To illustrate:



If you look at the Olympic Peninsula, you can see that the east side gets far less rain than the west side.
The route of US 101 west side roughly follows the 120-inch line - that's a lot of rain.
(And that's why you have temperate rainforest in the region.)
The route of US 101 east side roughly follows the 60-inich line along Hood Canal.
(And in the rain shadow around Sequim its only 30 inches.)

Even in mid-summer you can get long wet stretches in the west.
These are broken up with warm sunny days - some years more so than others.
If you happen to ride during one of these sunny stretches it can be lovely.
But if you have three days of chilly drizzle, it can be nasty.



This past July had slightly below normal temps and normal precipitation.
Early July was yucky - followed by two weeks of nice weather - then two weeks of iffy weather.

Oh, and has anybody mentioned the Olympic Discovery Trail from Port Angeles to east of Sequim?
Paved, with a few stretches right on the water. Avoids the busiest stretch of US 101.

You can always play it by ear -
If the weather is nice, head west - - if questionable, head east.

BTW, three days is a stretch - would almost force you to do east side with no side trips.
(You did, after all, take 9 days to do the Oregon Coast and there is, apparently a "we" in this.)
If you want to do Hwy 105 and a side trip into Olympic NP you need to give yourself four days, minimum.

Although I disagree with Beko on US 101 route, I agree that there much to see on the Washington coast.
It just takes a little more effort since there is no coastal highway like in Oregon.
My pick for best "detour" - - Neah Bay and Shi Shi Beach - - fairly quiet on a weekday.