diff --git a/changes/one-wind.md b/changes/one-wind.md
new file mode 100644
index 00000000..2c718318
--- /dev/null
+++ b/changes/one-wind.md
@@ -0,0 +1,25 @@
+bump: minor
+type: feat
+One wind, and everything in the valley is moved by it.
+
+The grass had a gust built from two sines and the trees had NO gust term at all - just a
+per-instance wobble - so the meadow rippled and the canopy above it swayed to an unrelated
+rhythm and nothing ever crossed the valley. A real gust is a WAVE: you watch it come over
+the grass, it reaches you, and it goes on into the trees behind you.
+
+wind.glsl is prepended to EVERY stage, so the grass's vertex shader, the crown's vertex
+shader and the water's fragment shader read the same field at the same world position and
+cannot drift apart. No uniforms are declared in it on purpose - u_time and u_wind already
+exist in several of those files and redeclaring them is a compile error in whichever stage
+includes both - so the caller passes what it already has.
+
+Two numbers mattered. The gust's WAVELENGTH has to fit inside a view or nothing is ever
+seen to travel: the first cut was 209 m crest to crest, longer than the meadow you can see,
+so the whole frame sat in one phase and read as everything breathing together. It is 74 m
+now and a front crosses a normal view in a couple of seconds. And `stiff` lets one field
+move a blade a long way and a bole hardly at all.
+
+R3D_DEBUG_WIND=1 paints the field on the ground, which is the only way to SEE a gust in a
+still: two shots a moment apart show the fronts and show them moving.
+
+Measured: no cost. 400 frames, GL 6.9 s, VK 7.2 s.
diff --git a/packages/ludic.render3d/programs.ludic b/packages/ludic.render3d/programs.ludic
index d3ffe198..665c7104 100644
--- a/packages/ludic.render3d/programs.ludic
+++ b/packages/ludic.render3d/programs.ludic
@@ -17,6 +17,7 @@ var r3d_root_found: bool = false
 var r3d_global_defs: string = ""
 var r3d_noise_src:    string = null
 var r3d_lighting_src: string = null
+var r3d_wind_src: string = null
 
 function r3d_set_paths(root: string, assets: string) -> void { r3d_root = root;  r3d_assets = assets }
 
@@ -51,7 +52,11 @@ function r3d_shader_file(name: string) -> string {
 function r3d_shader_src(name: string, defines: string, is_frag: bool) -> string {
   if r3d_noise_src == null { r3d_noise_src = r3d_shader_file("noise.glsl") }
   if r3d_lighting_src == null { r3d_lighting_src = r3d_shader_file("lighting.glsl") }
-  var s = "#version 410 core\n" + r3d_global_defs + defines
+  # the wind goes to BOTH stages: the grass and the crowns move in the vertex shader, the water
+  # ripples in the fragment one, and they have to be reading the same field or the meadow and
+  # the lake disagree about the weather
+  if r3d_wind_src == null { r3d_wind_src = r3d_shader_file("wind.glsl") }
+  var s = "#version 410 core\n" + r3d_global_defs + defines + r3d_wind_src
   if is_frag { s = s + r3d_noise_src + r3d_lighting_src }
   return s + r3d_shader_file(name)
 }
diff --git a/packages/ludic.render3d/shaders/grass.vert b/packages/ludic.render3d/shaders/grass.vert
index d9ac3c1a..3a7132ff 100644
--- a/packages/ludic.render3d/shaders/grass.vert
+++ b/packages/ludic.render3d/shaders/grass.vert
@@ -148,9 +148,11 @@ void main() {
   if (far) { bw = max(bw, spacing * 0.35); tall = min(tall, spacing * 0.3); }
   vec3 p = vec3(a_pos.x * bw, a_pos.y * tall, a_pos.z * tall * (0.6 + 0.8 * h4));
   vec3 n = vec3(0.0, 0.3, 1.0);
-  float gust = sin(xz.x * 0.09 + u_time * 1.1) * 0.5 + sin(xz.y * 0.13 - u_time * 0.8 + xz.x * 0.05) * 0.5;
+  // The shared field (wind.glsl), so the gust that crosses this meadow is the same gust that
+  // reaches the trees behind it a moment later. The two sines that used to live here were a
+  // standing wobble: the grass moved, but nothing ever travelled.
   float ph = u_time * 1.7 + seed * 6.2831 + xz.x * 0.05 + xz.y * 0.07;
-  float sway = (sin(ph) * 0.6 + sin(ph * 2.3 + 1.0) * 0.4 + gust) * u_wind;
+  float sway = windSway(xz, u_time, ph, 0.0) * u_wind;
   float hgt = max(p.y, 0.0);
   p.x += sway * hgt * hgt * 0.35;
   p.z += sway * hgt * hgt * 0.15 * cos(ph * 0.7);
diff --git a/packages/ludic.render3d/shaders/model.vert b/packages/ludic.render3d/shaders/model.vert
index e0bf27b8..8f121ca6 100644
--- a/packages/ludic.render3d/shaders/model.vert
+++ b/packages/ludic.render3d/shaders/model.vert
@@ -76,7 +76,11 @@ void main() {
   // sway grows with height above the base; gust phase from the instance seed
   float hgt = max(p.y, 0.0);
   float ph = u_time * 1.7 + i_rot.z * 6.2831 + i_pos.x * 0.05 + i_pos.z * 0.07;
-  float sway = (sin(ph) * 0.6 + sin(ph * 2.3 + 1.0) * 0.4) * u_wind * i_rot.w;
+  // A crown had NO gust at all - only this per-instance wobble - so the canopy swayed to a
+  // rhythm of its own while the meadow under it rippled to another. It is the same field now,
+  // read at the tree's own place in the world, so a gust crosses the grass and goes on into
+  // the trees. `stiff` is 0.35 because a bole resists what a blade cannot.
