@MagpieRacer I don't think it's factual to say it's 'broken'. It may just be a decision that they have taken that the majority of players aren't again of - it's possible it was done this way because they believed people wanted the extra challenge over realistic weather patterns.
Currently it's working as intended. There are four times of day cycled through in order each time (day, sunset, dusk, night) and one of the available weather conditions chosen at random for that time of day.
Now, don't get me wrong, I think it sucks like this and is the game's main drawback for me personally (the only major one to me) and I hope they do something about it, but I don't think you can say as a fact that it's broken, just that it's proving unpopular.
To me, some steps need taking:
1) we need more weather options for the available times of day. At the moment, most dusk and sunset stages only have one or two options. For example, in the USA sunset is always wet, whereas dusk is always dry. In every event.
2) Either more times of day to be added to the cycle (early and late morning, noon and early and late afternoon) or a chance of multiple day stages in a row and a percentage chance of each of the evening types (say 80% chance of sunset, 40% chance of dusk and 20% chance of night).
3) A 'pattern' of weather options. So, if the first stage in Spain is daytime and sunny, there should be a 90% chance that the next stage is sunny. A small percentage chance of clouds and a small percent of rain. This would be one epic flowchart to make for each location, but would give the impression of weather that is believable for a 'day'.
Now I accept that this wouldn't be the work of a moment, but IMO it's the direction that needs to be taken.
More importantly, I want to see some blog post or long forum post where Codemasters acknowledge the issue, explain it and say what, if anything, they plan to do about it. Even saying 'we can't do anything about it' would be better than nothing.