SPOKANE, Wash. — A friend of mine in Indiana asked me "why did it go from snowing to seventy degrees in two day?"
This wouldn't be the first time we've heard of something like this happening. Huge temperature swings from cold to warm are fairly common in the winter time across the U.S. And that leads me into this topic: temperature whiplash.
There are two common meteorological factors that go into extreme temperature shifts. The first is the jet stream and the second is how mountains influence local weather patterns.
Starting with the jet streams, there are two jet streams that circle the northern hemisphere, the polar jet stream and the subtropical jet stream. The jet streams themselves are a result and mechanic of temperature differences between the tropics, mid-latitudes, and polar regions. The more extreme the temperature gradient, the strong the jet stream becomes.
The temperature difference on either side of the polar jet stream is more pronounced of the two. And in the winter time, the polar jet stream sags southward and is normally draped across the northern U.S. As a result, temperature swings from storm systems, warm fronts and cold fronts tend to have a larger change in the winter than similar systems in the summer time.
I know I've seen 24-hour temperature change maps in the northern U.S. reach ± 50 degrees.
But in the western U.S., the mountains play another factor when it comes to large temperature changes. The most notable phenomena is known as the "chinook winds."
The chinook winds, also known as the "snow eater" are winds that slope down the mountain side and warm as a result. There's a lot of physics at play here - so to simplify why that happens, it's because as the air drops in elevation, it's pressure go up and as a result the temperature increases too. If you ever took high school physics, that relates to the "Ideal Gas Law" (PV=nRT).
The rate at which the air warms is called the "dry adiabatic lapse rate" and it's 10 degrees Celsius per 1km. That can warm an air mass significantly on it's own merit.
One final thing to note, the chinook winds can become even more pronounced if there is a temperature inversion in place. That means cold air is sitting on the valley floor while the air in the mountains is warmer. If that warmer air sinks and displaces the colder air, it both warms and replaces the cold air mass creating an extreme effect.
This affect I just describe led to what because the world record for the fastest temperature change ever. In Spearfish South Dakota on Jan 22, 1943, the temperature changed from -4 degrees to 45 degrees in just two minutes!
You can read more on this world record even from NWS Rapid City here.
Weather Classroom is produced and broadcasted by KREM Meteorologist Thomas Patrick is you can watch and chat live on his Facebook page Thursdays at 1 p.m. Pacific Time.