| definition |
- Forecasts of the likelihood (from 1% to 99%) that the daily geomagnetic activity level will reach a particular activity category. The four categories are Quiet to Unsettled, Active, Minor Storm, and Major to Severe Storm. The geomagnetic category assigned to a day is determined by the highest observed k-index for the day. Quiet to Unsettled = k 0 to k 3, Active = k 4, Minor Storm = k 5, and Major to Severe Storm = k 6 to k 9. Middle-latitude forecasts are verified against Fredericksburg, VA observations and High-latitude forecasts are verified against College, AK observations. Forecast lead times range from one to three days.
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