Here is a Web Appbuilder widget for viewing the ISU Nexrad Radar WMS service, for anyone who would like it.
This is a panel widget, the widget code, widget config and example site config json are attached.
You can pick up the latest version of this widget , from widget downloads in the web appbuilder custom widgets group.
ArcGIS Web Application site using widget.
WMS service from Iowa State IEM generated NEXRAD composites