A northern lights forecast is really three forecasts stacked on top of each other: how active the aurora will be, how dark your sky will be, and whether clouds will be in the way. The aurora part is only trustworthy in detail about 30–90 minutes ahead, and in outline one to three days ahead. In practice the cloud forecast decides most nights.
This guide walks through each layer in the order you will actually use them, explains what the Kp number means for your location, and ends with a short routine for deciding whether to go out tonight. For the definitions behind the numbers, see our explainers on the Kp index and G scale and how our score works.
The three layers of an aurora forecast
| Layer | What it tells you | Useful horizon | Where to look |
|---|---|---|---|
| Geomagnetic activity | How bright the aurora will be and how far towards the equator it reaches | 30 minutes to 3 days | NOAA SWPC, our map and expert panel |
| Darkness and moon | Whether the sky is dark enough for faint aurora | Exact, for any date | Our tonight pages and trip planner |
| Clouds | Whether you can see the sky at all | Hours to about 2 days | Your national weather service and satellite images |
Most aurora apps show only the first layer. That is why they can buzz with a "high Kp" alert while you stand under solid overcast.
Long range: the 27-day outlook
Every week NOAA's Space Weather Prediction Center (SWPC) publishes a 27-day outlook of daily Kp. The Sun rotates about once every 27 days as seen from Earth, so a coronal hole that sent a fast solar wind stream past us last month may do so again. That recurrence is what the outlook captures.
Use it to choose a rough week for a trip, not a night. It cannot see coronal mass ejections (CMEs) that have not erupted yet, and it says nothing about cloud. We deliberately do not turn it into a nightly score for the same reason.
One to three days: the Kp forecast and storm watches
NOAA's 3-day forecast gives predicted Kp in three-hour blocks, in UTC. Two habits make it far more useful:
- Convert the blocks to local time. In Tromsø (UTC+1 in winter) the 21–00 UTC block is 22:00–01:00, the heart of the night. In Fairbanks (UTC−9 in winter) the same block is mid-afternoon, and the blocks that matter are 06–12 UTC.
- Read the forecast discussion, not just the numbers. When a CME is heading for Earth, SWPC issues a geomagnetic storm watch with the expected G level. The text tells you how confident forecasters are and whether the arrival could slip.
CME arrival times are uncertain by several hours, and the strength depends on the magnetic orientation inside the cloud, which nobody can measure until it passes the spacecraft upstream of Earth. A "G3 watch" can deliver a G1 evening or a surprise G4. Treat a watch as a reason to be ready, not as a promise.
What Kp really means for you
Kp runs from 0 to 9 and summarises global geomagnetic disturbance over three hours. The useful question is not "is Kp high?" but "is Kp high enough for my latitude?". SWPC's rule of thumb is that the equatorward edge of the auroral oval sits near 66° geomagnetic latitude at Kp 0 and moves about 2° towards the equator for each Kp step.
| Where you are | Kp that typically brings aurora into view | What it usually looks like |
|---|---|---|
| Under the oval: northern Norway, Swedish and northern Finnish Lapland, Fairbanks, Yellowknife | 1–3 | Overhead or to the north on most clear, dark nights |
| Iceland, Rovaniemi, Whitehorse | 2–4 | Often overhead in active spells, otherwise to the north |
| Northern Scotland, southern Norway and Sweden | 4–6 | A low arc or glow on the northern horizon, brighter in storms |
| Northern US states, Ireland, northern England | 5–7 | Low on the horizon, often clearer on camera than by eye |
| Central and southern US, central Europe | 8–9 | A rare red glow during severe or extreme storms |
The lower rows follow NOAA's own space weather scales: at G2 (Kp 6) aurora "has been seen as low as New York and Idaho", at G3 (Kp 7) as low as Illinois and Oregon, and at G4 (Kp 8) as low as Alabama and northern California. Those are best cases on clear nights, not typical views.
Two consequences surprise people. First, a stormy night can be worse for someone in Svalbard, because the oval moves south past them. Second, in the Arctic you do not need a storm at all: Kp 2 under a clear sky beats Kp 6 under cloud.
Tonight: the OVATION map and the solar wind
Once the evening starts, switch from Kp to the real-time tools.
- The OVATION aurora forecast. NOAA's 30-minute forecast turns solar wind measurements into a map of where aurora is likely in the next half hour or so. It is the green-to-red oval on our live map. If the bright part of the oval reaches your latitude, or sits within a few hundred kilometres poleward of you, it is worth looking.
