Are Pacific Northwest Summers Becoming More Humid?

A number of people have told me that Pacific Northwest's summers are getting more humid.    Is this true?

Let's examine this issue by looking at trends of dew point, which is probably the best measure of stickiness and unpleasantly moist conditions.  Dew point, the temperature at which the air becomes saturated when it is cooled, is a good measure of the amount of water vapor in the air.  If there is more moisture, you don't have to cool as much to get saturation.  Thus, high dew points mean more water vapor in the atmosphere. When dew point gets into the 60s F, we start to feel uncomfortable. 70s is unpleasant.  80s are oppressive.

I will begin by showing you the daily dew points over the past 20 years at Seattle Tacoma Airport.   You don't need to be a meteorologist to see there is no apparent trend, either up or down.   You will also notice that Seattle dew points rarely rise to the mid-60s, reflecting our very pleasant climate.

A longer period plot  (35 years) for summer dew point at Seattle is shown below.  Again no trend.

What about Yakima, along the eastern slopes of the Cascades during the past two decades?  As shown below, there is no temporal trend there either.

Next, let's consider summer precipitation, could that be increasing?  More humidity might be expected to enhance rainfall.  Here is plot of Washington State precipitation over the last century--no apparent trend is obvious.  During the past 30 years, there has been a drying trend, if anything.

The bottom line of the above information is that there is really no evidence that Pacific Northwest summers have been getting more humid.