Here is a web site that may help.

http://www.fhwa.dot.gov/trafficinfo/index.htm

Where in Montana? It is a huge state.

We are heading pretty much straight up through it we will be passing through Butte and Helena. Our final destination is Calgary, Alberta Canada.

The drive is about 1,500 miles. That would be three days and two nights, if I were driving straight through (which I am not inclined to do).

Snow is possible (even likely) at high elevations in March and April. You can learn road conditions by dialing 511 within a state or by calling a toll-free number out of state. For instance, by Googling "Montana Road Conditions," I found that the out-of-state number to call for road conditions in Montana is 800 226-7623.

Road conditions for each state is also available on line.

HTTY

If you take I-80 to Salt Lake City and then I-15 into Idaho and Montana, snow on the ground is very probable in Montana and even Idaho. The pass over the Divide in MT could be icy. As HTTY said, check the road conditions by phone or online just before you leave and en route.

All you can do is have a vague sense right now. Upon arrival of your dates, check the weather at that point, and modify your trip to go EAST first and THEN NORTH if the weather is troublesome.

Were it during the middle of summer, for example, you'd want to approach through Missoula and Kalispell before going through Glacier National Park. But the winter weather will probably render that impossible.

You probably won't have any serious difficulty if sticking with I-15 the whole way. Indeed terrible, blizzard-like weather can happen through at least the middle of April, and as such it may require that you hunker down in one locale for a couple of nights.

The best you can do is to have a couple of plans mapped out and let the weather in the moment determine which path you will take.