- The solar wind at L1. Spacecraft about 1.5 million km sunward of Earth measure the wind before it arrives, giving roughly 30–90 minutes of warning depending on its speed. On our expert panel watch three numbers: Bz (the north–south part of the magnetic field; sustained negative values let energy in), speed (faster drives stronger aurora) and density. A common hunters' rule of thumb is that Bz staying below about −5 nT for half an hour or more, with speed above about 500 km/s, is a good sign. It is a heuristic, not an official threshold.
- Observed Kp and magnetometers. Observed Kp lags by up to three hours. Local magnetometers, such as the FMI stations in Finland, react within minutes when a substorm begins.
Cloud is the forecast that decides
Under the oval, a dark, clear night usually brings at least some aurora. The Finnish Meteorological Institute (FMI) says that on a dark, cloudless night aurora is seen on about three nights in four at Kilpisjärvi. So spend as much time on the cloud forecast as on the space weather.
- Low cloud blocks everything. Thin high cirrus often lets a bright aurora through. Our score weights low cloud most heavily for this reason.
- Use the local service. MET Norway's yr.no for Norway and Sweden, FMI for Finland, the Icelandic Met Office cloud map for Iceland, the Met Office for the UK, and Environment Canada or the US National Weather Service for North America.
- Look at satellite images after dark. A forecast can be an hour off; a satellite loop shows where the clear gaps are now.
- Be ready to move. Driving 30–90 minutes inland or across a mountain range often changes everything, which is how chase tours earn their money.
A 10-minute routine before you go out
- Open your place on our tonight page or map. Check when it gets fully dark and where the Moon is.
- Check the cloud forecast for the next three hours, then a satellite loop.
- Check the OVATION oval: is the bright band over you or just poleward of you?
- Check Bz and speed on the expert panel. Sustained southward Bz means "go now".
- Glance at a live webcam near you. If cameras to the north already show aurora, it is real.
- If it looks promising, go somewhere dark with an open view towards the pole and give it at least 30–60 minutes. Activity comes in bursts.
- If not, set an alert and sleep. You will be woken only if your own place crosses your threshold after dark.
Why aurora forecasts bust
- Kp is a global three-hour average. A 20-minute substorm can light up the sky during a "Kp 3" block, and a "Kp 6" block can be quiet where you stand.
- CMEs arrive early, late or weak. The magnetic orientation inside the cloud is the biggest unknown.
- Predicted Kp tends to run high at moderate levels. Our own score damps NOAA's Kp forecast slightly above Kp 3 for this reason; the method is in how our score works.
- Weather is local. A fjord can be clear while the airport 20 km away is overcast.
If you are planning a trip rather than a night, the forecast matters less than the calendar and the climate. Our guide to the best time to see the northern lights in 2026–27 and the ranking of 21 places by clear-sky odds cover that side.
Frequently asked questions
How accurate is the northern lights forecast?
It depends on the horizon. The 30–90 minute view from solar wind data at L1 is the most reliable part. The 1–3 day Kp forecast is a reasonable guide to whether a night will be active, but the arrival time and strength of a coronal mass ejection are often off by hours or by a whole storm level. Anything beyond three days is a planning hint, not a forecast.
What Kp do I need to see the northern lights?
It depends on your geomagnetic latitude, not on a universal number. Under the auroral oval in Tromsø, Abisko, Fairbanks or Yellowknife, Kp 1–3 is often enough. Iceland and southern Lapland do well from about Kp 3. Scotland usually needs Kp 5–6, the northern US Kp 6–7, and the southern US Kp 8–9.
How far in advance can the aurora be predicted?
Roughly 30 to 90 minutes in detail, from solar wind measured about 1.5 million km upstream of Earth. One to three days ahead you can expect a storm watch when a CME is on the way. NOAA's 27-day outlook only flags likely active periods from recurring solar wind streams.
What time zone is the aurora forecast in?
NOAA's 3-day Kp forecast uses three-hour blocks in UTC. Convert them to local time before you decide when to go out; in Alaska, for example, the 06–09 UTC block falls in the late evening.
Does a high Kp guarantee I will see the aurora?
No. Kp is a three-hour global average. Cloud, moonlight, twilight and city light can still hide a strong display, and activity often comes in 20–40 minute bursts with quiet gaps between them.