Steve Quayle News Alerts

July 31, 2003
Shaun McKinnon
The Arizona Republic

The thunderstorm that raked the Valley on Tuesday night broke a 104-day dry spell and slapped a steamy exclamation point on July, which is set to end today as the hottest month ever at Sky Harbor International Airport.

That's no misprint: the hottest month ever, or at least the hottest in a century of record-keeping. The average temperature through the first 30 days of July was 98.2 degrees, which eclipsed the old mark, set in July 1989, of 97.4 degrees.

Without the storm, this July would have ended as one of the driest ever, as well. The 0.61 of an inch that fell at the airport Tuesday still leaves the month below normal but kept it from becoming the third July on record with no measurable precipitation. The airport had been dry, in fact, since April 15.

Rainfall totals Tuesday night ranged from 0.04 of an inch at Cave Creek and 0.08 of an inch at Queen Creek to 0.71 of an inch at Avondale and 0.75 of an inch at Papago Park in Phoenix. Wind speeds hit 47 mph during the storm's peak, with gusts of 56 mph.

Damage was spotty and included several lightning-caused fires and a series of traffic accidents. No injuries were reported, although authorities said they received numerous emergency calls. More than 31,000 homes and businesses lost power at the peak of the storm, but utility officials said nearly every customer was back on line by late Wednesday.

The power outages, which hit both Arizona Public Service and Salt River Project, affected the Phoenix police call room briefly but did not hamper service, police Sgt. Randy Force said.

"It complicated things in what is already a very busy work setting," Force said. "It was a very busy work night, but we had no major incidents or loss of life, so I think the city rode it out pretty well."

The Phoenix Fire Department responded to more than 300 calls over about two hours, about the same number the department normally answers in a 24-hour period, Assistant Fire Chief Bob Khan said.

Most calls were for lightning strikes, tree fires, fallen power lines and minor car collisions.

"It was hard-hitting and fast-moving, and came with a bang," Khan said. "But once it was all over, we had it pretty well packaged up by 11.

In Scottsdale, downed power lines forced the closure of Hayden Road from Chaparral to Jackrabbit roads for about six hours. Rain damaged part of a townhouse complex in the area, buckling a flat roof and flooding several units.

Rest of July was dry

The storm capped an otherwise hot, dry July, normally one of the Valley's wetter months. The monsoon arrived late but brought only muggy afternoons and hazy skies.

Although daytime temperatures climbed as high as 117 degrees (on July 16, a daily record), the fire in July's furnace was fueled by a stretch of miserably hot nights. The record for the hottest night ever, 93 degrees, was tied July 14 and then shattered a day later, when the mercury dropped no lower than 96. The average low for the month was 86.7 degrees, breaking the record of 85 set in 1989.

Demand for power up

Still other records fell as a result. On July 9, demand for electricity from APS reached 6,089 megawatts, breaking a record on the same day a year earlier. Five days later, as the hot spell intensified, the utility reported another record demand, delivering 6,420 megawatts.

SRP eclipsed its old record on July 12, delivering 5,335 megawatts of power. That record fell the next day, when demand hit 5,446 megawatts and yet again July 14, when demand reached 5,673 megawatts.

"The heat definitely showed up on power usage," SRP spokesman Scott Harrelsen said. "Folks got home from work and turned on their air-conditioners."

Urban heat island effect

Meteorologists attributed part of the record heat to a stubborn high-pressure system that camped out over the Four Corners for days on end, trapping hot air and deflecting storms. But the unusually hot nights appear to be further evidence of how the Valley's growth is affecting its climate, said Andrew Ellis, an Arizona State University climatologist.

Atmospheric conditions - the high pressure system, the lack of moisture in the air - can push temperatures up during the day, but the desert typically cools off at night, Ellis said. The fact that the nights remain so hot "suggests our influence might be at the heart of it all; it's because of the urban heat island, without a doubt."

Urban heat islands grow from the ground up and are not connected to the more controversial theories of global warming. In an urban heat island, concrete and asphalt absorb the heat during the day and then hold onto it after the sun goes down, releasing it slowly through the night. It's like a separate source of heat.

Add to that a high-pressure system, the stagnant air, the missing monsoon and, "you've got the hottest July on record," Ellis said. "It's been very warm and dry, kind of a double whammy. And when you're in the middle of a drought, that's not what you need."

A low of 100?

So might there come a day when the overnight "low" will fail to dip below 100 degrees?

"That's a number people talk about a lot," Ellis said. No one will venture a guess about when it might happen, but if the Valley continues to grow outward, "it's realistic."

http://www.azcentral.com/arizonarepublic/news/articles/0731hotjuly31.html