Aurora Forecast: How to Read Kp, G-Scale, and Find the Northern Lights Tonight

An aurora forecast tells you whether the northern lights will reach your latitude tonight. The system is built on solar wind measurements, two scientific scales, and a NASA-affiliated forecast model. Below is how to read the Kp index and G-scale, where to look up tonight’s forecast for free, and the practical tricks for catching an aurora once one is on the way.

How an Aurora Forecast Works

Auroras come from charged particles streaming off the Sun (the solar wind) interacting with Earth’s magnetic field and atmosphere. NOAA’s Space Weather Prediction Center (SWPC) measures the solar wind in real time using satellites, including the DSCOVR satellite parked at the Earth-Sun L1 point about 1 million miles toward the Sun. When the solar wind picks up speed, gets denser, or carries a southward-pointing magnetic field, conditions favor aurora visibility farther south on Earth.

Forecast lead time is short. The L1 satellite gives 15 to 60 minutes of warning before the solar wind reaches Earth. That is why aurora forecasts run on 30-minute updates rather than week-ahead predictions.

The Kp Index: 0 Through 9

The Kp index is a 0-to-9 scale of planetary geomagnetic activity, updated every three hours. The higher the Kp, the further south the aurora is visible.

Kp 0 to 2. Quiet. Aurora visible only inside the auroral oval, roughly Alaska, northern Canada, Iceland, northern Scandinavia.

Kp 3 to 4. Active. Aurora reaches the northern US border and southern Canada.

Kp 5 (G1 storm). Aurora visible across far northern US (Maine, upper Michigan, Minnesota, Wisconsin, North Dakota, Montana, northern Idaho, Washington).

Kp 6 (G2). Aurora reaches central US (New York, Illinois, Iowa, southern Wisconsin, Oregon).

Kp 7 (G3). Aurora reaches Pennsylvania, Ohio, Indiana, southern Iowa, Nebraska, Wyoming, northern California.

Kp 8 (G4). Aurora visible from Virginia, Kentucky, Missouri, Kansas, Colorado, central California.

Kp 9 (G5). Aurora potentially visible from Texas, Oklahoma, Arkansas, Tennessee, North Carolina, southern California. Rare. Only a few G5 events per solar cycle.

The G-Scale: Geomagnetic Storm Strength

NOAA layers a second scale on top of Kp for emergency-management context. The G-scale runs G1 (minor) through G5 (extreme) and corresponds roughly to Kp 5 through 9. The G-scale also describes broader effects: G3 and above can cause radio blackouts, GPS errors, and grid voltage corrections. G5 events can damage transformers and disrupt satellites. The May 10 to 11, 2024 G5 event was the first since the Halloween storms of October 2003.

Free Aurora Forecast Sources

NOAA SWPC dashboard. The official source. Includes 30-minute aurora-oval forecasts (the OVATION model), 3-day outlooks, and 27-day Kp predictions. Visit swpc.noaa.gov.

SpaceWeatherLive. Free site and app with current Kp, Bz (magnetic-field direction), solar wind speed, and a clean visualization.

My Aurora Forecast. Free phone app with location-aware push notifications.

University of Alaska Fairbanks Geophysical Institute. Long-running aurora forecast at gi.alaska.edu.

The Three Key Variables

Kp is the headline number, but three readings together tell the full story.

Kp. The geomagnetic activity index.

Bz. The north-south component of the interplanetary magnetic field arriving with the solar wind. When Bz is negative (pointing south), it cancels Earth’s northward field and lets solar particles funnel into the atmosphere. Negative Bz is what drives strong aurora.

Solar wind speed. Faster wind delivers more energy. Above 500 km/s is favorable; above 700 is strong.

When and Where to Look

Time of night: 10 PM to 2 AM local time is the strongest window. Auroras peak around magnetic midnight.

Direction: Look north. From far southern US during a strong storm, you may see overhead.

Light pollution: Drive 20 to 30 miles outside city lights when possible. Aurora is faint at low latitudes; light pollution swamps it.

Sky conditions: Clear sky required. Cloud cover blocks aurora completely.

Eye adaptation: Allow 15 to 20 minutes for your eyes to adjust to darkness. Aurora often looks faint to the naked eye but vivid to a long-exposure camera.

Coronal Mass Ejections and Solar Cycle 25

Major geomagnetic storms come from coronal mass ejections (CMEs), eruptions of plasma and magnetic field from the Sun’s corona. A CME takes 1 to 3 days to reach Earth, which gives forecasters a heads-up for major aurora events.

Aurora frequency tracks the 11-year solar cycle. Solar Cycle 25 began in 2019 and reached its peak in late 2024. Cycle 25 has been more active than predicted; the May 2024 G5 storm and several G4 events through 2024 to 2025 are part of that pattern. Strong aurora visibility at low latitudes is expected to continue through 2026 or 2027 as the cycle declines from peak.

Aurora Photography Settings

Manual mode. Aperture wide open (f/2.8 if you have it, otherwise the widest your lens supports). ISO 1600 to 6400. Shutter 10 to 25 seconds. Manual focus to infinity (autofocus fails at night). White balance daylight (5500 K) or tungsten (3200 K) for cooler tones. Tripod required.

Frequently Asked Questions

What is an aurora forecast?

A short-range prediction of where the aurora borealis (and aurora australis) will be visible based on solar wind data. NOAA’s Space Weather Prediction Center runs the official US forecast on 30-minute, 3-day, and 27-day timescales.

What is the Kp index?

A 0-to-9 scale of planetary geomagnetic activity. Kp 5 corresponds to a G1 minor storm with aurora visible across the far northern US. Kp 9 corresponds to G5 extreme storms with aurora potentially visible as far south as Texas and the Gulf Coast.

What time is best to see the northern lights?

10 PM to 2 AM local time. Auroras peak around magnetic midnight, which usually falls within this window. Look north, away from city lights.

What was the May 2024 aurora event?

A G5 (extreme) geomagnetic storm on May 10 to 11, 2024, the first G5 since the Halloween storms of October 2003. Aurora was visible as far south as Texas, Mexico, the Bahamas, and the Caribbean. Solar Cycle 25 has been more active than forecast.

What is Bz and why does it matter?

Bz is the north-south magnetic-field direction in the solar wind. When Bz is negative (pointing south), it cancels Earth’s northward magnetic field and lets solar particles enter the atmosphere. Strong aurora requires sustained negative Bz. SpaceWeatherLive and SWPC both display it.

Will aurora season continue past 2026?

Yes, with declining frequency. Solar Cycle 25 peaked in late 2024 and will continue producing strong aurora events into 2027 to 2028 before activity drops. The next solar peak (Cycle 26) is projected for the mid 2030s.