That's the natural color of the streams. Here's an explanation from Wikipedia: "Rock flour, or glacial flour, consists of clay-sized particles of rock, generated by glacial erosion or by artificial grinding to a similar size. Because the material is very small, it is suspended in river water making the water appear cloudy. If the river flows into a glacial lake, the lake may appear turquoise in color as a result."
Weather-wise, the eastern two-thirds of Montana is often radically different from the western third. I lived along the front for 5 1/2 years and have vivid recollections of big wind, especially in winter. If it came from the north, then buddy, it was bone-breaking cold. If it came from the south, you could almost wear a t-shirt in February. It was hard to get bored with it, though. I remember sitting next to the a bull chutes on the July 4th rodeo in Augusta. Little piles of snow accumulated on the fence rails. Amazing place.