As time rolls on, the details for this forecast are becoming clearer. We are not going to see a major snowstorm, and we are now only really looking at one possibility of snow (Sunday night). We could still see some snow Monday night though.
As you can see, the amounts over Seattle are not very impressive. The 4km mm5 GFS model gives us an inch of snow tops. Still, that is more than enough to cause a 2 hour late start because it will likely stick to the roads since they are so cold.
A convergence zone will form up north by snohomish county (see the two bands of snow there) and a secondary one, more like an arctic frontal boundry, will form over the San Juans.
Monday will be our last cold day. Snow may fall for a brief period in the afternoon before switching over to a cold rain later at night. Later in the week, temperatures will rebound to the upper 40s and a more rainy pattern will take hold. Some of the rain could be quite heavy. Look at the above storm! Been a while since we've seen something like that.