Open data and method

Every number on this site can be traced to raw bytes we fetched, with a sha256 recorded at the moment of fetching. Here is what we use, how we score, and the live ledger.

Sources

Source	Used for	Notes
NWS CLI, Boston (CLIBOS)	Truth source: the observed daily maximum at Boston Logan	First complete report after the climate day (00:00–24:00 EST). Whole °F. Polled every 2 hours; corrections within 7 days re-score.
NWS gridpoint forecast	Reference lines M2 (raw) and M5 (calibrated)	Fetched daily at 21:30 UTC, before the 23:00 UTC cutoff; reference lines submit at 22:15 UTC through the same ledger.
NCEI U.S. Climate Normals 1991–2020	Reference line M1 (daily normal maximum)	Static table for station USW00014739.
NCEI GHCN-Daily	Audit comparison only	Never changes a result. Different revision schedule from the CLI.

We use public NOAA/NWS/NCEI data. This does not imply their partnership or endorsement. CLI values are preliminary and can be revised by the provider.

The exact error formula

A forecast is stored as t, an integer number of tenths of °C. The CLI reports F, an integer °F. Instead of converting and rounding, we compute the error as an exact fraction:

error °C = |9t − 50F + 1600| / 90

Worked example: forecast 14.0 °C, so t = 140. Observed 57 °F, which is exactly 125/9 °C (13.888...). Then |9·140 − 50·57 + 1600| = |1260 − 2850 + 1600| = 10, and 10/90 = 1/9 °C. Displayed half-up to two decimals: 0.11.

A mean over n rounds is the sum of numerators over 90·n, still exact. Ties are judged on the displayed value; hidden digits never break them.

Fetch ledger

Each time the pipeline fetches a source, it writes a row with the sha256 of the exact bytes received. Archived CLI products can be downloaded by their hash.

Audit chain

Important events (round created, manifest frozen, observation imported, result versioned) are appended to a hash chain: each entry includes the hash of the one before, so history cannot be rewritten quietly.

Source code

During Season 1 the scorer and pipeline code is public on request: use the contact form on the Partners page (choose 'other'). The hash rules are fully described on this page and on the Verify page, so you can recompute receipts and errors without our code.