Winter Hazards

Case Study: Atlanta Snowpocalypse

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 <0.40 km for 3 hrs

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