How to use the 27-day aurora outlook

A planning tool for the weeks ahead

NOAA’s 27-day outlook offers a broad view of expected geomagnetic activity over the coming weeks. It is issued weekly and lists a largest expected Kp value for each reporting day, alongside planetary Ap and 10.7-centimeter solar radio flux. Our site displays this published NOAA product; it is not a prediction generated by a separate Aurora Forecast machine-learning model.

Use the outlook to identify periods worth watching, especially when your plans are flexible. A more active-looking stretch can be a reason to keep an evening free or revisit a forecast later. It is not enough information to choose an exact viewing hour, and it does not establish whether any particular city will have a visible display.

Read a maximum as a maximum

A daily maximum Kp of 5 does not mean Kp will stay at 5 throughout the day. It describes the largest value NOAA expects somewhere within that reporting period. The outlook does not supply a complete three-hour timeline, so we do not fill the gaps with invented hourly values or apply that maximum to every hour.

We convert each period’s start and end into your browser’s timezone. Because the source periods are full UTC reporting days, one can cross two local calendar dates. Select a tile or open the table to see the exact window. The issue time is also localized. Faded tiles represent reporting periods that have already ended, not additional future predictions.

Why approximately 27 days?

Some solar and geomagnetic patterns recur as the Sun rotates. NOAA’s longer-range guidance relies substantially on activity recurring from one approximately 27-day rotation to another. Persistent coronal holes can make that pattern useful, but the Sun evolves and recurrence is not equally reliable throughout the solar cycle.

Sudden events can change the picture. A coronal mass ejection and the magnetic field it carries can alter conditions closer to the event. Treat a quiet-looking date as limited planning guidance, not a promise that nothing will happen. Likewise, an active-looking date should prompt another check rather than an assumption that a display is certain.

What Ap and F10.7 add

Planetary Ap is another measure of geomagnetic activity. F10.7 describes solar radio flux at a wavelength of 10.7 centimeters and is reported in solar flux units. They provide useful background for readers exploring the underlying space weather. Neither is a percentage chance of seeing aurora, and neither replaces a local visibility check.

Move from a possible date to a useful night

As a date approaches, revisit the three-day forecast and then the short-term aurora map. Check your destination’s model reading, darkness, and cloud forecast. Keep local weather and safe access in the decision: a promising global activity outlook can still coincide with daylight, cloud, or an obscured horizon.

Our backend checks for an updated outlook independently of the other feeds and keeps the last valid report if an update fails. Read the issue date and any older-report notice before relying on it. The printed horizon belongs to that weekly issue; refreshing the page does not create a new 27-day prediction every day.

Common questions