Forecasters are predicting heavy rains to hit portions of northern California by the middle of the week and last through the week. They are calling this an "atmospheric river," which is a long, narrow plume that brings deep moisture from the tropics to the mid-latitudes. Meteorologists predicts areas along the coast to receive as much as 10 inches of rain from this system and create erosion problems for cities that lie below the coastal range. The pacific northwest, which includes eastern Oregon and Washington, are used to getting this amount of rain, but forecasters fear this system may be sticking around for a couple of days. This could lead to flash floods in northern California and cause debris flows in recently burned areas. Residents residing in these areas should take precaution of the flood watch to ensure their safety.
http://www.weather.com/news/weather-forecast/california-flood-threat-20121126