Was the forecast right for Boston on Sun Sep 6?
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 6 high anywhere from 19° to 23°; by the final call the field had settled to a median of 20°. The day verified at 20° against the BOS observations, with 2.8 mm of precipitation — drizzle.
AIFS landed closest, off by 0.1°. GEM ran 2° hot.
What every model said, at every lead
Daily-high calls for Sun Sep 6 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 · 2026-08-22 | — | 27° | — | — | 19° | — | — | 19–27° |
| 14d · 2026-08-23 | 19° | 21° | — | — | 22° | — | — | 19–22° |
| 13d · 2026-08-24 | 20° | 23° | 23° | — | 19° | — | — | 19–23° |
| 12d · 2026-08-25 | 30° | 21° | 26° | — | 26° | — | — | 21–30° |
| 11d · 2026-08-26 | 24° | 27° | 25° | — | 20° | — | — | 20–27° |
| 10d · 2026-08-27 | 23° | 32° | 23° | — | 19° | — | — | 19–32° |
| 9d · 2026-08-28 | 25° | 25° | 19° | — | 22° | — | — | 19–25° |
| 8d · 2026-08-29 | 22° | 21° | 22° | 22° | 21° | — | — | 21–22° |
| 7d · 2026-08-30 | 22° | 22° | 20° | 18° | 21° | — | — | 18–22° |
| 6d · 2026-08-31 | 21° | 18° | 18° | 20° | 18° | 18° | — | 18–21° |
| 5d · 2026-09-01 | 22° | 17° | 20° | 21° | 20° | 22° | 24° | 17–24° |
| 4d · 2026-09-02 | 24° | 21° | 19° | 23° | 22° | 21° | 20° | 19–24° |
| 3d · 2026-09-03 | 20° | 21° | 19° | 22° | 20° | 22° | 20° | 19–22° |
| 2d · 2026-09-04 | 21° | 21° | 19° | 24° | 20° | 22° | 21° | 19–24° |
| 1d · 2026-09-05 | 20° | 20° | 20° | 22° | 20° | 21° | 21° | 20–22° |
| 0d · 2026-09-06 | 20° | 19° | 20° | 22° | 20° | 21° | 21° | 19–22° |
| actual | 20° |
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.