I will be at Yellowstone and Grand Teton parks next week. Also Mt Rushmore. What kind of weather should I expect? I plan to do the layering bit, but do I really need a heavy jacket(like the Lands End polartec)?

Check out www.nps.gov for the official Yellowstone and G.T. websites. They give typical weather highs and lows.

Last time I was in Yellowstone it was the first week of June and we had lots of snow.
I'd be ready for anything. Layers, heavy jacket, you name it.

http://www.nps.gov/yell/oldfaithfulcam.htm

web cam and temp.

We were in Yellowstone the first week of June 2000 and had beautiful warm weather. We were there in mid July a few years earlier and had a couple of inches of snow.

Go prepared for everything. Have a good trip.

Utahtea

Just got back from there yesterday. It snowed while I was there, but I never used my heavy jacket. It was cool in the morning and I dressed in layers with a light nylon jacket, and as the day wore on I discarded layers of clothing into the trunk.

Keep in mind that the west is really dry right now, and that this is not a typical year. Normally, it would still be coldish and snow on the ground. But, this year, every thing is fairly dry and it has been really hot in Denver. This coming week is bringing a drop in temperature, and possibly snow in the the mountains, including northern Rockies. SO, expect anything. In the mountains, it's not likely to be below freezing, but could get into the high 30's. Mt. Rushmore should be milder than GT and Yellowstone. I'd bring a polartec anytime of the summer in the mountains.It gets quite cool at night.