How Prevailing Westerlies Shape North American Weather

The mid-latitude prevailing westerlies (30°–60°N) are the dominant steering flow across North America. Their impacts:

• Maritime Mildness: Onshore flow delivers Pacific moisture and moderates temperatures along the West Coast (Seattle to San Diego), creating mild, wet winters and dry summers.
• Orographic Lift & Rain Shadow: Winds forced up the Cascades, Rockies, and Sierra Nevada drop heavy precipitation (rain/snow) on windward slopes; leeward basins (Great Basin, Intermontane) become arid.
• Storm Track: Extratropical cyclones ride the westerlies eastward, bringing sequential weather systems (rain, snow, fronts) to the Plains, Midwest, and East Coast.
• Snow Distribution: Mountains intercept moisture → deep snowpacks (Rockies, Wasatch, Sierra). East of the Rockies, cold, dry air masses dominate winter.
• Eastern Climate: By the time air reaches the Appalachians and Atlantic, it has lost much moisture; the East experiences greater seasonal extremes (hot summers, cold winters) than the maritime West.

In essence, the westerlies make the West Coast temperate, the interior continental, and drive the parade of weather systems across the continent.