Understanding Microclimates in Southwest Montana

By John Wallace, SIFT Farm Manager

Garlic in May snow.
Garlic in May snow. Photo: NCAT
Rain over the SIFT farm.
Rain over the SIFT farm. Photo: NCAT

Many factors can affect the weather in southwest Montana. The region is classified as a high-mountain dessert. With very little precipitation in the summer months, we rely on snowmelt to recharge our rivers. A microirrigation system is essential for the SIFT farm to ensure that intense solar radiation does not bake the soil. Mulch is also an essential tool for protecting the soil and retaining water.

Butte, which sits at about a mile above sea level, is surrounded by the Continental Divide on three sides. Though this elevation does preclude agricultural activities, the mountain valleys create their own weather patterns that make Butte especially difficult to grow in. In fact, the specific location of the SIFT farm has its own unique weather compared to the rest of the valley.

Being surrounded by the Continental Divide on the north, east, and south has some benefits because the wind predominantly comes from the west. Creating an orographic lift, we seem to pull a little extra precipitation from the sky than areas east of the divide. Whitehall is a town just 30 miles east of Butte and more than 1,000 feet lower. Though it often sits in a rain shadow, the lower elevation means more snowmelt funneled into the Jefferson River. The farmers and ranchers in Whitehall rely on this substantial source of water for irrigation.

Isolated summer rainstorm that skipped over us.
Isolated summer rainstorm that
skipped over us. Photo: NCAT
Regional weather data.
Regional weather data. Source:
Weather Underground

Because of Butte’s higher elevation, we typically have colder temperatures. The shape of the valley creates a bowl, which allows strong inversions to settle into the lowest parts of the valley. Uptown Butte sits up on a hill overlooking the Flat. I have seen a difference of 10 degrees on some days between the temperature uptown and down on the farm. This is because, during clear nights, the cold air rolls off the mountains into the valley. I’ve noticed a pattern to how this air snakes down. It seems to get drawn in from Elk Park, an elevated flat area tucked between two ridges just northeast of Butte. This cold air makes its way down past the Continental Pit, an active open-pit mine, and settles into the area east of town where the SIFT farm is located. Even at the same elevations within the valley, the area where NCAT’s headquarters is located will be nearly 5 degrees cooler than the airport. Because we are tucked near the East Ridge, we also have to wait an extra hour before the sun rises high enough for direct sunlight.

Monitoring these temperatures is important during the fall so we don’t damage irrigation pipes or lose crops to damaging frosts. One tool I use is the Weather Underground app, which uses a crowd-reporting method to collect weather data. When you are located in areas that are commonly affected by microclimates, it helps to see what others in the area are experiencing and if it is consistent with the central weather station. For instance, summer rainstorms can be so isolated that precipitation is difficult to monitor. Using technologies that allow users to share their data helps farmers and ranchers make more informed decisions.

Posted on: October 22nd, 2018