Looks like the Apache configuration file for weather radio hasn't been copied or is in a different place. Try first
sudo cp add-on/weatherradio/weatherradio.conf /etc/apache2/conf-available
and then try the a2enmod command again.
Hi, it's an error,
if you want to use a2enmod, you must to copy the file in mod-available.
Also, you must to use command a2enconf if you want to put in conf-available