On the Teton Valley Weather Facebook page, there were some really good questions about the cause and the timing of those fire breathing thunderstorms that blew though the valley Saturday. Why do they form when they do, time of day, time of year, and location?
The short answer to all of that is the same as the short answer to most questions you might have about weather when you think about it: Hot air rises.
We could go into the physics of what heat is and why hot air is lighter than the same volume of cold air; it all has to do with the speed of the tiny atoms and molecules in the air. Suffice to say that you can pack more kids into a small classroom if they’re still, sitting in their seats in nice rows like the molecules in cold air. When the kids start running around and behaving like natural children or the molecules in hot air, they need more room and may not fit in that tiny classroom anymore because they’re bumping into one another, bouncing off the walls, and if the walls don’t come down, the kids will spill out of the nearest door into the hall or out onto the playground. Moving kids take up more space, but there are fewer of them in any given spot at a time. Same with molecules in hot air, which is why an equal amount of it is lighter than that of cold air. Enough physics.
Since light things tend to float, warmer air, which is lighter for the same amount of space, floats upward in colder air like a cork in water, especially if something gives it a little nudge. And that is why we have rain, snow, wind, and thunderstorms. It’s also why hot air balloons work and what gliders look for to stay aloft all day long if they want to.
So when there is warmer air in place, as there was Saturday, and something gives it a nudge, like the leading edge of some colder air moving in as we also had Saturday, that warm air is going to rise. When warm, moist air rises and begins to cool off, it forms clouds. If it keeps rising, those clouds get taller. If they get tall enough, they can become thunderheads with enough rising warm air and falling cooler air, rain and hail rushing by one another rubbing electrons off of individual atoms. This is what the rug does to your feet before you touch the doorknob and get a spark, only these rushing streams of air are much bigger than your feet, and the spark they make is much bigger. We call it lightning. And that little snap you hear when you see the spark becomes thunder when the spark is huge.
In winter, we don’t normally have much warm air in place to rise, but in spring and summer we do. That’s why thunderstorms are rare in the winter and typically occur on hot summer afternoons. But the timing of Saturday’s storms was determined by the nudge, the front of some colder air pushing into some warmer air. We followed it as it moved from west to east across Southeast Idaho, from the Arco Desert to Idaho Falls (where the air was warmer so the storms were more fierce) and then on to us after being disrupted and weakened to some degree by the Big Hole Mountains.
We will undoubtedly see more thunderstorms as spring and summer progress. All thunderstorms are deadly; lightning kills hundreds of people each year. But when the storms produce a tornado, that adds to the deadly and destructive nature of thunderstorms. While tornadoes are extremely rare in Teton Valley, they have been known to occur, and lightning frequently does. The more you know about these storms, the better your chances of living long enough to enjoy and appreciate them and their powerful beauty.