Edition 2026-09-21 The Ledger Archive API RSS Weather Trader
Milepost
1164

TheForecast Post

A chronicle of American weather and climate  ·  Monday, 21 September 2026

Phoenix, Arizona Revisions MILEPOST 1163

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

102°F in the 20260919T00:00Z run, 95°F in the 20260920T18:00Z — the 3rd-largest revision of the 5 cities on the roster that moved at all. The current run's 10th-to-90th percentile spread at that hour is 10°F.

Successive cycles do not merely refresh a forecast; they leave a trail. For Thursday, September 24 at 00Z in Phoenix, that trail runs from 102.1°F in the 20260919T00:00Z cycle to 94.6°F in the 20260920T18:00Z — a move of -7.5°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)
-7.5 °F normal 0.0 °F · 3 of 5
8 synoptic cycles
10th-to-90th percentile spread at that hour
api.weather.city (nbm-qmd)
10.3 °F normal 7.5 °F
current run
Milepost
1163 · laid 2026-09-21T04:25:49Z
Model
nbm-qmd · cycle 20260920T18:00Z
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
41a339a09d50d8bfa0263e3e7be682c8a188dce06653dd963739059a8c4a9700
Machine
JSON