HELENA — The season for thunderstorms has returned to Big Sky Country. After a pseudo hibernation through the winter, storms come back to life usually around this time of year.
Thunderstorms are electric, exciting and dangerous. They can happen in Montana year-round, but typically do not occur in the winter because there is not as much instability and moisture in the atmosphere as there is in spring and summer. In the winter, the atmosphere is generally very stable with all levels being particularly cold and dry.
Of course, now it is late March and spring is in full swing. The days are longer with more solar energy reaching the earth's surface. Temperatures are warmer, and warmer air can hold more moisture.
For thunderstorms to develop, they need warm air to rise from the surface, then to cool and condense into a tall, vertical column of clouds. Warmer air is more buoyant than cold air. This creates more vertical motion in the atmosphere. Think of a towering thunderstorm. There is a lot of upwards motion that pushes that cloud high into the sky.
As the days get longer, more intense solar heating of the surface warms the ground and lower levels of the atmosphere. The upper levels of the atmosphere at this time of year are still fairly cold. The greater the temperature difference between a cloud and its surroundings, the faster, higher and more intense clouds can grow into thunderstorms.
This time of year in Montana, passing fronts often capitalize on the warmer temperatures and available moisture. These fronts provide additional lift and vertical motion and voila!...thunderstorms pop and rumble across our big sky.