Actual map settings are unknown, since it seems to've been usermade.
Although there was not a single cloud, and a sunny day, rain poured down like from bukkets.
Even if the map I played was usermade using the editor, the sliders/settings for weather+forecast should have prevented that from happening.
Not saying its a "all too major glitch", but it severly affected visibility, and lasted for a couple hrs.
Try with following Intel settings in mission.sqm:
startWeather=0.69999999; startWind=0.39999998; startRain=0.5; startWaves=0.099999994; startGust=0.12; forecastWind=0.39999998; forecastWaves=0.099999994; forecastRain=0.5; forecastLightnings=0.099999994; forecastGust=0.12; rainForced=1; windForced=1; year=2035; month=7; day=6; minute=15;
Unable to reproduce in the latest dev build. Closing, since this ticket is very old and has not recieved any attention in a long time.
If this issue is still reproducable for you, please create a new ticket for it.