In "To Build a Fire," why is the man not worried about the unusual weather conditions?

Even though the main character of the story had been warned multiple times about the severe cold he was going to walk through, he refused to listen to any of their advice.  One of the main character flaws that London mentions is that the man "was without imagination."  He understood, scientifically at least, what the thermostat meant when it said that it was 50 below zero, but in his mind, he could understand or predict the consequences as they would apply to him.  As well, London comments, "Such fact impressed him as being cold and uncomfortable, and that was all. It did not lead him to meditate upon his frailty as a creature of temperature, and upon man's frailty in general, able only to live within certain narrow limits of heat and cold; and from there on it did not lead him to the conjectural field of immortality and man's place in the universe."  For the man, he was invincible, until the moment when he was not.  It is at that moment, when he cannot build a fire to warm himself, that the panic sets in.  There were many warning signs before that: the tingling in his fingers when they were becoming frozen, the spittle and breath that froze on his beard, the dog's resistence to follow the man.  But the man does not follow any of those signs because of his lack of imagination, and in the end, it is what led to his demise.