“A rather extraordinary sequence of atmospheric events has unfolded over the Pacific Ocean and across adjacent North America over the past week or so.
The current pattern is strongly reminiscent of the extremely high amplitude wave pattern that dominated most of winter 2013-2014 and the latter half of 2012-2013. While the implications are a little different for California this time around–since the subtropical jet has thus far been a bit stronger, and allowed some occasional precipitation to affect the northern part of the state–in a large-scale sense the setup is remarkably similar to that which has occurred repeatedly in recent years. The “Warm West/Cool East” pattern, which is characterized by a persistent and well-defined pressure dipole (high pressure in the West and low pressure over the Midwest/Eastern Seaboard), results in unusually dry and warm conditions in California (while bringing impressive cold and snow to areas from the Rocky Mountains eastward). … ”