Rain forms when atmospheric temperatures remain above freezing (32°F) from the cloud level to the surface. Water droplets within clouds grow in size by colliding and coalescing with other droplets.

The atmospheric river-fed storms caused $4.7 billion in damage and 22 deaths, according to NOAA. Not all Januaries deliver a parade of soaking atmospheric rivers.

Holographic measurements of inhomogeneous cloud mixing at the centimeter scale. Science, 2015; 350 (6256): 87 DOI: 10.1126/science.aab0751 ...

Another atmospheric river in northern California earlier this month killed two people and caused two piers to collapse, leaving more than 180,000 homes and businesses without power.

These factors lead to less atmospheric mixing and means temperatures are colder near the surface. During normal conditions, the air is warmer near the ground and colder at higher altitudes.

he said. Newman said scientists don't yet know what causes atmospheric mixing to slow, but he said it's likely a key factor in ozone depletion over the Arctic.