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 heart of the Convergence Zone, where precipitation is heaviest, typically aligns along and adjacent to the King-Snohomish County border. This proximity prevents either county from being dry. Cities located north or south of this boundary, which are under the rain shadow of the Olympic Mountains, have annual rainfall similar to Seattle.