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Milepost
1108

TheForecast Post

A chronicle of American weather and climate  ·  Wednesday, 16 September 2026

Phoenix, Arizona Revisions MILEPOST 1097

Phoenix's forecast for Thursday has moved 13°F colder

98°F in the 20260913T18:00Z run, 85°F in the 20260915T12:00Z — the largest revision of any city on the roster. The current run's 10th-to-90th percentile spread at that hour is 16°F.

Successive cycles do not merely refresh a forecast; they leave a trail. For Thursday, September 17 at 00Z in Phoenix, that trail runs from 97.8°F in the 20260913T18:00Z cycle to 84.8°F in the 20260915T12:00Z — a move of -13.1°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 Thursday at 00Z
api.weather.city /v1/history (nbm-qmd)
-13.1 °F normal 0.0 °F · 1 of 6
8 synoptic cycles
10th-to-90th percentile spread at that hour
api.weather.city (nbm-qmd)
16.2 °F normal 13.1 °F
current run
Milepost
1097 · laid 2026-09-15T22:25:16Z
Model
nbm-qmd · cycle 20260915T12:00Z
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
8dd914b7d778b5656a37684fb6d1f80cdb09ae7a611e449d5bb53d3814ea259b
Machine
JSON