FORECAST SUMMARY:

Friday, July 19th, 2019 through Monday, July 22nd, 2019

THE CURRENT ACTION DAY ADVISORY IS EXTENDED THROUGH SATURDAY, JULY 20th IN THE FOLLOWING MICHIGAN COUNTIES...

IN WEST MICHIGAN:

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

Ozone:  8-Hour average Ozone concentrations will be a mixture Moderate and USG during Friday and Saturday.  Air Quality should return to Good and Low Moderate for Sunday and Monday. 

PM-2.5:  24-hour average Fine Particulate concentrations will be mostly Good to Low Moderate. 

FORECAST DISCUSSION

The hot, humid weather will continue through Saturday.  With the current high temperatures and humidity, if we get clear skies then elevated ozone potential is very high. 

The big question is how much cloud cover will we see?  During Thursday, cloud cover was enough to keep ozone production in the Moderate range.  As this forecast is being written Friday morning, cloud cover is present but looks to be thinning.  If that trend continues, we could see ozone numbers reaching the USG levels.

The cloud cover question is also an issue for Saturday.  The various forecast models are very inconsistent with their cloud forecast.  Some of the models have significant cloud cover for Saturday while others keep it mostly clear until late afternoon.  Knowing that clear skies would lead to high ozone concentrations, to err on the side of caution the current Action Day Advisories will be extended through Saturday.  

The threat will end on Sunday following a cold front passage Saturday night.

EXTENDED FORECAST:

Air Quality should be mostly Good to Low Moderate going into the next work week.

Forecast updated by Jim Haywood: Friday, July 19th, 2019
Next forecast update: Monday, July 22nd, 2019