The WP pattern is a primary mode of low-frequency variability over the North Pacific in all months, and has been previously described by both Barnston and Livezey (1987) and Wallace and Gutzler (1981). During winter and spring, the pattern consists of a north-south dipole of anomalies, with one center located over the Kamchatka Peninsula and another broad center of opposite sign covering portions of southeastern Asia and the western subtropical North Pacific. Therefore, strong positive or negative phases of this pattern reflect pronounced zonal and meridional variations in the location and intensity of the entrance region of the Pacific (or East Asian) jet steam. These anomalies exhibit a strong northward shift from winter to summer, which is consistent with the observed northward shift of the Eat Asian jet stream. A third anomaly center is located over the eastern North Pacific and southwestern United States in all seasons.
The positive phase of the WP pattern is associated with above-average temperatures over the lower latitudes of the western North Pacific in both winter and spring, and with below-average temperatures over eastern Siberia in all seasons. It is also associated with above-average precipitation in all seasons over the high latitudes of the North Pacific, and below-average precipitation across the central North Pacific especially during the winter and spring.