The West Coast is likely to face torrential rain in the coming days as the 3,000 mile long "Pineapple Express" atmospheric river will bring wet conditions to the region.
Landslides, moderate flooding and high winds are expected over the Western states of California, Oregon and Washington throughout this week as the weather system travels eastward in from the Pacific Ocean from Tuesday onwards.
Atmospheric rivers are long, narrow regions in the atmosphere that carry water vapor inland from the Pacific Ocean. When atmospheric rivers make landfall, they typically release this water vapor as either rain or snow, depending on temperatures, and can sometimes cause extreme rainfall.
The "Pineapple Express" is one of these stratospheric rivers which stretches all the way from Hawaii to the U.S. and Canada West coasts, sometimes bringing heavy rainfall and snow to the area.
In California, from Wednesday through to Friday, up to seven inches of rain can be expected at higher elevations while one to five inches can be expected at lower levels. Current guidance issued on Sunday by the National Weather Service (NWS) warns that minor flooding could take place along the San Lorenzo, Russian, and Navarro rivers throughout Wednesday. The latter two rivers currently have a "now have 50 and 65 percent chance of reaching flood stage," according to outlooks posted by the NWS on Sunday afternoon.
The NWS isn't expecting major impacts on local areas despite the deluge of rain on its way for parts of California. "The good news is that our main stem rivers are doing well and can accept quite a bit of runoff before becoming problematic," a report issued on Sunday by the NWS reads. "A notable change with this update is the increase in the chance that main stem rivers rise above flood stage. There is now about a 10-30 percent chance of main stem rivers reaching minor flood stage Thursday and Friday, with the higher end of those probabilities being for the North Bay rivers."
In the San Francisco Bay Area, the NWS has warned that shallow landslides are likely as soil becomes oversaturated due to heavy rain levels.
Those in Washington may have already experienced heavy rain throughout the weekend, with some rivers in the state already above flood stage according to the NWS, and extra rainfall is on the way thanks to the atmospheric river. "Additional rounds of moderate to heavy rainfall will be possible through midweek before a cold front finally pushes atmospheric river moisture east of the region late Wednesday into Thursday," the NWS has reported.
In an outlook posted on Sunday morning, the NWS warned that flooding is possible through the Olympic Peninsula and North Cascades due to abundant rainfall, though precise amounts predicted to fall have not yet been issued. Newsweek has contacted the NWS for comment via email.
"That jet stream is going to be oriented right from west to east, and that means very warm air and a lot of Pacific juice coming right across parts of California into northern New Mexico," Fox Weather meteorologist Bob Van Dillen said. "We see that fetch coming all the way from Hawaii, and that's going to stretch through the Pacific and into lower parts of California."
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