Colour Tables

Every table here can be applied to a field on any of the model pages, from the Colour table menu beside the field list. Nothing is re-rendered when you do: the rasters are 8-bit palettised PNGs, so a colour table is 387 bytes of palette inside a 519 kB file and switching one rewrites just that. The forecast data in the image is untouched.

A table that declares units is read at the field's own numbers — a °F ramp puts its freezing colour at 32 °F, wherever that falls on the scale. The 298 tables in the AWIPS pack name themselves by product rather than by quantity, so they carry no units and are stretched across the field's range instead. Both are useful; only the first is a statement about values.

They arrive from nine places. weathermapmaker and the AWIPS pack are registries, imported as-is. ECMWF ecCharts are the professional ECMWF palettes on their published HRES level breaks — discrete, because the banding is most of what makes a chart read as ECMWF's rather than as a generic rainbow, and a smooth version of one is a different table with the edges moved. The NCAR/HWT ensemble tables were read back out of the rendered charts, since those pages publish beautiful maps and no colour tables. Their colours are exact; their value axes are not, because the tick labels are pixels and nothing here reads text. Those are marked as having no known axis and are stretched, which is honest rather than a guess at the breaks. The NOHRSC snowfall scale came out of a rendered map the same way but keeps its axis: the National Snowfall Analysis draws a fixed published ladder — a trace, 0.1, 1, 2 and 6 inches, then 1 foot to 50 — and its legend labels sit on the band boundaries, so every break is known to the inch. One table therefore covers a single storm and a whole season.

Tables are frozen out of the weathermapmaker registry by ingest/import_ramp.py, with a content hash, so a ramp cannot drift underneath a published image. The same file schema is used by ecmwf-charts, so a table can move between the two.