Retained weather and GRIB downloads

Forecast data is expensive to keep and cheap to re-fetch, so WX Navigator normally holds a model cycle for a day or two and lets it go. That is fine for routing and useless for the questions asked afterwards: what did we actually see on the Thursday, and would the other model have sent us the other way.

A project can keep its weather. While its archive window is open, every relevant model cycle is cropped to the project's corridor and stored as a GRIB2 file for ninety days — downloadable, and readable by anything that reads GRIB.

The archive window

A date range on the project, defaulted from the race dates and editable. Archiving happens while now is inside it and not otherwise.

An explicit window rather than "whatever you were recently working on", because you have to be able to answer why is Tuesday missing from my archive, and a date range is answerable.

High-resolution models are archived four times a day rather than every hour. An open window on a week-long race would otherwise hold a hundred and sixty-eight nearly identical corridors of the same water.

Downloading a GRIB

The download builds a fresh file from the newest complete cycle, cropped to your course with a margin, at the model, layers, horizon and interval you choose. It is ordinary GRIB2 with simple packing — the same shape NCEP publishes — so it opens in the usual navigation software.

Layers available depend on the model: wind everywhere, gust and mean-sea-level pressure on the NCEP models, waves and currents where they are ingested. A layer that cannot be had for a given cycle is named in the response as omitted rather than quietly left out of the file.

The size estimate updates with your selection before you commit to it, because the difference between a coastal GRIB and an offshore one is two orders of magnitude, and the moment to discover that is not over a satellite link.

What is not supported yet

A corridor that crosses the antimeridian is refused with an explanation rather than exported wrongly. GRIB2 stores longitudes going east from Greenwich, and a file that straddles the date line is read inconsistently by the software that matters. Export the halves separately.

Reproducing an old run

A run inside a project keeps enough to be reopened, and while its weather is still archived, the corridor it was solved against is still there to compare against what actually happened.

Once the ninety days pass, the run, its request and its answer remain. The weather behind it does not.