January 2015 will go down in the record books as being the driest month in California, since record keeping began in 1849. However, things are looking different for the month of February. A winter weather system is moving over Northern California is expected to bring a huge soaking over the weekend.
So what makes this storm different from the storm that battered California in December?
For one, this storm is likely to be less ferocious and winds will not be as strong. While less violent than December’s big rains, the coming storms are fueled by atmospheric rivers, a mass of subtropical moisture over the Pacific, commonly dubbed a Pineapple Express. It’s expected to keep Northern California wet through Monday.
Another difference is that this storm will focus its energy on the northern half of the state, rather than the entire state as did the December storm. Rain totals have the potential to reach 15 inches throughout some of the interior regions. Due to the large amount of rainfall that are is forecasted, there is the possibility for landslides, debris flow, sharp rises on streams and rivers and urban flooding. Unfortunately, this storm will do nothing to ease the drought in southern California.
The pending weather system is also expected to bring snow to the Sierra, but only at the highest elevations over 7,000 feet, forecasters say. Therefore, these storms won’t help to build the Sierra snowpack, which remains at critically low levels.
Here are some more facts about atmospheric rivers:
- According to NOAA‘s Earth System Research Laboratory (ESRL), a strong atmospheric river can transport as water vapor up to 15 times the average flow of liquid water at the mouth of the Mississippi River.
- If an atmospheric river stalls over a particular area, significant flooding can be the result. In fact, a study by Ralph et al. (2006) found atmospheric rivers responsible for every flood of northern California’s Russian River in a seven-year period.
- Atmospheric rivers also important for western water supply considerations. According to NOAA/ESRL, 30-50 percent of the average annual precipitation in the West Coast states typically occurs in just a few atmospheric river events.