The height of the blue bars corresponds to how many deaths were reported each week from Jan. 1, 2017 through Oct. 3, 2020. The yellow line marks a maximum for the estimated number of deaths to expect for any week, based on previous years. This upper threshold for expected deaths helps determine when the number of observed deaths is unusually high compared to historical trends – like due to the flu in winter 2017-2018, and now due to COVID-19.