Good Friday Morning. There have been lots of questions regarding the upcoming pattern change that everyone is talking about. Over the last three weeks you have seen articles floating around on social media that the Polar Vortex was coming South. Some of these said it was in time for Christmas, some say it would occur around New Year's. There are several factors that these folks didn't take in when they were trying to forecast this.
So all Meteorologists have been watching a phenomenon underway called sudden stratospheric warming (SSW) over the Arctic. Earth's Atmosphere is comprised of many different layers. We live in the troposphere. This layer of the atmosphere holds 99% of Earth's water vapor. It varies but in our area the troposphere is approximately 11 miles in depth. It is shallower near the poles and deeper in the tropics. Above the troposphere is the stratosphere. This is the layer where the sun's ultraviolet radiation is absorbed. Because of that the stratosphere is warmer at the top and cooler in it's lower portion, closest to earth. It is the opposite than the troposphere, where we live ,because the higher you get in the troposphere the colder the temperature is. The next layer of the atmosphere is the mesosphere, named from the Greek word mesos which means middle, because it is the middle atmospheric layer. Again here, in the mesosphere, the temperature lowers with altitude, just like the troposphere. The mesosphere holds the coldest temperatures in the entire atmosphere. The mesosphere is located anywhere from 30-40 miles above Earth's Surface.
Now that you know a little bit about the atmosphere and the layers surrounding the stratosphere lets get to the point. So what is sudden stratospheric warming? Sudden stratospheric warming is the sudden rise of the measured temperature in the stratosphere of 90F. It is caused by a disruption in the westerly winds of the northern (Polar) jet stream (In the Northern Hemisphere Winter). That disruption can be caused by natural disturbances in the weather patterns located here in the troposphere. This year's sudden stratospheric warming event is a major one. The stratospheric westerly winds were disrupted and have become easterly. Now, before everyone starts freaking out, no the world isn't coming to an end and the clouds aren't falling. These events happen more than what you might realize . Major stratospheric warming events occur on average about once every two years. Minor stratospheric warming events are more common. In major stratospheric warming events the stratospheric polar vortex is either completely displaced from over the pole or split into two different pieces and then displaced. This eventually causes an impact to winds in the troposphere. Easterly winds over the North Pole (Westerly winds over the South Pole in the Southern Hemisphere Winter) back and become westerly causing a shift in Arctic Air down over Europe or North America. Some folks use the terminology as headlines that are meant to scare or get clicks on their site. The polar vortex is located in the stratosphere and doesn't come down to Earth's troposphere where we live. When sudden stratospheric warming occurs it affects the polar vortex and causes it to become displaced. That displacement of the polar vortex does cause colder than normal temperatures to become displaced from the pole, down over more populated portions of the globe. Its not always as cold and long lasting as what we saw during 2018's sudden stratospheric warming event that caused our area to remain below freezing for more than a week.
So what does this year's event have in store for us. The atmosphere began to suddenly warm in the weeks before Christmas. Many thought this meant the temperatures were going to crash in our area between Christmas and New Year's. It just hasn't happened. These events can take anywhere from a couple of weeks to a month to come to fruition. We do see signs that the pattern will turn colder around our area after January 10th, but more pronounced after January 20th. I still do not think that we are looking at a long sustained cold snap that will keep us below freezing for days on end like last year. I do think temperatures are going to fall back down below average though. As this occurs it looks like the southern jet stream may relax a little bit, allowing us to dry out just a little bit in between precipitation events. It doesn't look like it will relax completely though, so for snow and winter precipitation lovers stay tuned.
If you remember or look back at our winter outlook we indicated that the temperatures overall for Meteorological Winter (Dec-Jan-Feb) would end up landing just about average in our area. This means that there will be times of colder than average temperatures along with equal times of warmer than average temperatures. In the end we think it will average out. The one thing that continues to be a problem is the precipitation. While the southern jet stream will relax a little bit, as said, I still think January and February will end up above average in the precipitation side of things.
So lets summarize. In the coming week the temperatures will start to become cooler, turning chilly after January 20th. Precipitation will relax some going out past January 15th but we still look to remain wet. Storm systems will continue to yield high precipitation values because of El Nino causing more water vapor from the Equatorial Pacific to become entrained in the Southern Jet. Here are some snap shots from the long range models for the next 45 days.
Chief Meteorologist Chris White