Ontario Snow Day Predictor — Compare School Closures Across the Province
Ontario covers a vast area with distinct winter climates. A storm that closes schools in Sudbury may leave Toronto unaffected on the same morning. This page explains how closure probability differs by region, how Ontario boards reach decisions, and what separates a snow day from a bus cancellation.
Enter your city or postal code into the predictor on the homepage for a localized score. This page provides the regional context behind that number.
Heavy snowfall is the leading cause of school closures across Ontario regions.
Closure frequency depends on geography, snowfall patterns, and bus route length. The differences across Ontario are significant.
Greater Toronto Area and Southern Ontario
The GTA experiences the fewest closures in the province, typically two to five per year. TDSB, TCDSB, Peel, York Region, Durham, and Halton all serve dense urban areas with strong road-clearing infrastructure. Lake Ontario moderates temperatures, reducing extreme cold events. View the Toronto-area predictor →
Eastern Ontario, Including Ottawa and Kingston
Eastern Ontario sees five to eight closures per year. The Ottawa Valley storm track delivers frequent significant snow events. OCDSB, Ottawa Catholic, CECCE, and CEPEO operate in this region with independent decision processes. View the Ottawa-specific predictor →
Central Ontario, Including Barrie and Simcoe County
Central Ontario averages six to ten closures annually. Georgian Bay lake-effect snow is the dominant driver. SCDSB and SMCDSB serve this area, where narrow snowbands can deposit large totals within hours. View the Barrie-specific predictor →
Western Ontario, Including London and Hamilton
Western Ontario sees three to six closures per year. Lake Erie and Lake Huron generate periodic lake-effect events, though less severe than Georgian Bay’s impact on Simcoe County.
Northern Ontario, Including Sudbury and Thunder Bay
Northern Ontario experiences the highest frequency, eight to twelve closures annually. Heavy snowfall, rural road networks, and longer bus routes combine to push closure rates well above the provincial average. Boards here include Rainbow District, Huron-Superior, Rainy River, and Keewatin-Patricia. View the Sudbury-area forecast →
Transportation consortiums assess road conditions before sunrise to decide on closures.
Most Ontario boards follow a consistent early-morning process. Transportation consortiums begin assessing road conditions between 4:00 AM and 5:00 AM. Bus drivers report directly on route conditions during this window.
For overnight storms, many boards issue advance notice between 10:00 PM and 11:00 PM the night before. This early signal helps families prepare, though it is not always final.
Final decisions are typically confirmed by 6:15 AM. Decisions often involve transportation authorities such as Student Transportation of Peel Region, alongside individual board communications teams.
The Decision Threshold
Across Ontario, fifteen centimetres of snowfall or wind chill near minus thirty-five degrees Celsius are common thresholds referenced by transportation authorities. These numbers are not fixed rules. Each board interprets them against its own road network and historical closure pattern.
Why the Same Snowfall Means Different Things
Ten centimetres of snow affects boards differently depending on geography. For SCDSB in Barrie, where Georgian Bay lake-effect snow is routine, ten centimetres may be a normal winter event. For TDSB in Toronto, the same ten centimetres represents a more significant disruption due to urban traffic density, even though road infrastructure remains strong. Predictions calibrated to each board’s history reflect this difference better than a single national formula.
What a Bus Cancellation Means
A bus cancellation means school buses are suspended for the day. Schools remain open. Students who can travel independently, by car or on foot, are expected to attend. Students who rely on buses are excused from attendance without penalty.
What a Snow Day Means
A snow day means the school itself is closed. No students or staff are expected to attend, regardless of transportation method. This outcome is less frequent than a bus cancellation across most Ontario boards.
The Most Common Outcome
The combination of bus cancellation with schools remaining open is the most frequent result of a moderate winter storm in Ontario. Families should check both categories separately when reviewing a forecast. See school bus safety tips for winter routes →
Catholic and public boards sharing the same geography usually coordinate closure decisions, since they often share transportation consortiums and bus routes. However, each board makes an independent final call. In most cases the decisions align. Occasionally they do not, particularly where French-language boards operate alongside English boards. Read the full breakdown of how Ontario boards decide →
Lake-effect snow bands off Georgian Bay and Lake Huron drive closures in central Ontario.
Lake-Effect Snow
Lake-effect snow forms when cold air passes over relatively warm lake water, picking up moisture and depositing it as intense, localized snowfall downwind. Georgian Bay, Lake Huron, and Lake Erie all produce this effect across different parts of Ontario.
Wind Chill and Extreme Cold
Wind chill becomes a closure factor independent of snowfall when temperatures drop sharply. This is most relevant in northern and eastern Ontario, where wind chill below minus thirty degrees occurs more frequently than in the GTA.
Blowing Snow and Rural Visibility
Heavy overnight snowfall combined with blowing snow is a leading cause of closures in rural and semi-rural Ontario. Long bus routes cross exposed roads where visibility drops quickly during wind events, even if total accumulation is moderate.
This page provides regional context. For a precise score, the predictor on the homepage uses your city or postal code to generate an hourly-updated probability calibrated to local conditions.
Province-wide pages list every major school board, announcement timing patterns, and links to detailed city forecasts. Ontario and eastern Canada generally receive the most detailed board-level data due to the density of boards and historical closure records available.
The Best Time to Check
Check the predictor around 9:00 PM the night before a forecasted storm to set initial expectations. Check again between 5:00 AM and 6:15 AM, which aligns with when most boards finalize decisions. Learn more about the best times to check your forecast →
A single province-wide percentage cannot capture the difference between Sudbury and Windsor on the same day. Ontario’s size means regional calibration produces more useful results than a national or provincial average. Frequent closures can also affect classroom time — read about the impact of snow days on student learning → Compare prediction accuracy across different tools →
Which Ontario cities have the highest snow day frequency?
Northern Ontario cities, including Sudbury and Thunder Bay, average eight to twelve closures annually, the highest rate in the province due to heavy snowfall and long rural bus routes.
How many snow days does Toronto typically get?
The GTA averages two to five closures per year, the lowest in Ontario, due to urban infrastructure and Lake Ontario’s moderating effect on temperature.
What is the difference between a snow day and a bus cancellation?
A bus cancellation suspends school transportation while schools stay open. A snow day closes the school entirely. Bus cancellation with schools open is the most common winter outcome in Ontario.
Do Catholic and public boards always close together?
They typically coordinate due to shared transportation consortiums, but each board makes an independent final decision. Differences occasionally occur, particularly with French-language boards.
What snowfall amount typically triggers a closure in Ontario?
Fifteen centimetres of snowfall or wind chill near minus thirty-five degrees are common reference points, though thresholds vary by board and region.
When should I check the forecast for tomorrow?
Check around 9:00 PM the night before for initial expectations, then again between 5:00 AM and 6:15 AM when most boards confirm their final decision.