FORECAST SUMMARY: Saturday, may 18, 2024, through Monday, May 20, 2024
OZONE: 8-hour average Ozone concentrations are expected to be mostly Moderate (Yellow AQI), but locations along the western lakeshore and in the southeast may reach Unhealthy for Sensitive Groups (USG, Orange AQI) on Saturday; concentrations Sunday and Monday will range from upper-Good to Moderate.
PM-2.5: 24-hour daily average Fine Particulate concentrations will range between upper Good (Green AQI) and Moderate through the forecast period.
FORECAST DISCUSSION:
Weak high pressure is dominating conditions on Saturday, with warm surface and upper-level temperatures, plenty of sunshine, and a light southerly wind. This set-up creates conditions conducive to ozone development, especially in the most prone locations. Because of this threat, we have an AQA in place along the West Michigan shoreline and in the southeastern portion of the state. The timing for the highest concentrations will be in the afternoon, into the mid-evening hours. The threat of increased ozone will diminish after Saturday due to a frontal boundary passing the state on Sunday.
The Sunday boundary brings in a wind shift to the northwest. Precipitation with this boundary moves into the Upper Peninsula and Northern Lower on Saturday night into early Sunday. Less chances for precipitation will be seen across the central and southern lower portions of the state, aside from scattered development in the southeast on Saturday afternoon or evening. Areas across lower Michigan that remain sunny may reach Moderate for ozone concentrations on Sunday; otherwise, readings should be in the Good range. A mix of Good and Moderate ozone concentrations is expected again on Monday ahead of the next approaching weather system.
The frontal boundary that passed earlier this past week brought the first plume of wildfire smoke into the state. While only moderate increases in PM2.5 were experienced here in Michigan, we have been in generally the same airmass this week, and PM2.5 concentrations are still ranging from low-Moderate across portions of the state. Moderate concentrations may improve on Sunday behind the weak cold front, but southerly winds and increased moisture by Monday may keep daily averages ranging from Good to low-Moderate through early next week.
EXTENDED FORECAST:
Extended forecast models show a strong weather system moving in on Monday into Tuesday. Good pollution levels are anticipated across the northern portions of the state during this period, and readings by Tuesday will be back to the Good range in southern areas.
Next Forecast update: Monday, May 20, 2024