Begin with the time horizon
A current auroral oval and a ten-day geomagnetic outlook answer different questions. NOAA OVATION uses upstream solar-wind information for a short lead nowcast. A one-to-three-day geomagnetic forecast works at broader scales. Longer outlooks identify possible activity periods with substantially lower timing and spatial confidence.
If a display shows the same detailed oval for every future day, ask what model created it and whether that model has been validated. GreenHalos does not fabricate future OVATION textures for days when only Kp or broad geomagnetic context exists.
Read an auroral oval as a model
An oval is a modelled representation of auroral activity around the magnetic poles. It is not a satellite photograph of the visible sky and does not prove that every point under its colour will see aurora. Model time, source age, hemisphere and legend all matter.
A bright region poleward of an observer may still be visible low on the horizon. Conversely, activity overhead may be hidden by daylight or cloud. The oval should start a local assessment, not end it.
Use Kp and solar wind for context
Kp summarises planetary geomagnetic disturbance over three-hour intervals. It helps communicate broad activity but is not a local probability. Solar-wind speed and the north-south magnetic component Bz provide more immediate context, yet no single threshold guarantees an aurora display.
Watch for sustained patterns and source quality rather than isolated readings. A brief southward Bz or a forecast peak without timing context can be misleading. Operational alerts and watches should link directly to NOAA.
Check the sky at the location
Darkness is a hard practical constraint for visual observing. Cloud can fully block the view and must never default to clear when data is missing. Moonlight can reduce contrast, but it usually matters less than daylight or thick cloud. Light pollution, terrain and an obstructed poleward horizon are additional factors.
A combined score is useful only if its components remain visible. GreenHalos withholds a combined Viewing Potential when cloud data is unknown and states that light pollution and terrain are outside the launch model.
Demand timestamps, confidence and limitations
A trustworthy forecast shows the source observation time, forecast time, freshness and horizon-specific confidence. Stale information should keep its real timestamp and lose any live badge. A data outage should not be hidden behind a smoothly animated interface.
Use the current layer for near-term awareness, the Tonight view for darkness and cloud planning, the three-day view for broad geomagnetic potential, and days four to ten as a low-confidence reason to monitor updates—not as a booking guarantee.
Evidence register
Primary sources
Sources were checked on . Each record identifies which sections it supports.
- Aurora - 30 Minute Forecast NOAA Space Weather Prediction Center Supports: Begin with the time horizon; Read an auroral oval as a model
- Space Weather Prediction Center Products NOAA Space Weather Prediction Center Supports: Use Kp and solar wind for context; Demand timestamps, confidence and limitations
- Auroras NASA Science Supports: Check the sky at the location