Download The Weather

The Weather
Chrissy Magee
Unpredictable
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Not predictable with absolute certainty
Can make reliable predictions
With experience your predictions
become more reliable
Weather Change
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White fleecy clouds,
with winds:
North to northeast
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No rain for 48 hours
Southeast to
southwest
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Rain within 24 hours
Rain or Snow
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Light gray to black
clouds, with winds:
Easterly to southerly
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North to northwest
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Heavy rain or snow
Light rain
West to north
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No rain
Uncertain Sky
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Fish scale clouds,
with winds
Northeast to
southwest
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Possible short, late
afternoon rain
Other winds
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No rain
Weather Information
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Local television news
Local newspaper
Weather channel radio
NOAA website (www.noaa.gov)
Air Pressure
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Cold air sinks
High-pressure
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Hot air rises
Low-pressure
Barometric (Air) Pressure
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Air pressure is measured in:
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Standard sea-level pressure
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Inches of mercury
Millibars
29.92 inches of mercury
1,000 millibars
Above 29.92 indicates high-pressure
Effects of Air Pressure
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Cold, sinking air
High-pressure
Cool/cold weather
Dry
Stable
Barometer Rising
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Hot, rising air
Low-pressure
Cloudy
Stormy
Unstable
Barometer Falling
Winds
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Cold air sinks and becomes heated,
moving towards low-pressure areas to
replace the air that is being lifted
Wind
Cold Front
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Region of warm air displaced by
colder air
Forces warm air to rise
Potential for heavy rains or snow
Line of thunderstorms
Precipitation is brief
Cumulonimbus and stratus clouds
Cumulonimbus Clouds
Stratus Clouds
Warm Front
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Warm air replaces colder air
Warm air rises above colder air
Light, steady rain or snow
Up to 2 day warning
Precipitation over extended period of
time
Cirrus clouds and stratus clouds
Cirrus Clouds
Local Winds
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Caused by the terrain
Use to determine campsite
At night mountains cool quicker than
valleys
Cold winds flow to the valleys
Set camp off the valley floor
Standard Lapse Rate
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With every 1,000 foot gain in altitude:
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Temperature decreases 3.5 degrees
Under clear and stable weather
As high as 5.5 degrees in unstable
To estimate temperatures
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Use 4 degree change
Standard Lapse Rate Example
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Obtain temperature at starting point
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Trailhead at 1,000 ft and 80 degrees
Calculate temperature at destination
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Camp at 4,500 ft and 66 degrees
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Varying between 69 and 61 degrees
Thunderstorms & Lightning
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Descend as quickly as possible
Take cover under lowest tree
Move away from any metal objects
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Backpack
Tent poles
Trekking poles
Keep spread out when in open terrain
Weather Where You Are Not
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Flash floods in the Desert
Swelling rivers in the Mountains
Other Weather Considerations
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Research average temperatures and
rainfall
Contact forest service rangers
Long-ranged forecasts are less reliable
Prepare for the worst
Remember
The only time weather conditions need to
be considered are:
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Any time you hike or backpack
Questions?