1. MOUNTAIN WEATHER
Monica Spicker 2007
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2. Objectives Explain basic causes of weather.
Identify incoming bad weather on the basis of clouds and altimeter readings.
Explain what to do if caught in a lightning storm.
Appropriately take weather into consideration in mission planning.
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3. Causes of Weather Energy flow along gradient Temperature differences
Pressure differences
Moisture differences
The bigger the difference, the stronger the wind and other weather effects.
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4. Large Scale Influences
Prevailing Wind: SW.
Jet Stream.
Mountain Ranges.
Ocean and Lakes.
Season.
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5. Small Scale Influences
Local topography
Orographic Lifting
Elevation
Time of day
Up slope winds in morning.
Afternoon thunderstorms build above ridges.
Down slope winds at night.
Quiet times at sunrise and sunset
Season
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6. Good Weather Sinking, stable air Cool Dry High pressure Anticyclone
Clockwise air flow in northern hemisphere
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7. Bad Weather Rising unstable air Warm Wet Low pressure
Counter-clockwise flow in northern hemisphere
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8. Fronts: Warm Front Warm air over cool air Comes slowly
Brings much precipitation
Warms up after passage
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9. Fronts: Cold Front
Cold air overtaking and coming up underneath warm air
Comes quickly, often violently
Thunderstorms
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10. Clouds Tell the Tale!
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11. Clouds Tell the Tale! B M O C

12. Clouds Tell the Tale! High clouds 24 to 48 hrs before low
Sun Halo
Warm front w/i 24 hours
Cirrus & Mare’s Tails
Cirrostratus
Lenticular clouds
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14. Clouds Tell the Tale! Middle clouds Altostratus
Warm front is still coming – 12 to 24 hours away!
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15. Clouds Tell the Tale! Low clouds Nimbostratus and nimbocumulus
Warm front is here!
Rain or snow
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16. Clouds Tell the Tale! Cumulonimbus Sudden uplift – very unstable
Often accompanies cold front
Reaches to stratosphere – anvil shape
Irregular, direction changing winds
Rain, hail, sleet, lightning
Mammutus clouds are associated with severe winds and tornadoes.
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17. Cumulonimbus buildup from orographic lifting
Clouds Tell the Tale!
Cumulonimbus buildup from orographic lifting
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18. Clouds Tell the Tale! Cumulus = “Fair weather clouds”
Actually indicate high humidity and unstable air
Can develop into local storms.
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19. Cold front
What kind of front…?

20. Lightning Safety Stay alert for signs of thunderstorm development.
Bolt can go up to 10 miles!
Don’t stand near tall objects, hilltop or terrace edges.
Go down hillside
Stay away from vertical rock walls and caves.
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21. Lightning Safety Go to lowest point Remove metal objects.
Stay away from others.
Minimize ground contact.
Make yourself small & compact.
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22. Other Signs of Approaching Weather
Altimeter reading rises in a given place means low pressure system approaching.
Changing direction and strength of winds.
Low = shift from N, NE to SE; increasing speed.
Cold front = shift from SE to SW
High = shift from SW to N
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23. Estimating Wind Speed
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24. Other Considerations Weather patterns prior to trip Current forecast
Use altimeter
Monitor clouds and temperature changes.
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25. Where to Get Forecasts
NOAA National Weather Service
State and Province DOT
Weather Underground – worldwide Seattle.html
Local news or newspaper
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29. Fluid flow – gas & liquid

30. “Weather…
the mother of all avalanches. When Momma ain’t happy, ain’t nobody happy” Staying Alive in Avalanche Terrain Bruce Tremper Utah Avalanche Center, USFS