About the Aurora & Space Weather Forecast
“Kp 6 tonight” means nothing until you know what your latitude requires — and that is the number every generic aurora app skips. This tool converts your coordinates to geomagnetic latitude (the aurora orbits the magnetic pole in Arctic Canada, not the geographic one), looks up the Kp level at which the auroral oval reaches you, and compares it against NOAA’s live readings and 3-day forecast — during your actual dark hours, because a Kp 7 spike at noon helps nobody.
It is built for aurora chasers timing a drive north, photographers picking a night worth losing sleep over, and anyone at mid-latitudes wondering whether tonight’s headline storm is real where they live. The solar-wind row — speed and the Bz orientation — tells you whether a forecast is likely to verify or fizzle.
Location detection happens from your connection and is used only to compute the threshold and fetch sunrise/sunset — nothing is stored. Override it with any city for trip planning.
Expectation-setting is deliberate here: at your threshold Kp, expect a gray-green glow on the horizon, not the saturated overhead curtains in photographs — those need a storm one or two levels stronger, or a camera sensor doing what eyes cannot.
NOAA’s daily max-Kp outlook one solar rotation ahead — for planning trips around active stretches.
Major (G3+) storms of the past decade and roughly how far south naked-eye aurora was credibly reported. Rows highlighted green reached your geomagnetic latitude.
Each saved spot’s required Kp against tonight’s forecast max, at a glance.
How to Use the Aurora Forecast
Let the tool detect your location (or search any city you are planning to visit) and read the verdict: it compares NOAA’s forecast Kp against the Kp your geomagnetic latitude requires, counting only the three-hour blocks that fall during your local darkness. The two condition toggles matter — a threshold-level display is invisible from a bright suburb or behind a treeline, so switching either off honestly downgrades the verdict. Then check the solar-wind row: a fast stream with a southward Bz is what turns a paper forecast into sky.
The Kp Index and Storm Levels
Kp condenses magnetometer readings from stations worldwide into a 0–9 scale every three hours. From Kp 5 upward, NOAA assigns storm levels: G1 (Kp 5, minor) through G5 (Kp 9, extreme — a few times per solar cycle). Each step pushes the auroral oval a couple of degrees equatorward, which is why the threshold table in this tool is really a map: Fairbanks needs Kp 1, Minneapolis roughly Kp 6, Denver Kp 8, and anything south of about 40° geomagnetic waits for the storms that make national news. The scale is quasi-logarithmic — Kp 7 represents far more than 40% more disturbance than Kp 5.
Geomagnetic vs Geographic Latitude
The aurora rings the geomagnetic pole, currently in the Canadian Arctic — offset about 9° from true north. The practical consequence: North America gets aurora “cheap.” Minneapolis (45°N geographic) sits near 55° geomagnetic, while London (51.5°N geographic) sits near 47° geomagnetic — so the less-northern city sees aurora far more often. This tool computes your geomagnetic latitude with a dipole approximation good to about ±2°, which is tighter than the natural fuzziness of the oval’s edge on any given night.
Reading Solar Wind Data
Three numbers, measured a million miles upstream at the L1 point, preview the next half-hour to hour of geomagnetic activity. Speed: 300–400 km/s is quiet; above 500 km/s means a coronal-hole stream or CME is arriving. Density adds punch to whatever is flowing. And Bz — the north-south tilt of the interplanetary magnetic field — is the gatekeeper: south-pointing (negative) Bz lets the solar wind couple into Earth’s field and drive aurora; north-pointing Bz largely deflects it. Chasers’ folklore is accurate here: a mediocre forecast with Bz at −15 nT beats a great forecast with Bz stuck at +5.
Solar Cycle 25 and the Late 2020s
Solar activity runs an 11-year cycle, and Cycle 25 peaked stronger than forecast — the May 2024 G5 superstorm that painted skies to the Gulf Coast was its signature. The years just after solar maximum historically produce the most severe storms (the declining phase throws the largest coronal holes and still-frequent CMEs), which makes the mid-to-late 2020s the best aurora window until the 2030s. If your latitude needs Kp 7+, these are the seasons to keep this forecast bookmarked and your dark-sky site scouted.
Your Eyes vs Your Camera
A camera on a tripod integrates light for seconds; your dark-adapted retina cannot, and its color-sensitive cones barely function at night. At threshold Kp expect a colorless or faintly green glow low on the horizon that a 10-second exposure renders as vivid curtains. Overhead structure and naked-eye color arrive one to two Kp levels above your minimum. None of this makes threshold nights not worth it — watching the glow pulse while the camera reveals the color is the standard mid-latitude experience — but it is why this tool’s verdicts say “possible low on the horizon” instead of promising postcards.
Into sky-watching math? Pair this with the Projectile Motion Calculator and the Scientific Calculator. Browse all Math & Science tools for more.
Frequently Asked Questions
What is the Kp index?
Kp measures global geomagnetic disturbance on a 0 to 9 scale, computed every three hours from magnetometer stations worldwide. Higher Kp pushes the auroral oval toward the equator: Kp 3 is a quiet-night show for Fairbanks, while the northern US states typically need Kp 6 to 7 and mid-latitudes need a rare Kp 8 to 9 storm.
Why does the tool use geomagnetic latitude instead of regular latitude?
The aurora forms around the geomagnetic pole, which sits in the Canadian Arctic, not at the geographic pole. That offset is why Minneapolis sees aurora more often than London despite similar map latitude. The tool converts your coordinates before comparing against the Kp thresholds.
What does a southward Bz mean and why does it matter?
Bz is the north-south orientation of the interplanetary magnetic field carried by the solar wind. When it points south, negative in the data, it couples with Earth's field and transfers energy efficiently, supercharging aurora. A strong forecast with a stubbornly northward Bz often fizzles.
Will the aurora look like the photos?
Usually not. Cameras accumulate light over seconds; your eyes cannot. At the threshold Kp for your latitude expect a gray-green glow low on the northern horizon, with color and overhead structure reserved for storms one or two Kp levels above your minimum. The tool's verdict wording sets this expectation.
When is the best time of night and year?
Statistically 10 pm to 2 am local, with a peak near magnetic midnight, and around the equinoxes in March and September when geometry favors coupling. Any dark, clear night during a strong storm beats a perfect-season quiet night, so watch the forecast strip rather than the calendar.
