diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index 2d185c3..d2a63aa 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -4370,10 +4370,18 @@ public sealed class GameWindow : IDisposable
                 new AcDream.Core.World.SkyStateProvider(
                     grp.SkyTimes.Select(s => s.Keyframe).ToList()));
 
+            // Phase 3e: drive the atmospheric weather (rain/snow emitters,
+            // fog-override categories, lightning strobe) from the retail
+            // DayGroup name. Stops the legacy WeatherSystem.RollKind hash
+            // from spawning rain particles on a "Sunny" day (user-observed
+            // rain regression 2026-04-23 after the retail picker landed on
+            // DayGroup[6] "Sunny" but the internal hash picked Rain).
+            Weather.SetKindFromDayGroupName(grp.Name);
+
             Console.WriteLine(
                 $"sky: PY{absYear} day{dayOfYear} → DayGroup[{idx}] \"{grp.Name}\" " +
                 $"(Chance={grp.ChanceOfOccur:F2}, {grp.SkyObjects.Count} objects, " +
-                $"{grp.SkyTimes.Count} keyframes)");
+                $"{grp.SkyTimes.Count} keyframes, weather={Weather.Kind})");
         }
     }
 
diff --git a/src/AcDream.Core/World/WeatherState.cs b/src/AcDream.Core/World/WeatherState.cs
index 15fc543..5f421fd 100644
--- a/src/AcDream.Core/World/WeatherState.cs
+++ b/src/AcDream.Core/World/WeatherState.cs
@@ -125,6 +125,12 @@ public sealed class WeatherSystem
 
     private int _rolledDayIndex = int.MinValue;  // unrolled == "pick one"
 
+    // Phase 3e — when GameWindow (via RefreshSkyForCurrentDay) pushes
+    // the active retail DayGroup name through SetKindFromDayGroupName,
+    // the internal RollKind hash becomes unused. This flag stops Tick's
+    // auto-roll so external control can't fight the internal one.
+    private bool _externallyDriven;
+
     private readonly Random _strikeJitter;
 
     public WeatherSystem(Random? rng = null)
@@ -154,6 +160,46 @@ public sealed class WeatherSystem
         _rolledDayIndex = int.MaxValue;  // "forced" sentinel — don't re-roll
     }
 
+    /// <summary>
+    /// Drive the weather kind from the active retail DayGroup name
+    /// (see <c>SkyDesc::PickCurrentDayGroup</c> port at
+    /// <c>LoadedSkyDesc.SelectDayGroupIndex</c>). Retail has ONE source
+    /// of truth for weather — the DayGroup roll — so this replaces the
+    /// internal <see cref="RollKind"/> hash once the real DayGroup picker
+    /// is live. Cases are loose substring matches (Dereth day groups use
+    /// names like "Sunny", "Clear", "Cloudy", "Rainy", "Stormy", "Snowy"
+    /// per the region dat dump 2026-04-23).
+    ///
+    /// <para>
+    /// Once called at least once, the internal auto-roll in
+    /// <see cref="Tick"/> is DISABLED for the rest of the session —
+    /// control is now external. Tests that drive <see cref="Tick"/>
+    /// directly without calling this method remain on the legacy hash
+    /// roll unchanged.
+    /// </para>
+    /// </summary>
+    public void SetKindFromDayGroupName(string? dayGroupName)
+    {
+        _externallyDriven = true;
+        WeatherKind mapped = MapDayGroupNameToKind(dayGroupName);
+        if (mapped != _kind) BeginTransition(mapped);
+    }
+
+    private static WeatherKind MapDayGroupNameToKind(string? name)
+    {
+        if (string.IsNullOrWhiteSpace(name)) return WeatherKind.Clear;
+        string lc = name.ToLowerInvariant();
+        // Order matters — "thunderstorm" contains "storm", match first.
+        if (lc.Contains("storm"))    return WeatherKind.Storm;
+        if (lc.Contains("snow"))     return WeatherKind.Snow;
+        if (lc.Contains("rain"))     return WeatherKind.Rain;
+        if (lc.Contains("cloud")
+         || lc.Contains("overcast")
+         || lc.Contains("dark")
+         || lc.Contains("fog"))      return WeatherKind.Overcast;
+        return WeatherKind.Clear;    // "Sunny", "Clear", anything else
+    }
+
     /// <summary>
     /// Advance the state machine. Call once per frame from the render
     /// loop. <paramref name="dayIndex"/> is the in-game day (derived
@@ -167,8 +213,13 @@ public sealed class WeatherSystem
         if (_transitionT < 1f)
             _transitionT = Math.Min(1f, _transitionT + dtSeconds / TransitionSeconds);
 
