Not sure what kind of cloud formation this is. My best guess, based upon this excerpt from Wikipedia, is that it is an example of nimbostratus clouds:
"A nimbostratus cloud is a multilevel, amorphous, nearly uniform, and often dark-grey cloud that usually produces continuous rain, snow, or sleet, but no lightning or thunder.Although it is usually a low-based cloud, it actually forms most commonly in the middle level of the troposphere and then spreads vertically into the low and high levels. Nimbostratus usually produces precipitation over a wide area."
Linking again today with Skywatch Friday.