Judy and I drove to the parking lot at 100th South and went south on the Parkway. I stopped at the bench, as I've been doing all this week, and she went to the tunnel at 106th South. She walks faster than I jog or walk and thus goes farther. The sky was overcast and a slight wind was blowing, but the temperature was in the mid 50s (F), and it was nice to be out. We left home in the late afternoon but finished our exercise before it got dark.
Today (Saturday, and the forecast for Monday) was a Green day. We went from a Green day last week to Yellow days, indicating an inversion with bad air was beginning to form. However, instead of progressing to an Orange day and then a Red day with bad air, we went back to a Green day. This change was caused by warm air that came into the valley during day times. Inversions require cold air on top of warm air. On Green and Yellow days, I go outside to run and walk. On Orange and Red days, I go inside at the rec center to run and walk. I check the air quality each day before I run to help me make a final decision about going outside or going inside.