Weather
Bomb Cyclone on the West Coast: These are the areas that could suffer flooding and power outtages today, Thursday Nov. 21
Powerfall storms are impacting the West Coast of the US, and more rain is on the way, leading to power outages and flood warnings.
Officials are warning residents of Northern California, Oregon, and Washington to prepare for flooding and power outages as a “bomb cyclone” moves through the area, and more storms are expected over the weekend. The storm has already begun impacting Washington, where more than 300,000 residents are without power across King County. To a lesser extent, power lines have been affected in Northern California, where more than 20,000 residents are without electricity in Lassen, Humboldt, and Siskiyou counties. According to the National Weather Service, a bomb cyclone is an extremely powerful low-pressure system that must drop more than 24 mb (0.71 in Hg) over 24 hours.
The atmospheric river over California
The storm is bringing an atmospheric river to California that has already begun and is expected to continue through Friday, dumping around 6 to 12 inches of rain on the Golden State as the ground struggles to absorb all of the moisture that has fallen so far. These conditions create many risks, and the NWS is already warning that, as the ground cannot cope with the weight of the rainfall, there is an increased chance of rockslides and “dangerous flooding.” The NWS advises drivers to avoid any unnecessary travel and, if one must travel during the storm, to try to obtain road closure information beforehand.
How to stay up to date with weather alerts from the NWS
As the alerts issued by the NWS can change rapidly, we have compiled a short guide to find those related to this storm as it passes through and is replaced by another storm over the weekend that will impact Oregon and Washington more than California.
When it comes to flooding, there are four main warnings that can be issued:
Flood Warning(FLW)
"In hydrologic terms, a release by the NWS to inform the public of flooding along larger streams in which there is a serious threat to life or property. A flood warning will usually contain river stage (level) forecasts."
Flood Watch
"Issued to inform the public and cooperating agencies that current and developing hydrometeorological conditions are such that there is a threat of flooding, but the occurrence is neither certain nor imminent."
Flash Flood Warning
"Issued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely."
Flash Flood Watch
"Issued to indicate current or developing hydrologic conditions that are favorable for flash flooding in and close to the watch area, but the occurrence is neither certain or imminent."
Source: National Weather Service: Glossary
Flooding Advisories - Keep informed
In addition to those four, the weather agency can also issue a Flood Advisory which warns residents of a specified area where the risk level has not reached that which prompts warnings, but nonetheless, officials want people to be prepared in case conditions change. These advisories are in effect across California from the Napa Valley to Humboldt County. For those who live along the coast, the most up-to-date Coastal Flooding Advisories can also be found on the Coastal Flood Advisory. As these are only in advisories, those affected should check in regularly to ensure that there have been no changes in the risk level.
Flood Watch - Get prepared and stay informed
As these warnings are issued when flooding could occur, it is critical to come up with a plan if you are in a low lying area or one that could see erosion during times of heavy rain.
So far a Flood Watch has been issued across Northern California, including Shasta Lake, Northern Sacramento Valley, Central Sacramento Valley, and surrounding foothills. Northwestern California, including Del Norte, Humboldt, Trinity, and Mendocino counties. In these areas, anywhere between three to six inches of rain is expected, but some counties in the foothills and mountains could see up to ten. This level of rain creates a risk of flash flooding, landslides, and urban and roadway flooding that residents should be prepared for.
In the North Bay and Coastal regions of the state, covering Marin, Sonoma, Napa counties, a Flood Watch has also been issued as two to six inches of rain are projected to fall. At higher elevations more rain is possible. Residents should be aware of road closures, as well as creek, river, and urban flooding risks depending on where they live.
In Southern Oregon, a Flood Watch is in effect near areas close to the South Fork Coquille River at Myrtle Point, where heavy rains could lead the river to flood.
Lastly in Washington’s Mason County, a Flood Watch is in effect through Friday night as rain could lead rivers, creeks, streams to flood.
Flood Warnings - Avoid unnecessary travel and listen to advice from authorities
As mentioned earlier, these alerts are sent when flooding is underway or the threat is imminent. Find the most up to date list on the NWS’ website.
In Siskiyou County, California a Flood Warning will remain in effect through Friday Night. The area has already seen between two and six inches of rain and another three to seven are on the way. Flooding is expected in Flooding in Mount Shasta City, Weed, Callahan, Tennant, and surrounding locations.
Additionally in Southwest Oregon and Northern California, covering Coos, Curry, Jackson, Josephine Counties, residents have already seen between one and six inches of rain and another three to seven are expected. In low lying areas floods are expected, and rivers and streams are also expected to overflow out of their traditional path.
Residents are being told that evacuation orders might be imposed.