Dry air then sinks forming a high pressure found at 30 degrees latitude. The rotation of the earth is responsible for deflecting this air and creating a complex circulation pattern over the planet. The combination of the Coriolis force and the effect of friction from air moving over land and water causes air within the high-pressure system to spiral outward clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. A cold front comes from the Gulf of Alaska. The earth's rotation and the differing influences of land, sea, ice and mountains force cold, dry, dense air from the north toward the south wedging under warm air.
Foul weather begins at the coast given prevailing movement of storms from west to east.
When a low-pressure system is moving across the Pacific, the first clouds visible in the Pacific Northwest are usually associated with a warm front. Warm air is listed and gradually slides up and over cooler air at the earth's surface. As it passes over a peak, moisture condenses as water droplets or ice crystals. Lenticular clouds are mostly formed to the lee side of mountain ranges. They are most frequently found east of the Cascades in the Northwest.