Kp Index Now: Live Value and 3-Day Forecast

It depends on your geomagnetic latitude, which is not your map latitude: at Kp 3 the auroral oval's equatorward edge sits near 60° geomagnetic, so Kp 3 is a good night for places at or above that line and too little for places well below it. When the aurora is bright it can still be seen low on the poleward horizon from up to about 1000 km (600 miles) beyond the edge. The ladder on this page and the search box give the Kp your own place needs. Kp is a probability signal, not a guarantee — clouds and darkness still decide the night.

Kp 5 and above. NOAA's G-scale maps directly onto Kp: G1 (Minor) is Kp 5, G2 (Moderate) is Kp 6, G3 (Strong) is Kp 7, G4 (Severe) is Kp 8 and G5 (Extreme) is Kp 9; anything from Kp 0 to 4 is below storm level. A storm enlarges the auroral oval, so the aurora can reach latitudes that rarely see it — but the Kp describes the size of the oval, not the sky above you, and a storm under cloud or in daylight shows nothing.

Good for the day ahead, a guide further out — and no Kp forecast is exact. The three-day forecast is an outlook: a disturbance leaving the Sun is seen one to three days before it arrives, so the day is known roughly and the strength is not. What decides the strength is the north–south direction of the magnetic field that arrives with it (Bz), and that can only be measured 15 to 60 minutes before it reaches Earth. Treat tomorrow's Kp as a likelihood, check again on the evening itself, and look at the figure marked "estimated" for what is happening now.