You open SnowSense™ and see "67% Snow Day Probability." Now what? Do you pack your backpack? Set your alarm? Text your friends?
Here's the correct way to read that number — and why most people interpret probability scores wrong.
What "67% Probability" Actually Means
A 67% snow day probability means: if this exact weather pattern occurred 100 times in your region, school would be cancelled approximately 67 of those times.
It is not a personal prediction. It is not a guarantee. It is a statistical estimate based on current conditions compared to historical closure data.
Think of it like a weather forecast saying "70% chance of rain." That doesn't mean it will definitely rain. It means conditions strongly favor rain based on everything the model can measure.
The Three Probability Zones
Low: 0–35% — Go to School Conditions don't favor a closure. Pack your bag and set your alarm. A probability this low means even if some snow falls, it's unlikely to reach the threshold your district uses for cancellation.
Middle: 36–65% — Prepare Either Way This is the genuine uncertainty zone. Have your backpack ready. Check [SnowSense™](/) again at 10 PM and again at 5 AM. This range is where storm track changes and overnight temperatures make the biggest difference.
High: 66–100% — Strong Cancellation Signal **Very Likely.** Conditions strongly favor a closure. At 80%+, you can reasonably plan for a snow day while keeping in mind the superintendent still makes the final call.
What Drives the Percentage Up or Down
The four factors that control your probability score:
Snowfall — More accumulation = higher score, but rate matters more than total depth.
Ice Risk — Freezing rain or black ice potential pushes the score up faster than any other factor.
Storm Timing — Snow forecast for 2–5 AM dramatically increases the score. Same snow at 2 PM barely moves it.
Regional Calibration — Your city's infrastructure and historical tolerance modify the raw score. Boston needs higher raw scores to reach the same probability as Atlanta.
The probability score is most useful as a *trend* rather than a static number. A score climbing from 30% at 6 PM to 65% at 10 PM to 82% at midnight is telling you the storm is developing faster and stronger than forecast. A score dropping from 70% to 40% overnight means conditions are improving. Watch the direction, not just the number.
⚡ The Trench Truth
Confidence Score vs. Probability Score
You'll notice SnowSense™ shows two numbers: Probability and Confidence.
- •Probability: The estimated chance of cancellation
- •Confidence: How reliable the forecast data is
A 75% probability with 90% confidence means the model is very sure about its prediction. A 75% probability with 45% confidence means the storm track is uncertain and the model is less sure. Always look at both.
Check Your Current Score
Get your real-time probability and confidence score at the SnowSense™ calculator or browse by city at our snow day calculator by location.