Much of the Central Plains, Great Lakes, Southeast, Mid-Atlantic and Northeast experienced elevated air quality indices (AQIs) today (top left). Peak PM2.5 measurements reached Code Yellow (Moderate) levels, however several isolated areas across the Great Lakes and Mid-Atlantic reached the Code Orange (Unhealthy for Sensitive Groups) range. Unfortunately, widespread cloud cover over the polluted regions of the United States impeded Aerosol Optical Depth (AOD) readings from the MODIS overpass on board NASA's Terra satellite (top right). High pressure associated with atmospheric ridging in the upper-levels of the atmosphere over the Mid-Atlantic weakened the low-level flow over the region, likely contributing to low particulate dispersion in the planetary boundary layer, and therefore elevated PM2.5 (middle left). Observations from various stations across Maryland support this notion, as surface wind measurements were nearly stagnant throughout the afternoon (middle right). This weather pattern is forecast to remain in the region, tomorrow, motivating air quality forecasters to call for another, perhaps more widespread poor air quality day for Maryland (bottom).