weather: add synthetic rain and snow simulation states

vendor/clouds3d.js

@@ -5973,9 +5973,11 @@ function hex(rgb) {
 var WEATHER_DENSITY = {
     sunny: 0.25,
     cloudy: 0.50,
-    // rain and storm both map to 'stormy' (open-meteo codes 51-67, 71-77,
-    // 80-86, 95+). Full 1.0 packed the deck so hard that the march showed
-    // its own layering, so the top end is capped below overcast.
+    rain: 0.75,
+    snow: 0.65,
+    // Thunder/rain/storm codes are split into rain/snow/stormy themes.
+    // Full 1.0 packed the deck so hard that the march showed its own
+    // layering, so the top end is capped below overcast.
     stormy: 0.80
 };
 var LAST_NON_NIGHT_CLOUD_DENSITY = WEATHER_DENSITY.cloudy;