-        // Day changed → re-roll. Skip the sentinel (forced).
-        if (dayIndex != _rolledDayIndex && _rolledDayIndex != int.MaxValue)
+        // Day changed → re-roll. Skip the sentinel (forced). Also skip
+        // when weather is externally driven by the retail DayGroup name
+        // (Phase 3e) — the internal RollKind is a fallback only for
+        // tests / offline code paths.
+        if (!_externallyDriven
+            && dayIndex != _rolledDayIndex
+            && _rolledDayIndex != int.MaxValue)
         {
             _rolledDayIndex = dayIndex;
             var newKind = RollKind(dayIndex);
diff --git a/tests/AcDream.Core.Tests/World/WeatherSystemTests.cs b/tests/AcDream.Core.Tests/World/WeatherSystemTests.cs
index e2c8d48..9623f4f 100644
--- a/tests/AcDream.Core.Tests/World/WeatherSystemTests.cs
+++ b/tests/AcDream.Core.Tests/World/WeatherSystemTests.cs
@@ -99,4 +99,47 @@ public sealed class WeatherSystemTests
         Assert.Equal(kf.FogStart, snap.FogStart, precision: 2);
         Assert.Equal(kf.FogEnd,   snap.FogEnd,   precision: 2);
     }
+
+    [Theory]
+    [InlineData("Sunny",       WeatherKind.Clear)]
+    [InlineData("SUNNY",       WeatherKind.Clear)]
+    [InlineData("Clear",       WeatherKind.Clear)]
+    [InlineData("Cloudy",      WeatherKind.Overcast)]
+    [InlineData("Overcast",    WeatherKind.Overcast)]
+    [InlineData("Dark skies",  WeatherKind.Overcast)]
+    [InlineData("Fog",         WeatherKind.Overcast)]
+    [InlineData("Rainy",       WeatherKind.Rain)]
+    [InlineData("heavy rain",  WeatherKind.Rain)]
+    [InlineData("Snowy",       WeatherKind.Snow)]
+    [InlineData("Blizzard",    WeatherKind.Clear)]   // no matcher — default
+    [InlineData("Stormy",      WeatherKind.Storm)]
+    [InlineData("Thunderstorm", WeatherKind.Storm)]  // "storm" wins over no match
+    [InlineData("",            WeatherKind.Clear)]
+    [InlineData(null,          WeatherKind.Clear)]
+    public void SetKindFromDayGroupName_MapsRetailNames(string? name, WeatherKind expected)
+    {
+        var sys = new WeatherSystem();
+        sys.SetKindFromDayGroupName(name);
+        sys.Tick(0, 0, 100f);  // finalize transition
+        Assert.Equal(expected, sys.Kind);
+    }
+
+    [Fact]
+    public void SetKindFromDayGroupName_DisablesInternalRoll()
+    {
+        // Once driven externally, advancing dayIndex must NOT re-roll
+        // to a different kind via the internal RollKind hash.
+        var sys = new WeatherSystem();
+        sys.SetKindFromDayGroupName("Sunny");
+        sys.Tick(0, 0, 100f);
+
+        var clearKind = sys.Kind;
+        Assert.Equal(WeatherKind.Clear, clearKind);
+
+        for (int d = 1; d < 50; d++)
+        {
+            sys.Tick(0, d, 100f);
+            Assert.Equal(clearKind, sys.Kind);  // stays put — no auto-roll
+        }
+    }
 }