NOAA Aurora Forecast Explained: How to Read It

Almost every aurora app, website and social post ultimately quotes NOAA. The Space Weather Prediction Center, part of the US National Weather Service, publishes openly the space weather data the rest of the field builds on. That is why "the NOAA forecast" gets treated as a single number, when it is really several products answering different questions on different timescales. This guide explains what each one is and where it stops. AuroraMe is independent and is not affiliated with or endorsed by NOAA.

The 30-Minute Aurora Map: OVATION

The image most people mean by "the NOAA aurora forecast" is the 30-minute aurora map. It shows a modelled auroral oval over each hemisphere, coloured by the intensity of the aurora the model expects, together with a line marking how far from the pole the display might be seen on the horizon under clear, dark skies.

It comes from OVATION, an empirical model that turns current solar wind conditions into an estimate of auroral power and where it is deposited. The inputs are measured by spacecraft at the L1 point, roughly 1.5 million kilometres sunward; solar wind takes about 30 to 90 minutes to cross that gap, and that travel time is the product's lead time — NOAA names the product for the short end of that window and describes it as a 30 to 90 minute forecast.

What it tells you

• Whether the oval is currently expanding toward lower latitudes, and on which side of the planet
• Roughly how bright the display is in model terms, which correlates with how far equatorward it can be seen
• An immediate answer to "is something happening right now", faster than any three-hour index can give

What it does not tell you

• Whether your sky is clear. Cloud is invisible to this product and ends more aurora attempts than low Kp does.
• Whether it is dark where you are, or how much moonlight is washing out a faint display
• Anything about substorm timing. The oval brightens and fades in bursts of minutes; a single frame is a snapshot, not a promise about the next hour.

Read it as a nowcast of position and strength, then answer the local questions separately — our map layers guide covers reading cloud, darkness and light-pollution overlays alongside an oval like this one.

The 3-Day Forecast and the 27-Day Outlook

The 3-day forecast is issued every 12 hours and predicts the planetary K index for each three-hour block over the coming three days, alongside probabilities for geomagnetic storms, radio blackouts and solar radiation events. This is the product to use for planning: it is the only NOAA output that tells you whether Friday night is worth committing to.

Its accuracy is uneven by construction. A forecast that follows an observed coronal mass ejection has a physical basis for the day the disturbance should arrive; a forecast several days out, with nothing in transit, is closer to climatology. Treat a predicted Kp for tomorrow night as a real signal and the same number for day three as a hint. The separate 27-day outlook rests on solar rotation: the Sun turns in about 27 days, so a region that stormed recently can face Earth again a month later.

NOAA also issues watches, warnings and alerts: a watch when a disturbance is expected, a warning when it looks imminent, and an alert when a threshold has actually been crossed. Alerts are the ones that fire when something is genuinely happening.

The Planetary K Index

Kp is a global index of geomagnetic disturbance on a 0 to 9 scale, derived from magnetometer readings at a network of ground observatories and reported for each three-hour interval. The definitive index is derived and published by GFZ in Germany; NOAA publishes an estimated planetary K index in near real time so that operational users are not waiting for the final numbers.

Two properties cause most of the confusion. First, it is global: one number for the whole planet, which cannot separate a display over Alaska from one over Siberia. Second, it is a three-hour average, so a sharp substorm is smoothed into the same figure as three quiet hours. Kp characterises planetary disturbance; it was never built to plan an evening.

What turns Kp into a local answer is magnetic latitude: the further your location sits from the pole in magnetic terms, the higher the Kp needed before the oval reaches you. Our Kp index guide works through the scale, and the live Kp index page shows the current estimated value.

The G-Scale

NOAA's space weather scales describe the effects of an event in plain terms, and the geomagnetic branch is the G-scale. It begins where Kp reaches storm level and runs in five steps.

Below Kp 5 there is no G level; conditions are quiet, unsettled or active. The scale communicates operational impact — on power grids, satellites, navigation and radio — so its wording is about infrastructure, not scenery. For aurora watchers it is shorthand: a G3 watch means the oval should reach mid latitudes. Our geomagnetic storm guide goes through the levels; the live storm page shows current conditions.

