This, by the way, is Jensi solution for all Weather Protocol issues:
the people who decide if it's okay to ride, have to drive the stage in an open cabriolet, no matter the weather. And if it's to hot or to cold for them to do so, you don't ride.
Edit: thinking about it for a second, this could only work as an instrument of measurement if the people in the car also can only wear what a cyclist could realistically use. Also they should be on home trainers, which means that there probably needs to be an open Truck on which they all sit on the home trainers. And because this is a TV sports event, they'd also do their own race, like the E-Giro.
I don't know why everyone keeps on overthinking the problem or 'guessing' about the actual conditions based on social media posts (which is what we seem to get non-stop from the media & people in the peloton).
It's simple, i.e. like in F1 where the safety car does some laps in the rain to gauge the amount of water on the track: enrol some retired cycling pros as part of the UCI organism/whatever it's called & get them to ride the descent/or whichever part of the route is 'problematic' in full gear for 20km in the morning before the stage & then report back.
If it's too dangerous or too cold (& the weather forecast shows no improvement), they'll let the organizers know immediately. If it's 'okay', they race (or they can also 'neutralize' timings & everyone can go slow in the dangerous part as a stop-gap measure).