In recent years the forest fire season has begun before the snow has melted off the trail and lasts until the snow itself is what extinguishes some the fires. So watching fire activity closely is important for a safe backpacking trip.
Note that in Washington the prevailing winds usually push smoke to the northeast, but not always. Last year I was introduced to Windy which is a pretty cool visualization of surface air movements.
The PCTA Interactive Map, built on the ArcGIS (geographic information system) platform, is the best way to view fire data relative to the PCT, since they added all the relevant layers in 2022.
When using any ArcGIS map you will want to have the correct layers turned on. I use the linear ruler feature to measure how far a fire is from the PCT.
Before the PCTA updated its ArcGIS map, FireMappers was the best ArcGIS map for fire information. It is supported by the NAPSG foundation.
Another ArcGIS map is maintained by the USFS Pacific Northwest Region and it shows
Note that closures still show on the map even after they have reopened so be sure to click-down and check the Closure End Date in the details.
The EPA maintains the AirNow air quality and smoke map. Is is a great way to see if the smoke from a fire is blowing towards the PCT or away from it.
The Washington State Department of Ecology has a similar map, but really, they should just use AirNow and save the effort.
PurpleAir is a crowdsourced air quality map that I find un-helpful for planning hikes because there are almost no private sensors near the trail.
InciWeb maps out manually entered incident data. It is maintained by the NWCG (National Wildlife Coordinating Group)
The NWCC (Northwest interagency Coordination Center) is a good place to get information about fire management activities in progress.