It's not possible to predict weather in the RMNP as it is different every year (and every month). It used to be we usually could count on Trail Ridge opening on Memorial Day but 2 years ago we had late heavy snow, about 20 feet so they couldn't clear it till middle of June; last year little snow, so warm it didn't need much clearing and very little run-off. June is usually beautiful if the snow is still on the high mountains and the streams are high. The wildflowers are just beginning and wildlife is coming out but you may not be able to hike very high without snowshoes or tourskis. Beetle kill and wildfires have ravaged some of the forests but there are still many wonderful trails and views. Late August may be hot and dry but it is always cool at night and camping is great. The campgrounds inside the park are usually filled and all need reservations; better to come during the week to avoid the crowds. Bear Lake area you will need to park and take a shuttle to the trailhead. There are two visitor centers where you can learn which trails are open and lots of info such as where you might see a moose, bighorns or elk and children can learn lots about the park. You may want to stay outside of the park on Hwy 7, St.Vrain canyon or the other side of Trail Ridge on two large lakes. If you're coming from the flatlands remember that you will need to acclimate to the altitude, be sure to bring some raingear and warm clothes. Weather forecasts don't help much; it can be 90 in Denver and 60 in the park. But it is beautiful all year round and if you love mountains as we do you will have a great trip. Some good info online and in travel books.