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Milepost
1198

TheForecast Post

A chronicle of American weather and climate  ·  Thursday, 24 September 2026

Phoenix, Arizona Revisions MILEPOST 1196

Phoenix's forecast for Wednesday has moved 8°F colder

90°F in the 20260921T18:00Z run, 83°F in the 20260923T18:00Z — the 3rd-largest revision of the 8 cities on the roster that moved at all. 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 Wednesday, September 30 at 03Z in Phoenix, that trail runs from 90.4°F in the 20260921T18:00Z cycle to 82.8°F in the 20260923T18:00Z — a move of -7.6°F across 8 runs.

The change sits well inside the run's own spread, which is the guidance converging rather than reversing.

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 03Z
api.weather.city /v1/history (nbm-qmd)
-7.6 °F normal 0.0 °F · 3 of 8
8 synoptic cycles
10th-to-90th percentile spread at that hour
api.weather.city (nbm-qmd)
16.1 °F normal 7.6 °F
current run
Milepost
1196 · laid 2026-09-24T16:25:20Z
Model
nbm-qmd · cycle 20260923T18:00Z
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
8d0598626abd2989cf54e032e039ae8ffaf0dd78c23a69ea8dc1b5201e3cccb4
Machine
JSON