Cloud Cover & Clearing Predictions

Space weather can be perfect, but if there's a solid deck of cloud between you and the sky, you're not seeing anything. Lumina pulls cloud forecasts for your saved locations and works out whether there's a clearing on the way — or whether you should try somewhere else.

Where the cloud data comes from

Lumina uses Open-Meteo , a free weather API that provides hourly cloud cover forecasts globally. The data includes:

Total cloud cover — percentage of sky covered (0% = completely clear, 100% = overcast).
Directional sampling — Lumina fetches cloud forecasts at five physically offset points around your location (centre, north, south, east, west) so it can tell whether a short drive in any direction would get you under clearer skies.

Cloud forecasts update every 15 minutes on the frontend and are cached for 30 minutes per location.

How Lumina analyses the cloud forecast

Lumina does a few smart things with the raw cloud data:

Southern-sky estimate

Aurora in the southern hemisphere appears on the southern horizon , so what matters isn't the cloud directly overhead — it's the cloud you're looking through toward the south. Lumina computes a dedicated southern-sky estimate by:

Sampling a point south of you — the distance is dynamically calculated from the aurora's elevation angle (typically 5–50 km south, defaulting to 20 km). The lower the aurora sits on the horizon, the further south Lumina looks to check for cloud obstruction.
Blending with local low cloud — thick low cloud at your own location can still block a low southern horizon even if the south sample point is clear, so Lumina blends the two when the local low-cloud reading is worse.

This southern-sky estimate is what drives the cloud badge on your dashboard (e.g. "Clear south," "Partly cloudy S") — it's a tailored measure of what the sky looks like in the direction aurora actually appears.

Best direction

In addition to the southern-sky estimate, Lumina checks cloud cover at all five offset points (centre, north, south, east, west) and picks the clearest one. This drives the worth travelling recommendation: if the centre is clouded but another direction has significantly clearer skies and the aurora probability justifies the drive, Lumina will suggest heading that way.

Since aurora appears on the southern horizon, a counterintuitive but effective strategy when you're under a cloud bank is to drive north — putting the cloud behind you and opening up a clear view to the south. Lumina's directional sampling picks this up: if the north sample point has significantly clearer skies than your centre and south readings, the recommendation may nudge you in that direction.

Clearing detection

Lumina scans the forecast timeline looking for a significant drop in cloud cover. If the sky goes from > 70% to < 30% in the forecast, it flags a clearing and tells you when to expect it. This is one of the most practically useful features — knowing that the clouds should break at 11 PM means you don't give up at 10 PM.

Worth travelling?

If your primary location is clouded out but one of your other saved locations has clear skies — and the aurora probability justifies the drive — Lumina will flag it with a travel recommendation. It considers the cloud differential, the aurora probability, and the distance between locations.

In field mode this becomes even sharper: Lumina picks the single best saved location by ranking all your spots on cloud cover, darkness quality (SQM), and southern-horizon obstruction. If that location is at least 20 percentage points clearer than where you are, a move alert fires — telling you which spot to head to, how much clearer it is, and an estimated drive time via road routing. You'll see something like:

Parsons Beach is much clearer — 15% vs 72% here • ~34 min drive

The drive time comes from the OSRM routing engine using your phone's current GPS position — it's actual road distance, not straight-line crow-flies distance.

Reading the cloud timeline

The Cloud Timeline component on the dashboard shows you the forecast cloud cover hour by hour through the night, with colour coding:

Green — 0–25% cover. Mostly clear.
Yellow — 25–50% cover. Partly cloudy. Might get lucky.
Orange — 50–75% cover. Mostly cloudy. Probably not worth it.
Red — 75–100% cover. Overcast. Stay home or travel.

The timeline is overlaid with the darkness window so you can see at a glance whether the clear periods line up with when it's actually dark enough to see aurora. A perfectly clear sky at 4 PM is great for a picnic but useless for aurora.

Limitations to be aware of

Cloud forecasts aren't perfect. Open-Meteo is good but not infallible, especially for patchy or convective cloud that can form and clear faster than the model predicts.
Thin high cloud can be reported as "clear" by cloud cover models but still significantly dim aurora. Cirrus is the enemy.
Fog and low cloud can form in valleys and coastal areas even when the forecast says clear — local topography matters.
Cloud cover percentages are averages over a grid cell — your actual sky might have more or less cloud than the forecast suggests.

The best strategy: use Lumina's cloud forecast as a guide, but always check something like the BOM satellite viewer before committing to a long drive.