Yes the weather is randomized, but in such a way to match the climate.
One additional thing to note though: with a turn length of 4 days, you would expect the weather in one turn to have some impact on the next turn. For example, a mud patch "lingering" close to a certain location on the map. We intentionally
disabled this for gameplay balance reasons, so don't try to "predict" the weather in this way, it won't work.