As noted by Graham yesterday, we have a high NO2 event going on in the midwest. The flow is blocked by an offshore high pressure area off the east coast so nothing is moving quickly. The high PM concentrations seen in the southern Great Lakes yesterday are worse on Saturday on now we are seeing some code red conditions below the bank of clouds in the region. We will watch this as it moves through the east tomorrow and Maryland Department of Environment has asked for lidar profiles at UMBC this weekend.
We also have a couple on interesting weather features on Saturday. In North Dakota, a line of low cloud/fog is seen and you can see a gravity wave feature that is nucleating these clouds. Off the West Coast, the drought is starting to get some relief but this weekend the "Atmospheric River" is flowing into Washington state.