This is the first segment of a three-part series on the monsoon.
Winter storms and the summer monsoon season are the yin and yang of the Colorado Plateau: snowstorms are cold and often wide-ranging, while summer rains are usually warm, patchy and irregular.
But the wet seasons echo one another in another way. Meteorologists have identified a pattern that brings hope to those longing for a lush summer this year. They found that poor monsoon seasons often follow wet winters, while dry winters (like this year’s) are often followed by bountiful summer rains.
There’s science behind this observation, though actual summer rainfall depends on the often-unpredictable interplay of several large-scale factors, and typically varies quite a bit from place to place.
One factor is the temperature of surface ocean waters. Cool water temperatures off the U.S. Pacific coast are correlated with an early start to the monsoon. That’s because cold water in the Pacific moves continental high pressure to the east in summer, and that allows monsoon moisture to move north into the Southwest.
Warm surface temperatures in the Gulf of California and Gulf of Mexico, meanwhile, help feed high levels of atmospheric moisture that move northward once the season gets going.
Local land conditions matter, too. Dry ground and high temperatures in late spring appear to help in the formation of good monsoon conditions. One study done in New Mexico showed that winters with lower-than-normal snowpack are almost certain to be followed by above-normal summer rains.
No guarantees! But meteorologists in the region believe indications are good for a promising monsoon season.
This Earth Note was written by Peter Friederici and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.
