diff --git a/docs/ISSUES.md b/docs/ISSUES.md
index cc50640e..3d0389a1 100644
--- a/docs/ISSUES.md
+++ b/docs/ISSUES.md
@@ -24,6 +24,28 @@ What does NOT go here:
 - Every session: scan OPEN issues at start; promote/close anything we touched during the session before ending.
 - Promoting to a Phase: mark as `DONE (promoted to Phase X)` + commit SHA where the Phase entry landed.
 
+## #423 — Atmospheric ray/shadow/volumetric day-group policy keys on the raw day-group index, not the DAT-classified WeatherKind
+
+**Status:** OPEN — filed 2026-08-23 at Campaign VM VM6 (spot-check); pre-existing from Campaign AR.
+**Component:** rendering / render packs — atmosphere policy
+
+**Description:** `BuiltInAtmosphericRenderPack.AtmospherePolicy()` declares
+`ActiveDayGroupMultiplier(0, 1.0), (1, 0.35), (2, 0.20)` and
+`AtmosphericPostProcessGraph.EvaluateDayGroupPolicy` applies it to sun-ray,
+directional-shadow and volumetric strength by the raw `activeDayGroup`
+INDEX, with an undocumented assumed meaning (0 = brightest … 2 = dimmest).
+Dereth's day-group index carries no weather meaning; the codebase classifies
+the group's DAT name into `AcDream.Core.World.WeatherKind` (Clear/Overcast/
+Rain/Snow/Storm, `WeatherState.cs:198-232`), which `DirectionalShadowQuality`
+already keys on. VM6's foliage wind was corrected to `WeatherKind` at
+`6cc5e183`; the ray/shadow/volumetric multiplier was left as-is because the
+owner accepted its look at the Stage-1 gate and re-keying changes it.
+
+**What to do:** re-declare as `WeatherKind`-keyed points (same shape as
+`FoliageWindByWeather`), choose the per-kind multipliers at an owner visual
+gate, and retire `ActiveDayGroupMultiplier`. Validator must reject unknown
+kinds. Same class as the VM6 fix; do not guess the values.
+
 ## #422 — Intermittent heap-corruption exit (0xC0000374) after a pack-on offline capture
 
 **Status:** OPEN — filed 2026-08-22 at Campaign VM VM3; VM7 gate item (fix or characterise before merge).