Just got an e-mail from Air Canada:
Montreal Advisory
You have an upcoming flight linked to Montreal (YUL) that may be affected by fog.
Currently, there is no change to your itinerary and no action is required by you.
If you would like to change your travel plans, we’re offering you self‑service options to rebook to a different flight at no charge within 3 days from your scheduled departure by
clicking here and selecting “change my flight”. Any change made will apply to all customers on this reservation.
We look forward to welcoming you on board.
Of course, latitude fare, this is changeable anyway... My wife, on a reward, has not received this e-mail so far.
Anyway, I checked the Montreal weather, and the forecasts I have seen point to clear sky tomorrow morning, followed by a sunny day. Of course A might have looked at a different source, or they do a better job than Environment Canada?