Our local health dept projects covid peak likely mid-may to early jun & maybe return to "almost normal" by july. also assumes best/worst scenarios re: # of confirmed & #deaths, w/#s varying a lot. how can they be so sure of how things will turn out?

Epidemiology is How: In medicine we use our best efforts to project the future by looking at the past. This is NOT always an accurate methodology since many variables exist. The estimates that we presently have take into account many assumptions which also may not be true. The estimates given are an "educated guess" at best and will likely change as more information is obtained. Don't worry about the numbers now.

COVID 19: Your health officials were likely using a model to predict this. Don't know where you live. The models may be accurate or flawed.I am responding in July 2020 - the virus spread is worsening throughout the US (with acception of states like NewYork and NewJersey). What may not have been taken into account was that some states would open too early & that many people refused to mask or social distance