How the Snow Day Calculator Works

A points model, invented for fun

The Snow Day Calculator does not look anything up. There is no forecast feed, no database of schools, and no statistics behind it — there is a short list of made-up point rules, written for this site, that turns the numbers you type in into a percentage. This page publishes the whole model, exactly as the code runs it, so you can check any score by hand and see precisely why the calculator said what it said. If a score ever surprises you, the answer is in the tables below — usually a threshold you just crossed.

Everything is added together and then clamped: no score can fall below 0% or rise above 100%, however extreme the inputs. (The inputs themselves are also clamped to sane ranges — snow between 0 and 60 inches, temperature between −80°F and 130°F, wind between 0 and 200 mph — so typing a million inches of snow won't break anything; it just snows 60 inches.)

The five factors, one by one

1. Snowfall — the heavyweight (up to 60 points)

Expected snowfall earns 6 points per inch, capped at 60 points — so the first ten inches do all the work and inches beyond ten add nothing. Six inches of snow is 36 points before anything else is counted; two inches is a modest 12.

2. Temperature — cold helps, warmth hurts (from −15 to +15)

The logic is playful but pointed: bitter cold keeps snow from melting, slows clearing, and makes waiting for a bus miserable, while a low above freezing means the snow is melting or falling as rain — the model's warmest band actually subtracts points.

3. Wind — blowing snow closes roads (up to +22)

Wind is the multiplier of misery: it drifts ploughed roads shut again and turns falling snow into whiteouts. In the model it is the second-largest contributor after snowfall itself.

4. Snow already on the ground (+8)

A flat +8 points if there is already snow cover. Yesterday's snow means today's falls on frozen, narrowed, half-cleared roads — and, in the model's world, a school system that has already used some of its patience.

5. School type — the adjustment (−18 to +10)

The caricature: preschools close at a whisper of snow because their pupils are four; colleges almost never close because their students can be trusted (in theory) to trudge. Public schools anchor the scale at zero.

A worked example, scored by hand

Take a Monday with 6 inches of snow expected, a low of 24°F, wind at 15 mph, snow already on the ground, and a public school:

48% lands in the 40–59 band, so the calculator's verdict is: “A coin flip — check the school website in the morning.” The verdict bands are fixed: under 20% "almost certainly open", 20–39% "probably open", 40–59% "a coin flip", 60–79% "likely closed", and 80% or more "almost certainly a snow day". Try the same weather for a preschool and a college — the ±adjustment alone moves the same morning across two verdicts — and you have understood the entire model. There is no more of it. That is rather the point: a toy you can fully inspect beats a black box pretending to be a forecast.

Frequently asked questions

Related pages

• Snow Day Calculator — the tool itself — now you know exactly what it does with your numbers
• How schools decide snow days — the real-world process this toy is loosely caricaturing
• About Handy Toolshelf — how the rest of the site's tools work, and where their data comes from