Level 1 - Classic
Tornadoes, damaging wind, and hail...oh my. Commonly reported weather conditions that will get out of hand quickly! Seeing one of these might make you say "Holy shnikes!".
Distinct rotating column beneath wall cloud in connection with the ground
Level 2 - Number 2's
Expanding on classic observation types, witnessing these could be a once in every three year occurrence!
Severe weather damage
Water vapor condensing into clouds at ground level
Liquid rain freezes to ground and elevated surfaces on contact.
Snow accumulating quickly with low visibility
Wind not associated with convective thunderstorm activity
Ice stones with diameter greater than pea-sized or 0.25"
Clear ice pellets or white graupel, mostly spherical in shape
Light or moderate accumulating snowfall
Thunderstorm wind gust either estimated or measured
Level 3 - Neature
Not always dangerous, but always neat!
Any situation where water is blocking land or roads causing problems
Level 4 - Just Cus
Liquid precipitation (inches)