Aurora and night sky · MeteoFrontier

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Two different things are shown here. NOAA's aurora forecast (official, Space Weather Prediction Center) says where aurora is likely. The MeteoFrontier viewing chance is our estimate of whether you could actually see it: it combines NOAA's forecast with our cloud forecast, darkness and moonlight. Neither is an official Canadian forecast.

How to use this page · tap any ? for a full explanation

Start with the map. It opens on the MeteoFrontier viewing chance at tonight's best hour. Drag the hour slider (or ← →) to step through the night; pinch or scroll to zoom, drag to pan.
Pick your airport: type an ICAO code or name, or click a dot. Its panel gives tonight's darkness window, the moon, a one-line summary and an hour-by-hour table in local time.
Switch layers to see why: NOAA's official aurora probability, our aurora visibility estimate, cloud cover, or darkness and moonlight.
Check space weather now on the evening itself: Kp, Bz south, faster wind - and NOAA's watches and warnings.
Plan ahead with the Night buttons and the 3-night outlook; come back on the day, forecasts change.
Go somewhere dark, look north, give your eyes 15–20 minutes. Phone night modes see faint aurora before eyes do.

Map layer

Explain: viewing chance · NOAA probability · estimate · cloud · darkness

Night

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Airport

Best bets tonight

Space weather now

All airports tonight

Click a column heading to sort, a row to select the airport.

How we compute this

The viewing chance

Viewing chance = aurora visibility estimate × clear sky × darkness. Each is worked out for every hour of the night on a grid of about 55 × 50 km cells and at each airport.

Aurora visibility estimate (from NOAA). For the first hours we use NOAA SWPC's OVATION nowcast, scaled so that OVATION ≥ 30 % counts as aurora almost certainly overhead, and spread equatorward with the view-line geometry: aurora 100–250 km up stays above about 5–10° elevation out to roughly 4–6° of latitude, so it can be seen low on the northern horizon south of the oval. Over the next 3 hours we hand over to NOAA's 3-hour Kp forecast, turned into an oval edge with SWPC's Kp–latitude relation (about 66.5° − 2° per Kp unit, geomagnetic) and the same view-line weights. Forecast Kp is blurred by about ±0.6 Kp tonight, growing each day, because Kp forecasts are often off by 1–2 units.
Clear sky (ours). At FRONTIER airports (western live, eastern shadow): FRONTIER's own layered cloud forecast, ceiling and fog probabilities, with thin cirrus counting far less than low overcast - this is the headline value. Elsewhere: 100 % minus total cloud cover from a weighted blend of HRDPS (2.5 km, weight 1.5), RDPS (10 km) and ECMWF IFS (25 km), averaged over each cell and nudged toward nearby FRONTIER airports on the map. Airport tables show both.
Darkness and moonlight (computed). Our own sun and moon positions (checked against USNO to 1–2 minutes). No aurora in daylight or civil twilight (sun above −6°); full darkness from −15°. A bright moon high in the sky lowers the factor by up to 35 %.

Transparency proxy

For stargazing, the Transp. column is a proxy (not a measured transparency): clear sky × (1 − 0.4 × high-cloud fraction) × a haze penalty when 2-m humidity is above 80 %. High cloud is ECMWF's high-cloud cover, or RDPS 300 hPa humidity where ECMWF has no step. Thin cirrus that hides faint stars barely affects a bright aurora, so the viewing chance uses total cloud only.

Honest limits

This is guidance, not an official forecast. Aurora forecasts are NOAA's; MeteoFrontier does not forecast geomagnetic activity. For Canadian space weather see Space Weather Canada (NRCan).
OVATION is a nowcast, good for about an hour; beyond that everything rests on the Kp forecast, which often misses the timing and strength of storms (CME arrival times are uncertain by ±6–12 hours or more).
Cloud forecasts are least reliable for thin or broken cloud, low stratus under inversions, and lake-effect cloud. A 50 % cloud cover can mean a clear northern horizon or an overcast one.
Geomagnetic latitude uses a centred dipole (within about 1–2° of corrected geomagnetic latitude over Canada). Light pollution and terrain are not included: get away from city lights and look north.
Local times follow each airport's time zone. Night outlooks for nights 2 and 3 use 3-hourly steps.

Sources

NOAA Space Weather Prediction Center (public domain, U.S. Government): OVATION aurora forecast, planetary K-index (observed, estimated, 3-day forecast), real-time solar wind, NOAA scales, alerts and watches, 3-day forecast and 27-day outlook. swpc.noaa.gov
Environment and Climate Change Canada HRDPS and RDPS (Open Government Licence – Canada); ECMWF IFS open data (CC BY 4.0).
Sun and moon: MeteoFrontier's own code (Meeus / Schlyter low-precision methods). Basemap: Natural Earth (public domain).

Glossary: words used on this page

Aurora (borealis): Light from oxygen (green, red) and nitrogen (blue, purple) 100–300 km up, excited by electrons from Earth's magnetosphere.
Auroral oval: The ring around each magnetic pole where aurora is most frequent; it widens and moves towards the equator as activity rises. Over Canada it normally lies over the territories and the northern provinces.
Auroral zone / sub-auroral zone / polar cap: NRCan's three Canadian regions: under the usual oval, south of it, and inside it (High Arctic).
View line: The southernmost place where aurora may be seen low on the northern horizon; south of where it is overhead.
OVATION: NOAA's model of where aurora is happening, driven by live solar-wind data; a 30–90 minute nowcast.
Kp index: 0–9 planetary measure of geomagnetic disturbance over 3 hours. Kp 5+ is a storm.
G-scale: NOAA geomagnetic storm scale, G1 (Kp 5) to G5 (Kp 9).
Geomagnetic latitude: Latitude measured from the magnetic pole (northern Canada, near 81° N 73° W) rather than the geographic one; aurora follows it. Canada sits closer to the magnetic pole than Europe does at the same latitude.
Solar wind: The stream of charged particles flowing from the Sun at 300–800+ km/s.
IMF, Bt and Bz: The interplanetary magnetic field carried by the solar wind; Bt is its total strength, Bz its north–south part (south = negative = good for aurora).
L1: The point 1.5 million km towards the Sun where solar-wind monitors (DSCOVR, ACE, IMAP) sit, 30–60 minutes upstream of Earth.
CME: Coronal mass ejection: a cloud of solar plasma and field that can reach Earth in 1–4 days and cause the biggest storms.
Coronal hole high-speed stream (CH HSS): Fast solar wind from dark regions of the Sun's corona; causes recurring minor storms every 27 days.
Substorm: A sudden 10–30 minute brightening and expansion of the aurora, often near local midnight.
Civil / nautical / astronomical twilight: Sun 0–6°, 6–12° and 12–18° below the horizon. Darker beyond 18°.
Polar night: When the sun stays below the horizon all day, north of the Arctic Circle in early winter.
Illuminated fraction: How much of the moon's disc is lit, 0 % (new) to 100 % (full).
Total / high cloud cover: Share of the sky covered by any cloud, or by cloud above about 6 km (cirrus).
Transparency: How clean the air is for seeing faint stars; reduced by thin cloud, haze, humidity and smoke. Shown here as a model-based proxy.
Viewing chance: MeteoFrontier's estimate of seeing aurora: aurora estimate × clear sky × darkness.

More weather words in the site glossary.

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