Although Snoqualmie Pass is generally the easiest way to traverse the Cascades, it does get snowy and sometimes closes during heavy storms.
Contact the Department of Transportation for the Mountain Pass Report (888/766-4636, www.wsdot.wa.gov/traffic/passes [1]). The website includes a webcam showing current conditions at Snoqualmie Pass.
Links:
[1] http://www.wsdot.wa.gov/traffic/passes