A comparison of California's extreme 2013 dry spell to the 1976-1977 drought
The extraordinary persistence of the Ridiculously Resilient Ridge of 2013
Zonal (west-to-east) flow typically predominates during the cool season in this region, which directs storm systems that develop over the ocean toward the West Coast. While the storm track does often vary in latitude along the West Coast over the course of any given winter, southward excursions of the jet stream usually bring periods of significant precipitation to much or all of California, which account for the vast majority of all precipitation observed in the state. 2013, however, has featured rather incredibly persistent atmospheric anomalies over the northeastern Pacific Ocean and the West Coast of North America. The typical zonal flow over the Pacific has been much weaker than average and displaced well to the north, occasionally as far north as continental Alaska. This means that the storm track has largely missed the West Coast entirely, bringing well-below-normal precipitation to California, Oregon, and Washington while parts of Alaska are subjected to record warmth and heavy precipitation.