I was told its the temperature difference between Port Alberni and Tofino which creates the thermals... especially when there is a fog bank off shore or at the far end of the lake!
1-5 C difference its iffy
5-10 its good
10 or more its nuking!
Add the wind forecast for juan de fuca straight.
If its supposed to blow a solid westerly, that indicates on-shore flow which will assist nitinat winds! If its gonna blow easterly in the straight, nitinat will probably be lighter, maybe still sailable, but not that windy.