Ash is abrasive and can damage sensitive mechanisms, so planes are kept far away from any ash clouds and could lead to regional flight cancellations or diversions. Air traffic in and out of southern Alaska could be affected for a while, especially at night when pilots can not visually see any ash plumes.
The odds of impacting air traffic around the Pacific Northwest are quite low. It would really have to be a mega eruption, plus the wind pattern would have to be just right to get any significant ash this far away, and even so, the ash would be much higher in the atmosphere, and likely well above normal air traffic. It could make for a hazy sky and some really red sunrises and sunsets, though.
But for those that want to track the volcano, here are some links to do just that:
Here, if you select how high the initial ash cloud makes it, it'll show you a computer forecast model projection, using one of the weather models, as to where the ash cloud will go.
This site also has some upper air wind trajectories.
In looking at the wider scale, it doesn't look like in the short term, the upper air flow is favorable for pushing any ash in our direction, keeping it up in Canada. The jet stream does appear to veer a bit more of a northwest path from Alaska to the northwest as we get into the late weekend and into early next week, so an eruption then could make for a hazier sky next week, but again, we are too far away to see any effects from ash on the ground.
But as I said earlier, it could make for some spectacular sunsets. If the volcano does erupt, keep those camera batteries charged! :)