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Milepost
1121

TheForecast Post

A chronicle of American weather and climate  ·  Thursday, 17 September 2026

New York, New York Revisions MILEPOST 1120

New York's forecast for Tuesday has moved 12°F colder

73°F in the 20260915T12:00Z run, 60°F in the 20260917T06:00Z — the largest revision of any city on the roster. The current run's 10th-to-90th percentile spread at that hour is 9°F.

Successive cycles do not merely refresh a forecast; they leave a trail. For Tuesday, September 22 at 18Z in New York, that trail runs from 72.6°F in the 20260915T12:00Z cycle to 60.2°F in the 20260917T06:00Z — a move of -12.4°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 Tuesday at 18Z
api.weather.city /v1/history (nbm-qmd)
-12.4 °F normal 0.0 °F · 1 of 7
8 synoptic cycles
10th-to-90th percentile spread at that hour
api.weather.city (nbm-qmd)
8.9 °F normal 12.4 °F
current run
Milepost
1120 · laid 2026-09-17T17:25:13Z
Model
nbm-qmd · cycle 20260917T06:00Z
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
cacee7333800a094646cd9d7d0110b214a3963fcda30754e430a58aa7982c4a7
Machine
JSON