What Is Lake-Effect Snow?
Lake-effect snow is snow that develops when cold air moves across a relatively warmer body of open water. The air picks up heat and moisture from the lake, helping clouds and snow develop downwind.
Lake-effect snow can be highly localized. One community may receive heavy snow while another relatively close by receives little or none.
The Great Lakes make lake-effect snow especially important in parts of Ontario. Depending on wind direction, communities downwind of lakes such as Huron, Superior and Georgian Bay can receive significant snowfall.
Related Conditions
| Condition | Description |
|---|---|
| Snow Squall | A sudden period of heavy snow that can quickly reduce visibility and cover roads. |
| Heavy Snowfall | Snowfall that produces significant accumulation over a relatively short period. |
| Snowband | A narrow area of concentrated snowfall that can produce much heavier snow than surrounding locations. |
| Snow | Frozen precipitation that forms as ice crystals in clouds and falls as snowflakes. |
| Whiteout | A condition where snow and poor visibility make surrounding features difficult or impossible to see. |
Related Alerts
| Alert | Description |
|---|---|
| Snow Squall Warning | Warns of snow squalls that can cause sudden poor visibility and hazardous travel. |
| Snowfall Warning | Issued when significant snowfall is expected to meet warning criteria for an area. |
| Winter Storm Warning | Warns of a significant combination of hazardous winter weather. |
| Blowing Snow Advisory | Issued when blowing snow is expected to significantly reduce visibility. |
| Winter Storm Watch | Alerts people to the potential for significant winter weather to develop. |
What Causes Lake-Effect Snow?
Lake-effect snow begins when cold air moves across a lake that is warmer than the air above it. Heat and moisture from the lake enter the lower atmosphere, making the air warmer and more humid.
As this air rises, it cools and the moisture begins forming clouds. If temperatures are cold enough, ice crystals develop inside the clouds and eventually fall as snow.
Wind direction determines where that snow travels. When winds remain aligned in the same direction for long enough, snow can become concentrated into narrow bands that repeatedly affect the same areas downwind of the lake.
This is why lake-effect snowfall can vary so dramatically over short distances. A persistent snowband can produce heavy accumulation in one community while locations outside the band receive much less snow.
Lake-effect snow generally becomes less intense as lakes freeze because ice limits the amount of heat and moisture transferred from the water into the atmosphere.
In Ontario, lake-effect snow can also develop into intense snow squalls that cause visibility and road conditions to deteriorate quickly. Our guide to how meteorologists predict snow explains how forecasters use temperature, moisture, wind and other information to predict snowfall.
FAQ
Lake-effect snow specifically develops when cold air passes over relatively warmer open water and gains heat and moisture. Snow can also form through many other weather systems without a lake being involved.
Lake-effect snow commonly affects areas downwind of the Great Lakes and Georgian Bay. The exact locations affected depend heavily on wind direction and other atmospheric conditions.
A lake can continuously supply heat and moisture to cold air passing over it. When conditions remain favourable, this can support persistent bands of heavy snowfall.
Lake-effect snow often forms in narrow bands. Wind direction determines where those bands move inland, creating large differences in snowfall over relatively short distances.
Lake-effect snow can become much less likely or weaker when a lake develops extensive ice cover because less heat and moisture can move from the water into the atmosphere.