Thanks to everyone for your feedback.
Nick, I need to look at the images closer and see about the color noise. It's interesting that the big blurry snowflakes all seem to have a greenish tone. Image #1 was shot at ISO 4000 so it is pretty noisy overall even though it was properly exposed. #2 was shot at ISO 800 but I underexposed almost a full stop. However, moving the color slider doesn't seem to have any affect. #3 was properly exposed at ISO 2000 and moving the slider doesn't do much. #4, it seems I underexposed about 1/2 stop at ISO 1250 but I don't think the noise came from adjusting exposure. That shot, I further processed in NIK Color Efex and I seem to have introduced color noise in that step so I'll have to go back and figure out where that happened. Thanks for prompting me to study that closer.