Kp index now, and what it means for your sky
Kp is a 0–9 measure of how disturbed Earth's magnetic field was over a three-hour window, from thirteen ground observatories. The higher it is, the further from the poles the aurora reaches — but it is a global, three-hour index, so it cannot tell you what is over your head right now. This page shows the live estimate, the next hour, the three-day forecast, and the row on the latitude table that is yours.
Now, next hour, three nights, 27 days
Reading NOAA…
The last seven days, observed
Reading NOAA…
The chip at the top is a one-minute estimate from a subset of stations; the strip is NOAA's observed three-hour value from eight of them; the German Research Centre for Geosciences in Potsdam computes the official Kp from all thirteen a day or two later (its feed cannot be read from a browser, so it is not shown here). On a quiet day they agree to a third; in a storm the estimate can run a full step high or low.
How far the aurora reaches at each Kp
NOAA's rule of thumb: the geomagnetic latitude the oval's equatorward edge reaches at each Kp. The table is NOAA's own, from Tips on viewing the aurora. Aurora is visible on the horizon from up to about 1000 km further toward the equator than the edge itself. The marked row is your pin's magnetic latitude (from the 2025 dipole; ≈ two degrees in places).
| Kp | NOAA scale | Oval edge, magnetic latitude | Overhead, roughly | On the horizon from |
|---|---|---|---|---|
| 0 | quiet | 66.5° | Tromsø, Fairbanks, Yellowknife, Kilpisjärvi | Iceland, Lapland, Anchorage |
| 1 | quiet | 64.5° | Reykjavík, Rovaniemi, Whitehorse | Shetland, southern Norway, Anchorage |
| 2 | quiet | 62.4° | Trondheim, Umeå, Fort McMurray | Orkney, Bergen, Edmonton |
| 3 | unsettled | 60.4° | Shetland, Oslo, Edmonton | Scotland, Stockholm, Winnipeg, northern Minnesota |
| 4 | active | 58.3° | Inverness, Stockholm, Winnipeg | Glasgow, Copenhagen, Michigan's Upper Peninsula |
| 5 | G1 minor | 56.3° | Glasgow, Newcastle, Copenhagen, Calgary, Duluth | Hamburg, Seattle, Chicago's north |
| 6 | G2 moderate | 54.2° | Hamburg, Seattle, Toronto | London, Berlin, Portland, Detroit, Boston |
| 7 | G3 strong | 52.2° | London, Berlin, Portland, Boston | Paris, Warsaw, New York, Chicago, Denver's north |
| 8 | G4 severe | 50.1° | Paris, Warsaw, New York, Chicago | Munich, Vienna, Washington DC, San Francisco |
| 9 | G5 extreme | 48.1° | Munich, Vienna, Washington DC, Denver | Rome, Madrid, Atlanta, Los Angeles (red only) |
Three hours, thirteen stations, one number
Kp is derived from the K index at thirteen observatories between 44° and 60° magnetic latitude, each rating the largest deviation of its magnetometer over a three-hour UTC window on a quasi-logarithmic 0–9 scale — a range index, not an average. The planetary value is the mean of the thirteen standardised K values, in thirds: 4−, 4o, 4+ are 3.67, 4.00, 4.33.
Why "Kp 5" and no aurora both happen
A three-hour average can be 5 because of a twenty-minute substorm at 01:00 UTC that was over before your sky got dark. Kp says how much energy went in; it says nothing about when in the window or where on the oval. That is what the OVATION grid and the solar wind are for.
Why the aurora is seen at Kp 3 in Scotland and not at Kp 6 in Spain
Latitude — magnetic latitude. The oval is a ring around the magnetic pole, which sits over Canada's Arctic islands, so Europe and the eastern United States are magnetically further south than their maps suggest and western Canada further north. Kp moves the ring's edge; it does not move you.
The G scale
NOAA's storm scale is Kp renamed: G1 is Kp 5, G2 Kp 6, G3 Kp 7, G4 Kp 8, G5 Kp 9. The 10–11 May 2024 storm reached Kp 9 (G5); the 11–12 November 2025 storm was a G4. Whether one is in effect now is here.
Forecast Kp is a forecaster's judgement
The three-day table is written by a human at SWPC three times a day from coronal-hole and CME timing, and they publish their rationale in a sentence. That sentence is quoted on this page verbatim, because "Kp 5 expected" and "Kp 5 expected if the CME arrives on time" are different nights.
What to watch instead, for the next hour
Bz and speed in the solar wind at Earth. When Bz turns sharply south and stays there, the oval brightens within an hour, whatever Kp was at the last three-hour mark. The forecast page shows both.