Governor Ducey declares Monsoon Awareness Week
Monday marked the start of Arizona monsoon, according to the National Weather Service. Starting in 2008, the NWS designated the official season from June 15 to Sept. 30.
Meteorologists consider monsoon conditions to start after three or more days of dew points of at least 55 degrees Fahrenheit. Prescott hasn't quite hit that standard, based on weather data collected at the Prescott Airport.
The typical timeframe for the start of monsoon is from about June 20 to July 10, Darren McCollum, meteorologist at the NWS station in Bellemont, said.
Gov. Doug Ducey declared the week of June 14-19 as Arizona Monsoon Awareness Week, and the National Weather Service and emergency preparedness organizations are using the week to remind Arizona residents and visitors of the hazards associated with monsoons.
The word "monsoon" comes from the Arabic word "mausim," meaning "season" or "wind-shift," describing the change in conditions that bring frequent thunderstorms during the hottest part of the summer in the Southwest.
"The flora and fauna of Arizona - most of it wouldn't exist without the monsoon," McCollum said. "A lot of things would die in the desert if it didn't rain as much as it did."
According to the Arizona State University School of Geographical Sciences & Urban Planning, winter weather patterns generally come to Arizona from the west, generally from Nevada and California.
"When we get into the monsoon season ... that westerly flow shifts northward," McCollum said. "It's all related to the shift of the high (pressure)."
He explained the high pressure that normally sits over Mexico moved north and sits over Arizona and New Mexico and tropical moisture follows from the Pacific Ocean west of Mexico.
The dramatic change in weather patterns often brings daily thunderstorms driven by the extreme surface heat. McCollum said the typical pattern is for thunderstorms to start in mountainous areas, moving to lower elevations later in the day.
The Southwest monsoon is typified by breaks and bursts - a pattern of a few days with thunderstorms, then a couple of clear days before the storms return.
"A lot of us longtime Arizona residents look forward to it," McCollum said. "There's a certain excitement to the way it rapidly comes in."
But the rapid changes in weather bring with them a range of localized phenomena, like lightning, flash floods, 70-100 mph downbursts and, mostly in the southwest part of Arizona, dust storms.
McCollum said lightning and flash floods are among the chief safety concerns. After extreme heat, those two weather events claim the most lives in Arizona.
Emergency preparedness officials remind residents and visitors in Arizona to pay attention to weather forecasts and conditions around and overhead.
"One of our ongoing concerns for Yavapai County is driving in flood waters," Yavapai County Sheriff's Office spokesman Dwight D'Evelyn said. "We have seen lots of folks who are determined to reach their destination take a chance and drive through high water crossings and end up requiring rescue."
He said 6 inches of water will reach the bottom of most passenger cars, causing a loss of control and possible stalling. A foot of water will float many vehicles and 2 feet of rushing water can carry away most vehicles including sport utility vehicles (SUV's) and pickups.
The Sheriff's Office advised against crossing flooded roads as the depth of water is not always obvious, and the road bed may be washed out under the water, leaving drivers and passengers stranded or trapped.
D'Evelyn reminded drivers not to drive around a barricades.
"Barricades are there for your protection," he said. "Turn around, and go the other way."
He added that shortcuts may be clocked, and drivers should stick to designated evacuation routes.
"Be especially cautious driving at night when it is harder to recognize flood dangers," D'Evelyn said.
He also urged people to keep away from river banks to avoid slipping into rushing water.
"These are not play areas during high water incidents," he said.
Weather and emergency preparedness experts offer several tips for what to do during a storm (see related story). And it's important to be prepared before the storm arrives.
According to NWS preparedness information, a safety kit should contain a flashlight and extra batteries, battery-powered weather radio receiver and commercial radio, extra food and water (3 gallons per person), first-aid supplies, canned food and a can opener, extra clothing, bedding, an extra set of car keys, and a credit card or cash. Depending on a family's needs, other items to consider are diapers, baby formula, prescription or essential medications, extra eyeglasses or hearing aids, and pet supplies.
In addition, every member of a family should know what to do when a storm hits and where to meet after a disaster.