Warm fall weather causes air quality to drop again
No, it’s not wildfire smoke, but once again Puget Sound area air quality is on the decline. This time, it is our current dry, sunny, fall weather pattern creating poorer air quality.
High pressure aloft has put a lid of warmer air on top of the cooler-than-average air near the surface, creating what is called a temperature inversion.
These inversions trap pollutants close to the surface, creating stagnant conditions. The warmer air aloft has freezing levels near 9,000 feet Tuesday morning.
Monday morning, many Puget Sound area air quality sensors rose from the good to moderate category. The Puget Sound Clean Air Agency has put a Stage 1 Air Quality Burn Ban in place for parts of the Puget Sound area. High levels of wood smoke during nighttime hours have resulted in poorer air quality. Other pollutants like auto and industrial emissions also accumulate under a temperature inversion.
Though air quality may improve during the day, the nighttime stagnant conditions could lead to air quality values being unhealthy for sensitive groups.
Also, it has not rained since Nov. 8 with essentially no rain expected heading into this weekend. So the temperature inversion and resulting stagnant conditions are expected to continue through this week.
What is a temperature inversion? An inversion is when the air aloft is warmer than cooler air near the surface. An analogy would be a mountain lake during summer. The water near the surface is warm, but if you jump in, it is much colder just a few feet below. The same temperature profile in a temperature inversion occurs on a grand scale like we are experiencing right now.
Autumn involves longer nights and shorter days. During extended weather patterns with clear skies and light winds, temperature inversions can become established.
A temperature inversion can occur at any time of the year but is most frequent during the fall and winter seasons. Cooler air is heavier and tends to slide into low-lying areas like valleys. Many outlying areas like Olympia and Arlington had temperatures drop into the 20s. Meanwhile, temperatures in the mountains were in the 30s and 40s.
The next threat of rain appears to be sometime early next week. But until then, air quality in the Puget Sound area is not anticipated to improve.
Follow Ted Buehner, the KIRO FM news meteorologist on Twitter