It's a beautiful sunny day, and not a cloud can be seen in the sky above Big Mountain. Rather, the clouds lie thousands of feet below, lining the bottom of the Flathead Valley. Often in our early season, bluebird days on the mountain are the product of a temperature inversion in the valley below!

But what is an inversion and how does one form?

Typically, air gets cooler the farther you go up, with the warmest layers hugging the ground. An inversion is just what it sounds like: The layers of air get inverted, or flip-flopped, so the warmer layer is up top, trapping cool air underneath.

Inversions are more common in the winter and oftentimes in the mornings. They form when there is natural variation of pressure and density in the Earth's atmosphere. Think really hard to recall from your high school days that an increase in pressure means an increase in temperature (PV=nRT, right?). So typically, the higher the altitude, the lower the pressure and therefore the temperature will be.

When conditions are just right, however, you'll see clouds on the valley floor instead of up in the sky! This can happen in a few ways:

The cold morning ground keeps the air immediately above it cooler.

This is the most common type of inversion. Clear and still nights allow the layer of air hugging the frozen ground to cool more completely than the surrounding atmosphere. The cold layer of air stays cooler longer in the morning, even as the sun begins to warm the rest of the atmosphere, creating a striking inversion. The inversion tends to clear up as the sun warms the lower layer of air.

A large body of water cools the air layer on top of it.

Think of Flathead Lake! A deep, circulating body of water takes a much longer time to heat up than the surrounding atmosphere in shifting temperatures, especially during the turn of seasons or after a long cold spell. This creates a cold, dense layer of air that settles on the valley floor and will be especially apparent once the day warms up a little.

Atmospheric variations.

There are two main atmospheric variations that can cause an inversion. A shallow cold front can move into low altitudes, layering itself under warmer air. Or, a warm high-pressure system can move in, creating a "cap" and promoting sinking air layers. This cap pushes down colder layers of air and prevents the gradual mixing of warm and cool layers. In all cases of inversions, the cap is where fog and condensation get stuck, producing clouds in the lowlands.

Inversions produce some of our most iconic scenes and sunrises here at Whitefish Mountain Resort. Terrain on the frontside of the mountain, especially groomed trails like Inspiration and Toni Matt, offer some of the best vantage points. To experience an inversion, try checking our snow report or weather page to see if we have the right conditions for an inversion today!

Skiing in the sun, perfect corduroy underfoot, a sea of dreamy clouds stretching out from the base of the mountain … I couldn't think of a better day!