Here we see the Puget Sound Convergence Zone, ordinarily found up north of the King County line. Moisture-laden westerly winds off the Pacific run into the Olympic Mountain range and split into a south-around branch (via southern Puget Sound) and a north-around branch (via the Strait of Juan de Fuca). Looking north from Seattle’s First Hill, we can see under the cloud layer of the south-around flow to observe the clouds of the north-around flow.
The most famous example is the Intertropical Convergence Zone ITCZ about 7 deg north of the equator. That is where the trade winds out of the NE collide with the southern trade winds out of the SE. Surface air is pushed up into cooler air and so that’s a line of thunderstorm one sees.
