It happened again. A great question from a reader on the Teton Valley Facebook page got me thinking about something I had noticed and thought strange but never really stopped to think about why it happened. The reader’s question made me think about why and figure it out.
Here’s what Adam asked:
“Random weird question but why does the snow fall north to south when the storm is moving south to north right now?”
Wow! My wife asked me the same thing once. And I wondered about it too; how can the storm be moving against the wind instead of along with it? But here I am, on the spot, gotta come up with a reasonable answer. Ok, here we go.
Storms are created by low pressure air rising up, carrying water vapor up with it, and then cooling as it rises to the point that the water vapor condenses into droplets and forms a cloud. When the cloud gets thick enough, the water droplets violate social distancing guidelines, join together and form a drop big enough to fall as precipitation. Meteorology 101, right? Or maybe 7th grade science? But then what? When the air rises to create the storm, does that leave the rest of us in a vacuum without air? I hope not! Instead, air from all around the storm rushes in to fill the vacuum. So that means that no matter which way a storm is moving, the wind at the surface will generally be blowing in toward it from all directions. So if the storm is moving south, the wind behind it will also be blowing to the south toward the storm while the air ahead of it will be blowing to the north toward the storm. And to the sides, the wind will be blowing east or west in toward the storm as well. Simple, right? Well… not so fast. Nothing is that simple in the real world.
In the real world, there are surface features like mountains and temperature differences that turn the wind to a different direction than it would go in a perfect world. Other things turn it too; even the rotation of the earth affects the way large scale winds blow. And there are big exceptions, too. Some thunderstorms develop strong downdrafts which overwhelm any wind trying to blow in toward the storm and create strong outflow wind instead. So no, not simple. Weather always seems to be a contest between the simple rules of thumb and the complications that come up to break those rules. And it seems that no place likes to throw complications into the forecast and break the rules more than Teton Valley. It’s Teton Valley weather; it’s endlessly challenging and endlessly interesting. Keep asking those questions and together we will do our best to figure them out.