Can a wet winter lead to a drier monsoon?

If you think forecasting precisely tomorrow’s observed weather hour-by-hour can be tough, try predicting weather conditions months in advance! What I find encouraging about studying the atmosphere is that despite the uncertainty that inherently exists in the finer details of any weather forecast you can still create a decent generalized conceptual model in your head justifying a potential future weather outcome by applying the basic physical processes of meteorology. This can often get you in the right “ballpark” for a reasonable weather forecast. To help answer this topic’s question, let’s first dig in a bit more on how a monsoon develops.

Wet monsoon climates are characterized by a seasonal change in prevailing winds that transport water vapor from nearby water sources to fuel thunderstorms. For the summer North American Monsoon, primary moisture sources include the Gulf of California, subtropical air masses over Mexico, and Gulf of Mexico. Note all these major moisture sources are south and southeast of the Desert Southwest region, meaning to have an active monsoon it is crucial to have sustained winds blowing from these moisture sources!

The strength and persistence of a monsoon circulation is highly dependent on how the lower and upper atmosphere couples with each other! It begins with intense heating of the surface stretching over a broad area from the southern Rockies down to Mexico during the late spring and summer months. Over time, hot and buoyant air rising from the land results in low pressure (also called a “thermal low”) since air mass is being removed near the surface, but at the same time creates upper level high pressure because air mass is collecting aloft from below. How does high pressure spin in the Northern Hemisphere? Clockwise due to the Coriolis Effect, which was touched upon in an earlier post! In Part II, I’ll bring multiple concepts together to reason how winter weather may make or break the summer monsoon! As a hint, how could you weaken a future monsoon circulation?

Photo Credit: Jonny William Malloy