NWS

The allocated frequencies are:

If your radio is equipped with S.A.M.E (Specific Area Message Encoding) – you can cause your radio to filter the alerts presented. This is useful, for example, so that a tornado ‘watch’ does not wake you up, nor does a tornado ‘warning’ in some other nearby county – but a tornado ‘warning’ for your county does alarm. Very useful.

For full details on the system – please see the following link.

http://www.weather.gov/nwr/indexnw.htm