weather: add dynamic procedural snow cover

config.js

@@ -149,12 +149,25 @@ window.CONFIG = {
             dryMinutes: 30,       // roads dry out after this many dry minutes
             roadGain: 0.8,        // extra road-ribbon glow when wet
             lightGain: 0.35       // extra halo on vehicle lights when wet
+        },
+        snowCover: {
+            enabled: true,
+            meltMinutes: 90,      // snow melts after this many warm minutes
+            baseLineM: 900,       // snowline at about +5 C
+            tempLineMPerC: 80,    // snowline moves down as temperature drops
+            minLineM: 0,          // full snowline in deep cold
+            maxLineM: 2500,       // no snow above this line when warm
+            transitionM: 120,     // soft transition band around the snowline
+            slopeMax: 0.72,       // steep slopes keep less snow
+            gain: 0.85            // maximum whiteness of the snow albedo
         }
         // weatherEffects: { enabled: false }
         // weatherEffects: { rain: { maxAlpha: 0.55, speed: 1.4 }, snow: { enabled: false } }
         // weatherEffects: { lightning: { gain: 2.0, minDelayS: 3, maxDelayS: 12 } }
         // weatherEffects: { wetRoads: { enabled: false } }
         // weatherEffects: { wetRoads: { dryMinutes: 10, roadGain: 1.4, lightGain: 0.7 } }
+        // weatherEffects: { snowCover: { baseLineM: 600, tempLineMPerC: 120, gain: 1.0 } }
+        // weatherEffects: { snowCover: { enabled: false } }
     },
 
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