ABOUT THE DATA

ECMWF's high-resolution forecast (HRES) is the deterministic run of the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecasts, started four times a day at 00, 06, 12 and 18 UTC. This site reads the 0.1° global dissemination — a 3600 × 1801 grid, hourly to 90 hours and three-hourly to six days (the 06 and 18 UTC runs stop earlier) — through the same feed that Forecast Euro draws from. It supplies everything at the surface: temperature, dewpoint, wind, gusts, pressure, precipitation, cloud cover, visibility and precipitable water.

ECMWF open data — the same forecast published at 0.25° under the CC BY 4.0 licence — supplies the fields the 0.1° set here does not carry: the 850 hPa temperature, the 500 hPa height, the 250 hPa wind and the sea-ice thickness from ECMWF's coupled ocean–ice model. It is three-hourly, so those maps change every three hours; between frames the explorer keeps the latest one and says which hour it is from.

CAPS, the Canadian Arctic Prediction System, is run by the Meteorological Service of Canada, part of Environment and Climate Change Canada, at 3 km on a rotated grid that covers the whole Arctic Ocean and its coasts, centred on the Canadian Arctic Archipelago. It runs at 00 and 12 UTC out to 48 hours, and is fetched from ECCC's MSC Datamart exactly as Forecast Canada fetches it.

Nothing here is re-forecast or post-processed beyond what a map needs. Each field is taken from the model's own files; wind chill is computed from the model's 2 m temperature and 10 m wind with the North American (JAG/TI 2001) formula; and because neither model is published on a polar grid, every frame is resampled once (bilinearly, winds turned to the map's axes) onto a square grid on the projection below.

The projection. Every map is north polar stereographic, true to scale at 70°N, with the 45th meridian west pointing straight down — the layout the U.S. National Snow and Ice Data Center uses for sea ice (EPSG:3413), with Greenland at the bottom, Alaska at the upper left, Siberia across the top and Scandinavia on the right — on the 6 371 229 m sphere both models are defined on. The pole is in the middle, where it belongs, instead of smeared across the top of a Mercator map. The explorer can turn the map so any side of the Arctic is down.

Reading values. Frames are 8-bit indexed images in which every colour stands for one value, so the pointer can read the model's number back out of any pixel. Values are quantised to 255 steps per field — about half a degree for temperature — and the station pages sample each model on its own native grid instead.

The relief under every map is drawn here from elevation data, not taken from a tile service: NOAA NCEI's ETOPO 2022 global relief model — the Greenland ice sheet on land, the floor of the Arctic Ocean at sea — shaded, tinted and projected in the Forecast Network's own atlas pipeline, with coastlines, glaciers and ice caps from Natural Earth. The place names are set in EB Garamond Italic, the atlas voice of every Forecast Network map; the towns and stations in Overpass.

Not for navigation, aviation or any decision where safety depends on it. This is an independent visualisation of raw model output, published as it arrives and without a forecaster's review. For flying, sailing, travel on the sea ice or on land, and anything else where the weather can hurt you, use the official forecasts and warnings: the Norwegian Meteorological Institute, the Danish Meteorological Institute for Greenland, Environment Canada, the U.S. National Weather Service in Alaska, the Icelandic Met Office, and the national ice services.

The Arctic bends the usual rules. Shallow winter inversions over the ice are the hardest thing for any model to get right, and a few metres of difference between the model's ground and the real one can mean several degrees. Sea-level pressure over the Greenland ice sheet is a convention, not a measurement. Precipitation is water equivalent; the snow it makes is usually ten times deeper, and blowing snow — which can bring visibility to zero on a clear day — is not precipitation at all. The model's visibility sees fog and falling snow; it does not see a whiteout.

Times are UTC throughout, with Longyearbyen (Central European) time alongside on the ECMWF maps and Iqaluit (Eastern) time on CAPS.

The Forecast Network. Forecast Arctic is one of a family of independent weather sites: Forecast Antarctica draws the other pole, Forecast Euro the whole of ECMWF's output, Forecast Canada Environment Canada's models, and Forecast Alaska, Forecast Norway and Forecast Finland the countries whose north is the Arctic. None of them is affiliated with, or endorsed by, the agencies whose data they draw.