Sudden Stratospheric Warming Event What is it? And why are cold weather enthusiasts getting excited about a warming event? The image below (from Today’s GFS) shows the result of a sudden stratospheric warming event on Nov 8th in the stratosphere. Notice the red blob directly over the North Pole… that is a ridge of warmth that evolves rather suddenly, although as I have shown you it can be seen coming from a long way ahead, if you know what to look for… A sudden stratospheric warming event is defined in either, or both, of the following 2 ways: 1) temperatures in the polar stratosphere rise >25°C in less than 1 week. 2) the normally westerly band of winds located at 60°N reverses to Easterly. The first condition qualifies it as a sudden stratospheric warming event, but if it also meets the 2nd criteria then it qualifies as a major SSWE. The result of the warming over the pole is that the cold air that is normally locked up there by the polar vortex is forced outward and into the mid-latitudes. (See the areas of blue). The important thing to note here is that the effects seen at the surface do not happen immediately. Depending on the exact dynamics involved, you could have a lag time as short as a week or as long as a month. To make a long story short, the sooner the troposphere “couples” to the stratosphere, the sooner we will see the impacts at the surface. What are those impacts? Well, this time of year the cold air pool is not yet mature so the cold air that comes will be November cold, not January or February style cold. However, November cold can still be cold enough for snow, especially at elevation. Once the SSWE occurs and the troposphere starts to couple, we will see a much wavier (north-south) jet stream develop. From there, we watch where each wave will have an opportunity to amplify and that’s where we’ll start looking for a storm. So, even though it’s called a “warming event” it can lead to some exciting winter weather. 🥳 ~Meteorologist Mark Margavage