Key Facts

• The possible moisture corridor is an atmospheric river, a narrow band that carries large amounts of water vapor; a corridor extending from near Hawaii is often called a Pineapple Express.
• Two storm systems—one moving in from Alaska and another developing off Washington—could help draw tropical moisture westward.
• Tropical Rainstorm Olana, near Hawaii, could also contribute moisture to the system.
• In the more likely scenario described by AccuWeather, Los Angeles, San Diego and Palm Springs would receive less than an inch of rain, while some south- and west-facing mountain slopes could get up to 3 inches.
• If the storms and tropical moisture combine earlier, Southern California could see heavier, longer-lasting rain and more widespread flash-flood risk.
• Arizona, Utah, New Mexico and Colorado could face renewed flash flooding, debris flows and significant river rises from late this weekend into early next week.
• Much of the Southwest could receive 1 to 2 inches of rain; some upslope areas of central Arizona, southwestern Colorado and Utah could get 2 to 4 inches.
• Mountain areas could receive heavy snow, while steep slopes and places recently affected by wildfires may be vulnerable to mudslides and debris flows.