I was in Portand one year in early June and Washington Park International Rose Garden was in full bloom.
Their annual Rose Festival was in progress at the time.
The 103rd Annual Portland Rose Festival will be held then with the Grand Floral Parade on Saturday, June 12, 2010 at 10:00 AM at the Memorial Coliseum to Downtown. There's also a large Rose Garden in Seattle
heck out the link below for more info.

Here is a link that might be useful: Portland Rose Festival.

Least chance of rain and maximum bloom in most gardens will be the end of June to the end of July. The roses really start showing up at the end of May but most hybrid teas do not even start their peak bloom until mid June. As you travel through the area you can see a great many roses in the warmer areas away from the ocean earlier. Portland OR. has its peak bloom a little before the Seattle WA. area because it is warmer there earlier in spring.

If you go east of Portland or Seattle the temperature goes up while the humidity goes down. 80's to right around 100 is common during late June to late July in the eastern part of either state. It would be quite nice for you though since the humidity is down around 20 percent.
Lance

If you have a chance to travel east at all, I recommend you see Coeur d'Alene, Idaho. Lake Coeur d'Alene is beautiful and only a few miles from Washington state. July is a hot month, but June is still pretty reasonable and in May and most of June the grass is still green on the hills and the landscape is very pretty. July and August are hotter and the grasses turn brown, but the pine trees are dark green, so it's still very nice.

I live five miles from Idaho and I love this area. While Seattle and Portland have the opportunity with their climates to really excell at roses, there is a very pretty park in Spokane WA that has a rose garden. Manito Park was designed by the Olmstead Brothers, who designed Central Park in NY. It also has a formal garden, Japanese garden and other gardens as well. If you do make it to Spokane, you might also want to see the downtown Riverfront Park, which was the former site of Expo '74. It's very pretty and has served as a model on how to design other expo areas for use once the exposition has ended. Enjoy your trip :)

If you have a chance to travel east at all, I recommend you see Coeur d'Alene, Idaho. Lake Coeur d'Alene is beautiful and only a few miles from Washington state. July is a hot month, but June is still pretty reasonable and in May and most of June the grass is still green on the hills and the landscape is very pretty. July and August are hotter and the grasses turn brown, but the pine trees are dark green, so it's still very nice.

I live five miles from Idaho and I love this area. While Seattle and Portland have the opportunity with their climates to really excell at roses, there is a very pretty park in Spokane WA that has a rose garden. Manito Park was designed by the Olmstead Brothers, who designed Central Park in NY. It also has a formal garden, Japanese garden and other gardens as well. If you do make it to Spokane, you might also want to see the downtown Riverfront Park, which was the former site of Expo '74. It's very pretty and has served as a model on how to design other expo areas for use once the exposition has ended. Enjoy your trip :)

Just South of Portland, off Hwy 5 is Heirloom Roses nursery. It has several large fantastic display gardens of old and modern and species roses. I would check with them re peak bloom, but if I had to guess I would guess June. However, I have been there in August, and I would say 75% of the roses were blooming madly.

Jackie

When we went, we went in July. It rained one day is all, and that wasn't much. Everything was blooming like crazy. The big rose garden in Portland was in full bloom, and everything around Seattle/Tacoma was in full thrall. It was hotter then you can imagine here, but out there, it was great. I really hated to come home.

I've lived here almost 30 years and think July and August are the warmest and driest months. Sure, we sometimes get into the 90's and rarely 100's but our humidity levels are typically much lower than east coast levels. Link below for the Portland Rose Gardens....enjoy!

Here is a link that might be useful: It's Rosey!

We went to Vancouver Island for 9 days at the end of June one year and the roses were magnificent. Butchard Gardens, of course, were magnificent including their amazing rose garden. We also loved Royal Roads University just outside of Victoria on the island - they had a really lovely rose garden, featuring many David Austin roses. We took a ferry over to Hornby Island to see Old Rose Nursery - another amazingly beautiful garden, featuring lots of rambling roses. Everything was in full bloom at that time, so it was a wonderful treat. You need more than a day to see Vancouver Island - I'm glad we made it the focus of our vacation that year because there was so much to see.

We missed first bloom in the Seattle area several years in a row when we were doing our search for where to retire. The upside was that we got to see the rhodendron, and they are awesome.

One of my favorite memories was on Vancouver Island, at the Gov. General's estate, with the sun breaking through the clouds and the Olympic Peninsula mountains rising from teh Stratis of Juan de Fuca (and the little bitty sail boats with their spinakers racing back to Victoria Harbour). We were in the rose garden but it wasn't in bloom. But it was in bud and the buds were so thick that I just knew what the majesty would be in several more weeks.

Roses love the ability to grow slowly and steadily through their late spring. Lots of blooms and big blooms - but you have to be willing to wait.

This year it was Summer from May to October. I had Roses still blooming until mid November.
That's unusual for us but July and August is usually a safe bet and even September is fairly safe.
Lots to see here in the PNW and folks are friendly.

Thanks for asking the question and for the responces I enjoyed the links

There are always lots of things to do and places to see out there. If you also like dahlias, Point Defiance Park in Tacoma has a dahlia display and test garden along with roses and fuchsias on display. As previously noted, in June there is the Portland Rose Festival, and many rose shows are held in June on weekends. Some are also in July. You may want to check listings on the American Rose Society pages if they have them yet. In August, there is the big Seattle Seafair festival and torchlight parade complete with pirates. Especially these days, if you are going to the PNW, please book your flights early. If you are traveling in Oregon, and you are feeding the car, the gas station attendants are required to pump the gas. Oregon has held on to those gas station jobs. There is also no sales tax as of this date in Oregon, so, shoppers can have a little break with that. Worthwhile stops are the Saturday Market in Portland and the Pike Place Market in Seattle. Also, in Seattle is the much expanded Boeing Museum of Flight. It is well worth the trip to see that. They put a lot of effort into their displays, and they have an old Air Force One presidential plane and a Concorde SST. Then, on clear days, there are the drives up to Mount Rainier, Mount St. Helens, the Steven's Pass road over to Leavenworth, WA, and I think there are roads to Mount Hood, Multnomah Falls, some Columbia River cruises, cruises around Puget Sound, and the trip from downtown Seattle to Blake Island for the Native American displays. Some of these are a little pricey, but most are not. The roses in Washington Park in Portland and Woodland Park in Seattle are wonderful. If you go, please take some pictures to post for the rest of us to drool over. Have fun.