As Dangerosa explained, it’s much more an issue with ice than it is with true snow acculumation. The 12/25/2004 snowfall in New Orleans did accumulate (maybe an inch or two) on lawns and rooftops, but it didn’t last long on the concrete (streets, parking lots, etc.). However, icy patches did form all over the place on the roads and expecially on the bridges that cover the many canals.
Here in the sticks of rural eastern KY, schools are often perched atop hills up windy little roads. Buses also have to make their way out into the hindquarters of nowhere, on roads that are difficult to manage in the middle of a summertime drought, much less under a few inches of snow.
The threshold for shutting the schools down runs on a several-year cycle. People complain when they cancel school for spurious reasons, so with each passing year they become a little more tolerant of how bad it has to be before they close. Then one year they’ll take a chance on an iffy forecast and a bus will get stuck, or they won’t be able to get down the hill and the kids will have to spend the night at the school. Then the next year they’ll close for every flurry, and the cycle starts over.
I grew up in eastern Kentucky and as DoctorJ says, the roads are not easy travelling anytime, but if you slide off because of ice you may wind up going down several hundred feet of hillside. They were usually very quick to close schools when we had ice or snow on the roads, but I don’t really recall them ever closing based on a forecast.
I live in western Kentucky now and I think our district does a fairly good job. It is not really a matter of whether we have snow or not, but whether it is on the roads. Many roads out in the county are either low on the plowing priority list or don’t get plowed at all. So the call is not really based on how much snow or ice is on the road, but what are the chances of someone sliding on it. I think they consider both buses and the fact that there would be quite a few high-schoolers out driving on the roads.
If the forecast is calling for snow in the morning and especially if the counties to the west are already receiving the snow or ice, they may cancel school preemptively to prevent having to send the students home in the middle of it, but if the forecast is for later in the day, they will have school and if it looks as if we are going to be hit with the weather soon, they will release early.
I have friends from upstate New York who were freaking out because schools were closed here on Thursday (and delayed this morning). True, we didn’t get much on the ground. But what we did get was mostly ice and we just don’t have the equipment to make the roads drivable, especially on the secondary roads. We had four fatal weather-related accidents in our area on Thursday and I bet this school superintendent wishes he had made a different decision.
I live near Boston. Our superintendent had to be FORCED to cancel by the police several times. If it was cancelled, it was by 6 that morning, and it had to be actively snowing. BTW, I was born a month after the storm all other storms are measured against around here.
Back here in VA, all the schools are still closed today. It stopped snowing around 8pm last night, and most of the roads are clear. Maybe the buses can’t get out? Its the only reason I can think of…
It’s only December and they just announced we’ve pretty much ran through our snow removal budget. Niiiiice. I don’t recall school being cancelled yet, my boss would have mentioned it if his kids didn’t have to go.
Trying to remember what it took for a cancellation when I was kid. I can’t find specific guidelines on the school division website, but IIRC temperature-wise it had to be -40C/-40F without the windchill to be cancelled and -50C/-58F with the windchill. Snow-wise it was a lot more touch and go. Very few snow days, I think I got to stay home when we couldn’t get the front door open for all the snowdrifts.
Canada: when it comes to winter, we’re hardcore. As soon as summer comes around, we all melt.
You reminded me of the only school cancellation I remember from my two grade school years in Washington State, when we got some Arctic winds blasting through and the temperature was about -40. No snow to speak of, but some interesting ice formations. For the few days before they decided to close the schools until it passed, students spent most of their free time between classes wrapped up in blankets and sitting on top of the heater registers. 
We had a ridiculous school layout for the region as well, multiple separate buildings with an open courtyard between them, designed for some reason after a school in southern California, where cold and snow were never going to be a problem. A few years after I graduated, they enclosed the space and incorporated several of the existing buildings into a single new building. That was weird.
Last year I taught at a California style school–in St. Louis. It doesn’t snow all that much here, but it does occasionally get very cold, and we do get are extremely violent thunderstorms with horizontal rain. I have no idea why anyone would put that kind of school here.
My high school expanded too quickly and had to use an old church building down the block. Thankfully, they realized a ‘keep your coat in your locker’ policy could never work. But damn did we ever hate running back and forth for classes.
In Saskatchewan, no less. Hope that didn’t last too long.
This is why I am :dubious: about continued stories saying that people aren’t used to snow around D.C. and surrounding areas in Virginia and Maryland and don’t know how to drive, go into panic mode etc with small amounts of snow.
If continually getting belted with these kinds of severe storms doesn’t lead to your taking 2-4 inches in stride, there’s something wrong with your mindset.