The top graph plots the annual average lead time of K6 Short-Term Warnings. Lead time is defined as the time between the warning being issued and when a K6 is measured at the Boulder magnetometer. A missed warning, where a K6 is observed but no warning was issued, is counted as a lead time of 0 minutes. The middle plot shows the annual average of the Heidke skill score. This score ranges from -1 to +1, where all correct warnings give a score of +1, no correct warnings give a score of -1, and no K6 observed or no warnings issued give a score of 0. The bottom histogram plots the annual frequency of K6 observed, warning hits, warning misses, and warning false alarms (Boulder, Colorado data). The K6 warning began in 1999 following the availability of continuous real-time solar wind data from the NASA ACE spacecraft.

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