Image caption
Total precipitable water (mm) forecast for the eastern Pacific and western United States for mid-day April 6, 2018 using the GFS weather model run 12 hours earlier. Precipitable water is a measure of the amount of liquid water in the air should all water vapor (water in gas form) become liquid water. A narrow band of incredibly moist air, known as an atmospheric river, was forecast to be directed at the West Coast of the United States bringing torrential rains. NOAA Climate.gov image repurposed from an image from NESDIS.