Chicago, Illinois Revisions
MILEPOST 1128
Chicago's forecast for Wednesday has moved 9°F colder
72°F in the 20260916T00:00Z run, 63°F in the 20260917T18:00Z — the 3rd-largest revision of the 10 cities on the roster that moved at all. The current run's 10th-to-90th percentile spread at that hour is 8°F.
Successive cycles do not merely refresh a forecast; they leave a trail. For Wednesday, September 23 at 18Z in Chicago, that trail runs from 72.0°F in the 20260916T00:00Z cycle to 62.5°F in the 20260917T18:00Z — a move of -9.4°F across 8 runs.
The change is larger than the run's own 10th-to-90th percentile spread — the guidance did not merely narrow, it moved off its previous position.
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 Wednesday at 18Z api.weather.city /v1/history (nbm-qmd) |
-9.4 °F | normal 0.0 °F · 3 of 10 8 synoptic cycles |
| 10th-to-90th percentile spread at that hour api.weather.city (nbm-qmd) |
8.3 °F | normal 9.4 °F current run |
- Milepost
- 1128 · laid 2026-09-18T04:25:21Z
- Model
- nbm-qmd · cycle 20260917T18:00Z
- 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
- 30903d8da2a07a04fd35fb9edd90c0d652a7b5bbced29fbe39c7092bb8da6517
- Machine
- JSON