A tenacious temperature inversion has finally eroded over Denver,CO allowing temperatures to rebound back above freezing. The persistent sub-zero temperatures, light winds, and little atmospheric mixing in the planetary boundary layer appears to have generated a classic winter poor air quality scenario today as folks burned wood to stay warm in an atmosphere conducive to rising PM2.5 concentrations. The impact such an arrangement can have on air quality, as Ray mentioned in yesterday's post, is visible in Denver's AIRNow AQI loop (bottom left). From about 12AM - 5AM LST PM2.5 concentrations increased to Code Orange (Unhealthy for Sensitive Groups) levels, until finally beginning to taper off. Although the inversion weakened, light winds are forecast to continue, and therefore generate poor visibility conditions and elevated PM2.5 concentrations through Tuesday (bottom, right). A Residential Burning Restriction was issued from Monday 4PM- Tuesday 4PM to help reduce potentially hazardous conditions.
Looking ahead, the 32 degree Fahrenheit isotherm (bold red line) is forecast to remain well south of the Rocky Mountain States through Wednesday as northerly flow filters chilly Canadian air southward (bottom left, courtesy UNISYS). Elsewhere, air quality was mostly good, however the HMS analysis team did report a few areas of light smoke over northwest Washington and California (bottom right).