fgdata/Models/Weather/thunderstorm.xml

<?xml version="1.0"?>

<PropertyList>
 <path>thunderstorm.ac</path>

 <animation>
  <type>range</type>
  <min-m>0</min-m>
  <max-m>50000</max-m>
 </animation>

 <animation>
  <type>alpha-test</type>
  <object-name>ThunderCloud</object-name>
  <alpha-factor>0.01</alpha-factor>
 </animation>

 <animation>
  <type>range</type>
  <object-name>ThunderCloud</object-name>
  <min-m>0</min-m>
  <max-m>2000</max-m>
 </animation>

 <animation>
  <type>range</type>
  <object-name>ThunderCloudLowRes</object-name>
  <min-m>2000</min-m>
  <max-m>50000</max-m>
 </animation>

	<animation>
		<type>noshadow</type>
	</animation>
</PropertyList>