J. Miles Coleman of Sabato's Crystal Ball has a terrific deep dive on turnout patterns in the 2020 primaries with lots of nice maps. His summary points:
"--With very few exceptions, statewide turnout in the 2020 Democratic primary has been higher than 2016.
— Suburban areas have seen some of the sharpest turnout increases — though these areas tend to have higher population growth, they’ve also trended blue in general elections, perhaps a positive indicator for Democrats looking to the fall.
— Meanwhile, some rural areas that have been trending away from Democrats in places like North Carolina and Oklahoma saw turnout lag behind 2016.
— While Bernie Sanders seems to have a stronger opponent in Joe Biden than he did with Hillary Clinton, Sanders’ prospects may have been hurt by partisan realignment since 2016."
His conclusion on political implications, which I think is very reasonable.
"One clear pattern...is that the geographic trends in the Democratic primary are lining up with the contours of recent general elections. Greater turnout in suburbs has buoyed Joe Biden’s prospects and given us an idea of what the Democratic coalition may look like in November — the bigger question will be if that coalition is good for 270 electoral votes, particularly if Democrats continue to lose ground in areas outside major metro areas. That Biden did significantly better than Hillary Clinton in outstate areas in many states may also be an encouraging sign for the fall, but — again — primaries are not general elections, and the overall movement away from Democrats in these kinds of places showed up in the turnout patterns in some states as well."
That is indeed the dynamic that will decide the 2020 election.