From 78 degrees on Tuesday to snow on Wednesday? Swings like this aren’t unusual in the central United States, where weather can quickly shift from one extreme to another. That’s especially true in the springtime, when conditions turn into a roller coaster, with balmy spring days followed by abrupt returns to winter.
These wild swings have been on full display this spring, with a record-setting cyclone on March 13-14 and a second system this month bringing very heavy snow and intense winds to a broad area from Colorado to Minnesota. For researchers like me, this region is a fascinating, and sometimes frustrating, place to study weather and climate. It’s no accident that places like Colorado and Oklahoma are among the world’s hubs for atmospheric science.
Where the winds meet the mountains
What generates such “big weather” on the Great Plains? It starts with geography.
As you travel west across the central United States, the Plains gradually slope upward. Then, in central Colorado, the terrain quickly rises into the Rocky Mountains, creating big changes in elevation, along with more subtle ridges and river valleys. This topography sets the stage for our region’s complex weather systems.
Southeastern Colorado and the bordering panhandles of Texas and Oklahoma form a breeding ground for extratropical cyclones – the large, low-pressure systems that routinely move across the country, bringing rain, snow, thunderstorms and strong winds. As troughs of low pressure aloft move from west to east over the Rocky Mountains and then emerge on the other side, the columns of air are “stretched” vertically. This makes them spin at increasing rates, just as figure skaters do when they draw their arms in.
These features interact with the usual south-to-north gradient in temperature that exists east of the mountains – that is, warmer in the south and colder in the north – kicking off a process in which strong cold and warm fronts develop, and a cyclone can rapidly intensify. Along those fronts, widespread precipitation forms, including everything from heavy snow to severe thunderstorms.
So the day or two before the cyclone develops, temperatures are often well above average, only to quickly plummet as the strong cold front associated with the cyclone blasts through. In other words, the rapid changes in temperature that we see east of the Rockies are not just an interesting aspect of these storms – they are key to their development and intensification.