The Pineapple Express and Atmospheric Rivers
California’s Great Flood of 1862
Published in The EarthSphere Blog
This past weekend, Northern California passed from drought to flood as a narrow band of fast-moving air, supercharged with moisture, dumped its wet load. Welcome to the Pineapple Express, an atmospheric river bringing moist tropical air from Hawaii to the West Coast of the USA. The National Weather Service called the storm a “dangerous, high-impact weather system.”
An atmospheric river is a narrow, elongated flow of moist air in the lower atmosphere. The flow corridor measures up to 2,000 km in length and is typically 400–600 km wide. The heavily moisture-laden air is in the lower atmosphere stretching up to 3 km above the earth’s surface.
Atmospheric rivers, like the Pineapple Express, form along the front edge of slow-moving, low-pressure weather systems related to the polar jet stream. The cyclone nature of these weather systems in the northern hemisphere causes winds to flow from southwest to northeast. Hence, the warm moist air from the tropics reaches the US West Coast traveling as far north as Washington and Oregon.
The current atmospheric river drenching California brought heavy, record-setting rainfall to areas in the lowlands and thick snow in higher elevations. The…
