FORECAST SUMMARY: Tuesday, August 22, 2023, through Wednesday, August 23, 2023

PM-2.5: 24-hour average Fine Particulate levels will range between middle Good and low Moderate.

OZONE: 8-hour average Ozone concentrations are expected to be Good to Moderate across much of the state, with USG possible in the southwest Wednesday.

FORECAST DISCUSSION: As expected, a complex of showers and storms is moving through the Upper Peninsula southeast towards the Detroit area Tuesday. This area keeps clouds and precipitation in the forecast for all but the southwest portion of the state. High pressure which has been dominating with a northeasterly flow the past two days tracks east Tuesday. As this happens, a frontal boundary to our south begins moving north towards the state. The easterly flow Tuesday switches to the south Wednesday ushering in warm/humid conditions, especially in the southwest. The frontal boundary is expected to stall across central lower Michigan into Thursday and associated moisture keeps showers and storms in the forecast across northern, central, and eastern locations.

Good to low Moderate ozone and PM2.5 levels can be expected Tuesday thanks to easterly winds and cooler surface and upper-level temperatures. Clouds and precipitation near and north of the frontal boundary Wednesday should keep ozone from reaching higher than Moderate, but models show less clouds in the southwest. More sunshine in the southwest along with southerly winds and increases in temperatures makes ozone conditions likely. Forecast models seem to align with our thoughts, picking up on this ozone increase as well. To cover the threat for ozone in the Unhealthy for Sensitive Groups (Orange AQI) range, we have issued an Air Quality Action Day on Wednesday for the southwestern counties listed above. The threat for increased ozone looks to continue Thursday so we will evaluate current trends and weather maps Wednesday morning to determine if the Action Day will be continued and/or expanded Thursday.

Wildfire smoke maps were reviewed and there is still a light plume lingering over the region, but PM2.5 levels have improved to mostly Good early Tuesday. We do not expect wildfire smoke to be a large influence in pollution levels this week, however, increases of PM2.5 into the Moderate range can be expected in central and southern areas with the southerly flow, humid conditions, and pooling that typically happens along frontal boundaries.

EXTENDED FORECAST: The warm-up Wednesday and Thursday may be short-lived due to a cold front expected to pass through late in the week. If this pans out, the threat for increased ozone should come to an end Friday.

Next Forecast update: Wednesday, August 23, 2023