Lecture 15 Flashcards
Blizzard
Visibility < 400 m because of wind speeds of >40 km/h
and blowing or falling snow for 4 hours or more
Interaction between upper-level low pressure trough and surface low pressure
Different locations have different classifications
Sleet
Rain/snow melts, then refreezes near ground level, forms mostly <1 mm diameter ice particles
Freezing rain
Supercooled rain freezes when it contacts ground
How do blizzards form?
Interaction between upper-level low pressure trough and surface low pressure
Fronts
Boundary between two air masses of different density and temperature
Advancing cold front
Forces warm air up
Creates clouds and heavy precipitation
Advancing warm frount
Forces warm air over cooler air
Creates clouds and precipitation
Special weather statements
Least urgent type of alert
To let you know conditions are unusual and could cause concern
Advisories
Issues for specific weather events that are less severe but could still significantly effect Canadians
Watches
Alert you about weather conditions where there is potential for a significant storm or severe weather to occur
Can be upgraded as more information becomes known
Warnings
Urgent messages that severe weather is either occurring or will occur
Updated regularly
Snowfall warning
A snowfall accumulation of 15 cm or more is expected in 12 hours or less
Freezing Rain Warning
Freezing rain is expected to last for 2 hours or more, or if slippery or hazardous walking or driving conditions due to freezing precipitation is expected
Frost warning
When the air temperature is expected to fall below or near freezing ( 0°C ) during growing season
Winter storm warning
When severe and potentially dangerous winter weather conditions are expected, including:
A major snowfall (25 cm or more within a 24 hour period); and
A significant snowfall (snowfall warning criteria amounts) combined with other cold weather precipitation types such as: freezing rain, strong winds, blowing snow and/or extreme cold
Alberta clipper
a fast-moving winter weather system originating in the lee of the Canadian Rockies that typically brings snow, high winds, and cold temperatures across the prairies
Maritimes Nor’easter
Warm moist air picked up in the tropics moves north up the coast with Gulf Stream; origin often Cape Hatteras, NC
A mass of polar air from Eastern Canada and the North Atlantic moves south
Somewhere in the vicinity of Cape Cod the warm air hits the cold air.
The warm air moves up and over the cold layer.
Low pressure develops, counterclockwise cyclone means that coastal areas get northeasterly winds as the storm approaches
Colorado low
Low-pressure area that forms in southeastern Colorado or northeastern New Mexico, typically in the winter. After forming, the system moves across the Great Plains
Direct effects of blizzards
Frost bite, hypothermia (death)
Heart attacks during shovelling
Indirect effects of blizzards
Loss of electricity
Auto accidents
# of blizzards deaths = or greater than tornado deaths in Canada and US
Where are blizzards most common in Canada?
Southern prairies, Atlantic Canada, eastern Arctic
Where are blizzards rare in Canada?
Wester NWT, BC and Yukon
How may lives do winter storms and excessive cold claim every year in Canada?
100
More than combined toll from hurricanes, tornadoes, flood, extreme heat and lightning
White Juan
Halifax, Yarmouth, Charlottetown
1m in 24h
Province wide states of emergency for 4 days
Nightly curfew for 3 days
>5 million in unbudgeted snow removal and wire repair
1998 Quebec Ice Storm
January Quebec, NB, Ontario, NFLD 80 hours of freezing rain, some sleet >25 deaths $7 Bil, US 550, 000 without power 130 major transmission towers 30, 000 utility poles 120, 000 km of power lines and telephone cables
Mitigation (6)
1) Better forecasts (not 12 hrs, but 24 hrs)
2) City planning for snow removal from sidewalks
3) Remind seniors at risk of heart failure
4) Dress appropriately
5) Remove trees near electrical wires
6) Consider underground infrastructure
