Europe definitely doesn't have the same kind of sunny weather we have in California. Right now around my area of central CA in Salinas CA we're experiencing beautiful 70+ degree F temps but unfortunately we're being shorted our winter rain the past month.
When I lived in Oberammergau Germany in the 60's I certainly remember that it snowed in June there. It wasn't much and didn't last long on the ground.
I think the problem is there's no middle ground between clear and mud turns, either you can move around normally or you're stuck in the mud. The problem is so many mud turns in the spring and fall. In the 1809 scenario there's so much mud for so many turns that it bogs the game down from anything like the historical timetable. Having middle ground Rain turns would slow down movement somewhat but would allow for something like historical timetables to be met.
While I favor somewhat historical weather modeling on a first turn of a scenario I really don't want it to be so predictable. I think the solution lies in the frequency of mud happening, it happens far too often and really bogs the game down. In my two games of 1809 War on the Danube I had mud almost every turn almost everywhere for atleast 10 turns, well into June before it cleared up. There really wasn't much of a mud problem for slowing down marching around the Danube despite the fact that the Danube was flooding at the time.
I think it's a matter of looking at each scenario's timeframe and figuring out the frequency of weather and then using that info to set more realistic percentages of any particular weather type happening. That way we can have the best of both worlds with unpredictable weather but realistic for that scenario. One weather model doesn't work as weather patterns differ from year to year so weather percentages should be annualized to better fit that year's weather particulars.