fgdata/Models/Weather/rain.xml

<?xml version="1.0"?>

<PropertyList>

 <path>rain.ac</path>

<!--
 <animation>
  <type>blend</type>
  <object-name>rect</object-name>
  <property>/velocities/airspeed-kt</property>
  <factor>0.2</factor>
  <min>0.4</min>
  <max>1.0</max>
 </animation>
-->

 <animation>
  <type>select</type>
  <object-name>rect</object-name>
  <condition>
   <and>
    <equals>
     <property>/sim/current-view/internal</property>
     <value>true</value>
    </equals>
    <greater-than>
     <property>/environment/metar/rain-norm</property>
     <value>0</value>
    </greater-than>
    <less-than>
     <property>/position/altitude-ft</property>
     <property>/environment/clouds/layer[0]/elevation-ft</property>
    </less-than>
   </and>
  </condition>
 </animation>

 <animation>
  <type>rotate</type>
  <object-name>rect</object-name>
  <property>/velocities/airspeed-kt</property>
  <factor>-1.0</factor>
  <min-deg>-90</min-deg>
  <max-deg>0</max-deg>
  <center>
   <x-m>0.0</x-m>
   <y-m>0.0</y-m>
   <z-m>0.0</z-m>
  </center>
  <axis>
   <x>0</x>
   <y>1</y>
   <z>0</z>
  </axis>
 </animation>

 <animation>
  <type>texmultiple</type>
  <object-name>rect</object-name>
  <transform>
   <subtype>textranslate</subtype>
   <property>/sim/time/elapsed-sec</property>
   <factor>1.0</factor>
   <axis>
    <x>0</x>
    <y>1</y>
    <z>0</z>
   </axis>
  </transform>
  <transform>
   <subtype>textranslate</subtype>
   <property>/velocities/airspeed-kt</property>
   <factor>0.01</factor>
   <axis>
    <x>0</x>
    <y>1</y>
    <z>0</z>
   </axis>
  </transform>
 </animation>

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