As with all things in aviation, there is a "checklist" for such things, some may be a mental checklist. But you want to gather information such as the age, sex, symptoms etc first, then typically solicit medical personel onboard if symptoms warrant. During this a cockpit member is patched through to a Dr who is on stanby on the ground to handle such situation. The DR will ask his questions, and the fight crew will give the information they have gathered. The DR will recommend continuing, diverting, or other medical advice, and the flight crew will make a decision based on his advice, dispatch, weather etc....Flight crews deal with snowy, rain, sun etc all the time and is really not an "issue". The only issue may be if airport may be an overhead thunderstorm, or snowed in. Cheers.