Puget Sound Convergence Zone - Most Common Locations

Most Common Locations

Puget Sound Convergence Zones, variable in both location and strength, tend to form in the general vicinity of central and southern Snohomish and northern King counties in Washington, from Everett to the Northgate neighborhood of Seattle. The strongest part of the Convergence Zone (where the heaviest precipitation falls) tends to lie along and adjacent to the King-Snohomish County line so that neither county is left dry. The proximity of the Convergence Zone to the King-Snohomish County line is the reason that cities located just north or south of the line, which are located within the rain shadow of the Olympic Mountains, approach Seattle in annual precipitation. The effect of the Puget Sound Convergence Zone nearly offsets that of the rain shadow. Without PSCZ, cities such as Edmonds, Mountlake Terrace, and Lynnwood in Snohomish County and Shoreline, Lake Forest Park, and Bothell in King County would be noticeably drier than Seattle.

The PSCZ has been suggested as the cause of greater precipitation over Glacier Peak relative to other mountains in the Cascades to the east of Puget Sound. As there are no weather stations near Glacier Peak, it remains unclear whether that area actually receives greater precipitation than elsewhere in the Cascade Range.