Valley could see first 90-degree day next week - East Valley Tribune: News

Valley could see first 90-degree day next week

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Posted: Wednesday, March 11, 2009 3:09 pm | Updated: 12:53 am, Sat Oct 8, 2011.

Feel as if it's getting too hot too soon? Blame the Valley's growth.

On the heat-shimmering horizon may be the first 90-degree day of the year. A warm-up across the West is expected to start early next week, according to the National Weather Service. By Tuesday, highs could reach the upper 80s if not beyond.

"It's certainly within the realm of possibilities there could be temps around 90 in the Phoenix metro (area)," said Tony Haffer, the meteorologist in charge of the local Weather Service office.

If that mark were reached next week, it would be far earlier than the climatological norm for Phoenix. Based on the long-term data compiled by the Weather Service, the first 90-degree day occurs, on average, by April 4.

However, that date has been slowly moving up in the year, and climate experts said that most likely is due to the Valley's increasing urbanization. Based on the past 25 years, the typical date is around April 1. And before 2008's 90-degree debut on April 13, the average during the previous decade was March 29.

Arizona State University climatologist Randy Cerveny said all those square miles of buildings and roads collects the heat from the sun's rays during the day. At night, the "urban heat island" is slower to cool down than desert land.

Minimum temperatures are most changed by the heat island. Overnight lows in the Valley during the summer have been creeping upward in recent years.

Cerveny said the island also affects, to a lesser degree, temperatures during the day.

Although growth in the Valley has slowed due to the collapsed housing market, what was constructed during the boom will be felt for years to come.

"Even if you don't have people, if the houses are foreclosed, you still have the heat island," Cerveny said.

However, Cerveny added, once a city gets to be built up, the effects of the heat island in the metropolitan area's center eventually level off. It's on the outskirts where the effects are most dramatic when compared to just a few years before.

Before the heat arrives late in the weekend, highs will hover in the mid-70s, typical for this time of year.

Thursday's high topped out at 77 degrees.

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