Winter Hazards

Case Study: Atlanta Snowpocalypse

* Jan 2014, Atlanta Georgia experienced ‘snowpocalypse” when \~ 5 cm snow fell
* Drivers lacked experience driving in snow and icea
* accidents halt traffic flow
* poor emergency response:
* many municipalities sprawl across the region
* no comprehensive, regional emergency coordination
* 1200 traffic accidents
* 2000 children had to sleep on buses or in police stations
* several deaths
* commerce disruption
* airport shut down

what temperature must body maintain?

* 37ºC

what is hypothermia?

* when core temperature drops below safe range
* mild, then severe, shivering
* death results if core stays below 33.3ºC

what is frostbite?

* occurs when body tissue freezes

what is wind chill?

* your body creates a thin layer of warm air next to your skin
* wind strips away warm layer, causing you to lose heat
* wet skin cools faster than dry skin due to evaporation
* faster moving wind = faster layer striped away

what is wind chill temp?

* represents heats loss when dry skin is exposed to wind
* depicts exposure time that leads to frostbite

what is a polar front?

* the boundary between cold polar air and warmer air
* stretches around the globe, normally at high latitude
* can sometimes stretch far south
* may persists for weeks
* creates hazards for people living in temperate climates

what is a polar vortex?

* counterclockwise flow of polar air
* circulates around the North Pole

what is a polar jet stream?

* traces out the southern edge of the polar vortex

what are cold waves?

* defined relatively to normal, expected conditions
* requires society to take precautions against cold

what does snowfall intensity depend on?

* visibility
* light: visibility > 1 km
* moderate: visibility 1-0.5 km
* heavy: visibility < 0.5 km

heavy snow may accumulate at _________ cm/hr

* \~2.5
* occurs rapidly

melting snowpack may cause?

* flooding

why is snow important for?

* groundwater recharge
* insulating soil

what is a blizzard based on?

1. winds>56 km/h
2. visibility

what are whiteout conditions?

* visibility reduced to 0 km
* people cannot distinguish between the ground n sky
* snowdrifts may grow to several meters deep

what are ground blizzars?

* occurs in clear weather
* wind blows dry snow \~15 meters high

winter precipitation

winter precipitation

* Location A: Rain
* Air is above-freezing
* Location B: Freezing rain
* 0ºC isotherm is near ground
* rain falls n is supercooled
* supercooled rain freezes on contact w/ surfaces
* Location C: Sleet
* Warm air wedge is not vv deep, nor vv warm
* snow falling thry warm air wedge partially melts
* Location D: Snow
* air is below freezing

Great Ice Storm 1998

* Montreal n Ottawa shut down due to ice hazards
* Ice snapped tress, power lines, and transmission towers
* Millions w/o power
* 30 fatalities from hypothermia
* Livestock and wild animals perished
* Industries shut down
* Total damage> $6 billion

other hazards winter hazards may bring?

* transportation closures; Traffic accidents
* Heart attack from shoveling
* falls on slippery surfaces
* carbon monoxide poisoning
* ice accumulation can be a danger to aircrafts
* water mains may burst
* electric grid may fail
* deaths of livestock and crops; can lead to famine

what are causes of winter storms?

* mid latitude cyclones
* oceanic cyclones
* lake-effect snow
* mountain snowstorms

mid-latitude cyclones - Nor’easters

* Mid-latitude cyclones on east coast
* warm coastal waters provide moisture for precipitation
* storms with strong winds blowing from the NE
* create severe storms along east coast of N. America
* they can create a storm surge, blizzards, and ice storms

what are oceanic cyclones?

* wintertime mid-latitude cyclones over the ocean
* stronger than continental ones:
* warm water provides energy for the storm
* wind has no barrier to block or slow its flow
* create intense storms when making landfall

lake-effect snow

* the great lakes retain the moisture late into the yr which adds moisture to passing cold air
* land cools faster than water
* clouds form and precipitate snow on downside shores
* common in late Nov and early Jan
* Impact zone is \~50 –80 km from shore
* they dev after a mid-latitude cyclone’s cold front has passed
* high snow removal costs r common

mountain snowstorms

* orographic uplift creates clouds on windward flanks
* clouds precipitate snow during winter months
* create the heaviest snowstorms and snowpacks in the world
* common in Rocky Mountains, Ca
* melting snowpacks provides drinking water, power generation and irrigation

hazardous winter weather in Asia

* frigid, dangerously cold may flow east into China
* may encounter warm, moist air from Indian Ocean
* Creates hazards for densely pop chinese cities

China worst winter; feb 2008

* primary disaster:
* burst water pipes flooded thousands of homes
* elec grid failed
* snow and ice collapsed roods
* over 1M livestock died
* 10% forest damaged or killed
* 40% winter crops destroyed
* Secondary disasters:
* Erosion
* landslides
* insect infestations
* wildfires
* Economic loss>$22.3B

what are avalanches?

* rapid downslope movement of snow as flow

what factors contribute to avalanche formations?

* alternating times of freezing n thawing
* a min of 30cm of snow
* slopes of 20-40 degrees
* sun exposure can promote partial melting
* recent precipitation
* strong winds
* added weight

what are the 3 main parts of avalanches?

1. motion is initially in the Start Zone (S)
2. moves downslope forming a track (T)
3. as it loses momentum it spreads n slows in the run-out zone (R)

what do dry avalanche involve?

* the movement of powdery or granular snow forming loose, turbulent flows down slope
* speed : 60-200 km/hr
* compressed air forms wind gusts capable of knocking down trees

what are wet avalanches?

* composed of loose wet or moist snow
* higher density than dry - can be more deadly
* occur during periods of prolonged melting - usually in later winter/spring

what are slab avalaches?

* involves detachment of blocks of snow
* most common
* contain greater vol of snow than powder avalanches n there is a high probability for burial

avalanche as a hazard

* kills approx 200 peep/yr
* in Ca, 10-15 peep die due to avalanche activity
* most avalanches in Ca r associated w/ recreational accidents