When is monsoon season in Arizona? It can rain here

While monsoon season may have technically begun in Arizona, metro Phoenix is waiting with bated breath for the first storm of the season.

However, the onset of the monsoon does not bring a promise of impending showers, just an increased chance of rain.

So when are the first monsoon showers expected in the Valley? After hazy conditions and storms east of Phoenix last week, metro Phoenix was expected to remain warm and dry with temperatures around 110-114 degrees, officials said.

Here’s what you need to know about the start of the monsoon in Arizona and when it might finally rain in metro Phoenix.

When is monsoon season in Arizona?

The monsoon season in Arizona starts approximately in June and lasts through September. Since 2008, the National Weather Service’s designated dates are June 15 through September 30.

These dates only indicate a higher chance of storms, so don’t be confused if it doesn’t rain between these dates.

Before the weather service set these dates, the start of the season was heralded by three consecutive days of average dew point temperatures of 55 degrees or higher. The dew point means the temperature to which the air must be cooled to become saturated with water vapor. This is what forms clouds.

Heat, wildfires and monsoon: What you need to know about the triple threat looming over Arizona

When will it rain in metro Phoenix?

Ryan Worley, a meteorologist with the National Weather Service in Phoenix, said Phoenix residents are unlikely to experience the first monsoon storms this week.

The chance of rain on June 24 hovered around 10-15%, with some areas north and east of the Valley more likely. However, as the week progresses, the chance of storms decreases.

“We’ll see those low probabilities get even smaller, dropping to 10% in the coming days and even lower after that,” Worley said.

Worley said warm weather would continue through June 30 with highs between 110 and 114 degrees.

Does the monsoon come early in Arizona?

Although the season officially began on June 15, monsoon activity does not typically increase until early July. Phoenix has a 30% to 40% chance of showers and storms on June 29 and June 30.

“This is very early,” says Michael Crimmins, a climatologist at the University of Arizona. “We normally don’t see precipitation this early in the season, so that will surprise people a bit. It’s almost a month earlier than last year.”

The monsoon begins when a subtropical ridge shifts north from Mexico in spring and early summer, bringing hot temperatures and moisture across the Southwest. The series of high temperatures likely contributed to the storm’s development.

See what they looked like: Phoenix’s oldest pools were freezing

“There’s really no heat dome over the Southwest,” Crimmins said. “Heat dome is an informal term used more broadly to talk about large high-pressure systems that bring high temperatures.”

A large high-pressure system responsible for heat waves in the eastern US has shifted southwest, bringing the heat, and heat is one of the elements that typically triggers monsoon activity.

“We’re definitely not under it, but we are under its influence,” he said.

To the west, a low-pressure system is over California that brought cooler temperatures this week. Arizona lies between these two major weather features, contributing to the increased heat and humidity. A former tropical cyclone, Alberto, produced its own plume of moisture from the southwest.

Storm chances vary from state to state, but the Southeast is likely to see some activity that could extend into the high country and northeastern part of the state, according to Crimmins.

Arizona Republic reporter Raphael Romero Ruiz contributed to this article.