What Is Heavy Snowfall?
Heavy snowfall is a period of snow that produces a large amount of accumulation over a relatively short time. It can occur during major winter storms or in smaller, more localized areas.
How quickly snow accumulates matters as much as the total amount. When snow falls faster than roads and sidewalks can be cleared, travel conditions can deteriorate quickly.
Heavy snowfall can make roads difficult to navigate, reduce visibility and lead to school, business and transportation disruptions. Strong winds can make conditions worse by creating blowing snow, snowdrifts and, in more severe situations, whiteout conditions.
Related Conditions
| Condition | Description |
|---|---|
| Snow | Frozen precipitation that forms as ice crystals in clouds and falls as snowflakes. |
| Lake-Effect Snow | Snow that develops when cold air moves across relatively warmer, open lake water. |
| Snow Squall | A sudden burst of heavy snow that can quickly reduce visibility and cover roads. |
| Blowing Snow | Loose snow lifted and carried by the wind, often reducing visibility. |
| Snowband | A narrow area of concentrated snowfall that can produce much heavier snow than nearby areas. |
Related Alerts
| Alert | Description |
|---|---|
| Snowfall Warning | Issued when snowfall is expected to reach warning criteria for the affected region. |
| Winter Storm Warning | Issued when a significant combination of hazardous winter weather is expected. |
| Snow Squall Warning | Warns of snow squalls that can cause sudden near-zero visibility and hazardous travel. |
| Blizzard Warning | Warns of strong winds and blowing snow producing very poor visibility. |
| Blowing Snow Advisory | Issued when blowing snow is expected to significantly reduce visibility. |
What Causes Heavy Snowfall?
Heavy snowfall needs two main ingredients: cold air and enough moisture in the atmosphere. Snow forms when temperatures in the atmosphere are at or below freezing and water vapour develops into ice crystals inside clouds.
The temperature at ground level does not always need to be below 0°C for snow to reach the surface. As the National Snow and Ice Data Center explains, snow can still reach the ground when ground temperatures are above freezing if atmospheric conditions are right.
Heavy snow is often associated with relatively warmer winter air because warmer air can hold more water vapour. When that moist air rises and cools, it can provide a steady supply of moisture for snow. Extremely cold air is often much drier and may produce little snowfall.
Some weather patterns can concentrate that moisture over a smaller area and produce especially heavy snow. Lake-effect snow, for example, can develop when cold air moves across relatively warmer, open lake water and picks up additional heat and moisture. This can lead to narrow snowbands that produce much heavier snowfall in one location than another nearby.
Meteorologists look at temperature, moisture, wind, storm tracks and other atmospheric conditions to estimate where heavy snow will develop and how much could accumulate. Our guide to how meteorologists predict snow explains how these forecasts are made.
FAQ
There is no single snowfall amount that defines heavy snowfall in every situation. How severe it becomes depends on the snowfall rate, total accumulation, location and how quickly the snow falls.
During intense snowfall, several centimetres of snow can accumulate within a few hours. The fastest accumulation rates are often associated with strong winter storms, snow squalls and lake-effect snow.
It can be. Heavy snow can make roads slippery or difficult to clear, reduce visibility and make travel more difficult. Large accumulations can also add significant weight to roofs, trees and other structures.
Heavy snowfall describes the amount or intensity of falling snow. A snowstorm is a broader weather event that may include heavy snow along with wind, blowing snow and other winter conditions.
Heavy snowfall can occur over a large area and last for many hours. A snow squall is typically more localized and can cause conditions to deteriorate very suddenly.
Yes. Heavy snow can fall when winds are relatively light. Strong winds are not required for heavy snowfall, although they can create additional hazards.
Yes. Snow can fall when surface temperatures are slightly above 0°C, although warmer ground and air temperatures can reduce how much snow accumulates.