Ice Storms Flashcards
What is supercooled water?
Water that freezes upon impact
Supercooled water is water that exists below 0 degrees, as 0 degrees is a melting point but not necessarily a freezing point
For liquid water to freeze there must be ice nuclei present in the atmosphere
Synoptic Conditions for an Ice Storm
Synoptic: A simple explanation for the large scale environment of the weather patterns
Often occurs to the north of a warm front and to the west of a surface cyclone (about 72% of the events)
Often occurs on the cold side of a cold front in a cold-air dome associated with a high pressure system
Cyclone Development
Initially there is a boundary, or front, separating warm air to the south from cold air to the north. The front is often stationary.
Winds tend to blow in a counter clockwise fashion around the low pressure system.
As the cyclone continues to develop, the warm moist air will override the cold, denser air which hugs the ground. This is the warm conveyor belt.
This produces precipitation, which occurs in narrow bands along the front. However the type of precipitation will depend on the temperature structure in the atmosphere.
What temperature structure is needed for freezing rain to occur?
An inversion is needed, where a deep warm layer exists in the atmosphere. Inversions occur in conditions of atmospheric stability.
Snow falls out of the first cold layer, then into the deep warm layer which turn it into supercooled water, and then freezes again upon impact with another cold layer.
What makes an ice storm so severe?
Persistent nature of an ice storm is key to the severity
○ Ex. 1998 ice storms fell over the course of 5 days
Intensity of precipitation
○ High precipitation in a super cooled phase increases severity
Location
The Montreal Ice Storm
→ More than 90% of freezing rainstorms in North America last less than 5 hours
○ This ice storm lasted 5 days
→ Freezing Rain occurred for more than 80 hours during the storm
→ This was due to a frontal system that separated warm and cold air masses staying stagnant at the St. Laurence River
→ Usually, their exist a cold air circulation around Labrador and a warmer circulation around Ontario, however the St Laurence river pulls this cold air downwards and creates a front between the two temperatures. This forces the warms air upwards and causes precipitation.
Why is Montreal so vulnerable to ice storms?
Montreal gets more freezing rain because it is located in a valley surrounded by mountains
Causes a channeling effect that traps cold dense air
Most winds come from the Northeast or Southwest, along the river valley
Cold air damming
when cold air gets dammed up against the boundary of a mountain
Safety Measures
→ Warning for a freezing rainstorm can come up to one day in advance
→ If power and heat are lost:
○ Use heat as efficiently as possible
○ Avoid penetration of cold air onto warm rooms
○ Stay hydrated
○ Make sure to properly ventilate your house if you are using an alternative heat source
