From the National Weather Service:
[6 PM Winter Storm Update] Winter Storm Warnings & Watches continue, for an impactful storm affecting our region Sun afternoon to early Tue. Northern interior areas should see mostly snow. However much of the area is also expected to a transition from snow to a wintry mix Sunday night into Monday morning. Precipitation changes back to snow for most of the area during Monday, before concluding early Tuesday. For more detailed thoughts see the forecast discussion at weather.gov/boston
See latest briefing graphics below. Note how close the rain/snow line is to the bridges.