If a major snowstorm spanning several days strikes, Metro will activate a newly designed Emergency Service Network for its fleet. When the network is activated, Metro’s regular routes will be replaced with 70 pre-identified “priority” snow routes across the county designed to be reliable in severe weather conditions. Metro will make every attempt to keep service operating on these routes as long as transportation service providers are able to keep roads passable. I've heard that they're using a color system whereas yellow means some changes and red means complete changes.
Below is the Emergency Service Network for North King County. Notice that many routes are missing; 77, 301, 303, 304, 315, 316, 330, 346, 347, 373.
Metro recommends people sign up for "Transit Alerts"; these cover all types of emergencies. Go to Metro Signup. This way, you'll be notified of any changes to your favorite bus routes. You may set up an alert for individual routes. Notice that another tab is "Construction & Events," click on this to see other, more minor changes to Metro routing.
There's also a road alert website.
For transportation disruptions that off-times affect any type of commute, such as road paving, try "Eye on Your Metro Commute"
Lastly, here is a good traffic website
Emergency Service Network North King County
If your bus route number is not listed, assume that it is not operating during emergency service.
Route Destination Route Map
5 Broadview - Greenwood - Downtown Seattle [PDF]
234 Kenmore P&R-Juanita-Kirkland [PDF]
251 Kenmore P&R-UW Bothell-Woodinville P&R [PDF]
312 Kenmore-Lake City-Downtown Seattle [PDF]
331 Aurora Village TC-Kenmore PandR [PDF]
345 Broadview-Northgate [PDF]
348 Richmond Beach - Northgate TC [PDF]
358 Aurora Village TC-Downtown Seattle [PDF]
372 Kenmore-U District [PDF]
522 Woodinville-Bothell-Kenmore-Downtown Seattle [PDF]
935 Kenmore-Juanita-Totem Lake TC map*
* DART routes run on their snow routes during emergency service
--Brian Doennebrink
Metro Bus Photo from Oran Viriyincy