Originally Published: June 25, 2009 11:16 p.m.
Mother Nature is blowing away the old wives' tale that it has to get really hot and dry in Arizona for the monsoon weather pattern to kick in.
Despite the unusually cloudy weather over the past month and unusually cool June temperatures - several Northern Arizona natives told The Daily Courier they've never seen anything like it - the monsoon flow pattern has arrived.
"This is a monsoon pattern," said Darren McCollum, a meteorologist with the National Weather Service in Flagstaff. "This is the flow we look for when moisture moves into Arizona.
"It's a little early, but not unusual."
In general terms, the wind now is coming out of the south and a large-scale high-pressure system has shifted to the north. Next week it almost will reach the Four Corners, he said.
"As it stays to the north, we're going to continue to see a chance of thunderstorms," he said. "It doesn't look like it's going to go away for any significant time."
Officially, starting this past year, the National Weather Service says the North American monsoon occurs between June 15 and Sept. 30. Actual monsoon storms tend to start hitting the Prescott region around the Fourth of July.
Monsoon weather patterns started arriving in southern Arizona late Monday. Typically, that weather shift begins some time between June 20 and July 1 in North America as the Earth heats up from the long days, McCollum said.
Steady, light rain was falling in Prescott at press time on Thursday.
By late Thursday afternoon, the Weather Service was calling for a 40-percent chance of rain today, then a 20-percent chance Saturday and Sunday.
A high-pressure center over Texas and a low-pressure center off the San Francisco coast are pushing moisture up here from the south.
The chance for moisture here should drop early next week and then pick up again toward the end of the week.
Heavy rains hit southeastern Arizona Thursday, producing at least one flood advisory.
The Weather Service has been tracking the recent unusually cool and wet weather in larger Arizona cities that have detailed weather records.
Flagstaff set a record for cold weather earlier this month when its temperatures stayed below 70 degrees every day between June 5 and June 16. The 12-day stretch shattered the previous June record of eight days in 1932 and 1951. The records go back to 1898.
"The unseasonably cool weather was the result of southwesterly flow from the East Pacific driven by a persistent West Coast trough of low pressure," the Weather Service record notice stated.
Prescott ended up with 0.93 inches of rain in May at the Sundog measuring site on the northeast side of town, which is 198 percent of the 111-year May average of 0.47 inches. Despite the frequent cloud cover, it also was unusually warm.
June precipitation totals for Prescott hit only 0.06 inches by Wednesday, compared to the 111-year average of 0.39 inches.
Tucson didn't experience any triple-digit temperatures between June 5 and June 21. That 17-day stretch below 100 degrees in June was the city's fourth-longest streak in June.
An El Niño pattern now setting up in the Pacific could bring a wet winter if it's strong enough, McCollum said.
It is unusual for El Niño to start setting up this early in the year, according to the National Weather Service office in Tucson. It could affect the monsoon patterns toward the second half of the season.