+  float sway = windSway(i_pos.xz, u_time, ph, 0.35) * u_wind * i_rot.w;
   p.x += sway * hgt * hgt * 0.35;
   p.z += sway * hgt * hgt * 0.15 * cos(ph * 0.7);
 #endif
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diff --git a/packages/ludic.render3d/shaders/spv/f34dce08.frag.spv b/packages/ludic.render3d/shaders/spv/f34dce08.frag.spv
index 3114c34f..11860be7 100644
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diff --git a/packages/ludic.render3d/shaders/spv/f34dce08.vert.spv b/packages/ludic.render3d/shaders/spv/f34dce08.vert.spv
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diff --git a/packages/ludic.render3d/shaders/spv/f4382918.frag.spv b/packages/ludic.render3d/shaders/spv/f4382918.frag.spv
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diff --git a/packages/ludic.render3d/shaders/spv/f4382918.vert.spv b/packages/ludic.render3d/shaders/spv/f4382918.vert.spv
index 7051758f..c19cd525 100644
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diff --git a/packages/ludic.render3d/shaders/spv/f4a2b586.frag.spv b/packages/ludic.render3d/shaders/spv/f4a2b586.frag.spv
index b5246909..d51f1c25 100644
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diff --git a/packages/ludic.render3d/shaders/spv/f4a2b586.vert.spv b/packages/ludic.render3d/shaders/spv/f4a2b586.vert.spv
index 1d28416e..db1380f8 100644
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diff --git a/packages/ludic.render3d/shaders/terrain.frag b/packages/ludic.render3d/shaders/terrain.frag
index a347dd30..b2081fde 100644
--- a/packages/ludic.render3d/shaders/terrain.frag
+++ b/packages/ludic.render3d/shaders/terrain.frag
@@ -536,6 +536,11 @@ void main() {
 #ifdef DEBUG_MAT
   col = dbg_mat;
 #endif
+#ifdef DEBUG_WIND
+  // The wind field itself, painted on the ground: R3D_DEBUG_WIND=1 with two shots a moment
+  // apart shows the gust fronts and shows them MOVING, which no still of grass ever will.
+  col = vec3(windGust(p.xz, u_time)) * vec3(1.0, 0.95, 0.75);
+#endif
 #ifdef DEBUG_ALB
   col = dbg_alb * 3.0;
 #endif
diff --git a/packages/ludic.render3d/shaders/wind.glsl b/packages/ludic.render3d/shaders/wind.glsl
new file mode 100644
index 00000000..c17054f7
--- /dev/null
+++ b/packages/ludic.render3d/shaders/wind.glsl
@@ -0,0 +1,44 @@
+// ---- ONE WIND, and everything in the valley is moved by it ----------------------------------
+//
+// Before this the grass had a gust term built from two sines and the trees had NO gust at all -
+// just a per-instance wobble - so the meadow rippled and the canopy over it swayed to an
+// unrelated rhythm. Nothing ever crossed the valley. A real gust is a WAVE: you watch it come
+// over the grass, it reaches you, and it goes on into the trees behind you, and that single
+// fact does more for "this place is alive" than any amount of extra detail.
+//
+// It is prepended to EVERY stage (programs.ludic), so the grass's vertex shader, the crown's
+// vertex shader and the water's fragment shader all read the same field at the same world
+// position and cannot drift apart. No uniforms are declared here on purpose: u_time and u_wind
+// already exist in several of those files, and redeclaring them would be a compile error in
+// whichever stage happened to include both. The caller passes what it already has.
+
+// The prevailing wind down the valley. Maroon Creek runs roughly north-east, and a mountain
+// valley funnels its wind along itself rather than across.
+const vec2 WIND_DIR = vec2(0.86, 0.51);
+
+// 0 = still, 1 = the middle of a gust. Mostly low with fronts travelling through it, because
+// real wind is gusts separated by calm and not a constant shaking.
+float windGust(vec2 xz, float t) {
+  float d = dot(xz, WIND_DIR);
+  float across = dot(xz, vec2(-WIND_DIR.y, WIND_DIR.x));
+  // three scrolling bands: a fast narrow front, a slow broad swell, and a slight variation
+  // along the front so it does not arrive as one straight wall
+  // The wavelength has to fit INSIDE a view or nothing is ever seen to travel: at 0.030 the
+  // front was 209 m from crest to crest, longer than the meadow you can see, so the whole
+  // frame sat in one phase and the gust read as everything breathing together. At 0.085 it is
+  // about 74 m and a front crosses a normal view in a couple of seconds.
