The western states of California, Nevada, Oregon and Washington have been developed as a group and at a high resolution owing to the significance of the recent drought and current ENSO event. This has led to widespread extreme events largely dry but the prospect of wet periods especially this coming winter. The importance of these States to the US economy and the risk posed by recent weather events points to a specific need for this region to be mapped separately from the rest of the continental USA.
The West Coast of the United States has an oceanic climate in its Northern edge towards the Canadian border, but from the Californian border towards the Mexican border the climate is Meditterarean. The coastline sees significantly mild temperatures when compared to the inland areas, with differences of 19 °C between Eureka's and Redding's July temperatures, in spite of less than 100 miles separating the locations. Similar fluctuations can be seen all through the coastline, and could partially be explained by the cold currents in the Pacific Ocean moderating coastal temperatures. The northern half of the Californian coast has the coldest low-elevation summer daytime high temperatures for the 37th to 40th parallel in the Northern hemisphere, normally associated with humid subtropical climate or humid continental climate with hot summers and cold winters. This does not only occur in the San Fransisco Bay Area, but it also affects Santa Monica, in Los Angeles, Southern California, with very little yearly temperature differences but with cool summers. Inland summer temperatures are compatible with the rest of the United States on the same parallels, sometimes warmer due to prevailing winds from the Nevada and Arizona hot desert climate.