Pineapple express a flood threat to California, Southwest

Key Points:

• An atmospheric river known as the "pineapple express" is expected to bring heavy rain to the Desert Southwest and Southern California over Halloween weekend, following recent destructive flooding in the region.
• Two rounds of rain are forecast: one on Friday affecting western Texas, New Mexico, and Arizona, and a second starting Saturday in Southern California and the Southwest, continuing into Monday with rain and high mountain snow.
• Flash flooding risks are elevated due to saturated ground from previous storms, with the greatest concern in northern Arizona, southern Utah, western Colorado, and areas affected by recent wildfires prone to debris flows and mudslides.
• Rivers in northern Arizona, such as the Little Colorado and Verde, may run high for several days, and outdoor activities in southern Utah, Colorado, and Arizona parks are advised against due to life-threatening flash flood hazards.
• The moisture fueling this event originates from a jet stream-driven atmospheric river near Hawaii, potentially bringing 2 to 3 times the average moisture for late October, which could be near-record for Halloween weekend and indicative of a wetter Southwest during the upcoming El Niño season.