Locating…

The gauge compares tonight's Kp to a rolling baseline built from the readings we have on hand — roughly the last three days of stored snapshots. The shaded band is the middle half of that recent range (25th–75th percentile); the dot is now. It is deliberately simple, and honest about its limits: this is "usual lately," not "usual for this place and season." Kp is a planetary index — the same number everywhere on Earth at a given moment — so the baseline says nothing location-specific on its own; what makes it local is the "needed here" line, set by your magnetic latitude. A proper per-location seasonal climatology would need years of history and a real model; that's a later milestone (a longer-term data store), not this.

Kp is a 0–9 planetary index of geomagnetic disturbance, issued every three hours by NOAA from a network of magnetometer stations. Higher means the Earth's magnetic field is being shaken harder by the solar wind, which pushes the auroral oval further from the poles. It's a global average, not a local reading — so a high Kp is necessary but not sufficient to see aurora where you are; that depends on how far the oval reaches your latitude (next card).

Aurora sits over the geomagnetic poles, which don't line up with the geographic ones — so what matters for you is your magnetic latitude, not the one on a map. We estimate it with a centred-dipole approximation (a tilted-bar-magnet model of Earth; pole near 80.6°N, 72.7°W). The "Kp needed here" figure uses the well-known rule of thumb required Kp ≈ (66 − |magnetic latitude|) ÷ 2. It's a rough estimate, not a precise forecast — it ignores the non-dipole wrinkles of the real field and local sky conditions — but it's honest about which places need a big storm (low magnetic latitude) versus a quiet night (under the oval).

OVATION Prime is NOAA's short-term auroral-precipitation model. Every few minutes it estimates, on a 1° global grid, the chance of visible aurora overhead — driven by live solar-wind measurements from the DSCOVR/ACE spacecraft upstream of Earth. The "chance here" number is that model's value at your exact grid cell (we snap your coordinates to the nearest degree). It's a genuine physical model, but a short-range one: it says what the sky is likely doing in the next ~30 minutes, not tonight as a whole, and it can't know your clouds.