clouds: raise weather coverage floor so clouds stay visible

vendor/clouds3d.js

@@ -685,8 +685,8 @@ var FRAG_SRC = [
             'float stepSize = (tExit - tEnter) / 24.0;',
             'float t = tEnter + stepSize * 0.5;',
             'float coverage = clamp(uDensity, 0.0, 1.0);',
-            'float baseThresh = mix(0.72, 0.22, coverage);',
-            'float densityGain = mix(0.25, 1.0, coverage);',
+            'float baseThresh = mix(0.62, 0.20, coverage);',
+            'float densityGain = mix(0.45, 1.0, coverage);',
             'float sunUp = smoothstep(-0.20, 0.05, uSunAlt);',
             'float cosT = dot(rd, uSunDir);',
             'float phase = 0.30 + 0.70 * pow(max(0.0, cosT), 2.5);',