Was the forecast right for Boston on Sun Sep 20?
Boston, Massachusetts · daily high temperature in °C · forecasts from each model's archived runs, verified against the BOS observations
13 days out, 4 models put Boston's Sun Sep 20 high anywhere from 16° to 23°; by the final call the field had settled to a median of 16°. The day verified at 17° against the BOS observations, with 2.5 mm of precipitation — drizzle.
ECMWF landed closest, off by 0.2°. AIGFS ran 2° cool.
What every model said, at every lead
Daily-high calls for Sun Sep 20 as each model's runs approached it — the last archived run per day. NBM and The Spread's own blend are consensus products and stay out of these ranges and rankings; the Boston scoreboard shows them, labelled.
| Lead | AIFS | AIGFS | ECMWF | GEM | GFS | ICON | UKMO | Range |
|---|---|---|---|---|---|---|---|---|
| 15d · 2026-09-05 | — | 22° | — | — | 26° | — | — | 22–26° |
| 14d · 2026-09-06 | 21° | 20° | — | — | 16° | — | — | 16–21° |
| 13d · 2026-09-07 | 23° | 16° | 21° | — | 21° | — | — | 16–23° |
| 12d · 2026-09-08 | 19° | 22° | 24° | — | 21° | — | — | 19–24° |
| 11d · 2026-09-09 | 19° | 17° | 19° | — | 24° | — | — | 17–24° |
| 10d · 2026-09-10 | 20° | 25° | 19° | — | 24° | — | — | 19–25° |
| 9d · 2026-09-11 | 18° | 23° | 18° | — | 16° | — | — | 16–23° |
| 8d · 2026-09-12 | 23° | 22° | 26° | 20° | 21° | — | — | 20–26° |
| 7d · 2026-09-13 | 24° | 24° | 18° | 25° | 17° | — | — | 17–25° |
| 6d · 2026-09-14 | 18° | 17° | 23° | 23° | 20° | 22° | — | 17–23° |
| 5d · 2026-09-15 | 16° | 14° | 20° | 17° | 17° | 19° | 21° | 14–21° |
| 4d · 2026-09-16 | 17° | 15° | 17° | 17° | 16° | 17° | 19° | 15–19° |
| 3d · 2026-09-17 | 16° | 15° | 17° | 18° | 15° | 16° | 21° | 15–21° |
| 2d · 2026-09-18 | 16° | 15° | 17° | 19° | 18° | 16° | 20° | 15–20° |
| 1d · 2026-09-19 | 16° | 14° | 18° | 18° | 16° | 17° | 18° | 14–18° |
| 0d · 2026-09-20 | 16° | 15° | 17° | 17° | 16° | 15° | 18° | 15–18° |
| actual | 17° |
Read it honestly
This is one date, not a league table. A model can win a day it deserved to lose; rankings only mean something over a window. For that, see which model has been most accurate in Boston — or every city The Spread scores.
Forecasts are what each model's archived runs said at the time, captured at The Spread's sweep times — never reconstructed after the fact. Truth is the BOS observations. Archive depth varies by city; receipts exist only for dates the archive watched arrive.