Any forecasts out further than 3 days have a very high error rate. Past 5 days the error rate is so high I don't even worry about it.
For the NW the best forecast to use for mountain weather is NWAC Mountain Weather forecast http://www.nwac.us/forecast/weather/current/ which gives snow levels, estimated precipitatiion in water eq (you usually need to estimate new snowfall based on those).
For Colorado I've been checking out the colorado powder forecast: http://www.coloradopowderforecast.com/
I've also just started reading PowderChasers whcih attempts a 7 day outlook for new snow: http://www.powderchasers.com/
or a local news channel