[Data Viz] School’s Out For Winter

Thank you r/dataisbeautiful for constant inspiration

We came upon this very cool Data Map showing the amount of snow it takes on average for schools to cancel and/or shut down for the day, which is particularly relevant considering how recent snow storms have been pummeling the Northeastern and Midwestern United States.

High school geographer Alexandr Trubetskoy of Washington, DC put this map together based on Reddit user responses in a thread about school cancellations. He then “interpolated the data using NOAA’s average annual snowfall days map”

The way to look at this map, according to Alexandr:

The lightest green says “any snow” but also includes merely the prediction of snow. Also, this is snow accumulation over 24 hours/overnight.

In much of the Midwest and Great Plains, school closing often depends more on wind chill and temperature than on snow accumulation (“cold days”). Thus, this map may be misleading in those areas.

Many jurisdictions in California and other western states have significantly varied snowfall, depending on elevation. This makes it difficult to find an “average” number, or often makes it misleading.

Urban areas like Chicago and New York have more resources to clear snow and often need more to cause closings.

To everyone saying “I grew up in so-and-so and we never closed school,” policies have changed in the last 20 years to make closing a much more common occurrence. Just because schools stayed open back then doesn’t mean they do these days.


Snow, Atlanta and traffic is a match made in frozen-over Hell. Image by AP Photo, via Politico

We were still curious if Waze data would reflect these findings, so we looked into data for the city of Atlanta, which historically does not do well with snow.

Let’s look at the change in activity for Atlanta during the winter of 2014:


That first spike on Tuesday, January 28 coincides with the infamous January snow storm that “paralyzed” the Greater Atlanta Area for 24 hours. During that time, Waze mounted a very aggressive word-of-mouth campaign to help drivers avoid the already-gridlocked highways. This is probably the only example of activity increasing during severe weather. In nearly every other case, people just stop driving.

Speaking of which, if you look at the chart, you’ll note the significant drop in activity on Wednesday, February 12, where only 36% of regular drivers were on the road. This also coincides with a sever weather alert; in fact, Governors across 7 Southeast US States issued Severe Weather Warnings to their citizens the day before a terrible ice storm hit. Georgia’s governor even declared a “State of Emergency” cautioning drivers to stay off the road. It worked: February 12 was not only the least active day in February, it was the least active day in 2014.

One of the most interesting things about Alexandr’s map above is that it illustrates how equipped different regions are to deal with snow. There are certainly some green areas on the map where snow just doesn’t happen, or happens so rarely and so fleetingly that it doesn’t warrant any kind of additional infrastructure. Places like Los Angeles, southern Arizona and other southern, dry areas don’t have to worry about snow or ice, outside of freak occurrences. But it does snow in the southeast, pretty regularly. It snows at least once a year, even in low elevation areas. The recent Atlanta snowstorm “paralysis” certainly underscores the need for better resources and preparations. Even though drivers are at more risk during inclement weather, you never see places like Maine or Michigan grind to a halt over 2 inches of snow.

We can conclude Alexandr’s map is at least somewhat accurate even if the original data is mostly anecdotal. Additionally, the Atlanta case study is a pretty good incentive to check Waze before you leave work or the house- you never know how these kind of events are going to affect your commute, and no one wants to be stuck in a car on the highway for 16 hours.

In closing, an announcement to governors, lawmakers, and city officials everywhere: please keep telling citizens to stay off the roads during inclement weather. It works, and you’ve probably saved people’s lives.