The West Coast is famous for its "feast or famine" approach to the weather, and true to form, people from southern California through British Columbia are getting clobbered by an immense storm. The storm is causing so many issues that it's tough to list them all. Welcome back to the world of weather, West Coasters.
As of the writing of this post, there were 31 different types of watches, advisories, and warnings in place across the western United States. The alerts range from flash flood warnings to an air quality alert for Salmon, Idaho, where a temperature inversion is trapping fireplace/wood stove smoke at ground level.
Aside from the fact that this many alerts can prove confusing to the public (especially since so many of them overlap), it shows how much more robust and dynamic Pacific storms can be compared to storms typically seen in the rest of the United States.
Heavy rain is the biggest and most welcome story with this system, but as usual, too much at once does more harm than good. Forecast precipitation values for the next seven days from the Weather Prediction Center show a huge portion of central and northern California seeing five or more inches of precipitation—rain below freezing, snow in the mountains above the freezing level.
The highest rainfall totals will occur along the higher elevations near San Francisco, with the combination of tropical moisture and orographic lift (enhanced lift caused by higher terrain) producing more than six inches of rain. A couple inches of rain are even possible down around Los Angeles.
The area desperately needs rain, but too much rain falling all at once causes flooding and doesn't let the water seep into the ground effectively. Drought essentially causes the soil to develop malabsorption—the dry soil doesn't absorb rainwater instantly. It takes a long, steady, light to moderate rain to moisten the soil and help replenish its nutrients. The good thing about all of this, however, is that this rain is helping to refill the reservoirs that supply communities their drinking water.
Communities (especially valleys) caught under the heaviest bands of rain are experiencing flash flooding. Flash flood warnings are in effect for many areas across central California this afternoon as storm sewers can't handle the runoff from the heavy rain. The NWS has issued flash flood warnings for Sonoma County down to Santa Cruz County.
The difference between a flood and a flash flood is that water rises very rapidly in the latter, with water possibly measuring several feet deep in a matter of minutes.
Radar estimates show that bands of showers and thunderstorms coming in off the coast are producing rainfall rates of up to two inches an hour. Radar estimates also show that most of the San Francisco area have seen upwards of four inches of rain over the past day or so, with measurements exceeding five inches in northern parts of the state.
The video at the top of this post (showing a person kayaking in the streets) was taken in Healdsburg, California, a city in central Sonoma County north of San Francisco. The area has seen about four inches of rain so far, and rain will continue coming down at a steady clip through nightfall.
Speaking of drinking water, most of the water that California residents use comes from snow melt in the Sierras. Blizzard warnings are currently in effect for the mountain peaks as heavy snow and incredible winds (on the order of 100+ MPH) are expected to occur as the storm moves further inland this afternoon. The highest elevations could see three or more feet of snow on the ground by Saturday evening.
— NWS Reno (@NWSReno) December 11, 2014
The other big story with this storm is the winds. Pacific storms are notorious for the ferocious winds they produce when they crash ashore. The highest elevations in California are measuring wind gusts above 100 MPH, with one location seeing a 113 MPH wind gust earlier this morning.
— Jeff Van Sant (@JEFFQ13) December 11, 2014
The wind is also whipping up house-sized waves, with heights reaching more than 30 feet from British Columbia through northern California. The rough seas are causing major problems for beaches and coastal communities, with at least one house (above) washed into the ocean thanks to erosion.
The weather should start to clear by tomorrow and it'll be out of here by the weekend, causing issues for the rest of the country. This isn't the worst storm they've ever seen, but it is the worst the West Coast has seen in five years, and that seems like forever when you've been in a drought for so long.