Sunny days were once a rarity for Tryndamere as a young boy since he used to live more north where weather was always cloudy, snowy, and in the winter; harsh so like most young boys when the sun showed, so did smiles and laughter.  Because the tribe depended so much on hard work, play for boys was not so often, especially during the harsher times but when weather was peaceful, when the sun trickled over the clouds, the kids would play as it was a treasure.  

As he grew older and faced the Darkin, he does not care much about the weather one way or another but he still always reminisces of his past of those sunny times, bringing him more pain since he knows all those people he once played with, argued with, got in trouble because, all those memories he shared in the sun–he knows–they are dead.

If the sun is too bright, typically when visiting another city-state, he actually can not stand the heat since he is so used to the cold of his homeland.  The heat makes him very tense and angry too.  He does not like being uncomfortable.