Hot summer, fall rains likely to usher in a wetter winter

We’re less than a month away from the official start of fall; the first day of the new season is Sept. 22. Up until this point, the summer of 2010 has been warm. July’s average temperature was 0.3 degrees above normal. As of early this week, the mean temperature for August was about 2 degrees above normal. We’ve only had eight days with readings at or above 90 degrees this summer. However, there were 10 days with highs in the upper 80s. Despite a forecast of cooler temperatures into next week, I still expect to see a few warm-to-hot days in September.

On average, September is the third-driest month of the year, with 0.78 inches of precipitation at Spokane International Airport. In Coeur d’Alene, the normal amount of rain is 1.58 inches. Last year, we were below normal with only 0.49 inches of precipitation in Spokane. September 2009 was 4.7 degrees warmer than normal thanks in part to El Niño, the warm sea-surface temperature in the south-central Pacific Ocean.

This year, El Nino has been replaced by the cooler-than-normal sea-surface temperature, La Niña. Although I expect to see occasional showers over the next three to four weeks, the fall rains should begin as usual in late September and early October, especially if La Niña continues to strengthen as predicted. Frosts and freezes will also be possible, even at the lower elevations, by early October. In elevations above 3,500 feet, we’ve already seen some frosty temperatures.

The normal precipitation for October at the airport is 1.06 inches. The normal for Coeur d’Alene is 1.93 inches. Moisture totals should be above normal levels this year, especially toward the middle and end of October.

Snow is not common in October, but elevations above 5,000 feet may see measurable snowfall. The most snow ever measured in October at Spokane and Coeur d’Alene happened on Oct. 22, 1957, when the airport reported 5.9 inches while Coeur d’Alene measured 6.8 inches. With the increased precipitation, temperatures this October chould be slightly cooler than normal. If all goes according to plan, many area ski resorts may be open in time for Thanksgiving.

As I’ve mentioned before, we had a strong La Niña and very little sunspot activity during the harsh winters of 2007-’08 and 2008-’09. Based on current patterns, I expect to see a lot more snow compared with the winter of 2009-’10. However, it doesn’t look like the pattern for the all-time record snows we had from late 2007 to early 2009.