In fact, a plot of the dew points at Seattle Tacoma Airport reveals that the dew point Thursday night were the highest for the entire summer! The air has a bit of that "East Coast" feel to it.
Why high dew points and thus serious sweating? You start with light rain, which evaporates into the relatively warm air...this pushes up the dew point. The fact the surface is now relatively moist helps of course. Onshore flow, strangely enough, is relatively dry (low dew point) because the Pacific Ocean is cold (around 50F) and cooler air can't hold as much water vapor as warm air. So the weak onshore winds (produced by the absence of he Pacific High) allows the dew points to rise in the interior.
The moist, wet conditions we have experienced have produced a lot of low clouds, and the combination of the clouds and the high humidity does not allow the surface to cool effectively (water vapor and clouds absorb and reradiate back down the infrared radiation from the surface). Thus, the minimum temperatures during the last few days have been high. Check out a plot of the Sea Tac temps:
RECORD EVENT REPORT NATIONAL WEATHER SERVICE PORTLAND OREGON 451 AM PDT FRI AUG 16 2013 ...RECORD HIGHEST LOW TEMPERATURE SET AT VANCOUVER WA... A RECORD HIGHEST LOW TEMPERATURE OF 67 DEGREES WAS SET AT VANCOUVER WA YESTERDAY...AUGUST 15TH 2013. THIS BREAKS THE OLD RECORD OF 65 SET IN 1950. ...RECORD HIGHEST LOW TEMPERATURE SET AT SALEM OR... A RECORD HIGHEST LOW TEMPERATURE OF 65 DEGREES WAS SET AT SALEM OR YESTERDAY...AUGUST 15TH 2013. THIS BREAKS THE OLD RECORD OF 64 SET IN 2008.Remember the stories about increasing summer heat waves that were in the press last month? This is going to be another example--but I don't think anyone is going to the hospital from it.
Anyway, our perfect weather will return this weekend, but today's humidity is a reminder of why we are lucky to be living here, rather the humid summer miasma of the eastern U.S.!