Grand Tetons/Yellowstone in May

I'm planning a last minute trip to Grand Tetons and possibly Yellowstone from May 18 to May 23. with two days gone for travel time to and from Calgary and Jackson/West Yellowstone, that really only leaves 4 days of actual time at either grand Tetons and or Yellowstone.

I wanted to find out what the weather is usually like during this time period at these two parks. I know that here in Canada most lakes are still frozen in Banff and Jasper until June, and some access roads are closed until Mid-June.

Are places like Ox-bow bend, and snake river still frozen over during this time of the year? Are access roads open in Grand Tetons and yellowstone during this time period?