There’s lots of buzz here in Northern California about a series of upcoming storms starting today and through the weekend that are expected to bring gusty winds and significant rain. So much rain in fact, that there is likely to be flooding. Some reports have my area of NorCal getting as much as 20″ of rain (~75% of the normal seasonal total). I think that is over-forecasted, but it certainly is a possibility. I remember one similar event in the El Niño years of the 1990′s, a “March Miracle” that dropped ~17″ of rain in a 24 hour period in the mountains just east of me at a DWR weather station called “Four Trees” above the Feather River Canyon. It was such an anomaly that former California State Climatologist Jim Goodridge and I set out to see if maybe the rain gauge had a urinal attached or some other such issue. It turned out that the station was fine.
The setup of this series of storm systems in not unlike that event though, a strong, deep, Arctic low will guide the storms with its rotation right into Northern California as an “Atmospheric River” (AR) or “Pineapple Express” as we often call it.
TWC writes:
Amazingly, according to NOAA’s Earth System Research Laboratory (ESRL), a strong AR can transport as water vapor up to 15 times the average flow of liquid water at the mouth of the Mississippi River!
Suffice to say, if an AR stalls over a particular area, significant flooding can be the result. In fact, a study by Ralph et al. (2006) found ARs responsible for every flood of northern Calfornia’s Russian River in a 7-year period.
According to NOAA/ESRL, 30-50% of the average annual precipitation in the West Coast states typically occurs in just a few AR events. With that in mind, one such AR is poised to soak parts of the West Coast this week.
The Quantitative Precipitation Forecast (QPF) model for this event is quite striking, putting the most significant rainfall into Butte County (where I live), Tehama County, and Plumas County from about Midnight Thursday to 10AM PST Friday as seen in these two plots:
