 29, 2:56 AM PDT | Wind Advisory | MTR | 31 hr |
| May 18, 4:47 AM PDT | Wind Advisory | MTR | 48 hr |
| May 20, 11:10 AM PDT | Wind Advisory | MTR | 10 hr |
| Jun 6, 1:48 PM PDT | Wind Advisory | MTR | 30 hr |
| Jun 14, 1:17 PM PDT | Heat Advisory | MTR | 4 days |
| Jul 8, 3:33 AM PDT | Excessive Heat Warning | MTR | 4 days |
| Jul 16, 11:20 AM PDT | Fire Weather Watch | MTR | 26 hr |
| Jul 17, 1:47 PM PDT | Red Flag Warning | MTR | 37 hr |
| Sep 5, 6:34 AM PDT | Dense Fog Advisory | MTR | 3 hr |
| Sep 27, 11:31 AM PDT | Beach Hazards Statement | MTR | 35 hr |
| Oct 7, 2:21 PM PDT | Fire Weather Watch | MTR | 61 hr |
| Oct 9, 1:50 PM PDT | Wind Advisory | MTR | 54 hr |
| Oct 10, 3:03 AM PDT | Red Flag Warning | MTR | 62 hr |
| Oct 19, 1:39 PM PDT | Wind Advisory | MTR | 14 hr |
| Oct 22, 10:48 AM PDT | Flash Flood Watch | MTR | 65 hr |
| Oct 22, 12:56 PM PDT | High Surf Advisory | MTR | 10 hr |
| Oct 22, 1:38 PM PDT | Wind Advisory | MTR | 57 hr |
| Oct 22, 2:18 PM PDT | High Surf Warning | MTR | 4 days |
| Oct 24, 4:19 PM PDT | Areal Flood Advisory | MTR | 10 hr |
| Oct 24, 8:19 PM PDT | Areal Flood Advisory | MTR | 9 hr |
| Oct 26, 10:41 AM PDT | High Surf Advisory | MTR | 9 hr |
| Oct 28, 8:37 AM PDT | Beach Hazards Statement | MTR | 9 hr |
| Nov 7, 1:24 PM PST | Wind Advisory | MTR | 38 hr |
| Nov 12, 7:37 AM PST | Dense Fog Advisory | MTR | 2 hr |
| Nov 12, 11:02 PM PST | Dense Fog Advisory | MTR | 13 hr |
| Nov 13, 9:35 PM PST | Dense Fog Advisory | MTR | 13 hr |
| Nov 26, 9:48 AM PST | Beach Hazards Statement | MTR | 8 hr |
| Dec 2, 12:37 PM PST | Coastal Flood Advisory | MTR | 3 days |
| Dec 11, 12:58 PM PST | Wind Advisory | MTR | 51 hr |
| Dec 11, 1:12 PM PST | High Surf Advisory | MTR | 4 days |
| Dec 12, 8:41 AM PST | Flash Flood Watch | MTR | 40 hr |
| Dec 13, 4:29 AM PST | Areal Flood Advisory | MTR | 18 hr |
| Dec 13, 5:31 AM PST | Areal Flood Advisory | MTR | 7 hr |
| Dec 13, 9:14 AM PST | Areal Flood Advisory | MTR | 3 hr |
| Dec 13, 10:45 AM PST | Flash Flood Warning | MTR | 60 min |
| Dec 13, 12:00 PM PST | Flood Watch | MTR | 13 hr |
| Dec 13, 1:26 PM PST | Areal Flood Advisory | MTR | 11 hr |
| Dec 13, 7:51 PM PST | Areal Flood Advisory | MTR | 114 min |
| Dec 15, 7:14 PM PST | Wind Advisory | MTR | 8 hr |
| Dec 15, 10:43 PM PST | Areal Flood Advisory | MTR | 2 hr |
| Dec 23, 7:36 AM PST | Areal Flood Advisory | MTR | 3 hr |
| Dec 23, 8:12 AM PST | Areal Flood Advisory | MTR | 2 hr |
| Dec 24, 1:55 AM PST | Areal Flood Advisory | MTR | 95 min |
| Dec 25, 8:37 AM PST | Areal Flood Advisory | MTR | 3 hr |
| Dec 25, 10:10 AM PST | Areal Flood Advisory | MTR | 2 hr |
| Dec 25, 10:41 AM PST | Areal Flood Advisory | MTR | 2 hr |
| Dec 25, 10:44 AM PST | Areal Flood Advisory | MTR | 2 hr |
| Dec 27, 6:02 AM PST | Areal Flood Advisory | MTR | 3 hr |
| Dec 29, 1:39 AM PST | Areal Flood Advisory | MTR | 2 hr |
| Dec 29, 9:57 AM PST | Areal Flood Advisory | MTR | 3 hr |
By product
Every kind of product issued here, grouped by hazard. Each opens the same place narrowed to that product.
| Product | Alerts |
|---|---|
| Flooding | |
| Flash Flood Warning | 3 |
| Flash Flood Watch | 3 |
| Flood Watch | 1 |
| Areal Flood Advisory | 20 |
| Heat | |
| Excessive Heat Warning | 1 |
| Heat Advisory | 1 |
| Wind and dust | |
| High Wind Warning | 2 |
| High Wind Watch | 1 |
| Wind Advisory | 15 |
| Fire | |
| Red Flag Warning | 2 |
| Fire Weather Watch | 2 |
| Fog and smoke | |
| Dense Fog Advisory | 5 |
| Coast and beach | |
| High Surf Warning | 2 |
| Coastal Flood Advisory | 3 |
| High Surf Advisory | 9 |
| Beach Hazards Statement | 7 |
The busiest days
Days with the most alerts issued, by UTC date.
Nearby
Alerts in force nowTornadoes on recordForecastThe radar archive20202022
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.