Hello! Thanks for your feedback back and sorry for the late response.
1. Yeah that is intentional. As an F tier skill it is supposed to be rather situational.
The weather is stated by the GM at the start of the race day, and you can equip skills right before choosing your starting gate so If the weather is sunny I wouldn't recommend equipping this skill.
2. In the sections "Acquiring Training Points" and "Calendar" (in the campaign chapter) we explain how the the game outside racing should flow and when the GM should call for checks.
We've been discussing about adding a GM section for a while now. We'll take your post into consideration!