Figure 1: Calibration of forecast accuracy as a function of ensemble spread.

Retrospective forecasts of outbreak peak timing initiated for each of the 2003–2004 through 2011–2012 seasons, excluding the pandemic seasons of 2008–2009 and 2009–2010. Retrospective forecasts were made for 115 cities, which were then aggregated by census division or nationally. Plots present the probability that an ensemble predicted mode peak timing is accurate within ±1 week of the observed ILI+ peak as a function of ensemble predicted peak timing variance log transformed. (a) Training and forecast made using climatological AH, census division aggregation; (b) as in (a), but aggregated nationally. The coloured lines are for ensemble mode peak predictions 10+ weeks in the future (magenta), 7–9 weeks in the future (blue), 4–6 weeks in the future (cyan), 1–3 weeks in the future (red), 0–2 weeks in the past (green) and 3–5 weeks in the past (black).