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Winter Season Weather Watches and
Warnings in Ontario Region

Special Weather Statements

Special Weather Statements are initially issued to flag the approach of significant or severe weather under one of the following conditions:

• To alert that severe weather is on the horizon but at least 24 hours away (up to 36 hrs.) In this case, the special weather statement flags the possibility of winter severe weather. The information provided is an overview with few details about the type or amount of precipitation expected and the areas affected.
• To alert that a weather system of inconvenience is approaching and is 6 to 24 hours away. In this case, Environment Canada does not expect the criteria for a weather warning to be reached but the public may be inconvenienced by the weather.
• To focus attention on weather events that are less common or occur as initial events in the winter season. These might include

• the first significant snowfall of the year
• extensive thick fog with low visibility
• various and less common combinations of winter precipitation types and/or wind events
• unusual weather events such as thunderstorms or winter thaws in January that could produce minor flooding or other inconveniences

Please note that special weather statements continue to also be issued as weather summaries or as winter storm wrap-up's.

Winter Season Weather Watches

• During the winter season, winter storm watches, will normally be the only type of weather watch issued. Severe thunderstorm or tornado watches will be issued if conditions warrant. These latter are normally summertime phenomena
• A winter storm watch is issued whenever the meteorological conditions indicate that there is a significant potential that any one of the winter warning criteria will be met or exceeded (See the winter weather warning criteria listed below)
• Winter storm watches will normally be issued 12 to 24 hours before the onset of the significant winter weather. The amount of lead time will depend on the intensity and predictability of the storm.
• Winter storm watches will be updated, ended, or upgraded to warnings as weather conditions warrant, or prior to the next issue of the regular public forecast
• Winter storm watches will be carried as "flags" in the regular public forecast. (See the section on flagging procedures)

Winter Season Weather Warnings

• Winter season weather warnings are issued when conditions indicate that warning criteria will be reached
• These warnings are generally issued 3 to 18 hours prior to the onset of the storm. The amount of lead time depends on the predictability of the storm
• Warning messages will be updated, changed, or ended by a new warning message as weather conditions warrant or prior to the next regular public forecast
• The following is a list of all the warning types issued in Ontario for winter season weather

1. Heavy Snow
2. Snow squall
3. Blizzard
4. Wind
5. Freezing Rain
6. Heavy Rain
7. Windchill
8. Cold Wave
9. Flash Freeze
10. Winter Storm

• Warnings will be carried as "flags" in the regular public forecast (see the section on flagging procedures).

Winter Weather Warning Criteria

Weather warnings are issued when forecasts indicate the following conditions will be met or exceeded...

1. Heavy Snow Warning

• 15 cm or more of snow within a 12 hour period

2. Snow Squall Warning

• 15 cm or more of snow within 12 hours or
• 4 hours or more of near zero visibility under snow squall conditions even if the accumulation criteria is not met (These conditions may also be covered by a "Blizzard Warning")
• Snow squall warnings are limited to storms that occur in bands (often quite narrow) that develop in the flow off the open waters of the Great Lakes or other large bodies of water
• Snow squall warnings will be issued at the county level in Southern and Eastern Ontario, and at the public forecast region level elsewhere.

3. Blizzard Warning

• 4 or more continuous hours of all of the following conditions:

• visibility of 1 km or less in blowing snow
• wind speeds of 50 km/h or more
• wind chills in excess of 1600 watts per square metre

4. Wind Warning

• Surface winds are forecast to reach sustained speeds of 60 km/h or more for a period of 3 hours or more and/or
• any occurrence of wind gusts to 90 km/h or more.

5. Freezing Rain Warning

• 2 or more continuous hours of light freezing rain
• 2 or more continuous hours of moderate to heavy freezing drizzle
• Any occurrence of moderate or heavy freezing rain.

6. Heavy Rain Warning

• If ground is sodden or frozen with little or no snow cover then rainfall warning criteria is 25 mm rain or more in 24 hours.
• If ground or snow cover can absorb water then rainfall warning criteria is 50 mm or more in 12 hours.

7. Windchill Warning

• Wind chill values in excess of 2200 watts/m2 for the far northern portions of Ontario
• Wind chill values in excess of 2000 watts/m2 for remaining portions of Northwestern Ontario, Northeastern Ontario, and Parry Sound- Muskoka, Peterborough and the Kawarthas, Frontenac-Lanark, Ottawa-Hull-Cornwall
• Wind chill values in excess of 1800 watts/m2 for remaining portions of Southern Ontario

8. Cold Wave Warning

If within a 24 hr period, temperatures are forecast to fall from a near or above normal temperature regime to reach and persist at the following low values:

For all of Northern Ontario, and Parry Sound-Muskoka. Peterborough and the Kawarthas, Frontenac-Lanark, Ottawa-Hull-Cornwall

• Minimum temperatures fall to -30^oC or colder and
• Maximum temperatures do not exceed -20^oC

Remaining portions of Southern Ontario

• Minimum temperatures fall to -20^oC or colder and
• Maximum temperatures do not exceed -10^oC

9. Flash Freeze Warning

Is issued when forecast conditions include a combination that is likely to produce rapid ice formation on road surfaces. This involves a combination of the following:

• Air temperatures are forecast to fall rapidly from above zero Celsius to well below zero
• Significant precipitation is occurring just prior to or during the rapid temperature fall through zero Celsius

10. Winter Storm Warning

• 2 or more of the warning elements (i.e. snow and wind) are forecast to reach warning criteria
• May also be used for the larger snow amounts typically in excess of 25 cm in 24 hours

Flagging Procedures

• All winter season weather watches and warnings will be flagged in the public forecast. Special weather statements will not be flagged
• Flags will consist of a statement detailing the status of the weather watch or weather warning. The status will either be, "in effect", or "ended". Temporal or spatial qualifiers may be included within a flag
• Flags will follow the list of forecast regions to which they apply, ahead of the forecast content.
• Flags will be preceded and followed by two dots (..)
• Examples of flags

• ..winter storm watch in effect..
• ..freezing rain warning ended..
• ..winter storm watch in effect for tonight and tomorrow..
• ..Snow squall warning in effect for Bruce County for tonight..

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Webmaster Last Modified: May 17, 1999 URL: http://www.on.ec.gc.ca/canwarn/winterseason-e.html Copyright © 1999, Environment Canada. All rights reserved.