Northern Hemisphere Ozone Hole

For the most part, there has been good news concerning the ozone layer in recent years as efforts to reduce ozone-depleting chemicals appear to be working. 

However, unusually low stratospheric ozone concentrations are presently found over the high latitudes of the northern hemisphere.  Below is the total ozone over the Northern Hemisphere on Friday showing a clear ozone hole.   

Source: https://ozonewatch.gsfc.nasa.gov/NH.html

One can compare that to the long-term climatology to illustrate that those concentrations are unusually low. 

Source: https://ozonewatch.gsfc.nasa.gov/NH.html

Another way to look at it is to compare to past observations made during the satellite era (beginning in 1979.  The graphs below show the range of highest and lowest values of stratospheric ozone in the polar region (top) and temperature (middle) illustrating that both stratospheric ozone and temperature have been exceptionally low and occasionally at or below the lowest on record for the respective day of the year over the past 2-3 months.  

Source: https://ozonewatch.gsfc.nasa.gov/NH.html

I suspect the record low ozone and temperatures are closely related.  The low temperatures enable the formation of polar stratospheric clouds, which in the presence of CFCs enable the reactions to occur that lead to ozone depletion.  These observations are also consistent with the remarkably strong polar vortex that persisted for much of the winter.  The low ozone, low temperatures, and strong polar vortex are, however, all related like chicken-and-egg, so I'm forced to wait until the stratospheric chemistry and dynamics experts weigh in to know why this has happened this winter.   For a bit more detailed discussion, see this article in Nature.