If we define “summer” as June through August, the summer of 2010 was a cool one. Locally, we were 0.6 degrees cooler than normal for the three months. July was slightly warmer than normal, but August was a little cooler and June was very cool (by nearly 2 degrees).
Portland was even cooler. My friend Steve Pierce is Vice President of the Oregon Chapter of the American Meteorological Society, and really pays attention to Portland area weather. This week he wrote:
“Portland just finished its last full month of summer 2010, and with it comes the distinction of being the coldest “meteorological” summer (June, July & August) in the past 17 years. The last time Portland experienced a summer this chilly was in 1993. This was the exact opposite of last summer, which was the warmest summer on record at the Portland International Airport (1941-2010). This was also the first summer since summer of 1976 (nearly 35 yrs) that all three summer months (June, July and August) recorded back-to-back below normal average monthly temperatures. In fact, Portland has now been below average for five back-to-back months, beginning in April and continuing through August.”
I am definitely NOT ready for summer to end, but it is, and it will. So let’s turn our focus to fall and winter.
Last winter’s El Niño event, which can be blamed for the dry winter and wet spring, has faded and been replaced by a strengthening La Niña. According to the Australian Bureau of Meteorology, “A La Niña event is now well established in the Pacific Ocean. All computer models surveyed by the Bureau suggest Pacific Ocean sea surface temperatures (SSTs) will continue to exceed La Niña thresholds through the southern hemisphere spring, with the majority indicating the event will persist into at least early 2011.”
La Niña winters tend to arrive late, be very stormy in mid-winter, be associated with deep snowpacks, and give us increased chances of flooding. They also tend to be colder than average. In fact, our wettest and coolest winters in Oregon tend to occur during La Niña winters.
We also watch a long-term phenomenon called the Pacific Decadal Oscillation. This, I believe, is responsible for roughly 50-year “cycles” in weather in the Northwest (and elsewhere). We are in a long-term “negative” cycle and entering short-term negative values – which means that the typical La Niña characteristics above tend to be enhanced. With that in mind, here’s my forecast for the upcoming 8 months:
September- gradually cooling, but over all a relatively mild and dry month compared to average Septembers. A nice “late summer” month.
October- mild and relatively dry weather continues for most of the month. I expect beautiful fall weather for the most part.
November-February- A wet, windy, possibly wild winter. Lots of storms. Lots of rain. Lots of mountain snows. Possible Arctic outbreak. Possible low-elevation snow.
March-April- drier and milder than this year’s spring, which was among the “wettest-coolest” we’ve seen. Not necessarily warmer and drier than normal, but much more so than this year.
By the way, several of the Portland weather guys are predicting a big low-elevation snowfall year. I’m not brave enough to predict that, but I hope they’re right. I LOVE the snow!!