FORECAST SUMMARY: Friday August 15, 2025, through Monday August 18, 2025
Ozone:
Ozone concentrations are expected to be in the Good (Green AQI) to Moderate (Yellow AQI) range.
PM-2.5:
PM-2.5 concentrations are expected to be in the Moderate (Yellow AQI) range.
FORECAST DISCUSSION:
We incredulously enter mid-August this upcoming weekend with summer-like temperatures continuing in the lower peninsula and cooler temperatures in the upper peninsula. Surface high temperatures are expected to be in the mid-to-upper 80s for the lower peninsula with high dewpoints expected throughout southern Michigan. For the upper peninsula, a weak pressure system and frontal boundary will linger in the Northwoods this weekend to produce northerly flow, which in turn, will keep northern areas cooler and slightly drier.
With the majority of the southern Great Lakes dealing with high dewpoints and humidity, pop up showers should be expected throughout this weekend along with the possibility of a few lines of rain and potential storms. As of now, the areas with the greatest chance of precipitation will be western and northern areas. This weekend will not be a complete wash out, as some models are showing rain dissipating earlier than others, but some areas across Michigan will see precipitation.
For air quality, region-wide Moderate PM-2.5 concentrations are being reported currently with those concentrations expected to persist throughout the weekend. Relatively light winds will lessen the dispersion capability of these concentrations which is why they are expected to linger. For Ozone, a few of the ingredients for Ozone development will be present this weekend, but cloudy conditions and high dewpoints will help keep Ozone at bay. We have seen historically when dewpoints reach the upper-60s and into the low-70s, the Ozone chemical reaction does not react well within the atmosphere. One thought is that the air is too heavy and moist for the precursors to react with residual Oxygen atoms. Another is that there is too much moisture in the air so the UV radiation coming in is being scattered and refracted by the water droplets in the air, so the reaction to produce Ozone does not occur effectively. Due to these conditions in place this weekend, mid to potentially high Moderate Ozone concentrations are expected.
EXTENDED FORECAST:
The airmass this weekend continues into late Sunday with a cooldown expected early to mid-next week. Air quality is expected to range between the Good and Moderate range.
Next Forecast update: Monday August 18, 2025