Weather/Lightning Awareness
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Weather / Lightning Awareness
Educational Goals
To gain a general understanding of how to identify different types of weather patterns and basic tools for predicting the weather. Specifically, what a warm front, cold front, and occluded front portend; how to identify specific types of clouds and understand what weather patterns they correlate to; and how to make assumptions based upon these reading devices.
Key Points
Major weather systems are caused by the interaction of air masses. Weather moves from west to east in the continental US. Mountains heat up more quickly than valleys because they are closer to the sun; conversely, they also cool down more quickly than valleys. Land warms up more quickly than the ocean and also loses heat more quickly. Low-pressure systems occurs when the wind direction goes against the path of the sun; it moves counterclockwise from west to east. This typically heralds bad weather. A high-pressure system occurs when the wind direction goes with the path of the sun; it moves clockwise from east to west.
Clouds
Clouds are formed when the relative humidity of the air reaches 100%. Colder air holds less water and warmer air holds more water. As air rises, it cools and water vapor in the air condenses to form clouds. There are two main types of clouds: cumulus and stratus. Cumulus clouds are puffy and are formed when small areas of rising air cools to saturation point. Stratus clouds are in layers or sheets and are formed when a large layer of air is cooled to the saturation point. Their altitude classifies clouds. Cirro is the prefix which designates high clouds, alto is the prefix which designates middle clouds, and nimbo is the prefix which means rain. The type of precipitation from a cloud is determined by temperature.
Weather Fronts
Fronts are created at the boundaries of different air masses. Wet air is lighter than dry air; therefore low-pressure systems foretell rainy weather while high-pressure systems foretell fair weather. If birds are not flying or are flying low this may mean that there is a low pressure system and rain is on the way; a low pressure system means that the air is less dense which makes it difficult for birds to fly. Similarly, if smoke curls downward there may be a nearing low-pressure system. A frontal boundary is created when air masses of two different temperatures collide. A cold front is created when a cold air mass pushes beneath a warmer air mass. A cold front moves relatively quickly. Cold air sinks because it is dense and heavy Due to the shape and velocity of cold fronts there is a good chance of precipitation as high cumulus clouds lower to form layers of stratocumulus.
A warm front is created when a warm air mass comes in over a cooler air mass. A warm front is slow moving. A warm front is indicated by high wispy cirrus clouds, lowering to stratus clouds over a several day period. Due to the slow and expansive nature of warm fronts weather patterns can last for several days.
An occluded front occurs when faster moving air catches up with slower moving air and buoys it up. The result is a fast succession of forms of precipitation, nimbostratus give way to cumulonimbus. Thunderstorms are the result of large cumulonimbus clouds forming from rising, unstable, well-saturated, warm air. When the air rises it creates an up draft; it cools as it ascends. This becomes a cycle which eventually releases large, violent amounts of precipitation.
Lightning is the result of opposite charged regions within mature cumulonimbus clouds. The charge is created by the cycling air. Positive charges accumulate at the top of the cloud and negative at the bottom. Like charges repel, therefore the electrons in the ground are “pushed” by the cloud’s charge. Lightening occurs during the natural attraction of opposite forces: when the electricity which is in the cloud leaps either to another cloud (this is called sheet lightening) or to the ground (which is called stepped leader). 80% of lightening strikes are between clouds; 20% of lightening zigzags down towards the ground.
Lightning
Lightning almost always occurs with thunderstorms and is the greatest weather threat to outdoor travelers in the U.S., according to the National Weather Service. It is caused be the strong up and down drafts found inside cumulonimbus clouds. These violent air current create an intense electrical field which polarizes the cloud. The top of the cloud becomes positively charged, while the bottom gains a strong negative charge, along with some small positive charges. Normally the ground has a negative charge, but as the cumulonimbus passes overhead, it induces a positive charge in the ground. When the positive ground charges become strong enough they travel up tall objects to seek their opposites in the clouds. The strike occurs when the air between the cloud and the ground can no longer insulate the charges from each other.
Saint Elmo’s fire (a bluish glow about an object), humming metal objects (e.g. Climbing gear), hair standing on end, the burnt odor of ozone, or a crackling sound on wet rocks are all signs that an area is in imminent danger of a lightning strike. Another indicator is the distance the storm is away from you. To determine this, count the seconds between a lightning flash and its thunder. (Light travels 186,000 miles per second. Sound travels a fifth a mile per second.) Divide the elapsed seconds by five. This will tell you how far away the lightning is in miles. Simultaneous lightning and thunder indicates the storm is directly overhead.
If you expect lightning, avoid technical terrain during high-risk times. Seek shelter in a protected area. Stay away from solitary tall objects (ridges, trees, and summits) that may attract a strike. Lightning kills people two ways: with direct hits and with ground currents. Direct hits are usually lethal. Ground currents emanate from the lightning strikes and travel along the ground, shocking their victims until the currents dissipate.
Body position can reduce the hazard of ground currents. If you are caught out in the open assume the lightning safety position –squat as low as possible. Nonconducting insulation can also help shield you from ground currents. Crouch on an ensolite pad, on your pack (frame side down), or on a coiled rope. Make sure party members are spread at least 30 feet apart. Do not lean against rocks or bridge small gaps or depressions ground currents take the shortest path, which may be your body if you provide the bridge between two points. Place metallic equipment away from you. Untie from ropes if possible. Avoid standing in water, which is another good conductor.
Teaching Considerations
Weather is everywhere! Consider the site for your lesson. The out-of-doors is accessible and engaging. Remember that clouds, geography, and wind are the most easily observed/noted in open spaces. In other words, don’t do a weather lesson in a densely wooded area. The more you know about weather the more likely your students are to respond positively. Get creative with weather, try including ancient peoples’ interpretations and customs relating to weather. Get practical with weather, it affects all of us, not only our daily plans but our moods. It makes the most sense to learn about weather over extended period of time. When you are learning about lightening it is crucial that you are not out in the open observing it! As a leader/instructor it’s your job to know that every year about 100 people are killed by lightening in the United States alone and over 1,000 world wide. Lightening can strike anywhere, 15 miles or more from a cloud. Its more important for students to know what to do when lightening is around than what type of lightening it is.
