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 K 6 warning began in 1999 following the availability of continuous real-time solar wind data from the NASA ACE spacecraft.

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