Monsoon in Arizona officially started June 15. But the heavy rains, high winds and harrowing haboobs are AWOL. That’s not unusual. Significant monsoon activity typically doesn’t ramp up until July, and August is historically the wettest month.
What about this insane heat wave? Shouldn’t it trigger some storms? Thing is, heat is only half the equation. And you’ve heard this before: It’s a dry heat.
“Moisture is the key,” said meteorologist Andrew Deemer. “You can’t have storms without it.”
Waiting to Get Wet
Arizona is on the northern fringe of the North American Monsoon, which typically dumps more than 50 inches of rain in Acapulco. That moisture must move north to trigger storms here, explained Deemer, who works at the National Weather Service office in Phoenix. Last year, heavy thunderstorms didn’t really kick in until late July.
“We haven’t seen the moisture move into our area, especially for the lower desert areas,” Deemer told North Phoenix News. “We are starting to see some moisture move into the higher terrain and even into southeast Arizona,” he said, explaining scattered thunderstorms that have peppered the mountains in recent days. When storms do develop during the current conditions, they tend to die quickly, with any rain evaporating before it hits the ground, he said.
It’s not possible to predict when the moisture will move in.
“A good rule of thumb is that storms for desert locations pick up in frequency after the 4th of July,” Deemer said.
Arbitrary Start Date
Interestingly, the June 15 start date is somewhat arbitrary, set by the weather service in 2008. Before then, the start was declared only after three consecutive days with the dew point at 55 degrees or higher. That created confusion, especially in communicating risks to the public, as start dates ranged over the years from June 17 to July 25.
When the rains do come, there’s a good chance North Phoenix will get its share.
“As for Anthem and the general North Valley, those locations typically sees more rain than downtown Phoenix and other Valley locations due to the higher terrain, Deemer said. “Storms typically form over the higher terrain, so the closer you are to the mountains the more likely you are to experience storms.”
When will the sky cut loose this year?
“Unfortunately, there is no tell-tale signature that indicates when storms will arrive,” Deemer said. If there were, he added, “that’d make my job a lot easier.”