Snow Day Calculator

1. Open your local forecast on weather.gov. Enter the snowfall, when it falls, the low temperature, the wind speed, any ice and the alert in effect.
2. Read the score and the points breakdown. Each part shows how many points it added.
3. Optional: enter an area and your shoveling speed for clearing time, and a wage, head count and hours for the pay cost of a closed day.

A snow day calculator is a tool that turns a winter weather forecast into a rough signal of how disruptive the day could be. This one uses a points score that you can read and check line by line.

No official formula for a snow day exists. A superintendent or employer makes the call, and weighs road reports, bus routes, staffing, power and local habits. A town that sees snow every week reacts differently from one that sees it once a year.

The National Weather Service makes the same point about its own alerts. Each local office issues warnings on local criteria, and the snow that triggers a Winter Storm Warning in the Northern Plains is typically much higher than in the Southeast.

That is why this page gives a score and not a percent chance. A percent would claim knowledge nobody has. The score only organizes the forecast you already have.

The score adds four groups of points and caps the total at 100. The weights below are this site's own rule of thumb. They come from no official body.

The wind chill line is the National Weather Service formula, with T as air temperature in degrees Fahrenheit and V as wind speed in miles per hour. The NWS defines it only for 50 F or below and wind above 3 mph. Outside that range the tool uses the air temperature for the cold points.

Forecast. 6 inches of snow falling during the morning commute, 20 F, wind 15 mph, no ice, and a Winter Storm Warning in effect.

Snow. 5 x 6 = 30 points, times 1.0 for commute timing = 30. Ice. 0.

Cold. Wind chill = 35.74 + 0.6215 x 20 - 35.75 x 15^0.16 + 0.4275 x 20 x 15^0.16 = 6 F. That is above 0 F, so 0 points.

Alert. Winter Storm Warning = 20. Total = 30 + 0 + 0 + 20 = 50 of 100, the start of the high band.

Shoveling. A 600 square foot driveway at your pace of 10 square feet a minute takes 600 / 10 = 60 minutes. Five people at $20 an hour for 8 hours is 20 x 5 x 8 = $800 of paid time.

Timing of the Snow

Snow that ends before 5 a.m. gives road crews time to plow, so the tool counts 60 percent of the snow points. Snow that starts after school begins is more likely to mean an early dismissal than a closure.

Ice

The NWS says Ice Storm Warnings are usually issued for ice accumulation of around a quarter inch or more, an amount that makes travel dangerous or impossible. The top ice tier matches that figure.

Wind Chill

Cold alone closes schools in some regions. The NWS notes that the criteria for cold alerts are set locally. Its example office issues a Cold Weather Advisory from -15 F and an Extreme Cold Warning at -25 F or below. The cold tiers borrow those two figures.

The NWS Alert

An alert is the forecaster's own judgment for your area, on local criteria. It carries up to 25 points for that reason.

What the Score Cannot See

Road treatment, hills, rural bus routes, power cuts, unused snow days and local policy all matter. None of them is in the score.

The bands are plain labels for the total. They are not probabilities.

Cold can score with almost no snow. One inch at -10 F with a 20 mph wind gives a wind chill of -35 F and a total of 5 + 15 = 20. The wind chill calculator covers that figure in more depth.

The Night Before School

Enter the evening forecast to see which part of it carries the weight. Check again in the morning, because forecasts change overnight.

Planning a Shift or an Opening Time

A small business can pair the score with the paid hours lost figure to weigh a late opening. To turn a salary into an hourly figure first, use the salary to hourly calculator.

Budgeting Time to Clear Snow

Enter the area and your own pace to see how early to start shoveling before you need the car. For energy use by activity and body weight, see the exercise calorie calculator.

1. Reading the Score as a Percent Chance

A score of 50 does not mean a 50 percent chance of a closure. It means the forecast collected half of the available points.

2. Using Storm Totals for the Wrong Window

A forecast of 8 inches by tomorrow night may put only 2 inches on the ground by the morning commute. Enter what falls before and during the commute.

3. Entering Wind Gusts as Wind Speed

The wind chill formula uses sustained wind speed. Gusts give a wind chill that is too low.

4. Expecting Wind Chill to Freeze Things

The NWS states that wind chill applies only to people and animals. It cannot cool a car or a pipe below the air temperature.

5. Copying Someone Else's Shoveling Pace

Pace changes with snow depth, wet or dry snow and the shovel. Time yourself on a small patch and enter that.

The wind chill, shoveling time and pay cost are exact arithmetic on your inputs. The score is a transparent rule of thumb that has not been tested against real closure records.

The NWS adds its own cautions about wind chill. Bright sunshine may raise the wind chill temperature by 10 F to 18 F. Frostbite needs an air temperature below freezing, whatever the wind chill says. At 0 F with a 15 mph wind the wind chill is -19 F, and exposed skin can freeze in 30 minutes.

No calculator can predict a snow day with authority. A person decides each closure using local road, bus and staffing information that no formula has.

No fixed number exists. The National Weather Service notes that the snow needed for a Winter Storm Warning is typically much higher in the Northern Plains than in the Southeast, and school decisions vary the same way.

The score is a 0 to 100 total of points for snowfall, timing, ice, wind chill and National Weather Service alerts. It is a rule of thumb and not a percent chance.

The National Weather Service formula is 35.74 + 0.6215T - 35.75 V^0.16 + 0.4275 T V^0.16, with T in degrees Fahrenheit and V in miles per hour.

At 0 F with a 15 mph wind the wind chill is -19 F, and the National Weather Service says exposed skin can freeze in 30 minutes at that level.

A Watch means conditions are favorable for a significant winter storm. A Warning is issued for a significant winter weather event that includes snow, ice, sleet or blowing snow.

The National Weather Service issues a Blizzard Warning for frequent gusts of 35 mph or more with falling or blowing snow that frequently cuts visibility below a quarter mile for three hours or more.

Divide the area by your own pace. A 600 square foot driveway at 10 square feet a minute takes 60 minutes.

Use the forecast for your exact location on weather.gov. It lists expected snowfall, temperatures, wind and any alert in effect.

No. The calculator runs in your browser and nothing goes to our servers. Saved results stay in this browser only.

• Understanding wind chill: the formula, its limits and the 0 F at 15 mph example (National Weather Service).
• Winter weather warnings, watches and advisories, and their local criteria (National Weather Service).
• Winter safety: storms, alerts and hazards (National Weather Service).
• Wind chill safety: frostbite and hypothermia (National Weather Service, Denver/Boulder forecast office).