Local heat wave fades — for now

By Ronald Bond — Argus Observer
Tuesday, August 7, 2007 9:58 AM PDT

Boise — A predicted cooling trend arrived in the Treasure Valley this week after a July that registered as the hottest ever in Boise.

The average daily temperature for the month climbed to a toasty 98.6 degrees, according to the National Weather Service in Boise.

Meanwhile, Ontario wrapped up the month just as hot, posting an average daily high of 99.4 degrees.

The “cooling trend” this week is expected to deliver temperatures dropping below the 90 degree mark but further relief from the heat does not appear to be in the near future.

“We are getting a bit of a change coming this weekend, which will bring us back to near normal,” National Weather Service meteorologist Tim Barker said last week. “I take it as a positive sign that after the hot July we had it will, for the weekend and early next week, go closer to normal.”

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Barker said the record heat is the result of high pressure hovering over the Western portion of the United States.

Typically, the pressure will linger before being replaced by lower pressure, which usually brings in thunderstorms and major decreases in the temperature.

This summer, however, the storms have been rare because the pressure system has been what Barker called “really persistent.” The result was just 0.02 inches of precipitation in Boise for July, and only a trace in Ontario.

“The weather patterns that bring heat suppresses the thunderstorms,” Barker said. “When it’s as hot as it has been, it makes it difficult to get the thunderstorms. Typically our hottest weather is tied to high pressure, which keeps the moisture away from us.

“I think everybody would prefer a pattern that is changeable. This year it’s just been locked into sort of one pattern. It’s not that unusual. Some years are like that. Weather just varies like that.”

As a result, several heat records — not just the average high — were broken in Boise in July.

According to the National Weather Service, the city also broke records for the warmest overall average (83.1 degrees), warmest average low (65.9), number of days with a high temperature of at least 90 degrees (30), number of days with a low of at least 70 (nine) and number of days with a low of at least 60 (31).

The temperature also climbed above 100 degrees 14 times in July, one day short of the record set in 2003, and twice topped out at 105 (July 6 and July 14).

While it is not yet determined what records Ontario set, its numbers mirror those recorded in Boise. According to the National Weather Service, the average for the month was 82.3 degrees and the average low 67.5. Like Boise, Ontario also posted 30 days of 90 degrees or more, with 17 of those days reaching at least 100. The city also hit 105 twice and maxed out at 106.

Barker said he is unsure if the heat of this summer will affect weather in the near future, but based on past history, he does not expect it to have a big impact.

“Thankfully it’s not really tied that a hot dry summer could lead to a dry winter,” he said. “It could, but there’s not a strong relation of that in the past. I’m sure we will have summers like this again, but we’ll have other summers that are more variable. (It) may be more likely that they could be hotter, but that’s even on shaky ground to say that. There’s a lot of factors involved.”