If you spot a large tornado on the ground, first and foremost take shelter!  As important as your report is, it is critical to protect yourself fist.  Once it is safe to do so, relay your report to the NWS as soon as possible.  Do not simply say you see a tornado - clearly state that a large tornado is on the ground.  These extremely dangerous situations require heightened awareness.  If the tornado is wider than it is tall, you may report it as a wedge.  Be sure to report any debris or damage.  Try your best to remain calm when reporting a tornado on the ground so that your report is quickly and accurately received.