President Trump on Sunday said he was persuaded by coronavirus pandemic models to extend national social distancing guidelines through the end of April. The White House plans to lay out the data and assumptions behind the decision on Tuesday, and we look forward to that. Meanwhile, we thought readers might appreciate a dive into one of the more prominent Covid-19 models to look at the wide range of outcomes—and how much uncertainty there continues to be.

White House coronavirus coordinator Deborah Birx said its assessment...