Icing in cloud
I'd say it was more luck and inexperience you had going for you in past winters. Once you leave the College level, and move onto something with enough equipment to fly into known ice, you'll be startled by the variety and quantity of ice you can pick up. Inthe Arctic in the winter you can go for months without picking up any, and then run into enough in the Pittsburgh area to not be able to maintain level flight.
Importantly, (hence the SOP) your aircraft was not tested in the certification process for flight into known ice, so at the point you fly into icing, you become an experimental test pilot.
The MNR people around the corner have Twin Otters, so ask to see their Nasa Tail Ice Video. It's pretty revealing- you won't recognize the symptoms until you are about to have an exceptionally bad day!
While everybody wants to fly, especially at your present level, an important part of this business is learning when to say no.