Click here to listen to Episode 404 of Weather Break.
On the morning of January 22, 1943, the town of Spearfish, South Dakota set the all time record for greatest two-minute temperature change. This 49 degree temperature increase was due to a particularly strong example of what is known as a chinook. On today’s episode of Weather Break, Dr. Jon Schrage takes a look at what a chinook is and explains why the air was so warm on that day.
Where in the world is Spearfish, South Dakota?
The Wikipedia page about Spearfish features some details about the chinook. However, here at Weather Break we are bigger fans of this radio story produced by South Dakota Public Broadcasting.
Looking for more information about chinooks? Trythe University of Colorado, or Suite101.
Looking for more information about foehns? Try Wikipedia, tpub.com, or the Encyclopedia Brittanica.
The Santa Ana winds have been in the news a lot lately:
A couple of weeks ago I was driving across South Dakota on I-90, and when I saw the town of Spearfish, I had to stop. I had never been to Spearfish before, but like all meteorologists, I happened to know a thing or two about the town because of the amazing weather events there on January 22, 1943. You see, there’s a popular textbook in meteorology called “Severe and Unusual Weather”, and on the inside cover of that book, there’s a map of the world, with lots of locations labeled on it that have had remarkable weather. That’s where most meteorologists learned, for example, about the coldest temperature ever observed on Earth —- 127 degrees below zero in Vostok, Antarctica, to be exact. And, as it happens, there’s a marker on that map for Spearfish, South Dakota: home of the world greatest 2 minute temperature increase.
Okay, if that sounds like a strange “world record” to you, you’re right. Meteorologists don’t normally keep track of things like “2 minute temperature changes”, but the one in Spearfish in 1943 is certainly something to remember. At 7:30 on that morning in Spearfish, the temperature was a chilly 4 degrees below zero, but just 2 minutes later, the temperature stood at 45 degrees–an amazing 49 degree change! The temperature continued rise–albeit much more slowly–for the next hour or so, topping out at 54 degrees, which isn’t half bad for January in the Black Hills! However, the temperature suddenly started dropping, in the next 27 minutes the temperature fell 58 degrees and bottomed out again at 4 below.
What happened that day in Spearfish was an example of what meteorologists call a chinook. Chinooks aren’t particularly rare, although the one in Spearfish was certainly unusually strong. Chinooks happen when air sinks as it flows down the lee side of mountain. Anytime air sinks, it warms due to compression. If you’ve ever worked with an air compressor in your garage, you know that the sides of the air canister get pretty hot when the compressor is running. The same thing happens to air in the atmosphere whenever it sinks–as the air gets closer to the surface of the earth, the pressure increases and the air is compressed, which increases the temperature. And this warming is significant–it works out to about 30 degrees F for every mile the air sinks! Now, most of the time that air sinks and warms, it also mixes with some of the colder air around it, which decreases the effect of the warming, but apparently in Spearfish in 1943 a chinook wind flowing out of the northern Black Hills was able to reach the city with mixing much, and temperatures rose spectacularly for an hour or so while the wind passed through.
A few years ago, South Dakota Public Broadcasting did a story about the 60th anniversary of the Spearfish Chinook. They talked to people who experienced the event–there’s a particularly interesting interview with a woman who was a schoolgirl at the time of the chinook, and she talks about walking to school on that day in 1943. We’ll have links to these stories and more information about the Spearfish chinook on our website…