FORECAST SUMMARY: Wednesday July 26, 2023, through Thursday, July 27, 2023

OZONE: 8-hour average ozone concentrations are expected to be Moderate to USG

PM-2.5:  24-hour average Fine Particulate concentrations are expected to be Good to Moderate

FORECAST DISCUSSION:

..AIR QUALITY ACTION DAY ADVISORY FOR THURSDAY JULY 27...

The Action Day Advisory includes the following counties:

in West Michigan:

ALLEGAN...  BERRIEN…  CASS…  KENT...  MUSKEGON...  OTTAWA…  AND VAN BUREN COUNTIES

The Tuesday statewide Action Day advisory for fine particulates turned out to be an accurate prediction as we saw elevated concentrations at many of our statewide monitors.  In addition to the high smoke concentrations, we were surprised to see ozone values get as high as they did at several monitors.  This proves the amount of ozone precursor gases found in wildfire smoke.

 We did not extend the Action Day advisory into Wednesday as the smoke plume will be exiting the state and incoming rain and thunderstorms will help drop concentrations during the day.  That said, the eastern side of the state will be the last to see the benefits of the clearing, so I increased their AQI forecast to USG as a precautionary measure.  Although morning ozone concentrations are higher than normal, the increasing clouds and rain chances will discourage elevated production and bring those numbers back down.

 Tomorrow will be another story as it may be one of the hotter and humid days of the summer.  Predictions are for temperatures in the low 90’s with dew points around 70 degrees under sunny skies and low wind speeds.  Under normal conditions, this would qualify for elevated ozone.  But we also still have leftover ozone forming gases, courtesy of the exiting wildfire smoke, which could boost ozone production even more.  As such, I am issuing Action Day advisories in both West Michigan and Southeast Michigan for Thursday.

 Friday may be a continuation of the Action Day advisories, but I will wait until Thursday morning to make that call when the latest forecast products are available.

EXTENDED FORECAST:

 Air Quality should be generally Moderate to potentially USG through the remainder of the week.

Forecast updated by Jim Haywood: Wednesday, July 26, 2023

Next forecast update Thursday, July 27, 2023