Split weather data types from forecast derivation

docs/internal/forecast-derivation.md

@@ -5,14 +5,14 @@ This document describes deterministic forecast summarization in
 
 ## Purpose
 
-`internal/forecast` converts normalized bundle data into daily and period
-summaries used by briefing builders.
+`internal/forecast` converts normalized `weatherdata` bundle data into daily
+and period summaries used by briefing builders.
 
 ## Inputs And Outputs
 
 Inputs:
 
-- `forecast.Bundle`
+- `weatherdata.Bundle`
 - local date or resolved report period
 - timezone
 - configured daypart definitions
@@ -43,7 +43,7 @@ configuration.
 
 ## External Adapters Used
 
-None directly. Forecast data arrives through `forecast.Bundle`.
+None directly. Forecast data arrives through `weatherdata.Bundle`.
 
 ## State Or Manifest Behavior