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Thunderstorm production requires moisture, an unstable atmosphere, and a lifting force. In the mountains, the lifting force can come in a variety of ways.

1) Terrain Forcing

Terrain plays a vital role in the production of storms year-round. The size, location, and intensity of a storm depend on the direction of the wind, the surrounding terrain, the stability of the air, and the moisture content in the air being lifted.

Orographic lifting is one of the most common methods of thunderstorm production. When orographic lifting happens, wind is forced up a mountain ridge, and as it rises, it cools. Eventually, the air reaches saturation and forms a line of cumulous clouds. If there is enough moisture and instability, this can form a line of thunderstorms along the mountain ridge. This can make navigating the mountains very difficult, especially in the afternoon.

Check out the video below to see how orographic lifting forms clouds and storms...

2) Upslope Flow Convergence

When the sun rises and heats the side of a mountain, the air above the slopes begins to warm. This warm air rises, creating upslope winds that reach the peak of the mountain. At that point, the air detaches from the mountain and begins to rise vertically, converging with similar thermals on the other sides of the peak.

If moisture and atmospheric instability are present, a cumulus cloud will begin to rise and form a cumulonimbus cloud over the terrain. This is known as upslope flow convergence.

Check out the video below...

3) Convergence Displacement

As the sun heats mountain slopes in the morning, rising air from thermals converge above the ridgeline. If there are winds aloft, the rising thermals flow downwind and continue rising downwind of the ridgeline. In this phenomenon, the location of clouds/storms will be downwind of the ridgeline instead of directly over the top of the terrain.