HOW TO READ THE NORTHERN LIGHTS FORECAST STEP BY STEP
Are you heading to Iceland to see the Northern Lights but don't know what the coloured maps, Kp numbers or the abbreviation Bz actually mean? An aurora forecast can look like a confusing collection of technical data at first glance. In reality, you mainly need to watch a few things: auroral activity, cloud cover, darkness and the current state of the solar wind. Here's a step-by-step guide to reading the forecast and knowing when it's worth heading outside.
The Northern Lights are one of Iceland's biggest attractions. But even a high Kp index does not guarantee that you will actually see them. If the sky is cloudy, you can have a powerful geomagnetic storm directly above you and still see absolutely nothing.
On the other hand, Iceland can offer spectacular auroras even when activity is relatively low.
The key, therefore, is not to look for one magical number, but to learn how to read several indicators together.
1. First, find out whether it will actually be dark
It sounds obvious, but this is where the whole problem begins.
The Northern Lights are a phenomenon visible in the night sky. In summer, Iceland presents a major challenge: the sky simply does not get dark enough.
Always read the aurora forecast together with information about sunset, the beginning of true darkness and sunrise.
The official Icelandic aurora forecast from the Icelandic Meteorological Office combines auroral activity with cloud cover, sunlight and moonlight. The times shown on its map are based on Reykjavík.
Official Northern Lights forecast for Iceland – Vedur.is
So what should you look for?
sunset,
the beginning of true darkness,
sunrise,
and, where relevant, twilight.
If it isn't dark enough yet, high auroral activity won't help.
2. Cloud cover is often more important than Kp
This may be the most important rule in the entire article:
The Northern Lights can be above the clouds. You just won't see them.
That is why, when planning an aurora hunt in Iceland, it is worth checking the cloud-cover map first.
The official Icelandic Meteorological Office forecast shows cloud cover at different levels. On the map, cloudy areas are shown in green, while clearer areas are white. You can move through the forecast in time and see how conditions are expected to change during the night.
This is particularly important in Iceland.
For example, if:
Reykjavík – cloudySnæfellsnes – cloudySouth Iceland – clear
that does not necessarily mean you are out of luck.
It may simply mean that it is time to get in the car and change location.
3. Kp index: useful, but often overestimated
The Kp index is a global indicator of geomagnetic activity.
Its scale ranges from 0 to 9.
In general:
Kp | Meaning |
0–1 | Very low activity |
2–3 | Low to moderate activity |
4 | Elevated activity |
5 | G1 geomagnetic storm |
6 | G2 |
7 | G3 |
8 | G4 |
9 | G5 |
NOAA uses Kp 5 as the threshold for a G1 geomagnetic storm. Higher values indicate stronger geomagnetic activity, and during major storms the aurora can become visible much farther south than usual.
But there is an important point: you do not have to wait for Kp 5 in Iceland.
This is an important correction to many general guides.
Iceland lies in a region where auroras are relatively common. The Icelandic Meteorological Office therefore uses its own scale of expected auroral activity from 0 to 9. According to its explanation, even level 2 can produce beautiful auroras, while level 3 can be very impressive. Higher values are less common.
So:
Kp 2 ≠ no Northern Lights.
And equally:
Kp 5 ≠ automatically a spectacular aurora above your car.
4. Bz: the number that can suddenly change the forecast
Now we get to a parameter that sounds a little more like something from a physics textbook.
Bz describes the north-south orientation of the interplanetary magnetic field.
For observers on Earth, the situation of particular interest is when Bz is negative (southward).
Why?
When the magnetic field carried by the solar wind is oriented in the right direction, it can interact more efficiently with Earth's magnetic field, allowing energy to be transferred into the magnetosphere. NOAA notes that geomagnetic disturbances tend to be stronger when Bz is southward than when it is northward.
In practical terms:
Negative Bz → good news.
But that does not mean:
Bz = −5 → you will definitely see the aurora.
Bz is a variable parameter and can change significantly over a short period of time.
That is why it is more useful to monitor it in real time rather than rely on it several days in advance.
5. Solar wind speed
Another figure you may find on some space-weather websites is solar wind speed.
The solar wind is a continuous stream of charged particles flowing away from the Sun.
When a stronger stream of particles reaches Earth, it can increase geomagnetic activity.
