Temperatures in the Northeast this winter have been anything but “average”, and some meteorologists think they know why.
From late December through early January, the region experienced an unusual streak of colder-than-normal temperatures. Our friends at the Northeast Regional Climate Center note that this was one of the longest streaks of below freezing temperatures that the southern half of the region has ever seen. February has been extreme in the other direction with record high temperatures seen across the region on February 20th or 21st.
Both events are related to strange behavior in this winter’s polar jet stream, and there is growing concern that this strange behavior may be becoming more common. The National Weather Service describes jet streams as “relatively narrow bands of strong wind in the upper levels of the atmosphere.” The winds blow from west to east but the flow of these often shifts north and south. In the winter, the polar jet normally sits above Canada circling really cold air in the polar vortex. In recent years, however, the polar jet seems to be more often developing deep “kinks” that strongly affect our weather. The kinks allow a channel for frigid polar air to slide to the south. On the east side of these kinks, winds carry warm southern air back north. The same kink can be responsible for unusually cold and unusually warm temperatures in different parts of the country at the same time. A really cool tool to see the motion of the jet stream in action is located here: http://squall.sfsu.edu/scripts/jet_big_archloop.html
Start the tool on February 19th and run it for a few days to see the kink which brought to the Northeast 1-in-100 year warmth. There is concern that a warming arctic is responsible for this kind of unusual behavior of the polar jet, which can lead to more temperature extremes. However, there is not yet a consensus in what is now a very active area of meteorological research. For more details on how a warming arctic might be affecting our weather, see this recent publication (“Amplified Arctic warming and mid‐latitude weather: new perspectives on emerging connections” by J. Francis et al.).
More news about unusual winter weather and an unstable arctic vortex »By David Hollinger, Director, USDA Northeast Climate Hub