Meteorologists warn of a rare winter pattern not seen in decades
Meteorologists have been noticing a strange kind of winter pattern lately. Researchers at NOAA have found that parts of the atmosphere are aligning in ways they haven't seen in decades. These include La Nina and a stratospheric wind reversal, as well as a surprisingly early shift in the Arctic polar vortex.
Amy Butler at NOAA's Chemical Sciences Laboratory and Daniela Domeisen of ETH Zurich said that the slow-moving background conditions could have serious effects on the country's winters. We could be in for a rather unusual winter pattern if the predictions are correct.
NOAA reported that sea surface temperatures during September and October were lower than normal. Normally, La Nina is associated with a stronger polar vortex that affects air flow, but this year's vortex is not working that way.
Climatologist Judah Cohen explained the polar vortex as a kind of atmospheric fence that normally keeps cold air from rotating. However, this is changing due to large stratospheric warming events. These are bursts of atmospheric heat that weaken the vortex, sometimes even inverting it. Such warming can cause temperatures in the polar stratosphere to rise by about 30 to 50 degrees Celsius in just a few days.
In late fall, NOAA model forecasts had signaled signs of warming long before winter set in, which is quite unusual. The last recorded instances of seasonal disruptions of this magnitude were in 1958, 1968 and 2000. The peak season for sudden stratospheric warming is typically from January to March, so any major event is likely to occur between mid-December and mid-January.
What could cause these changes?
Arctic air moves south, often bringing with it sharp drops in temperature, along with heavy snowfall. In other words, places that have had mild temperatures all winter may suddenly have to deal with colder days.
If the changes in the stratosphere continue, we are likely to see a series of snowstorms in parts of the US and Europe. A turbulent vortex and a tidal current could also create longer storm corridors. These could bring thunderstorms and denser wet conditions. They could also bring pockets of snow to places that don't usually experience them during the winter.
However, these weather conditions won't be everywhere, nor will they all be there at the same time. Currently, NOAA's winter forecast shows the usual La Nina surface pattern. That includes a wetter Pacific Northwest, a drier South, and a warmer Southeast. But they have warned that stratospheric changes could change those expectations.
