Not a good day to be in Iowa. Multiple reports of severe thunderstorms through the region, including tornadoes in Adams, Pottawattamie, and Ringold Counties (west of Des Moines). Even more recently, Des Moines International Airport Control Tower reported a Tornado on the ground.
It's no surprise to see this, however...meteorologist have been highlighting this area for violent weather for a few days now. As highlighted in the picture below, this storm is fueled by warm, moist air from the Gulf of Mexico, and driven by frigid air from interior Canada. When these two airmasses meet, cold air moves over the warm air, which significantly destabilizes the atmosphere (because warm air likes to rise and cold air likes to sink....but the opposite is happening in this case).
To illustrate how drastic the two airmasses are from each other and how violent the battle can be between the two, Kearney, Nebraska is (when this was posted) 32*F and snowing. 250 miles east-southeast in Kansas City, the temperature is 75*F, with 50mph wind gusts. In fact, outside of damage from tornadoes reported, there have been reports of roofs being blown off structures from these winds.
So why is the wind blowing so hard? Simple....difference in temperature equals difference in pressure.
For example, we all know that when we freeze water in a glass cup, the glass cup will break because the pressure exerted on the glass by the water as it freezes increases. Now we know that pressure changes with temperatures...so how does that make wind blow?
Well, the pressure in your car tire is higher than the pressure of the outside air. That's why when you get a flat tire, the air rushes out, not in (wouldn't that be nice!?). The same happens with weather. Colder temperatures have higher pressure. Warmer temperatures have lower pressure. This causes wind to blow from the cold to the warm. If the cold is really cold, and the warm is really warm, then the wind blows even faster, because the pressure difference is stronger.
And in the case of Iowa and the Midwest today, not only do you have that, but you have an atmosphere that is forcing cold air on top of warm air.....that's like pouring ice water on a hot stove top...the immediate area doesn't like it very much.
You just geeked out for the day....
Dan Schreiber is a freelance meteorologist with experience