How to read the aurora map
The colours are the chance of seeing aurora overhead at that spot within the next hour or so, as NOAA's OVATION model estimates it. The three bands are the levels our forecast pages use for the same number: 5–20% moderate, 20–40% elevated, 40% and over high. Below 5% the map stays empty.
The ring is the auroral oval, and it is centred on the geomagnetic pole, not the geographic one. That pole lies in the Canadian Arctic, so on the map the oval sits off-centre, shifted towards North America. The empty middle is the polar cap, where aurora is less frequent, not more.
The colour means aurora overhead. A bright display can be seen low on the poleward horizon from up to about 1000 km (600 miles) beyond the edge of the oval, so a place just outside the colour is not out of luck. How far depends on how bright it is, which is why the map draws no fixed "view line".
Clouds and daylight are not on the map: a colour over your town under overcast or at noon shows nothing. Search for your place above — next to its name you get the aurora probability near it, its cloud cover this hour and whether the sky is dark.
How far ahead the map looks
The model looks 30 to 90 minutes ahead: that is how long the solar wind measured at the L1 point, 1.6 million km (1 million miles) upstream, takes to reach Earth. We fetch NOAA's new frame every 15 minutes. The frames of the last three hours show which way the oval is moving; they are not a forecast of the next three.
For this evening rather than the next hour, read the three-day Kp forecast and the ranking of places for tonight. A place's own forecast goes further than the map: its Aurora Score weighs the activity against that place's threshold and adds cloud cover, darkness and the moon — how the score is built. What a Kp number means at your latitude is in the Kp index guide.
