Air quality is forecast to continue to remain in the Unhealthy for Sensitive Groups to Very Unhealthy category for the 24 hour AQI across the state today; however hourly readings may be much higher at times. Most recent monitor observations are currently reading in the Moderate to Hazardous level for an hourly reading. Yesterday saw levels that ranged from Unhealthy to Hazardous across central Idaho and the Panhandle. Southern Idaho experienced widespread Moderate to Unhealthy conditions for the 24hr AQI. Areas most heavily impacted remain in and around central Idaho, especially the Camas Prairie area, with the remainder of central Idaho and the Panhandle not far behind. Slight improvement has been observed across southeastern and south-central Idaho with readings in the Moderate and Unhealthy for Sensitive Groups over southwestern Idaho.
The upper low pressure system will remain quasi-stationary and continue to provide unstable, moisture-laden air into southern Idaho. This will allow for a chance for afternoon thunderstorms over the elevated regions of the Central Idaho Mountains and the Southwest Highlands. Surface winds will be from the west across north and central Idaho at 5-10 mph. Southern Idaho will experience winds from the southwest at 5-10 mph with locally northwest winds within the Treasure Valley. Skies will be mostly to partly sunny when not obscured by smoke. Mixing heights will range from 3,000-8,000 feet AGL across all of Idaho today with poor to marginal ventilation over the Snake River Plain and from Weiser and south within the Snake River Plain to Gooding County. Transport winds will be from the southeast to southwest at 5-10 mph.
This system is expected to slowly track to the southwest through Sunday, further reducing its influence over Idaho. Tomorrow will see a widespread chance of afternoon thunderstorms over the highlands surrounding the Snake River Plain with surface winds ranging from 10-20 mph over all Idaho airsheds. Sunday will see southwest to northwest winds at 5-10 mph. By Monday, slight ridging is expected to occur which will serve to limit surface wind speeds and inhibit the clearing of smoke. An easterly wind component will develop over central and northern Idaho which could promote the advection of smoke into the area.
Improvement of air quality is expected across southern Idaho with the exception of the Lower Treasure Valley and north to McCall. It is important to note that while improvement will occur, conditions will remain degraded; however not to the extent experienced this past week. Improvement from Hazardous is expected over the border of Idaho and Washington on Saturday and Sunday; however levels will remain elevated. Expect nocturnal drainage smoke to enter the Upper Snake River Plain via the Birch, Little Lost, and Big Lost drainages and into the Lower Treasure Valley via the Weiser and Payette drainages each evening with an emphasis on Sunday night into Monday. North and central Idaho will continue to see very high levels of surface smoke throughout the weekend as the change in winds will bring smoke from fires burning in the Northwest and southern British Columbia.