But once again, speed alone is not a magic number.
It needs to be considered together with:
Bz,
solar-wind density,
the interplanetary magnetic field,
Kp,
and other indicators of geomagnetic activity.
6. Hemispheric Power: an interesting figure for advanced observers
Some forecasts also display Hemispheric Power (HP).
This is an estimate of the amount of energy being deposited into the polar region of the atmosphere.
Higher values generally correspond to greater auroral activity.
For an ordinary traveller, however, HP does not need to be the first thing you look at.
If you are checking an aurora forecast for the first time, focus initially on:
darkness → cloud cover → auroral activity → current solar wind conditions.
You can add HP once you want to follow the forecast in more detail.
7. What does the auroral oval map mean?
If you use NOAA or other specialised websites, you will encounter a coloured map around the North Pole.
This is the auroral oval – the region where the Northern Lights are statistically most common.
During increased geomagnetic activity, the oval expands and shifts towards lower geomagnetic latitudes. NOAA explains that during the expansion phase of a geomagnetic storm, auroras can become visible farther south.
For Iceland, the map is therefore particularly useful as a quick visual indication of where auroral activity is currently concentrated.
8. The Moon: enemy or ally?
A common piece of advice is:
“Only go after the Northern Lights during a new moon.”
That is not entirely true.
Moonlight can make a faint aurora less noticeable, but it can also beautifully illuminate the Icelandic landscape beneath it.
During a strong aurora, a full moon therefore does not necessarily present a problem.
In fact, it can be particularly interesting for photography:
green aurora + illuminated mountains + snow + ocean.
The Icelandic Meteorological Office therefore also provides moonrise and moonset times in its forecast.
9. How do you read the forecast in practice?
Let's look at a simple example.
Imagine that you check Iceland's conditions one evening.
Activity:3 – moderate
Cloud cover:Reykjavík – cloudySnæfellsnes – partly cloudyWestfjords – clear
Bz:negative
Darkness:yes
What do you do?
You drive to the Westfjords.
Not because they have the highest Kp value.
But because four important conditions have come together:
activity + darkness + clear skies + favourable magnetic-field conditions.
And that is the whole secret of reading an aurora forecast.
What should you look for in the forecast?
Factor | What it means | What you want to see |
Darkness | The aurora is visible only in a sufficiently dark sky | Yes |
Cloud cover | Clouds can completely hide the aurora | As little as possible |
Auroral activity | Expected intensity of the Northern Lights | Higher is generally better |
Kp | Global indicator of geomagnetic activity | Higher = more activity, but not decisive |
Bz | Orientation of the interplanetary magnetic field | Negative values are more favourable |
Solar wind | Stream of charged particles from the Sun | Increased activity can help |
HP | Energy deposited in the auroral region | Higher generally means more energy |
Moon | Can make a weak aurora less visible | Darkness helps, but a full moon is not a deal-breaker |
Time | The aurora requires darkness | Watch for true darkness |
Conclusion: Don't look for a single number
An aurora forecast is not like a temperature forecast.
You cannot look at one number and say:
“There will be an aurora tonight.”
Instead, you have to put several pieces together.
It needs to be dark.
The sky needs to be at least partly clear.
There needs to be sufficient auroral activity.
And if you want to follow the forecast in more detail, add Kp, Bz, solar wind conditions and the auroral oval.
In Iceland, you do not necessarily have to wait for an extreme geomagnetic storm. Even relatively low activity can produce beautiful auroras. The Icelandic Meteorological Office itself notes that low activity can still provide an impressive display.
And that is why the best advice of all is surprisingly simple:
When it is dark, the sky is clear and the forecast shows auroral activity, put on your jacket and go outside.
Because while you can watch the forecast on a screen, the Northern Lights are happening above your head.
About the Author
Iceland has fascinated me for many years. Over the course of numerous journeys across the island, I have driven tens of thousands of kilometers, experienced storms that changed travel plans within minutes, and witnessed days when choosing the right route meant discovering places that most visitors never see. I documented many of these experiences in my documentary film Island in the North.
Through this website, I share practical travel advice, up-to-date information, and firsthand experiences from the field to help others explore Iceland more safely and gain a deeper understanding of its unique landscapes and ever-changing nature.
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