Snoqualamie still is pretty icy as of last weekend but hopefully by mid March it will be ok. That goes up to about 2500 ft as I recall so keep an eye on the forecasts. This is a great drive I make it all the time. Plus if we end up at Snoqualamie Falls it is 4 miles from I-90 and everyone can head to the interstate for their treks home.
The most scenic route is Hwy 18 (pick it up right at I-5 at Federal Way heading towards Auburn) Take that all the way up to I-90 and cross it as it turns into Snoqualime Parkway and goes right into town to a "T". Take a left on 202 (Railroad Ave) and go about 1/2 mile and you are there.

I can print out a map if you like in Adobe Acrobat Reader PDF file format to post once you decide all the details.

There is also a great old time steam train ride there that takes about an hour and is a beautiful ride. And there is a terrific 50's style hamburger joint complete with juke boxes.

Don McCleery