+  float g = sin(d * 0.085 - t * 2.6)
+          + 0.65 * sin(d * 0.022 - t * 0.85 + 1.7)
+          + 0.40 * sin(across * 0.040 - t * 0.55);
+  // tighter than a plain smoothstep either side: gusts with calm between them, not a wobble
+  return smoothstep(-0.10, 1.35, g);
+}
+
+// What a plant actually does: a small constant tremble it always has, plus the gust, which is
+// most of the motion. `stiff` is how much the plant resists - grass near 0, a spruce trunk near
+// 1 - so the same field moves a blade a long way and a bole hardly at all.
+float windSway(vec2 xz, float t, float phase, float stiff) {
+  float tremble = sin(phase) * 0.6 + sin(phase * 2.3 + 1.0) * 0.4;
+  float gust = windGust(xz, t);
+  return (tremble * 0.30 + gust * 1.35) * (1.0 - 0.85 * stiff);
+}
diff --git a/packages/ludic.render3d/terrain.ludic b/packages/ludic.render3d/terrain.ludic
index 4e065ddb..cac569ee 100644
--- a/packages/ludic.render3d/terrain.ludic
+++ b/packages/ludic.render3d/terrain.ludic
@@ -421,6 +421,7 @@ function terrain_init_finish() -> void {
   var defs = ""
   if r3d_debug_shadow { defs = "#define DEBUG_SHADOW\n" }
   if r3d_env_has("R3D_DEBUG_MAT") { defs = "#define DEBUG_MAT\n" }
+  if r3d_env_has("R3D_DEBUG_WIND") { defs = "#define DEBUG_WIND\n" }
   if r3d_env_has("R3D_DEBUG_NRM") { defs = "#define DEBUG_NRM\n" }
   if r3d_env_has("R3D_DEBUG_ALB") { defs = "#define DEBUG_ALB\n" }
   # Elimination profiling. Measure these by FRAME TIME (prof_ft_report), not by the
diff --git a/tools/ludic-cli/shaders.ludic b/tools/ludic-cli/shaders.ludic
index ede3319c..3254e32c 100644
--- a/tools/ludic-cli/shaders.ludic
+++ b/tools/ludic-cli/shaders.ludic
@@ -152,6 +152,7 @@ function shd_bind_varyings(src: pointer, word: pointer, collect: bool) -> pointe
 
 var shd_noise: pointer = null
 var shd_lighting: pointer = null
+var shd_wind: pointer = null
 function shd_file(name: pointer) -> pointer {
   let s = read_file(`packages/ludic.render3d/shaders/{name}`)
   if s == null { err(`shaders: missing packages/ludic.render3d/shaders/{name}\n`);  return "" }
@@ -204,6 +205,7 @@ function cmd_shaders() -> int {
   if list == null { err("shaders: no packages/ludic.render3d/shaders/variants.list\n");  return 1 }
   shd_noise = shd_file("noise.glsl")
   shd_lighting = shd_file("lighting.glsl")
+  shd_wind = shd_file("wind.glsl")
   var outdir = "packages/ludic.render3d/shaders/spv"
   let tmp = tmp_path("shaders")
   if check { outdir = tmp_path("shaders-check") }
@@ -232,13 +234,13 @@ function cmd_shaders() -> int {
     let depth_remap = "\n#undef main\nvoid main() {\n  ludic_gl_main();\n  gl_Position.z = (gl_Position.z + gl_Position.w) * 0.5;\n}\n"
     # invariant: the foliage's depth prepass and its lit pass (depth EQUAL) are different variants,
     # and without it the compiler may compute their positions a hair apart and fail the test
-    var vsrc = "#version 460\n" + defines + "invariant gl_Position;\n#define main ludic_gl_main\n" + shd_file(parts[0]) + depth_remap
+    var vsrc = "#version 460\n" + defines + shd_wind + "invariant gl_Position;\n#define main ludic_gl_main\n" + shd_file(parts[0]) + depth_remap
     # A mesh shader stands in for the vertex stage (a variant whose first file is *.mesh): it writes an
     # array of positions, so it cannot be wrapped for the depth remap or take invariant gl_Position -
     # it remaps depth itself. Its SPIR-V keeps the .vert name, so the manifest and loader are unchanged.
     let is_mesh = Text.ends_with(parts[0], ".mesh")
-    if is_mesh { vsrc = "#version 460\n#extension GL_EXT_mesh_shader : require\n" + defines + shd_file(parts[0]) }
-    let fsrc = "#version 460\n" + defines + shd_noise + shd_lighting + shd_file(parts[1])
+    if is_mesh { vsrc = "#version 460\n#extension GL_EXT_mesh_shader : require\n" + defines + shd_wind + shd_file(parts[0]) }
+    let fsrc = "#version 460\n" + defines + shd_wind + shd_noise + shd_lighting + shd_file(parts[1])
     # one binding table for both stages, and one location table for the varyings between them
     shd_names = new []pointer
     shd_vary = new []pointer