Warm September caps above-average summer

Few will argue that September was one of the most beautiful and pleasant late summer and early fall periods we’ve ever seen. As of Tuesday, prior to the big cool-down, the average temperature for last month was over 5 degrees above normal. It was also drier than average with only a half-inch of moisture at Spokane International Airport.

Since May, mean temperatures in our region have been above normal levels. It was 1.3 degrees warmer in May, 1.6 degrees warmer in June, 3.5 degrees warmer in July and 1.7 degrees higher in August. There were 27 days with readings at or above 90 degrees during the summer. The hottest day was Aug. 1 with a scorching 101-degree temperature.

A warmer-than-normal sea-surface temperature event in the south-central Pacific Ocean, El Niño, may be at least partially responsible for the warmer weather in the Inland Northwest. As this phenomenon continues to strengthen, the subtropical jet stream also becomes stronger.

As mentioned last week, we’re beginning to see the effects of the new El Niño as the prolonged epic drought in the southeastern U.S. was suddenly broken with up to 20 inches of rain in parts of Georgia. Arkansas received more than a foot of precipitation in just 10 days. Many rivers and streams went over their banks, and croplands have becomes lakes.

Long-term droughts in central and Southern California have severely reduced vital supplies of irrigation water to farmers. Water supplies have also been strained by the record number of forest and brush fires. However, if El Niño doesn’t weaken in the next few months, the strengthening subtropical jet stream should bring heavier rainfall and possible mudslides to California and the desert Southwest as early as late October through early 2010.

While our region enjoyed a warm September, rare sleet and snowstorms last week hit parts of the mountains in Arizona, New Mexico, Utah and Colorado.

In the near-term, the high pressure system that brought us the great weather is breaking down. Showers will be increasing over the next few weeks as we’ve seen the last of the 90- and 80-degree temperatures until next year. However, we’ll still see some nice days in between the showers. The third week of October looks wet. It should be dry and cool for Halloween before more showers return in early November along with hard freezes.

Thanks to the new El Niño, our upcoming winter is expected to be drier and milder. It’s doubtful we’ll see snowfall totals anywhere near the record levels of the last two years. I’ll have a detailed snowfall forecast next week.