The answer is computed for your pin, not for your country: NOAA's aurora oval where it actually is, how high it stands over your northern horizon, the hours tonight that are dark enough, the cloud over those hours, the Moon, and how dark the ground is where you stand. Set a pin to replace the example.
The oval now, from the pole to 40°. Dashed line: how far south tonight's forecast Kp reaches. Your meridian points down.
Reading NOAA…
Tromsø, Norway
rows: dark · oval · clear · no Moon — the window is the run of green hours
Reading NOAA…
What Kp is, and what it cannot tell you → · Is there a geomagnetic storm today? →
From the oval's brightness right now (NOAA's hemispheric power) and the exposure law — not a generic table.
Bright, moving aurora smears at anything over about 4 s: open the aperture or raise ISO rather than lengthen the shutter.
Going out for hours? Plan the sequence · when you are back, drop the folder into the stacker — it keeps every frame's aurora and removes the satellites. The full photography guide →
NOAA's OVATION model gives the chance of aurora overhead in each one-degree cell. Aurora sits about 110 km up, so a bright arc 600 km toward the pole still stands 7° above your horizon. This page walks from your pin toward the magnetic pole and reports the best cell it finds, with its elevation — which is why a city that reads 0 % overhead can still be told to look north.
Kp (0–9) is the planetary geomagnetic index. The oval's edge reaches about 66° magnetic latitude at Kp 0 and 48° at Kp 9. Your magnetic latitude is what matters, and it differs from the map's: Michigan at 46° N is as magnetically north as Ireland at 53° N. The threshold shown is the Kp at which the oval is overhead, from NOAA's table and the 2025 dipole; a centred dipole is a couple of degrees off in places, which is a full Kp step, so read it as ±1. The horizon needs about four Kp less.
Aurora is faint. Civil twilight (Sun above −6°) hides all but a storm; nautical and astronomical twilight count for a quarter to three quarters; full night, the Sun at −18° or below, counts for all of it. The hour strip's first row is that ramp, in your pin's own time zone — printed, never assumed.
Low and medium cloud is a wall; a thin high veil dims. The forecast is MET Norway's, hourly for two days then six-hourly, and the card names the hour it read. No forecast means the verdict assumes clear and says so.
A full Moon high in the sky washes out faint aurora and does nothing to a G3 curtain — the October 2024 G4 storm was photographed across Europe and North America under a first-quarter Moon. The Moon factor bottoms at half, never zero.
The last number is the sky brightness of the ground you stand on, from this site's light pollution map (2 979 measured SQM readings behind its calibration). A 5° arc is invisible from a city park and obvious from a dark field 40 km north — the map finds that field.
The oval brightens when the solar wind's magnetic field points south (Bz negative) and blows fast. NOAA propagates the L1 measurement to Earth; that is 30–60 minutes of warning before Kp catches up.
The grid speaks for the next 90 minutes; the geospace model for the next hour; the forecaster's 3-day Kp for tonight and two more; the 27-day outlook for a trip. Each hour on the strip says which one it used.
The same verdict pinned to real observing sites, with each site's ground darkness read from the atlas.
It depends on four things at your location: whether the aurora oval reaches your horizon (NOAA's OVATION grid now, the Kp forecast for later), whether it is dark enough (the Sun below −6°, fully dark below −18°), whether low cloud covers the dark hours, and how much Moon is up. The card on this page computes all four for your pin and gives the hours they line up.
It is set by your magnetic latitude, not your map latitude. Roughly: Kp 0–2 under the oval (Tromsø, Fairbanks, Yellowknife), Kp 3–4 in Scotland and the Canadian prairies, Kp 5 (a G1 storm) for Michigan's north and Denmark, Kp 6–7 for London, Berlin, New York and Chicago, Kp 8–9 for Paris, Warsaw and Colorado. Those are the levels at which the oval is overhead; on the horizon it shows from three to four Kp less. The Kp index page marks your row.
OVATION's number is the chance of aurora directly overhead in your one-degree cell. Aurora sits about 110 km up, so a bright arc 600 km toward the pole still stands about 7° above your horizon. The page walks toward the magnetic pole and reports the best cell it finds, with its elevation and bearing.
It dims faint aurora and does little to a strong display: the 10–11 October 2024 G4 storm was photographed under a first-quarter Moon. The verdict treats the Moon as a discount that bottoms at half, never as a veto.
MET Norway's Locationforecast (CC BY 4.0), hourly for two days and six-hourly after, read by your browser for your pin rounded to two decimals. Low and medium cloud are treated as a wall; a high veil as a dimmer.
The pin is kept in your address bar and your browser's local storage. It is sent, rounded, to MET Norway to fetch the cloud forecast, and nowhere else. There is no account and no server of ours in the loop.
Aurora grid, Kp, solar wind, hemispheric power, scales and alerts: NOAA Space Weather Prediction Center, read live by your browser (public domain). Cloud and temperature: MET Norway Locationforecast (CC BY 4.0), which receives your pin rounded to two decimals — the only place it goes. Ground darkness: this site's light pollution atlas. Times are shown in the pin's own zone from an offline table. The pin stays in your browser (the address bar and local storage); there is no account and nothing is uploaded. Alerts by e-mail are being built.