How AuroraOdds works

Aurora Odds combines a provisional local activity model with darkness and a small moonlight contrast adjustment. Local cloud cover and weather are shown separately and do not change Aurora Odds.

These odds come from a model we're still checking against what people actually see. It is not a proven personal sighting probability, so the “not yet calibrated” label stays until enough observations support it.

Two things must line up

Aurora

Is there activity here?

Built from the short-range auroral oval when valid, geomagnetic latitude, the Kp outlook and fresh near-term space-weather signals.

Sky here

Can the sky be observed?

Cloud cover, darkness and moonlight guide the practical decision. Total, low, middle and high cloud are forecast context, not aurora inputs.

A strong aurora behind overcast is still a poor viewing opportunity. A clear sky during weak activity is not enough either.

Which page should I use?

Tonight: Choose an hour, then read the aurora and sky forecasts side by side.
Live: Use fresh solar-wind and regional signals to decide whether to look now.
Trip planner: Compare nights. Later dates use typical activity, not a live forecast.
Map: Find a place with less cloud. The map never boosts Aurora Odds for clear weather.

Live space weather, in plain language

Measurements made upstream of Earth can describe roughly the next hour. They cannot predict a specific Bz value later tonight.

Bz: Sustained southward Bz generally helps energy enter Earth’s magnetic field. One reading is not a trend.
Solar-wind speed: Fast wind can drive stronger activity, but direction and duration still matter.
Kp: A global three-hour disturbance index. It helps with the wider outlook but does not say what is over one town.

Live measurements come from NOAA’s active L1 spacecraft; regional ground response comes from the IMAGE magnetometer network.

Forecast timing and uncertainty

The auroral oval is a 30–90 minute forecast. Fresh Bz and wind adjustments fade out by three hours. Later hours use the Kp outlook and the local latitude model; CME notices are context and do not add a second boost.

The hourly bars, Best tag and strongest-activity window use the activity factor alone. Clouds cannot change their height or ranking.

Hourly ranges are fixed display guides: ±5 points more than two hours ahead and ±10 beyond four hours. They are not measured confidence intervals.

Darkness comes from the local sun position. Moonlight is retained as a small astronomical contrast adjustment. Weather has zero contribution to Aurora Odds.

Trip estimates and calibration

The planner runs 10,000 deterministic, correlated Kp scenarios through the same hourly model. A qualifying night is one whose strongest hour is above the usual activity level for that location and calendar month, while still meeting the existing minimum useful-activity level. The starting definition uses the upper third of the local monthly distribution.

Short or marginal trips show the chance of at least one above-norm night. Longer trips show the mean number of above-norm nights with a 10th–90th percentile scenario range. These are relative activity comparisons, not expected counts or probabilities of seeing aurora. Each night in the list shows only its best hour's Aurora Odds, which is the same value shown first when the night is opened.

Forecast uses NOAA's 3-day Kp forecast, Outlook uses NOAA's single daily 27-day value, and Typical draws from the recent definitive GFZ Kp distribution for that calendar month. Weather remains separate observing context.

Reports from people who looked are stored with the forecast issued at the time. Cloud context is retained for analysis, but it never changes the weather-independent aurora target. Voluntary reports are useful evidence, not proof of calibration.

What is stored

Technical inputs and limits

The local activity index is a conservative, uncalibrated combination of geomagnetic latitude, Kp and valid short-range inputs. Global Kp is never presented as a local probability. Terrain, local light pollution and cloud optical thickness are not modelled.

Each live reading is context inside the shared activity model, not a separate multiplier. The current labels summarize recent measurements; this is not a trend analysis or a guarantee of aurora.

Bz direction: The north-south part of the solar-wind magnetic field. Sustained negative (southward) Bz generally favours energy transfer into Earth's magnetic field; one reading cannot establish a sustained trend. Near now, a smooth adjustment favours southward Bz and reduces northward Bz, with no jump at 5 nT. The adjustment is bounded at +22% and -28% of the activity factor at -10 and +10 nT. These are uncalibrated model choices, not visibility probabilities or universal thresholds.
Bt field strength: The total magnetic-field strength, in nanoteslas. Read it together with Bz: a large Bt does not tell you the field's direction. Bt is shown as context. It is not a separate multiplier in the current AuroraOdds formula.
Solar-wind speed: How fast the solar wind travels, in kilometres per second. Faster wind can drive stronger disturbances, but the magnetic-field direction and how long conditions persist also matter. The near-term adjustment changes smoothly with speed: a reduction below 400 km/s and a small boost from 400 to 600 km/s, bounded at -12% and +8% of the activity factor. These are uncalibrated model choices. There is no speed that guarantees aurora.
Proton density: The number of protons per cubic centimetre. Density contributes to solar-wind pressure; a high number alone is not an aurora forecast. Density enters the model through the pressure estimate, rather than receiving another independent boost. Speed and density must come from the same measurement row.
Dynamic pressure: The pressure exerted by the moving solar wind. The displayed value is derived from proton density and speed, not measured independently. We use 1.6726 × 10⁻⁶ × density × speed², with density in protons/cm³ and speed in km/s, to estimate pressure in nPa. This proton-only approximation omits other ion species. Higher pressure can add a small near-term adjustment; Bz also affects that adjustment.

Source measurements: NOAA real-time solar wind. Forecast sources: NOAA aurora forecast and planetary Kp. Weather context: Open-Meteo.