Pineapple Express Threatens Southwest With Historic Flooding

Heavy rainfall from a tropical moisture system is raising the threat of severe flooding across the Desert Southwest and Southern California, prompting mandatory evacuations in parts of Arizona and Colorado. The atmospheric river, known as the Pineapple Express, could bring potentially historic river levels after recent storms left the region's ground saturated.

According to weather.com, evacuation orders are in effect near Oak Creek in Sedona, Arizona, and in parts of Archuleta County near Pagosa Springs, Colorado. The San Juan River is forecast to reach a height of up to 20 feet late Sunday night, potentially breaking historical records.

The latest rainfall threat follows storms that delivered 2 to 5 inches of precipitation across the region last week. Those storms triggered major flash flooding in northern Arizona, New Mexico, southern Colorado, and southern Utah.

Flagstaff, Arizona, Zion National Park in Utah, northern New Mexico, and southern Colorado are among the areas facing the greatest rainfall potential. Although Phoenix sits outside the most intense rainfall zone, it remains under a Level 2 out of 4 threat.

Additional rainfall could trigger widespread flash flooding, particularly in areas identified by darker green and yellow forecast zones. The most vulnerable locations include lower elevations in southwestern Colorado, the Four Corners region, the northern and eastern Phoenix metropolitan area, the Mogollon Rim, and canyonlands in southern Utah.

Recently burned areas also face heightened risks. Rainfall over wildfire-scarred terrain can trigger rapidly moving debris flows, rockslides, and mudslides, even when precipitation amounts are relatively modest.

According to the National Weather Service in Flagstaff, the Little Colorado and Verde rivers could remain elevated for several days following the latest rainfall.

Higher elevations across the Rocky Mountains and Sierra may receive snow instead of rain. The resulting conditions could make mountain passes slippery, particularly during Sunday and Monday.

The atmospheric setup driving the storm involves a southward dip in the jet stream near the West Coast. This circulation is drawing a concentrated stream of tropical moisture toward the Southwest.

The moisture source is located near Hawaii, giving the atmospheric river its familiar nickname, the Pineapple Express. Although meteorologists do not classify this particular system as an especially strong atmospheric river, its moisture content could reach record levels for this time of year.