Chapter 10: Winter Weather

Types of Weather Alerts

  • Advisory: Issued when hazardous weather is ongoing or imminent, but is generally less severe than a warning. It highlights potential inconvenience and danger to life/property that could arise if caution isn’t taken.

  • Weather Watch: Indicates a heightened risk of hazardous weather, but occurrence, timing, or location are still uncertain. People are advised to have a plan in place.

  • Warning: A serious alert indicating that hazardous weather is currently happening, or will happen soon, requiring immediate protective action.

Specific Winter Weather Alerts

  • Winter Weather Advisory: Freezing rain and/or snow expected that may cause inconvenience.

  • Winter Storm Watch: Hazardous winter weather is possible within the next 48 hours.

  • Winter Storm Warning: Conditions indicative of a winter storm are currently happening or imminent.

  • Blizzard Warning: Snow and/or blowing snow that reduces visibility to ≤ 0.40 km for extended periods, coupled with high winds.

  • Ice Storm Warning: Significant ice accumulation expected on multiple surfaces, creating dangers.

  • Freeze Watch: Temperatures projected to drop below 0°C in the next 1-1.5 days, potentially harming crops.

  • Frost Advisory: Risk of temperature falling below 0°C that could harm agricultural plants.

  • Wind Chill Advisory and Warning: Risk of frostbite or hypothermia due to the combination of cold temperatures and wind.

Historical Context: The 1998 Ice Storm

  • This event marked a significant historical weather disaster affecting southeastern Quebec and eastern Ontario, resulting in:

    • Over 100 mm of precipitation over five days.

    • 34 deaths

    • Widespread power outages and damage, affecting millions of people.

    • Estimated damages between $5-7 billion CAD.

    • Deployment of over 16,000 Canadian Armed Forces members for relief efforts.

Impacts of Winter Storms

  • Lack of appropriate shelter during cold weather can lead to severe health risks:

    • Hypothermia: Occurs when body temperature drops below safe levels.

    • Symptoms of hypothermia include:

      • Shivering (35.5°C- 37°C)

      • Violent shivering and irrational behaviour, loss of coordination (35°C - 33.8°C)

      • Body shut down (33.3°C)

    • Frostbite: The freezing of body tissues in extremities (ears, nose, fingers, toes).

Cold Waves

  • Definition: Cold wave is defined as a relatively rapid, prolonged fall in temperature that requires people to take precautions against cold weather.

  • Criteria: There is no standardized criteria for categorizing cold waves; the recognition may depend on local impacts and conditions.

Polar Vortex

  • Definition: The polar vortex is a flow of cold air, acting as a fluid, circulating around the North Pole.

  • Formation: It plays a significant role in influencing Arctic weather patterns and can contribute to cold wave conditions when it extends further south.

Polar Front

  • Description: The polar front is the boundary that separates cold polar air and warmer subtropical air, encircling the globe. It can significantly affect where cold air masses impact mid-latitudes.

  • Mid-latitude Cyclones: When a mid-latitude cyclone occurs in North America, the polar front may extend southward significantly, potentially reaching areas as far as the Gulf Coast or central Florida, which can lead to prolonged cold conditions.

Winter Storms

  • Snowfall Intensity: The intensity of snowfall in the U.S. is categorized based on visibility:

    • Light snow: Visibility > 1 km

    • Moderate snow: Visibility between 1 km and 0.5 km

    • Heavy snow: Visibility < 0.5 km

  • Blizzard Conditions: Blizzard conditions include wind speeds exceeding 56 km/h and visibility of less than ¼ mile for a duration of 3 hours.

    • Ground blizzards occur when snow is moved by winds 10-15 feet above the ground without new precipitation being added.

Ice Storms

  • Definition: An ice storm occurs when freezing rain accumulates on surfaces at ground level due to temperatures below 0°C.

  • Temperature Dynamics: The 0°C isotherm is an invisible boundary between warmer and cooler air.

Precipitation Types:

  • Rain: Snow descends past the 0°C isotherm; melts into rain after warming in the warmer air.

  • Freezing Rain: Rain crosses 0°C isotherm, becoming supercooled; freeze upon contact with cold surfaces, resulting in freezing rain.

  • Sleet: Snow partially melts while passing through warmer air and refreezes in colder air, forming sleet.

  • Snow: At a high altitude, snow falls through cold air directly to the ground without melting.

Causes of Winter Storms

  • Continental Midlatitude Cyclones

    • Where a cold front rotates and meets up with a warm front and creates storms

  • Nor’easters and Oceanic Cyclones

    • Nor’easters are mid-latitude cyclones that happens in the Eastern parts of North America and intensifies as it draws in moisture from the Atlantic Ocean

    • Oceanic Cyclones and Midlatitude cyclones that form over the open ocean

  • Air Damming

    • The trapping of a low-altitude cool air layer by a mountain range

  • Lake-Effect Snow Storms

    • When a large lake provides heat and moisture to the atmosphere and can produce local weather systems.

  • Mountain Snow Storms

    • Occurs from orographic lifting on the windward side of a mountain range.

Polar-Front Jet Stream

  • Description: The polar-front jet stream is a boundary that separates warm tropical air from cold air originating in polar regions.

  • Characteristics:

    • Located about 10 km high, it flows in fast currents over the polar front in wave-like undulations.

    • Ridge: Areas where the jet stream curves toward the poles.

    • Trough: Areas where the jet stream dips toward the equator.

Understanding these phenomena is crucial for grasping winter weather patterns and prepares individuals to make necessary adaptations during extreme weather conditions.