Rich moisture has been flowing into the desert southwest this week. Dew point temperatures, a measure of the amount of moisture in the air, are in the upper 50s and lower 60s in places like Phoenix and Las Vegas, causing a seasonal wind shift transporting rich subtropical moisture into the area. This wind shift is called the monsoon. The increased moisture combines with daytime heating to help set off widespread showers and thunderstorms in the afternoon.
Generally, warmer temperatures enhance the monsoon season by creating more instability in the atmosphere for thunderstorm growth. The monsoon is a run-on process started by the summer heat, but assisted by the greening of trees and shrubbery in northwestern Mexico and southern Arizona. This greening retains and produces moisture that keeps the humidity level higher in surrounding areas, which in turn makes it easier to form clouds, and, the clouds drop rain on plants and the cycle repeats.
Colorado normally sees monsoon activity peak between late July and mid-August, but, because the upper-level winds are often light in July and August, the storms move slowly and can produce flash flooding. Monsoon storms often contain intense cloud-to-ground lightning and sometimes even hail.
There are two necessary ingredients for monsoon production: hot temperatures and plentiful moisture. Temperatures in Colorado have been above-average in recent weeks, which makes this year’s monsoon season look very promising to bring us much needed, beneficial moisture.