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Today is the hottest day of the year for Portland, on average

United States
The Oregonian
09/08/2010

Everyone knows June 21 -- summer solstice -- is the longest day of the year.

But what's the hottest?

If you live in the Portland area, it's today. The average high on Aug. 9 is 84 degrees, from 60 years of data (1949-2009) recorded at PDX. That means there's roughly a 50-50 chance it will get hotter than 84 today.

How else do we measure hottest? Well, the hottest days ever -- 107 degrees -- occurred Aug. 8 and 10, 1981 and July 30, 1965.

Aug. 8, a kind of Babe Ruth of hot days, was the hottest in 1960, 1963 and 1978. Aug. 4 ties with three hot titles in 1949, 1993 and 2005. And inly two years between 1950-1959 reached 100 degrees; seven of the years between 2000-2009 had a high of more than 100.

The median or middle date of the hottest day of the year is July 30. The hottest day so far this year is July 8th at 97 degrees, though there's a roughly fifty-fifty chance that we'll beat that this year.

However you measure, late July and early August produce the hottest days. A hot day is only partially the sun -- mostly, it's the temperature of the ground underneath us, which heats the air around us. The ground takes time to heat up, and usually reaches maximum temperatures about a month and a half - an eighth of a year - after the sun is most intense, on the summer solstice.

According to Kelly Redmond of the Western Regional Climate Center, this one-eighth delay also occurs daily -- three hours is about an eighth of a day, and three o'clock is usually the hottest time of day -- and can be explained mathematically.

But it's no guarantee that today -- or tomorrow -- will be particularly hot.

Just ask Jensi Albright, who helps organize Good Sport Promotion's Hottest Day of the Year bike ride. The ride, cancelled this year due to lack of interest, is plagued with chilly weather. "It often has rained, or just been cloudy or grim," she says.

"It's just the contrary nature of Oregon weather."

This combination of short-term variability and long-term predictability -- the definition of randomness -- results from the regular movement of the Earth around the sun, yanking on the chains of water, soil and air as they play on the Pacific coast.

The solstice drags the hottest day of the year around the calendar behind it, but precipitation and proximity to the ocean also play a large role. Water heats more slowly than soil, rock, and concrete, so the coast experiences its highest temperatures later in summer.

Then, too, "your warmest day is gonna be a sunny day, almost always," says Redmond. "The average temperatures along the coast are declining by mid- to late-August, but at the same time, the highest temperature of the year often occurs in September." Those late highs never get quite as high as the early ones.

This is true in Tillamook, where Sept. 13 has the highest high -- 71 degrees, on average. And it partly explains why the hottest temperature ever recorded in Oregon -- 119 degrees -- was recorded in Pendleton, on Aug. 10, 1898.

Even taking this into account, the coast and inland geography keep weather unpredictable in the Northwest. The Pacific "is the largest weather-making machine on the planet," says KATU weatherman Dave Salesky, spinning storms in our direction in fall, spring and winter. Mountains, beaches and the gorge bounce those storms around, like a giant weather pinball machine.

Salesky says this year's coolest-ever June -- which slowed the soil's warming -- makes the chance of a record-breaking hottest day slim.

But don't give up hope altogether. In the six unpredictable weeks of Northwest summer still left, anything could happen.

 

The news content in this section is responsibility of the information agencies and does not necessarily reflect the position of the Government of Mexico on this or other related topics.

El contenido de las noticias que se presentan en esta sección es responsabilidad directa de las agencias emisoras de noticias y no necesariamente reflejan la posición del Gobierno de México en este u otros temas relacionados.

    

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