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Milepost
1143

TheForecast Post

A chronicle of American weather and climate  ·  Saturday, 19 September 2026

Nashville, Tennessee Revisions MILEPOST 1142

Nashville's forecast for Sunday has moved 7°F colder

66°F in the 20260917T12:00Z run, 59°F in the 20260919T06:00Z — 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 Sunday, September 27 at 12Z in Nashville, that trail runs from 66.1°F in the 20260917T12:00Z cycle to 58.8°F in the 20260919T06:00Z — a move of -7.3°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 Sunday at 12Z
api.weather.city /v1/history (nbm-qmd)
-7.3 °F normal 0.0 °F · 1 of 3
8 synoptic cycles
10th-to-90th percentile spread at that hour
api.weather.city (nbm-qmd)
16.1 °F normal 7.3 °F
current run
Milepost
1142 · laid 2026-09-19T16:25:23Z
Model
nbm-qmd · cycle 20260919T06:00Z
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
6bc2e989110bc2e3973c3c2e796f74a625ae12617b90469aab5df9fefa240cf5
Machine
JSON