Because of its microclimates, combined sewer system, and being wedged between two large bodies of water, bomb cyclones just hit San Francisco differently.
It won’t stop raining until next Wednesday. Or, at least, that’s what the most current weather forecasts show: potentially a month’s worth of rain soaking the San Francisco Bay Area over the next seven days.
After rapidly forming in the Pacific Ocean, the bomb cyclone — a term used in meteorology to describe a process called bombogenesis, which denotes the intensification of a cyclone in a short period of time — poised to strike Northern California and along the Pacific Northwest is expected to bring dangerous amounts of water. NorCal cities like Eureka and Mendocino will see hurricane-like winds, tidal surges, and downpours capable of significant destruction; these conditions also pose a great danger to human life as they will develop quickly.
Further down the coast here in San Francisco, conditions won’t be as severe … but they will, nevertheless, remain noticeable.
Between now and Monday, over three inches of rain could fall within the 49-square-mile city. Similar rainfall amounts will fall elsewhere in the San Francisco Bay Area; Oakland, Hayward, and San Jose will see upwards of two inches. Six-inch rainfall estimates placed on Napa and Santa Rosa counties present major flooding risks and could cause sizable road closures and a long list of evacuation notices.
Meteorologist with the National Weather Service notes the majority of these rainfall estimates will fall within the next 24 to 48 hours — “The heaviest rainfall is going to be over the North Bay in the next 24 to 48 hours,” Roger Gass, a meteorologist with the National Weather Service, told SFGATE. These rapid downpours further enhance the risk of dangerous conditions, overwhelming soil conditions, and rainwater mitigation infrastructure — (here’s your reminder that San Francisco’s sewers system is antiquated and unable to handle large rainstorms) — all of which greatly increase the chance of flash floods.
What makes this particular bomb cyclone more powerful is the existence of an atmospheric river inside of it. Described as narrow, concentrated bands of moisture in the atmosphere that can transport massive amounts of water, atmospheric rivers usually span hundreds of miles long, the longest of which can measure over 1,000 miles long. And because of their volume and intensity, they’re often pushed ashore by, you guessed it, bomb cyclones.
The past few years have introduced San Francisco as an “it girl” for bomb cyclones and the atmospheric rivers they often bring.
While not rare in actuality, only 7% of all “nontropical low-pressure systems” near North America from 1979 to 2019 made landfall as bomb cyclones, per a study by Northern Illinois University. This extrapolated outward to mean about 18 bomb cyclones affect North America each year, the majority of which strike along the East Coast.
But because of San Francisco’s unique atmospheric anomalies, microclimates, and the city’s inability to handle large amounts of water successfully — remember, San Francisco has no dedicated storm drain system, but rather a combined sewer system that is responsible for both sewage and rainwater — the effects of bomb cyclones are exacerbated when they hit.
Trees fall in spectacular fashion. Flooding severity from neighborhood to neighborhood varies widely depending on how high or low they are on any one of the city’s hills. Gale force winds get heightened by San Francisco’s position between the Pacific Ocean and the San Francisco Bay. Power outages are common … because of the “impossibility” of undergrounding SF’s powerlines and other utilities. Sandbags are given out to residents. Some of them go on to adopt nearby storm drains … because the City is unable to properly maintain them, often resulting in them becoming clogged during moments when they’re needed most to divert floodwaters.
Bomb cyclones, by characterization, are brat. Absolutely, for sure. Within that hyper-internet lore, San Francisco lives as the viral Apple Dance trend. And only the most chronically online “it girls” among us will be able to weave those references together.
Feature Image: Screenshot courtesy of Instagram via [at]news
