Oregon Chapter
American Meteorological Society

Wettest September In Nearly 25 Years

Portland, Oregon (October 1st 2010) - "September 2010 will go down in the books as another record setting month for Portland. In fact, records have been falling all across the Pacific Northwest this past month. September was the 7th wettest September on record at the Portland International Airport, picking up 3.36" of precipitation which is a full 211% of normal for the month. Records date back to 1940 at the airport. Last month's rainfall in Portland is the highest recorded for the month of September since 1986 (24 yrs ago) when Portland was drenched with 4.30" of precipitation. September 1986 still stands as all-time wettest September on record at the Portland Airport. More over, heavy rainfall on the evening of September 7th (1.03" in less than 60 minutes), washed away the Portland Airport's all-time single hour rainfall record of 0.93" set in May of 2008. Rainfall was not the only record falling in Portland last month. Did it feel abnormally muggy? It was! September 27th recorded the second highest dewpoint temperature (67 degrees) in the past 15 years in Portland, during the month of September. The kinds of dewpoint temperatures we were seeing for several days this past month were pretty rare for this late in the year. This is something more reminiscent of mid-July, not late September. Portland also set several records for warmest overnight lows during the past month with one of those being just one degree shy of the all-time warmest overnight low at the Airport for the month of September."

Water Year 2010 Comes To A Close Above Normal
"With the passing of the final day of September comes the end to the "water year" which runs from October 1st to September 30th. Ending last night, 39.24" of precipitation fell at the Portland International Airport during the 2010 water year. This water year's total is a little more than 2" above normal. In comparison, last year's water year saw a deficit of nearly 7" when it was all said and done. This year was one of just a few "above normal" water years in the past decade in Portland. The vast majority of water years over the past 10 years have been below normal at the Portland International Airport. What makes this year a bit unique is that Portland picked up so much rainfall this spring (May and June) and again in September. Had it not been for those three very wet months, we would have ended up below normal yet again this year."

"Another more obscure record was also broken. The transition from last year's El Nino to this year's La Nina registered the single fastest drop of the MEI (Multivariate ENSO Index) on record. The atmosphere went from one extreme to the other in record time. With a deepening La Nina, more records are likely to fall as we head into the fall and winter months."

Steve Pierce
Vice President, Oregon Chapter of the American Meteorological Society (AMS)
503-504-2075 (Portland)
e-mail: stevejpierce@comcast.net  
web site: http://www.ametsoc.org/chapters/oregon/