Minutes ahead: upstream measurements
NOAA OVATION uses near-Earth solar-wind measurements to model auroral activity with a short forecast lead, commonly around thirty minutes and varying with travel time. This is the horizon with the strongest basis for a detailed current oval.
Even here, the map remains a model. It does not include cloud, daylight, light pollution or every local auroral structure, and stale upstream data must reduce confidence.
Tonight: combine space and sky
For the next local dark window, forecasters can combine current activity, near-term Kp or geomagnetic guidance, darkness and weather. Timing uncertainty remains, especially before an incoming CME's magnetic field is sampled upstream of Earth.
A useful Tonight view describes a best estimated window and shows every factor. It does not call a viewing score a probability or treat unknown cloud as clear.
One to three days: broad geomagnetic potential
NOAA planetary Kp and three-day geomagnetic forecasts can identify periods of elevated planetary activity. They do not support an exact future auroral oval for every place and hour.
A CME arrival estimate may narrow the period, but speed can change and an event can arrive earlier, later or with a less effective magnetic orientation. Confidence should describe the horizon and data quality, not certainty of seeing aurora.
Four to ten days: an outlook
Longer-range products use recurrence patterns, solar observations and broad geomagnetic or solar indices. They are useful for situational awareness and deciding when to check again. They have substantially less exact timing and spatial information.
GreenHalos labels this layer a low-confidence geomagnetic outlook. It never turns a 27-day or 45-day product into a precise local percentage or a visually detailed future oval.
Accuracy is not one number
A forecast can be accurate about elevated global activity yet fail to predict the best minute at one location. Local cloud may then determine the observing outcome even when the space-weather part verifies.
Judge a product by horizon-appropriate resolution, timestamp, provenance, confidence and stated limitations. As the target night approaches, replace broad outlooks with current NOAA products and an updated local weather check.
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: Minutes ahead: upstream measurements; Tonight: combine space and sky
- Space Weather Prediction Center Products NOAA Space Weather Prediction Center Supports: One to three days: broad geomagnetic potential; Four to ten days: an outlook
- DONKI NASA Community Coordinated Modeling Center Supports: One to three days: broad geomagnetic potential