The x-ray activity on the sun is a good, leading indicator of how active the sun is and how likely increased geomagnetic activity (leading to stronger aurora) might be. Large solar flares are often (but not always) accompanied by geomagnetic disturbances and the flares may be observed several hours or days before the auroral activity picks up.
Use the information on the Solar Activity page to determine whether the sun is currently active or not. The colour coded graph shows x-ray flux as measured by the SXI instruments carried by the GOES satellites. The graph shows the x-ray flux at a resolution of 5 minutes along with 4 hourly maximums.
The Space Weather Prediction service issues alerts when x-ray flares reach M5, but Aurora allows you to monitor activity beneath this level.