Record Rainfall at PDX

by Steve Pierce, Oregon AMS

Wednesday, September 8th 2010

“Record setting rain fell on the Portland International Airport yesterday evening (Tuesday, September 7th) breaking an all-time record that stood since records began in 1940. Total rainfall measured at PDX yesterday was 1.55″ which is a record for the day. However, what makes this an even more significant record event is the fact that 1.03″ of the 1.55″ fell in just 60 minutes last night between the hours of 8pm and 9pm, as heavy showers rolled through the metro area. The one hour total of 1.03” surpasses the previous all-time “one hour” record of 0.93″ set just two years earlier, in May of 2008. Records at the Portland International Airport go back to 1940. This is a significant amount of rainfall by Portland standards, especially for this length of time. Vancouver, WA. and Hillsboro, OR also set less significant daily rainfall records yesterday. Here are a few other notes on yesterday’s record setting rainfall —

* Only two calendar days during 2010 have measured more than 1.00″ of calendar day rainfall at the Portland Airport. Oddly enough, those days are June 6th and yesterday, September 7th.

* Yesterday’s rainfall was tied for the 7th wettest calendar day in the past decade, as listed below —

11/6/2006 2.53″
1/1/2009 2.49″
1/31/2003 2.05″
9/30/2005 1.68″
12/2/2007 1.65″
12/3/2007 1.58″
12/13/2003 1.55″
9/7/2010 1.55″

Post script —

In a strange twist, in June of 1985 Portland experienced a very similar heavy rainfall event on the exact same day as this year. Not only once, but twice! On June 6th 1985 PDX saw 1.36″ of rainfall. On June 6th 2010 PDX saw 1.48″ of rainfall. Both events were quite extreme for June. Now, if that does not seem a little odd, this next part will. Then about September 1st 1985 we saw an abrupt end to summer and another significant rainfall event occurred in the first week of September 1985, almost exactly like it has here in 2010. On the 10th of September 1985 PDX measured 1.18″ of rainfall. This year we measured 1.55″ on September 7th. The first two weeks of September 1985 were quite wet before drying out the second half of the month.

Since 1985 is showing up in some of the recent analogs to the current pattern (500mb, etc…) I thought I would also mention that 1985 was also the last time Portland saw a significant arctic outbreak in the month of November. The MEI is also currently analogous to 1955. Both 1955 and 1985 are the two standout years for early November arctic outbreaks in the Portland area over the past 60 yrs and are spaced about equally apart to 2010. With this La Nina at “full tilt” right now, and record setting MEI readings month after month recently, nothing would surprise me at this point.

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About George Taylor

Climatologist, husband, father (3), grandfather (2)
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