While Arizona‘s monsoon season may technically have begun, the Phoenix metropolitan area is waiting with bated breath for the first storm of the season.
However, the onset of the monsoon is not a promise of imminent rain, just an increased chance of rain.
So when are those first monsoon rains expected in the Valley? After foggy and stormy conditions east of Phoenix last week, the Phoenix metropolitan area was expected to remain hot and dry with temperatures between 110 and 114 degrees, officials said.
Here’s what you need to know about the onset of the monsoon in Arizona and when it can finally rain in the Phoenix metro area.
When is monsoon season in Arizona?
Arizona’s monsoon season begins around June and continues through September. Since 2008, the dates established by the National Meteorological Service are from June 15 to September 30.
These dates only suggest 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 marked 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 saturate it with water vapor. This is what forms clouds.
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When will it rain in the Phoenix metro area?
Ryan Worley, a meteorologist with the National Weather Service in Phoenix, said Phoenix residents aren’t likely to see those first monsoon storms this week.
Rain chances were around 10-15% on June 24, with some areas north and east of the Valley having higher chances. However, the chance for storms decreases as the week progresses.
“We’ll see those low chances get even lower, dropping to 10% in the next few days and even lower after that,” Worley said.
Worley said the warm weather would continue with highs expected between 110 and 114 degrees through June 30.
Will the Arizona monsoon arrive early?
Although the season officially began on June 15, monsoon activity typically does not increase until early July. Phoenix has a 30% to 40% chance of showers and storms on June 29-30.
“This is very early,” said Michael Crimmins, a climatologist at the University of Arizona. “We don’t normally see precipitation this early in the season, so it will take people a little by surprise. It’s almost a month earlier than last year.”
The monsoon begins when a subtropical ridge moves north from Mexico during spring and early summer, bringing warm temperatures and humidity to the southwest. The series of high temperatures likely helped fuel storm development.
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“There really isn’t a heat dome in the Southwest,” Crimmins said. “Heat dome is a colloquial term used more broadly to talk about large, high-pressure systems that have high heat associated with them.”
A large high-pressure system responsible for heat waves in the eastern United States has moved southwest, bringing heat with it, and heat is one of the elements that normally triggers monsoon activity.
“We are definitely not under it, but under its influence,” he said.
To the west, there is a low pressure system over California that brought colder temperatures this week. Arizona falls between these two major climate features, contributing to increased heat and humidity. A former tropical cyclone, Alberto, produced its own plume of moisture from the southwest.
Storm chances vary across the state, but the Southeast is likely to see some activity that could reach the highlands and northeastern part of the state, according to Crimmins.
Arizona Republic reporter Raphael Romero Ruiz contributed to this article.
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