Solar Wind: Speed, Density and Bz

Underneath the modelled products sit the raw L1 measurements: solar wind speed, particle density, and the strength and direction of the interplanetary magnetic field. Its Bz component is what experienced watchers check first — when Bz turns southward, energy enters the magnetosphere far more readily, and a slow stream with a strongly southward Bz beats a fast one without it.

How to Read NOAA for Your Own Location

Putting the pieces together, a practical routine looks like this:

• Days ahead: check the 3-day forecast for a predicted Kp that clears your location's threshold, and look for any storm watch.
• The evening itself: check the estimated planetary K index for what has actually been measured, and the solar wind for whether Bz is southward.
• Right now: check the 30-minute map for where the oval is sitting and how far equatorward the view line has moved.
• Then answer the local half yourself: your magnetic latitude sets the Kp you need, and cloud, darkness and moon decide whether that Kp does you any good.

That last step is the one NOAA does not do, because it is not what the agency exists for. It is what AuroraMe automates: geomagnetic activity, cloud cover, moon phase, the darkness window, sky quality and magnetic latitude combined into one local answer rather than a set of global charts. The inputs are documented on our methodology page; the live view is the aurora tracker.

Frequently Asked Questions

What is the NOAA aurora forecast?

It is not one product but a family of them, published by NOAA's Space Weather Prediction Center. The best known is the 30-minute aurora map produced by the OVATION model, which estimates where the auroral oval sits now and shortly ahead. Alongside it sit the 3-day forecast of the planetary K index, the estimated planetary K index, real-time solar wind readings, and the G1 to G5 storm scale.

Why does the NOAA aurora map only look 30 to 90 minutes ahead?

Because the model is driven by solar wind measured in front of Earth. Spacecraft at the L1 point sit roughly 1.5 million kilometres sunward, so the plasma they sample reaches Earth roughly 30 to 90 minutes later depending on its speed. That travel time is the natural lead time of a nowcast built on those measurements, which is why NOAA describes the product as a 30 to 90 minute forecast even though it is named for the short end. The 3-day forecast and storm watches use different inputs and carry wider uncertainty.

Does a high Kp on the NOAA forecast mean I will see the aurora?

No. Kp measures global geomagnetic disturbance and says nothing about your sky. Four local conditions decide whether a given Kp is enough for you: your magnetic latitude, cloud cover, how dark it is, and how much moonlight is around. Kp 5 can be a spectacular night in Tromsø and completely invisible in London, and the NOAA products do not attempt to answer that question for a specific address.

What is the difference between the Kp index and the G-scale?

Two scales for the same disturbance. Kp runs 0 to 9 and comes from magnetometer observations. The NOAA G-scale grades storms in five steps starting where Kp reaches 5: G1 Minor at Kp 5, G2 Moderate at Kp 6, G3 Strong at Kp 7, G4 Severe at Kp 8, G5 Extreme at Kp 9. Below Kp 5 there is no G level.

Is AuroraMe affiliated with NOAA?

No. AuroraMe is an independent app. It reads publicly published space weather data from NOAA's Space Weather Prediction Center and combines it with cloud, moon, darkness, sky quality and your magnetic latitude to produce a local answer. Nothing here is endorsed by NOAA, and the agency's own products remain the authoritative source.

Sources

• NOAA SWPC — Aurora 30-Minute Forecast — the OVATION model map for both hemispheres
• NOAA SWPC — 3-Day Forecast — predicted Kp in three-hour blocks, issued every 12 hours
• NOAA SWPC — Planetary K-index — the estimated planetary K index in near real time
• NOAA SWPC — Space Weather Scales — the G, S and R scales and what each level means
• NOAA SWPC — Real-Time Solar Wind — speed, density and interplanetary magnetic field from L1
• GFZ — Kp index — the institute that derives and publishes the definitive Kp index
• NASA — Auroras — background on solar wind, the magnetosphere and auroral emission