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Weather and Risk Management
(For hiking, climbing, and generally enjoying
oneself in the mountains without being
completely miserable… or dangerous)
Sean Mackay
AMC SHP 2014
“The mountains will always be there, the trick is to make sure you are too.”
- Hervey Voge
“Good judgment comes from experience. Experience comes from bad judgment.”
- Evan Hardin
“Early up …. early down.” But why?
A few facts to make you think….
135 recorded fatalities in the Presidential Range of NH
•
•
•
•
Hypothermia ( 33 )
Drowning ( 6 )
Avalanche ( 13 )
Falling ice ( 6 )
•
•
•
•
Falls ( 43 )
Natural Causes ( 19 )
Causes unknown ( 3 )
Other ( 25 )
Of the deaths from hypothermia, 15 occurred during the summer (June-Sept)
Mt .Washington
• Average annual temperature = 27.2 ° F
• Average wind = 35 mph (gusts >100 mph occur several times each month)
• Annual precip. = 102 in of water equivalent (including 26ft of snow)
• Snows every month of the year (including August)
• Summit temperatures are typically 20-30 ° F colder than valley temps
• Summit winds are 20-100 mhp higher than valley winds
Meteorology 101
The earth
(in case you were confused already)
The sun:
Where it all begins
(not drawn to scale)
Energy dissipation and redistribution is the ultimate source of all weather
Complicated by…
• Earth’s rotation (Coriolis effect – imparts spin)
• Surface materials (differential heating /
differential drag)
• Ocean / Land
• Unique properties of H2O
• Topography
Meteorology 101
Just a few more basics…
• As air heats it expands and rises
• As air rises it cools
• As it cools to or beyond the dewpoint – it
produces clouds and/or precipitation
In the mountains, we experience “weather” associated
with both:
• Large scale / regional factors
• Pressure systems
• Fronts
• Local factors
• Topography
• Daily heating cycles
Meteorology 101
Large scale / regional factors
Low
High
Meteorology 101
Local topographic and orographic factors
Impacts on the hiker/climber
Learn to use basic concepts of meteorology and forecasting
to know when to avoid or expect/prepare for common
mountain weather hazards such as:
•
•
•
•
Lightning
Heavy precipitation
High winds
Sun exposure
• Excessive Heat
• Excessive Cold
• Poor visibility
Thunderstorms / Rain
• Associated with:
• Frontal boundaries (esp. cold fronts)
• Daily differential heating of the landscape under warm humid conditions
(typically in the afternoon)
• High mountains receive 5 times as many thunderstorms each year as coastal
environments
Thunderstorms / Rain
Lightening
• Origen: Collisions between water and ice in the cloud induce charge
separation; upper part of the cloud positively charged / lower negatively
charged. The negative charge at the base induces a positive charge on the
ground. Lightning occurs once the charge difference overcomes air resistance.
• Located several miles ahead of the storm in addition to directly beneath it.
• 200ppl/year die of lightning strikes in the US.
Annual lightning incidence map
Rain (up to ~125M gallons)
• Flooding
• Trail instability
Thunderstorms / Rain
If thunderstorms are forecast
• Do not hike or camp in narrow valleys / gullies
• Do not hike / climb in exposed areas (esp. above tree line)
• Watch small cumulus clouds for vertical growth – this is a sign for developing
thunderstorms
If you see a
thunderstorm…
• Get away from water
• Seek low ground
• Do not stand/sit
under a tree (good
luck with this in NE)
• Crotch, but do not
lay down
Gauge the movement of the storm by watching and listening….
• [Strike time – thunder (s) ] / 5 = distance to storm (miles).
• Do this several times to see which direction it is moving
Wind
Mountains both cause and alter winds considerably
• Valley winds / gravity winds
• I.E. Camping right at the base of the valley
wall can be a bit breezy
• Gap winds
• Occur at breaks in the topography (passes,
between two peaks, etc.)
• Wind speeds can double
• Foehn winds
• Cool air descends and adiabatically warms
- acceleration and rapid warming
• Katabatic winds
• Elevation exposure to upper atmosphere winds
wind
Low
Moderate
High
Use topography / landscape to
your advantage if possible
• Tree line
• Boulders, etc.
Wind Chill
Non-linear
decrease in
“apparent”
temp.
What about being too hot..?
Heat Index
• How hot a combination of temperature and humidity feels
• Based on the body’s capability to utilize evaporative cooling
Mountain weather forecasting
What if forecasts are either limited or unavailable?
Use valley temperature to estimate
temps at elevation:
• Temperature decreases 3.5 to 5.5 ° F
for every 1000ft of elevation
Learn how to read the wind, clouds, and air pressure changes….
Mountain weather forecasting
Cold front associated
Halo
Altocumulus
Cumulonimbus
Stratocumulus
24-48 hr.
before
precipitation
Potential for
thunderstorms/
showers
Isolated but
heavy rain,
lightning,
wind
Often follows
cold front,
possible light
showers
Warm front associated
No worries –
have fun!!
Cirrostratus
Nimbostratus
Widespread
steady
precipitation
Other
High winds!!
Lenticular
Mountain weather forecasting
Mountain weather forecasting
Wind direction / speed
(Northern Hemisphere)
• Shift E or SE  low front
approaching / precip.
Possible
• Shift SW or NW  cold
front passage / drying
likely
• Increasing from SW to
W High pressure
approaching / gusty
winds decreasing
Pressure changes over ~3 hrs. (altimeter/barometer?)
• Increasing pressure/decreasing ‘altitude’
Fair weather ahead – go play!!!!
• Decreasing pressure / increasing ‘altitude’
 0.06 inch or more…… high winds (definitely) / precipitation
(possibly) on the way
Risk Management
Risk Management
Objective Hazards
(environment)
x
Subjective Hazards
(you!)
=
Accident
Potential
Environment (objective) hazards
Terrain
- rocky trail, exposed ledges, etc., falling rock, falling ice
Weather
- cold, wind, precip, etc.
Other
- Beestings, poison ivy, overexposure to the sun, darkness
Equipment
- broken stove, improper clothing, boots not broken in, etc.
Risk Management
Objective Hazards
(environment)
x
Subjective Hazards
(you!)
=
Accident
Potential
You (subjective) hazards
Poor Planning
Weather, route, terrain knowledge, equipment
Individuals
lack of awareness, insufficient skills, poor conditioning,
fear / anxiety, careless attitude, ‘summit fever’, not
maintaining hydration/eating
Group
Lack of leadership, splintering into sub-groups,
scapegoating, poor communication, interpersonal friction
“New Guy syndrome”
“Old Guy Syndrome”
Risk Management
Risk rating = likelihood x consequence severity
Thank you
Happy hiking!
Sean Mackay
AMC SHP 2014