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How to read an aurora forecast: the best free tools and apps

How to read NOAA's 30-minute OVATION and 3-day forecasts, what Kp, Bz and solar wind speed mean for the aurora, and a neutral look at popular free aurora apps such as My Aurora Forecast, SpaceWeatherLive and Glendale App.

Three time scales: days, hours, minutes

Aurora forecasting works at three time scales, and each needs a different tool. Days ahead, forecasters watch the Sun for coronal mass ejections (CMEs) and coronal holes, and NOAA publishes a 3-day forecast of the planetary Kp index in three-hour blocks. [1] [2]

Hours ahead, the best information comes from spacecraft about 1.5 million km sunward of Earth, which measure the solar wind before it arrives. UAF notes that this gives roughly one to two hours' warning. [3] [4]

Minutes ahead, NOAA's OVATION model turns those measurements into a map of where the auroral oval is expected to be over the next half hour or so, updated every few minutes. [5] After that, only your own eyes and camera can tell you what the sky is doing.

NOAA's 3-day forecast: reading Kp blocks

The 3-day forecast lists predicted Kp for each three-hour block in UTC. Convert the times to your own time zone: for US Eastern Time, subtract four hours in summer and five in winter. Our Aurora tonight page does that conversion for you and lists the blocks in Eastern Time. [1]

Read Kp with the rough latitude rules in our Kp index guide. Kp 0–2 means aurora is mainly confined to high latitudes, and Kp 3–5 brings brighter displays at high latitudes such as Alaska and Canada. Kp 6–7 may make aurora visible from the northern edge of the contiguous US, and at Kp 8–9 it can appear overhead in northern states and be seen much farther south. [6]

Two cautions. First, Kp is a three-hour planetary average, so a short, bright burst can happen during a block with a modest number. Second, forecasts more than a day ahead depend on estimates of when a CME will arrive. Arrival-time errors are often many hours (see our CME guide), so a storm can come early, late, or weaker than forecast. [7]

The 30-minute OVATION forecast: reading the oval map

NOAA's OVATION product shows a green-to-red oval around the pole, giving the modelled probability of aurora in each area for the next short period. [5] The edge of the coloured band nearest you is the important part. NOAA also notes that aurora can often be seen low on the horizon from hundreds of kilometres equatorward of where it is overhead. So if the oval's southern edge is a few hundred kilometres north of you on a strong night, it is worth looking north. [6]

OVATION is driven by real-time solar wind data, so it reacts within minutes when conditions change, but it can't see more than about an hour ahead. Use it to decide whether to go outside now, not whether to plan a trip. [5]

Kp versus Bz and solar wind: the basics

Kp measures how disturbed Earth's magnetic field has been. It is a result, not a cause. The cause is the solar wind and the magnetic field it carries, the interplanetary magnetic field (IMF), which NOAA shows in its real-time solar wind plots. [4]

The most important single number is Bz, the north–south part of the IMF. NOAA notes that when it points southward (negative Bz), it couples more effectively with Earth's magnetic field and favours stronger aurora. [6] As a rule of thumb, a Bz that stays clearly negative for an hour or more is a better sign than a brief dip. Higher solar wind speed and density add energy, but a fast wind with a northward Bz often gives little aurora.

So when an alert says a CME has arrived, look at the solar wind panel: a jump in speed with Bz swinging and holding south is the sign that a storm may build. Our live dashboard shows speed, Bt and Bz from NOAA's data each build. [4]

Free apps: what they do (neutral notes)

Many apps repackage NOAA data and add alerts. We have no relationship with any of them, and we list only features stated on each app's own page, checked on 2026-10-21. Features, prices and privacy terms change, so check the listing before installing.

My Aurora Forecast & Alerts (JRustonApps B.V.). Its App Store listing describes the current Kp index, a likelihood of seeing aurora, a world map based on NOAA SWPC's OVATION forecast, free push notifications when activity is expected to be high, forecasts from the next hour to several weeks, solar wind statistics and aurora webcams. The listing says the app is free and ad-supported, and its privacy section lists location and identifiers among data that may be used for tracking. [8]

SpaceWeatherLive. The app page describes separate aurora and solar activity modes, a dark mode, graphs of real-time data, push notifications for events such as solar flares, geomagnetic storms and Earth-facing coronal holes, and a data archive going back to 1996. It is free with ads, which a paid subscription removes. [9] Its alerts page says geomagnetic activity alerts are sent every three hours while Kp is above storm level, and that individual alert types can be switched off. [10]

Glendale App (aurora-alerts.uk). This is a web app, not an App Store download. Its home page explains how to add it to your home screen, asks for your location to calculate local darkness and aurora probability, and says you must register to see live updates. Its panels include a real-time substorm tracker based on ground magnetometers and IMF and solar wind displays. It describes itself as free, with no advertising. [11]

Whatever app you use, alerts tell you when activity is likely, not that aurora is visible from your location tonight. Cloud, moonlight and light pollution still decide most nights, so pair the app with a local cloud forecast and a look outside.

A simple routine that works

Days ahead: check NOAA's 3-day forecast and any storm watch. [1] Evening of: check Aurora tonight and your weather forecast for clear skies. At night: watch OVATION and Bz, go to a dark spot with a northern view, and give it time. NASA describes aurora chasing as always a game of chance, which is the right expectation. [12]

If you are planning a trip rather than a night out, forecasts more than three days ahead are not useful. Choose a place under the oval, during the dark season, for several nights; our best places and times guide explains why.

Frequently asked questions

Sources

1. NOAA SWPC: 3-Day Forecast https://www.swpc.noaa.gov/products/3-day-forecast
2. NOAA SWPC: Coronal Mass Ejections https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections
3. University of Alaska Fairbanks Geophysical Institute: Aurora Forecast and FAQ https://www.gi.alaska.edu/monitors/aurora-forecast
4. NOAA SWPC: Real Time Solar Wind https://www.swpc.noaa.gov/products/real-time-solar-wind
5. NOAA SWPC: Aurora – 30 Minute Forecast (OVATION model) https://www.swpc.noaa.gov/products/aurora-30-minute-forecast
6. NOAA SWPC: Tips on Viewing the Aurora https://www.swpc.noaa.gov/content/tips-viewing-aurora
7. NOAA SWPC: Planetary K-index (product description) https://www.swpc.noaa.gov/products/planetary-k-index
8. Apple App Store: My Aurora Forecast & Alerts (JRustonApps B.V.), app listing https://apps.apple.com/us/app/my-aurora-forecast-alerts/id1073082439
9. SpaceWeatherLive: app page https://www.spaceweatherlive.com/en/app.html
10. SpaceWeatherLive: Space weather alerts https://www.spaceweatherlive.com/en/aurora-alerts.html
11. Glendale App (aurora-alerts.uk): home page https://aurora-alerts.uk/
12. NASA Science: NASA's Guide to Finding and Photographing Auroras https://science.nasa.gov/feature/nasas-guide-to-finding-and-photographing-auroras/

Sources were checked on 2026-10-21. Text on this page is original. Quoted figures are attributed and linked to the source. General education only, not for safety or operational decisions. Disclaimer.