Where the forecast comes from
When you enter a ZIP code, your browser looks it up in a table on this site built from the U.S. Census Bureau’s ZIP Code Tabulation Area internal points, which gives a point near the center of that ZIP. It then asks the National Weather Service API for the gridpoint forecast at that point, rounded to 0.01 degree (about a kilometer). That forecast includes hourly snowfall, ice accumulation, temperature, wind and wind chill. We read only the forecast for the school morning you pick.
How snow is scored
Snow is sorted by when it falls: before 3 am, 3 to 6 am, 6 to 9 am and 9 am to 3 pm. Each period counts for a share of an inch. For a closure, snow from 3 to 6 am counts fully, earlier snow 70 percent, snow from 6 to 9 am 80 percent and snow during the school day 35 percent. For a delay, snow just before the buses and during the morning commute counts more, and earlier snow less. The weighted inches are compared with the midpoint for your area: for a closure 3, 6 or 10 inches, and for a delay half of that.
Ice and cold
Ice adds points on its own. Freezing rain of 0.25 inch or more is treated as a serious hazard, and smaller amounts or a freezing rain risk add less. Extreme wind chill adds points in three steps that depend on your area’s snow setting. The highest of the snow, ice and cold scores sets the result, and the other two add 30 percent of their value.
Bands, not probabilities
The model gives each of closure and delay a score from 0 to 100 and shows a band: very low, low, moderate, high or very high. The score is not a probability, and we do not claim an accuracy rate because we have not measured one. When a closure is already likely, the delay score is reduced because a delay-only outcome is less likely.
What it cannot know
It cannot see your district’s rules, its snow removal equipment, whether it uses delays or remote days, or what neighboring districts are doing. It cannot see the actual road conditions on your bus routes. The forecast changes, and a ZIP code’s center point can be miles from your street. Treat the result as one input, and confirm with your district.
Privacy
The ZIP code is converted to a point in your browser and never sent to a geocoding service. The National Weather Service receives the rounded coordinates and your IP address, as any website does. This site does not store your ZIP code or the results.
Sources and further reading
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