ABOUT THE DATA

The Antarctic Mesoscale Prediction System is the numerical weather prediction system built for the United States Antarctic Program. It is run by the Mesoscale & Microscale Meteorology Laboratory of the National Center for Atmospheric Research in Boulder, with support from the National Science Foundation's Office of Polar Programs, and it is what the forecasters who send aircraft to McMurdo, the South Pole and the deep field read every day. Its forecasts are shared openly with the other national Antarctic programs.

AMPS is the Weather Research and Forecasting model (WRF) with physics tuned for the polar regions — the lineage of Polar WRF developed at Ohio State's Byrd Polar and Climate Research Center — started twice a day, at 00 and 12 UTC, from a global analysis with Antarctic observations assimilated on top. The output is published at www2.mmm.ucar.edu/rt/amps, and this site reads its GRIB files as each grid finishes, usually nine to ten hours after the start time.

Nothing here is re-forecast or post-processed beyond what a map needs: the fields are decoded from AMPS's own files, the wind chill and cloud path are computed from AMPS's own variables, and each frame is the model grid itself, pixel for pixel.

The projection is the model's. AMPS runs on a polar stereographic grid, true to scale at 71°S, on a sphere of radius 6 370 km. Every map here is drawn on that same projection — turned so the Greenwich meridian points up, as Antarctic maps conventionally are — so each model frame is its grid laid down exactly, with no resampling. It is also why the pole is in the middle rather than smeared across the top of the screen.

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 read the model grid directly 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 — ice surface on land, bathymetry at sea — and, closer in over the continent, the 100 m Reference Elevation Model of Antarctica (REMA) from the Polar Geospatial Center, shaded, tinted and projected in the Forecast Network's own atlas pipeline, with coastlines and ice shelves from Natural Earth. The place names are set in EB Garamond Italic, the atlas voice of every Forecast Network map; the stations in Overpass.

This is not an operational forecast. Decisions about flights, traverses, field work or ship operations belong to the official forecasters of the national programs — the U.S. Antarctic Program, Antarctica New Zealand and their counterparts — who read AMPS alongside observations, satellite imagery and experience no website can hold.

The plateau bends the usual rules. Sea-level pressure is blanked above 1 500 m and 500 hPa heights where the ground itself stands above 500 hPa. Surface temperatures under the winter inversion are the hardest thing for any model to get right. Precipitation is water equivalent; the snow it makes can be ten or twenty times deeper, and much of what falls on the coast is blown snow the model does not count as precipitation at all.

Times are UTC throughout. McMurdo, Scott Base and the South Pole keep New Zealand time, which the explorer shows alongside.