Street parking in Somerville is permit only I think, but I'm not 100% sure. From central square it's a 15 minute walk to my place via prospect and Hampshire. The 83 outbound can drop you off at inman square or the next stop (2-3 blocks from my house for ether) and the 91 outbound will bring you to Springfield and concord (one block from my place).
I almost always end up walking to central square for my morning commute, unless the buses are actually running on schedule or it's raining. Weatherunderground is saying 1-3 during the day starting sometime after 3 and 5-8 total snow once it's finished late tonight.