First of Its Kind: San Francisco Tornado Warning
San Francisco saw its first-ever tornado warning on Saturday morning as a strong band of rain moved onshore. Later that day, an EF-1 tornado touched down in Scotts Valley, CA.
The city of San Francisco, California, is hardly known for severe weather potential. To the contrary, most people associate the Bay Area with thick, maritime fog, most often depicted shrouding the Golden Gate Bridge.
But on the morning of December 14th, shortly before 6 AM, San Francisco set a new precedent for its own hazardous weather. The city fell under its first ever tornado warning.
Powerful Morning Storms
The tornado warning was issued in conjunction with a broad band of severe thunderstorms that moved northeastward onto the California coast. Loaded with Pacific moisture, these storms brought not only substantial rainfall but also severe wind gusts to coastal areas.
NWS San Francisco issued the tornado warning in response to an area of rotation within the line of storms. And although no tornadoes actually touched down in San Francisco, the city received wind gusts in excess of 80 MPH as the severe thunderstorms moved onshore.
California Tornadoes Are Infrequent
From a climatological perspective, it makes sense that no tornadoes touched down in the Bay Area. California is not the most favorable zone for tornado formation, and touchdowns in the state are relatively infrequent.
On average, California receives only one tornado in the month of December (NOAA). In fact, California's climatological norm is to see one tornado per month for seven months out of the year, with no tornadic activity in the other five months.
If the morning storms had produced a tornado, San Francisco might have set the state on course to reach its December "quota" of tornadoes. Instead, that distinction fell to a different California town, further south of the Bay Area.
Tornado in Scotts Valley
While the line of storms that moved over San Francisco certainly looked more ripe to produce a tornado, it was not until after the morning storms had cleared out that California saw a tornado touch down.
In the early afternoon, an eastbound storm rolled over the city of Scotts Valley, CA, dropping an estimated EF-1 tornado.
According to the NWS damage survey, the tornado roughly hugged Mount Herman Road, overturning multiple vehicles in its path. This tornado was fairly narrow and not long-lived; however, it was powerful while it persisted.
Stay Tornado Aware
The issuance of San Francisco's first-ever tornado warning, as well as the occurrence of the Scotts Valley EF-1, shows that even regions that are little known for severe weather can still experience powerful winds and destructive tornadoes.
HailTrace boasts a team of meteorologists who specialize in identifying weather hazards like these, with the aim of supporting impacted communities through real-time hail, wind, and tornado maps.
You can find HailTrace's range of hail, wind, and tornado maps on our website, HailTrace.com.
To read more about how HailTrace partners with emergency managers, check out our blog post on tornado maps.