After chilly week, it really is autumn

It didn’t take a change of season early today to tell people in the Inland Northwest that autumn has arrived.

Lows in the mid-30s in Spokane and Coeur d’Alene and freezing temperatures in outlying areas last week were proof enough that summer is gone.

Davenport reported a record low of 26 degrees before dawn on Friday. Deer Park dropped to 27. Both Spokane and Coeur d’Alene had lows of 36.

Autumn officially began this morning at 2:51 a.m. as the sun crossed the equator for the autumnal equinox.

Summer weather disappeared a week ago when a cold front last Sunday triggered a weeklong decline in temperatures. The first snow of the season was reported on at least two high mountain locations on Thursday.

Ron Miller, science operations officer for the National Weather Service in Spokane, said there is little likelihood of more 90-degree days this year. “We’re done,” he said. “The 80s might be tough to get back to, too.”

The Climate Prediction Center is calling for higher-than-normal precipitation and normal temperatures in October, November and December because of a La Niña cooling of Pacific Ocean waters. La Niña, the opposite of the El Niño warming in the tropical Pacific, can bring increased storminess and higher mountain snowfall.

Two of the past three La Niña episodes in 1998-99 and 1999-2000 brought normal to above-normal precipitation, Miller said, and a weaker La Niña in 2000-01 brought dry, cool weather.

The dramatic drop in temperatures last week came after the region had one of its hottest Julys on record. Spokane saw its second-warmest July with highs of 101 on July 5 and 13. The high on July 5 was a record for the date in Spokane.

But one hot month does not necessarily make for a hot summer.

June and August were both relatively normal, and the first three weeks of September were also close to normal.

At the end of the period, summer 2007 was about 2 degrees higher than normal.

One measure of summer heat is seen in the number of days in which the temperature hit 90 degrees or higher. Over the past 60 years, Spokane has averaged 18 such days each year. In 2007, there were 22 days of 90 degrees or more.

Climate experts have said that a single hot spell is not proof of global warming. However, the overall average temperature in the Spokane and Coeur d’Alene region has increased about 2 degrees in the past 60 years, a better indication that the climate is warming, they said. Even larger increases in average temperatures are being seen elsewhere in the Pacific Northwest.

Also noticeable in recent months was a shortage of rain. Since June 1, Spokane received 1.6 inches of rain compared with a normal of about 3 inches. April and May were also dry.

Persistent high pressure throughout the summer was the reason for both the heat and lack of rainfall.

Miller said the warm, dry conditions parched the land, making it vulnerable to fire. However, because of fewer lightning storms or windy Pacific cold fronts, the fires that occurred were generally less intense and easier to bring under control, he said.

Another result of the warm dry summer can be seen in low river flows. The U.S. Geological Survey on Friday reported that the Spokane River was flowing at 1,120 cubic feet of water per second, well below the average 1,800 cfs for this time of year during 116 years of record keeping.