Aurora are related to geomagnetic activity (the amount the Earth’s magnetic field varies with time), so by monitoring geomagnetic activity we are able to forecast auroral displays.  

In the diagram above, the black line shows today’s geomagnetic activity, which has been measured at Ministik, near Edmonton, Canada. For comparison, the blue line shows the geomagnetic activity for a geomagnetically quiet day, where there were no aurora displays.

As the geomagnetic activity increase, the black line will be further away from the blue line. 

The coloured bars show the hourly prediction of the likelihood of there being auroral displays tonight. These percentage values, shown on the right-hand side of the chart, are calculated using the data plotted by the black line for that hour. The Explanation section of this website provides a more detailed explanation of this chart, as well as how we forecast auroral displays.