Aurora Alerts
An aurora alert is a short, time-sensitive heads-up that geomagnetic activity has jumped — a KP threshold crossed, the magnetic field turned sharply south, or a storm suddenly hitting Earth. Here's what actually triggers one, and how to be outside looking north before the peak fades.
Open the live tracker →What an aurora alert really means
Aurora is bursty. A quiet sky can light up within minutes when a fast solar wind stream or a coronal mass ejection reaches Earth — and it can fade just as fast. An alert exists to close that gap: instead of refreshing a dashboard all night, you get pinged the moment the conditions that produce visible aurora actually line up. A useful alert is not a vague “maybe tonight.” It fires on a specific, measurable change — a number crossing a line — so you can act on it right away.
The strongest signals come from spacecraft parked at the L1 point, roughly 1.5 million km sunward of Earth. They sample the solar wind about 30–60 minutes before it hits our magnetic field, which is exactly the window a good alert is built around. That lead time is short, so the whole point of an alert is speed: see it, grab a coat, get to dark sky.
The four things that trigger an alert
No single number owns the aurora, so alerts watch several triggers. Any one of them crossing a threshold is worth your attention; when two or three fire together, that's a strong night.
KP crosses a threshold
The KP index runs 0–9. Crossing KP 5 marks a geomagnetic storm and the auroral oval sliding toward lower latitudes — a classic alert trigger. KP index →
Bz turns strongly south
When the field's Bz component swings negative and holds — say below −8 to −10 nT — energy pours into the magnetosphere. This is the earliest, most predictive trigger. Bz & solar wind →
Sudden storm onset
A CME shock front can slam density and speed upward in seconds. That abrupt jump — a sudden impulse — often precedes a fast-building storm. Solar wind →
NOAA G-scale watch/warning
NOAA rates storms G1 (minor) to G5 (extreme). A G-scale watch means one is expected; a warning means it's here now. Geomagnetic storms →
Watch, warning, alert — the words matter
Space-weather notices come in tiers, and mixing them up costs you sleep or aurora. A watch is a forecast: a storm is likely in the next day or two, often issued after forecasters spot an Earth-directed CME leave the Sun. A warning is near-term and specific — activity at a given level is expected within roughly the next hour. An alert (or observed-storm notice) means a threshold has already been crossed right now. In plain terms: a watch tells you to keep tonight free, a warning tells you to start getting ready, and an alert tells you to be outside. The space-weather feed and the live aurora map let you see which stage you're in at a glance.
How to react when an alert fires
The instant an alert lands, the clock is the enemy — geomagnetic peaks can last minutes to a couple of hours, not all night. First, glance at Bz: if it's still strongly southward, the storm has fuel and is likely to hold or build; if it has flipped north, the show may be winding down. Next, check the solar wind speed — anywhere from a calm ~300 km/s up toward 700–800 km/s in a strong stream tells you how hard the wind is driving. Then get away from city glow to a spot with a clear, dark view of the northern horizon, let your eyes adapt for ten minutes, and look low and north; from mid-latitudes the aurora often sits near the horizon rather than overhead. If you're deciding whether tonight is even worth it, the northern lights tonight read and the full aurora forecast give you the context behind the alert.
Aurora alerts FAQ
What KP level should an aurora alert use for my location?
There's no single number — it depends on your latitude. High-latitude spots (northern Scandinavia, Iceland, Alaska, northern Canada) can see aurora at KP 2–3, so a low threshold makes sense there. Mid-latitudes typically need a genuine storm, KP 5 or higher, before the oval reaches them, so alerting on anything lower just means false alarms. Set your trigger to the KP that historically brings the lights to your horizon. More on the KP index →
Why does an alert sometimes fire with no visible aurora?
KP is a planet-wide, three-hour average, so it can flag a storm that's real but happening on the night side of the globe away from you — or one that already peaked before you got outside. Cloud cover, moonlight, and city light also hide aurora that instruments still register. This is why the most responsive alerts lean on live Bz and solar wind rather than KP alone: those update continuously and reflect conditions right now. See why Bz leads →
How much warning does an aurora alert actually give me?
It varies by trigger. A NOAA storm watch tied to an Earth-directed CME can give a day or more of notice, but with wide timing uncertainty. Once the CME nears Earth, spacecraft at the L1 point measure the incoming solar wind roughly 30–60 minutes before impact, which is the sharpest, most actionable window. Alerts based on the KP index itself are essentially real-time — they confirm a storm is underway rather than predict it. How storms unfold →
Don't miss the next spike
Watch KP, Bz, solar wind and a single 0–9 Aurora Power score update live — so you know the moment activity crosses the line.
Open the live tracker →