“We’ve had a few thunderstorms in the area … kind of a
warm-up or a pre-game show, you might call it,” said David
Vondereide, meteorological technician for NWS in Flagstaff. “The
ground gets wetted down once you get into the (monsoon) season,
but the early part of the season, the air is still dry – like
what we’re seeing now. If you get lightning, it can start a fire
and fan it with the winds, with little to no rain reaching the
ground.”
Of the 23 wildfires currently burning throughout Arizona, 11
have been deemed caused by lightning, including the Hilltop Fire
burning almost 9,000 acres since it started June 25 on the San
Carlos Apache Reservation. Its current northeasterly course has
caused fire commanders to issue pre-evacuation notices for the
communities of Canyon Day and Cedar Creek on the Fort Apache
Indian Reservation.
Monsoon is a term borrowed from the Asian monsoon which means
“wind reversal.” In places such as India and Southeast Asia,
winds blow into those regions from the Pacific and Indian
oceans, causing what’s known as the “rainy season” between May
and September. Between October and April, the wind “reverses,”
flowing out from land across the oceans, hence the dry season.
In Arizona, Vondereide said the Southwestern monsoons do a
similar thing, only on a much smaller scale.
“The deserts heat up during June and a big high-pressure area
hovers over us, which is what we’re seeing right now,” he said.
“This year, it’s been unusually strong, which has made it
unusually hot. That does set things up. Probably sometime in
early July, we’ll start seeing some of that moisture coming up
out of Mexico and various sources.”
For the White Mountains, Vondereide said it’s not unusual
for moisture to flow from the Gulf of Mexico. Once dew
points begin rising, he said the area will start seeing a
change in the weather patterns.
A dew point is the atmospheric temperature — varying
according to pressure and humidity — below which water
droplets begin to condense and forms dew. Vondereide said
once the air becomes a little bit more moist, the “sun works
on it,” which in turn begins to form more coverage from
thunderstorms.
“Often you will see thunderstorms start initiating in the
high terrain, and because the chilled, cool air that flows
out from the thunderstorms will begin kicking off more
thunderstorms,” he said. “What that does is just keep
moistening the air, like a feedback thing.”
Once the monsoon starts, (lightning), Vondereide said, is
typically accompanied by showers and thunderstorms.
“Once the monsoons start, you’ll know because it an
almost daily occurrence,” he said.
