From Joshua Stevens at the NASA Earth Observatory:
But over the longer term, climate change is causing spring to begin earlier and earlier across the United States. These maps reveal just how much earlier spring is arriving in National Parks across the country. The data were published in 2016 by ecologists from the National Park Service, working in collaboration with colleagues at other agencies and institutions.
Limited to only national parks, the view still provides a good idea. For a model-based view at higher granularity, check out the USA National Phenology Network.