Science behind why it’s been so cold lately
With an average temperature of just 41.3 degrees, this spring has been one of the coldest astronomical springs ever recorded. Only 1983, 1926 and 1899 were colder. While it seems as if winter has had a firm grip on the nation for most of the year, Mother Nature will finally usher in the warmest air we’ve seen all year long. It will be a nice break from what has been a wild ride in the battle of the seasons.
But what caused the cold air and why has it been prolonging winter in the eastern half of the nation? It all comes down to two meteorological terms: The Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO). These are weather patterns that can be big drivers in weather across the world.
So what are these terms and how does that translate to colder temperatures for a good portion of the country? Simply put, the AO is an index with a positive or negative phase. The more negative the phase, the higher the heights in the atmosphere, which translates to a weaker polar vortex and atmospheric circulation. This leads to warmer air in the Arctic and colder air being dislodged farther south.
Usually directly correlated with the AO is the NAO, which is a measure of pressure differences between the Icelandic Low and Azores High. A positive phase leads to a strengthening low/high and allows cold air to drain off of North American instead of building up. A negative phase leads to a weakening of both pressures and allows cold air to build up.
When both phases are trending negative, as they have been for a large majority of the spring, the cold air in the Arctic and Canada becomes dislodged farther south into the United States. Data provided by the Climate Prediction Center show that the negative phases have been largely dominant since the start of meteorological spring on March 1.
Meteorological spring differs from astronomical spring in that it allows for easier record keeping. Since March 1, 60 percent of all of our days have seen below normal temperatures with only a handful at or above average.
Changes are on the way, however, that will finally make it feel like spring. The jet stream, which has been the primary focus for the cold lately, will finally lift to the north as an upper-level ridge builds into the area. This will squeeze out some of the warmest temperatures we’ve seen this year and likely bring the first 80-degree day since October 26. Unfortunately, winter looks to have one last hurrah, as a strong cold front is set to track through the region and bring the possibility for strong storms and a return to cold temperatures by the weekend.
Stay with ABC 17 Stormtrack as we continue to track the warmer days ahead and follow us on Twitter @ABC17Stormtrack.
