The Tour de France hits the Alps beginning tomorrow for what should be four exciting days of racing.
For your TDF weather entertainment purposes, below is a GFS forecasts for the days ahead. The loop begins 1200 UTC today and goes through 1200 UTC Saturday (add two hours for central european summer time). The GFS produces persistent shower activity over the Alps for much of the duration. I suspect this is overdone, and that this translates to a chance of showers and thunderstorms during the afternoons. Two passing weather systems bring an elevated risk of showers and thunderstorms late tomorrow (probably after the conclusion of the stage) and then on Saturday, with a bit of a break in between. Precipitation units in the color scale at right are mm.
With luck the weather will hold, but there is the potential for a bit of rain to affect the race. Valley highs will be near 30ºC during the period. That's warm climatologically, but a bit cooler than what they've been dealing with the past few days.