Western Slope looking much better while one more day to go east of the divide

 A workweek that has been plagued by out-of-state wildfire smoke may have a happy conclusion as the atmosphere finally gets cleaned out.  Step one of the process has already been completed:  the upper level transport winds from the Canadian wildfires have been shut down.  That means no additional smoke is expected to be pushed into Colorado over the next 24 hours.  Check out this morning's visible satellite image compared to the same time on Tuesday.  Note the milky look of Tuesday's image (left), particularly over eastern Colorado.  Eventually all of that smoke mixed down to the earth's surface and impacted the air that we breathe.  That smoke way up in the atmosphere is largely absent today (right).  So instead of particle pollution (PM2.5) increasing today we anticipate it will decrease, albeit gradually.

Visible satellite image at 7:30am Tuesday (left) vs. 7:30am Thursday (right)

However, folks in the eastern half of Colorado are not out of the woods just yet.  There's still quite a bit of smoke out there this morning and it will take some time to decrease.  We are also still dealing with elevated ozone for the Interstate 25 urban corridor including Ft. Collins, Boulder, Denver, Colorado Springs, Greeley, and surrounding areas.  Additionally, we have been breathing air filled with smoke for several days now.  So we are extending our health advisories for the entire eastern half of the state until midnight Thursday night/Friday morning.  Everyone should continue to follow the health recommendations we have been stressing all week -- reduce prolonged or heavy exertion, limit time outdoors, take extra breaks while being outdoors -- particularly for all of our neighbors that suffer from heart/lung disease, older adults, and children.  And for those that consider themselves healthy, it's still not a bad idea to push off outdoor exercise one more day as Friday should be much improved.  Not only will the smoke continue to naturally mix out of the atmosphere, scattered showers and thunderstorms Friday afternoon should finish off the job of cleaning things up.

For our friends in western Colorado, we are already starting to see the benefits of the changing air mass.  Smoke levels are anywhere from 25-50% lower than they were at this time yesterday.  So although we don't suggest running a marathon today in Aspen, Steamboat Springs or Alamosa, it is safer to spend a bit more time outdoors today.  The air quality improvement is expected to continue throughout the day today and into tomorrow.  The one wild card on the Western Slope today is elevated ozone again for the Grand Valley as the smoke has had some influence in the Grand Junction area the past few days.  We expect ozone to be a bit lower today, but we will be watching it closely and will issue another advisory for Grand Junction if needed.

How about the upcoming weekend?  The good news is that we are not expecting the upper level winds to shift back to the Canadian or Pacific Northwest fires.  However, we will need to keep an eye on upwind wildfires in central and southern California, Nevada and Utah.  However, at this point it looks like any smoke those fires produce should be nowhere near what we have seen so far this week.