so funny is in December it wont Alow you to make it snow you have to set it as January or June for it to snow ?
From what I've found, there's a certain date in November where it starts snowing and a certain date in February where it stops snowing. Any other time should be rain. Snow in June is certainly weird. It hardly snows in winter as it is (UK at least), never mind mid-summer.
The God mode mod allows the temperature to be set, if its over a certain temperature it won't snow regardless of time of year.
Internally the game only has one slider - precipitation, and whether that means snow or rain is based solely on temperature. Below zero it is snowing, above zero it is rain. Each route has a average temperature data for each date, which is used for timetable mode, and the temperature also changes during day and with altitude. So you can have the session start with rain, and it will switch to snow if it gets colder. So, if it is snowing mid june in a scenario, then the scenario author (just trains) messed that one up, and set the ambient temperature below zero.
Except, years ago, it did snow around May/June time in the UK. Can't recall if it was the year I was born or before that... My parents certainly told me about it enough times over the years.
