Current US precipitation

You can take advantage of AWS data sources, in this case Precipitation.US, to view dynamic data.

<?xml version="1.0" encoding="utf-8"?>
<mx:Application
xmlns:mx="http://www.adobe.com/2006/mxml"
xmlns:framework="com.esri.aws.osgi.framework.*"
xmlns:map="com.esri.aws.awx.map.*"
xmlns:layers="com.esri.aws.awx.map.layers.*"
xmlns:services="com.esri.aws.services.*"
layout="absolute"
>
<framework:Framework apiKey="19640523">
 <services:MapImageActivator/>
</framework:Framework>
<map:Map centerLat="35" centerLon="-93" scale="20000000">
 <map:basemaps>
  <layers:MapImageGroupLayer dataSource="ArcWeb:MX.Precipitation.US">
   <layers:layerVisibilities>
    <layers:LayerVisibility name="U.S. States" visible="false"/>
   </layers:layerVisibilities>
  </layers:MapImageGroupLayer>
 </map:basemaps>
</map:Map> 
</mx:Application>