Fall Avalanches

During the fall the atmosphere experiences significant cooling at
higher latitudes. As this cold northern air is mixed
progressively southward by fall storms, pronounced changes in the
air temperatures over the Northwest are a characteristic result.
These large temperature variations can result in rapid decreases
in the snowpack stability in areas with sufficient snow to slide.
Wet cool weather depositing substantial snowfall at the higher
elevations followed by rapid warming still common in the fall can
quickly produce greatly increased avalanche danger. In the fall
this problem is usually confined to permanent snow fields on the
volcanic peaks, as vegetation and other anchoring prevalent at
lower elevations generally prevents slides of a shallow snow
cover. Back-country travelers should make terrain, weather and
snowpack stability evaluations as they travel over snow covered
terrain. Remember that seemingly insignificant slides may be
dangerous. Almost half of all avalanche fatalities occur in
slides traveling less than 300 feet.

(Reprinted from the Northwest Weather and Avalanche Center)

Avalanche Facts
1. Most avalanches occur on slopes of 30 to 45 degrees, but large ones can occur on slopes as little as 25 degrees.
2. Snow is most unstable after and during snowfalls or prolonged heating by the sun, especially on steep inclines.
3. Sunballs and cartwheels on the surface during a warming period could indicate instability in deeper layers.
4. The most dangerous avalanches usually occur on convex slopes.
5. Avalanches can take place on short slopes as well as long ones.
6. Leeward slopes are dangerous because wind-blown snow adds depth, creating hard, hollow sounding wind slabs.
7. South-facing slopes are most dangerous in the spring.
8. Smooth grassy slopes are the most dangerous spots, but avalanches can start among trees under conditions of stress.
9. Avalanche danger can vary within a slope.
10. Following an old track does not necessarily mean a slope is safe.
11. Down-slanting trees and brush indicates previous avalanche launches.
12. Sun crust on old snow can cause new snow to slide off.
13. Rough surfaces generally favor stability of new snow cover.
14. Loose underlying snow layers are more dangerous than compacted ones.
15. Recent avalanches indicate dangerous conditions.
16. Snow falling at the rate of an inch or more per hour increases avalanche danger.
17. Snow crystals in the shape of needles and pellets result in more unstable snow conditions than the typical star-shaped snowflakes.
18. Snow saturated with water can avalanche, especially on south facing slopes and beneath exposed rock.
19. Rapid changes in wind, temperature and snowfall cause changes in the snowpack and may affect stability.
20. If the snow cracks and the crack runs as you step, the danger of slab avalanche, the most serious type of winter hazard, is high.
21. Gullies are many times more hazardous than open slopes because they act as natural avalanche chutes.


HYPOTHERMIA is called exposure by the news media. It is a lowering of the inner body core temperature beyond where you can not produce enough heat to stay alive. Dress with adequate clothing when going skiing that will insulate you from the cold. Use materials that will keep you warm even if you get wet.

FROSTBITE, or freezing of the tissues, usually affects the toes, fingers, and face. It occurs when your extremities lose heat faster than it can be replaced by circulating blood. It may occur from direct exposure to cold or high wind. Damp feet may freeze because moisture conducts heat rapidly away from the skin. Without activity the blood circulation to the extremities is reduced, accelerating the freezing process. With adequate equipment and clothing frostbite is not likely to occur. Prepare for extreme conditions when planing backcountry ski trips. Take a first aid class to prepare yourself for emergencies.

SNOW BLINDNESS is caused by failure to use adequate eye protection during bright sunshine on snow or light colored rock. The eyes are bloodshot, feel irritated and full of sand. Apply a cool wet compress to the eyes. Then wear two pairs of sunglasses. Aspirin helps the pain. Recovery may take two or three days... Snowblindness is not a permanent condition.

SUNBURN can be prevented by using sun screens. When you are at high altitude and on snow, cover yourself for protection from the sun's rays. Lips are vulnerable use special caution to protect them. Reflection from the snow can burn under the chin, around the eyes, inside the nostrils and ears, and even the roof of the mouth. Wear a hat to prevent scalp burns. Aspirin may be taken for pain, and drink liquids to replenish body fluids.

ACUTE MOUNTAIN SICKNESS can occur when a person ascends rapidly to an altitude higher than he/she is accustomed. Their body does not adjust to the new conditions. Breathing becomes more rapid to obtain more oxygen from the thinner air. Symptoms are loss of appetite, headache, weakness, apathetic, nauseated, dizzy and sleepy. Try to acclimatize, by spending time at altitude before exercising or exerting yourself. Rest with forced deep breathing to obtain more oxygen will help. Consume simple sugar such as; candy, oranges, or fruit juice.


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