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Autumn 2012 weather rolls from one extreme to the other

PROSSER, Wash. – Autumn is a time of transition, and never was that fact more on display than this year. The season may include three months, but Washington’s 2012 autumn weather came in only two parts. During September and early October, conditions were dry and summer-like. Wildfires raged, smoke filled the air and skies were cloud-free nearly every day. However, everything changed on Oct. 12. From mid-October onward, wet and stormy conditions dominated the weather. Significant rain fell in western Washington, while periods of rain impacted central and eastern Washington as well.

“We changed from the dry season to the wet season in one day. It was as if Mother Nature flipped a switch and turned on the fire hose,” said Washington State University AgWeatherNet meteorologist Nic Loyd.

A Web based, publicly available system, AgWeatherNet provides access to near real-time weather data and value-added products from WSU’s statewide weather network, along with decision aids for agricultural producers and other users.

“Long Beach recorded rain on just four of the first 41 days of the autumn season,” Loyd said. “Remarkably, however, there were only six dry days in the final 50 days of fall.” The longest dry streak at Long Beach since Oct. 12 lasted only two days. While drought and fires were the issues early in the fall, flooding and landslides were the biggest concerns late in the season.

Dry lightning in early September led to numerous wildfire starts along the east slopes of the Cascades. Stagnant conditions led to a deep, widespread smoke layer aloft that covered eastern Washington mid to late September. Smoke was also an issue at the surface, especially in the Wenatchee area. For several days during the third week of the month, surface solar radiation was limited to 40 percent of its potential, despite an absence of clouds.

The only other notable weather event during September was a cold storm that passed through the state on the 10th. In early October, a shot of cool, dry air from the north led to cold morning temperatures. Pullman dropped to 18 degrees on the morning of the 5th.

Wet weather and warm overnight temperatures returned during the middle of October. However, several chilly days occurred later in the month. Oct. 22 was the coldest day to that point since March in eastern Washington, and the mountains received their first notable snowfall of the season.

“The apple harvest was completed in November, while Christmas tree farms were preparing for their busy season,” said AgWeatherNet director Gerrit Hoogenboom. “However, the weather continued to affect Washington agriculture. The persistent wet weather has been beneficial for winter wheat producers, although many pastures and fields in western Washington were flooded by heavy rain.”

Nov. 18 was a particularly wet day, as 2.3 inches of rain fell at Tokeland.

Overall, November temperatures were well above average, especially at night. Moxee’s November average low temperature was 5.5 degrees above average and the second warmest since at least 1989. Aside from two cool periods around Nov. 10-11 and 26-28, most of the month featured above average temperatures.

In fact, the chilly period late in the month in central Washington was a consequence of a strong inversion and low clouds – not of a cold air mass. Still, low-lying areas in the Columbia Basin experienced highs of only around 30 degrees. On Nov. 10, the low temperature dropped to 18 degrees at Almira.

Warmer weather quickly returned to the region. On Nov. 19, the high temperature was a balmy 68 degrees at Wallula. Overall, autumn temperatures were 1.1 degrees above average at the WSU Research and Extension Center in Prosser. It was the warmest autumn since 1998.

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