The End Is Near

Source: http://www.keepcalm-o-matic.co.uk

After a 2nd winter of hideous air quality, we are now approaching the end of the inversion season.  

As shown in the graph below, days with PM2.5 concentrations > 17.5 (blue) and > 35 ug/m3 (red) are most common during the heart of the winter and drop off dramatically after the 7th week of the year (Feb 12-19).  

Source: Dave Whiteman, University of Utah

Thus we are almost out of the woods.  There are, however, some PM2.5 > 35 days all the way to the 8th week of the year (Feb 26-Mar 4) and an elevated frequency of PM2.5 > 17.5 through the 10th week of the year (March 5-12) (events after that are probably due to blowing dust).  For that reason, I won't stick a fork in it just yet.  

Nevertheless, poor air quality events later in the cool season (e.g., late Feb and early March) typically require a good snowstorm followed by a long-lived ridge.  We do have a ridge forecast to build in for early next week, and we might see an increase in PM2.5 concentrations for a couple of days, but it looks to be a short-lived event without snow cover, so I'm not expecting it to be anywhere near as nasty as what we saw in December and January.