Monsoon Q&A with Nancy Selover

Nancy Selover received her BS, MA, and PhD degrees in Geography/Climatology from Arizona State University. Her main interests are field study, instrumentation, and urban climate, and she has intensively studied the climate and evaporation rates of urban lakes. Serving as the State Climatologist for Arizona, Selover educates groups across the state on climate topics including the urban heat island, monsoon, drought, extreme weather, climate change, and Arizona's climate.


Q: We usually have more storms by this time of the monsoon, what’s with the delay?

Selover: The average start in the Phoenix area is July 6th, so we are not really late. It has started down in the southeastern corner of the state. The earliest start was June 16 in 1925, and the latest start was July 25th, 1987.


Q: Should we be expecting a dry monsoon?

Selover: I expect it to be a wet monsoon, as the last 5 years have had wetter than average monsoons.  The average summer rainfall for Phoenix is 2.61”.  Last year was 2.69”.


Q: Why are some monsoon storms more violent than others?

Selover: The strength of the thunderstorms is controlled by the amount of moisture available in the atmosphere, how unstable the atmosphere is, and how the winds aloft are steering the storms.  We get the gully-washers when we have a very moist atmosphere all the way down to the surface. In 2014 and 2015 we had moisture from eastern Pacific hurricanes mix with the monsoon moisture from Mexico to generate extreme precipitation events across Phoenix.  If we have eastern Pacific hurricanes that ravel northward up the coast or up through the Gulf of California, we may have more of those types of events this summer.  It’s always a possibility.


To schedule an interview with Nancy Selover, email