Chicago, Illinois Revisions
MILEPOST 1049
Chicago's forecast for Monday has moved 14°F colder
83°F in the 20260909T00:00Z run, 69°F in the 20260910T18:00Z — the largest revision of any city on the roster. The current run's 10th-to-90th percentile spread at that hour is 20°F.
Successive cycles do not merely refresh a forecast; they leave a trail. For Monday, September 14 at 18Z in Chicago, that trail runs from 83.4°F in the 20260909T00:00Z cycle to 69.4°F in the 20260910T18:00Z — a move of -14.1°F across 8 runs.
The change is about half the run's 10th-to-90th percentile spread, so the earlier forecast is still inside the current range of outcomes.
Model NBM-QMD, via api.weather.city /v1/history. Percentiles are the same run's own.
The numbers in this piece, with what they are measured against
| forecast revision for Monday at 18Z api.weather.city /v1/history (nbm-qmd) |
-14.1 °F | normal 0.0 °F · 1 of 8 8 synoptic cycles |
| 10th-to-90th percentile spread at that hour api.weather.city (nbm-qmd) |
19.7 °F | normal 14.1 °F current run |
- Milepost
- 1049 · laid 2026-09-11T04:25:13Z
- Model
- nbm-qmd · cycle 20260910T18:00Z
- Desk
- revision v1
- Method
- the same valid time read from successive synoptic cycles; the move is last run minus first run
- Source
- https://api.weather.city/v1/history
- Digest
- 8c1f8da65f978ae3c2cb5d5e145c2ecff021f0ff184827091ba596a3645b4663
- Machine
- JSON