Here in Minnesota, urban schools are less likely to close than rural schools, since rural schools have to travel longer distances by bus and car and use unpaved roads.
13 inches is an exaggeration, though. Many places close with just 4 inches, but that's only if it's truly blizzard like conditions. Schools in the snow belts north and south of the Twin Cities area less likely to close since they are better prepared. Growing up, my school never closed, because the superintendents always asked the head of the bus company if they could drive the roads with their buses, and he always would say they could, even when every other school district around did.
We don't even shut down for a whole day here. We're highly prepared for this stuff. We're not as prepared for ice storms that places further south of here get since we're usually too cold for those, though we had one last winter where we just holed up for a day or two while the plow drivers salted the roads.
We did have a day in 2005 where the governor issued an executive order that every school would be shut down for the day, but that was one of the few days I got off of school for the weather.