Our weather is in atmospheric river mode. The term describes the fact that there is the equivalent of a huge river system in the air coming out of the sub tropics to tropics and dumping itself on the west coast. These events are a big deal geologically and play a major role in shaping the land.
It is also a big deal for California. This is the visible satellite image from earlier today. Northern California will get some water in their reservoirs. Good news for almonds.
The infrared shows the moisture tap is from south of Hawaii. And there will be additional streams of atmospheric rivers from the same regions over the next couple of days.
Although rain will impact a large area from these storms, these storms have a tendency to have a relatively narrow band of very intense rainfall. In 2007 when of these narrow bands of precipitation locked into one location and triggered hundreds of landslides and wide spread flooding in southwest Washington and northeast Oregon. There were some other factors that made that storm so destructive, but the bulk of the trouble was from the huge precipitation band.
The NOAA CalWater study hopes to gather information that will give climate and weather folks a better handle on these types of storms.
There has been a fair bit of study of these storms and how they might behave in the future with some recent studies indicating that the events may increase in frequency and magnitude in the Pacific Northwest (Warner, Mass and Salathe, 2014) http://journals.ametsoc.org/doi/abs/10.1175/JHM-D-14-0080.1. These results are consistent with other other studies in the Atlantic Ocean.