From By Spending Time with the Land, You Know, by Susan Duncan:
Most people are aware of regional differences in climate. The Southeast is hot and humid. The Southwest is hot and dry. But in the Intermountain West, mountains affect air currents and moisture distribution to create many microclimates within just one valley. Visitors don’t recognize those microclimates. Most residents find out about them by trial and error. ...
The mountains and Bozeman Pass get the deepest snow, but south and southeast parts of the Gallatin Valley get the most valley accumulations because that’s where the storms bump into the mountains and drop their load of moisture. As you go west in this valley, the snow depth tapers off, but the temperatures are colder. It gets to minus 20 or colder in winter, but it doesn’t last long, only a few days to a week. Wear layers of clothing. It’s a dry cold.
Some of the actual climate relationships defy logic. Higher elevations usually mean colder temperatures. But cold air sinks, so it is actually colder at my house down near the West Gallatin River than it is here at the Museum. I get a good crop of apples off my apple trees about once every 3 years, because the flowers freeze in spring. But along the west face of the Bridgers, at a higher elevation, apple trees produce very well, year after year. It’s warmer there, even though the elevation is higher.
The growing season is about 90 days here. I plant on Memorial Day and expect frost anytime after Labor Day, though I’ve had 28 degrees on the 23rd of June and my potatoes have frozen flat on the 16th of August. I pick my tomatoes green and let them ripen in the house. But I garden in a cold spot.
Manhattan and Three Forks have a longer growing season. In spring, it greens up two weeks earlier in Three Forks than in Belgrade. The lilacs bloom in Belgrade before they bloom at my house.