“We are very worried. As Deepak Srivastava, a resident of San Franciscomillion Californians they have been ordered to evacuate or barricade themselves in their homes since Wednesday. One week after the passage of a “cyclonic bomb”, which literally froze the northern United States with temperatures below -31°C, a second has hit California head-on since Wednesday, bringing high winds and torrential rain. Since the beginning of winter, California experiences one storm after another.
“This could be the hardest and most impactful storm series in California in the past five years,” said Nancy Ward, director of California emergency services, on Cnn. 20 minutes returns this Thursday to this extraordinary storm.
When did these torrential rains start?
The first heavy rains fell on the American west coast on Wednesday. Northern California, especially around San Francisco and Sacramento, is the hardest hit region. The United States Weather Service (NWS) has forecast winds that could reach 110 km/h and very heavy rains with up to four inches of precipitation expected in the San Francisco Bay area, as well as more than a meter of snow in the Sierra Nevada mountains.
On Wednesday the wind blew over 130 km/h on the Nicasio Hills. In some counties of the region (Mendocino, Santa Cruz, Santa Clara) several roads have been cut due to flooding, fallen trees or landslides. In the night between Wednesday and Thursday, 178,000 homes and businesses were deprived of electricity. As of 10:30 this Thursday, more than 186,000 people were still without electricity, according to the PowerOutage website. As of Wednesday, 80 flights to or from the San Francisco airport have been canceled, according to Flightaware.
What arrangements have been made by the local authorities?
Authorities warned of landslides and floods, warning that this storm could kill people. Given the meteorologists’ forecasts, the local authorities immediately invited the population to isolate themselves, or even to evacuate, as in the district of Santa Cruz. “If you live in this red zone […] it’s better: play it safe, evacuate and obey the order,” said Das Williams, supervisor of the first district of Santa Barbara County, referring to the dozens of deaths caused by these winter rains over the past five years.
California Governor Gavin Newsom declared a state of emergency Wednesday morning to facilitate emergency response and simplify the reaction of the authorities in the event of an accident. San Francisco set up an emergency operations center and shut down its famous cable cars. “If you don’t have an obligation to be outdoors in San Francisco, avoid going out on the street,” warned Rachel Gordon, an official with the city’s public works department. Thousands of sandbags have been distributed to residents of risk areas.
Bars and restaurants were closed on Wednesday and some San Francisco residents were asked to work from home. City firefighters reported several fallen trees Wednesday morning and some minor flooding before the heart of the storm hit Thursday.
Why do these repeated rains cause so much damage?
The causes of this storm, i.e. a low pressure system, are fairly standard: two air masses, one very cold and the other tropical, meet causing a drop in atmospheric pressure. A depression is a low atmospheric pressure system, often synonymous with bad weather: its dynamics lead to updrafts that cause clouds and precipitation. Unlike a simple rain episode, air pressure here dropped by 24 hectopascals (hPa) in 24 hours, according to the NWS. This is called “explosive genesis” (or “cyclonic bomb”). Additionally, the rain in recent days comes from an “atmospheric river,” a narrow river-like band in the atmosphere that carries huge amounts of moisture from the tropics.
But in this rainy episode, the “cyclonic bomb” and the “atmospheric river” are not solely responsible for the consequences of the current torrential rains. Northern California is still feeling the effects of a series of storms. The latest occurred on New Year’s Eve and caused landslides and power outages. At least one person has died after being trapped in their car by the flooding.
On Dec. 31, San Francisco recorded the second wettest day in its history since the measurement was launched, with 14 inches of precipitation. However, the region’s soils, dried up by the drought that has hit the American West for two decades, are struggling to absorb a new flood, which increases the risk of flash floods. “Usually, amounts of rain like those predicted this week would not have a significant effect. But last weekend’s rains saturated the ground in much of California, say meteorologists at the New York Times, leaving it like a damp sponge and making it more susceptible to flooding and rapid runoff. »
How long before the rains stop?
In its latest Thursday morning bulletin, the National Weather Service, the equivalent of France weather in the United States, after a peak of rainfall on Thursday, it expects a slight calm for Friday. However, the rains should resume on Sunday, and last at least until next Tuesday. According to meteorologists, the series of storms currently hitting California will not stop. “We’re expecting another one over the weekend,” said meteorologist Matt Solum. And then potentially more storms for next week. And maybe even the following week. »
