The jet stream is the main “mover” of weather across the Continental US and the Northern Hemisphere. This fast-moving ribbon of wind at about 35,000 feet up in the atmosphere is generated by the difference of warm air near the equator and cold air at the North Pole. When the temperature difference is more extreme in the wintertime, the jet stream is stronger. Conversely, the jet stream is weakest in the summertime when there is less of a temperature difference north to south across the Continental US.

The normal state of the jet stream in winter is a rapid weather machine delivering cold shots of air via fronts like Alberta Clippers, but those systems usually do not deliver big local snows. To get a bigger snowstorm, you want to look for slower, looping sections of the jet that dip deep to the south and rise to the north. These types of patterns allow cold air to settle into the Northeast and Mid-Atlantic, while also bringing in a lot of moisture. (An old forecasting trick is to predict the cold air first, then predict the snow.) Similarly, a loopy, slow jet stream pattern is also responsible for heavy rainstorms as the centers of low pressure do not leave areas quickly while bringing a lot of moisture along with them.

By watching daily changes in the jet stream pattern, you can learn a lot about the upcoming weather while also understanding the dynamics of what goes into the bigger storm systems. Happy forecasting!

2021 ABC27 Weather Almanac