While the eastern half of the US is experiencing below average temperatures due to the second polar vortex of the season, the west coast had above average temperatures. The warm temperatures along the western US are associated with a high pressure system of the region (top left image, courtesy National Weather Service). Strong temperature inversions and stagnant air conditions associated with the high pressure system is enhancing particulate matter (PM) production. The temperature inversions trap pollutants near the surface from reduced turbulence and mixing with air aloft. During the winter these inversions are the strong. The warm air aloft on top of cooler air acts like a lid, suppressing vertical mixing and trapping pollutants at the surface leading to poor air quality.
The right top webcam image is from the US Forest Service San Gabriel webcam. The images captured the haze associated with the Code Yellow to Orange PM2.5 AQI (Airnow animation) levels experienced in California. PM2.5 Code Yellow-Orange was recorded along the Rocky Mountain states. The Kings Canyon fire in the San Joaquin Valley continues to burn, as shown in the MODIS Aqua RGB image, contributing to the poor air quality in the region.