Li Kao's rationalization was wrong, though.
Japanese schoolgirls are 100% resistant against the "tyranny of winter". They'd never let something as unimportant as
low temperatures keep them from wearing fashionable clothing - and school uniforms with really
short skirts happen to be fashionable at the moment. Thus, they might wear a thick cloak (short, of course) and wrap a thick
woolen scarf around their neck, but they'll
never wear their skirts even one inch longer than the minimum permitted by school rules, colds be damned!
The most likely reason for the lack of seifuku encounters is that is was the wrong time. After all, they're school uniforms, and outside of schools are therefore visible only on girls on their way from or to school, or in the evening if they have had no time to go home and change. Thus, during holidays or on sundays, as well as during school hours, the chances of meeting seifuku-clad girls are very low (well, except in image clubs, where you can "meet" one at just about any time).