While I agree rain would add a 'cool' element, back in the day, when it's 75ºF, it's like 0ºF at 20000ft. Which, if it rains at 20'000ft, it's freezing rain. And NO aircraft back in WWII had any gear or equipment to deal with freezing rain. No anti-ice boots, no pitot tube heaters, no real windshield defoggers. Wipers were people who cleaned your cockpit glass before takeoff - not something to clear rain from your windscreen.
Even at 10'000ft, you're at danger of rime or SLD icing. So in WWII, all flights were 'fair weather engagements'.