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P2 Course - Module 5b - Clouds

Most of the time our best indicator for the status of the atmosphere is the presence or absence of clouds. There are many different types of clouds and this information is by no means complete. For the purpose of serving you best as a beginner paragliding pilot, there are some cloud types that you will see often – some are good signs for flying, others are not.

Cumulus

These clouds are a thermal pilot’s best friend – they almost always are accompanied by consistent lifting air, or as you will hear many times in your piloting career: a thermal.

Cumulus clouds technically are formed when a parcel of air laden with moisture, rises to the dew point. At the dew point, a cumulus cloud forms. If the thermal doesn’t rise as high as the dew point, no cloud forms. In essence, cumulus clouds mark the tops of thermals. Small cumulus clouds that look like cotton balls, can be very friendly and indicate good lift.

When the lift becomes stronger, the cloud may start to become taller than it is wide. These “cumulus congestus” clouds should be avoided at all costs. They resemble Marge Simpson’s hairdo. The lift under them may be very strong and you may not be able to escape. Not only is flying in clouds illegal, but they may also be very turbulent inside, and you have no horizon reference. You should be aware of the risks of flying in thermic conditions before launching into a sky of cumulus clouds. Mountains can help generate cumulus clouds by providing the source for rising air or thermals. This is why mountain weather tends to be less stable than flatland weather. If cumulus clouds are the only clouds in the sky by mid- to late afternoon, there probably isn’t much risk of thunderstorms developing. When these clouds become taller than they are wide, they become cumulus congestus and the chance of thunderstorms rises greatly.

Cumulus Congestus

Watch these clouds carefully. They are the first stage of thunderstorm growth and can become dangerous in a matter of minutes. Thunderstorms are the most serious type of local weather. Since the sun’s heat energy is a major factor in thunderstorm generation, thunderstorms typically occur in the spring and summer. Winter sunshine simply doesn’t deliver enough warmth. For thunderstorms to develop, the air needs to be warm, moist, and unstable—typical spring and summer conditions. These white or gray clouds with flat bases are taller than they are wide. The earlier in the day that they appear, the greater the probability that they will develop into thunderstorms. Their growth can usually be seen with the naked eye, and the faster they grow the more likely they are to produce a thunderstorm. The air rising underneath them can be very strong and the risk of “cloud suck” rises.

Since the weather in the United States generally moves west to east, cumulus congestus clouds to your west are much more dangerous than cumulous congestus clouds to your east. This west to east airflow doesn’t always hold true – especially in mountain ranges – so try to  determine if the clouds are headed toward you so you can make a good decision on which way to fly to get as far away as possible.

Cumulonimbus

As the rising tops of a thunderstorm surge into the Jet Stream, the strong upper level winds drive the top of the cloud downwind forming the “anvil” shape of a cumulonimbus. At this stage a thunderstorm is capable of generating violent and unpredictable conditions including rain, hail, sleet, snow, lightning, flooding, gust fronts etc. If you see cumulonimbus clouds in the sky it is probably a good day to do something other than flying.

Sometimes cumulonimbus clouds can be obscured by general overcast conditions or haze or other mountain effects – in that case it is critical for the pilots to be aware of the overall weather conditions of the day and if significant vertical development is possible or forecasted.

Lenticular

These clouds are smooth contact-lens shaped clouds. They are formed when very fast moving air is forced over a mountain or another air mass and typically form over mountain peaks or over the top of overgrown cumulus or cumulonimbus clouds. These are only formed when the winds aloft are very high and are usually a good indicator that the day may be too windy to fly, or may become too windy later in the day – especially in the mountains.

Gust Fronts

Thunderstorms can throw out intense gust fronts with winds that exceed 40 Mph so if there is a possibility of thunderstorms in your area it is best not to launch. These “gust fronts” are caused by cool air flowing out from the base of a thunderstorm, and sometimes form a long, horizontal, arc-shaped cloud just in front of the thunderstorm. The arrival of the gust front is often the best sign that a thunderstorm is arriving. Rain and lightning usually follow the gust front. If conditions are favorable for thunderstorm development, the gust front of one  thunderstorm can actually act as a “cold wedge” and push up the warmer air in front of it, leading to the birth of yet another thunderhead. ​

It may be difficult to identify thunderstorms in unstable skies. Two common indicators are:

 

Cloud Indications of a Front

Most fronts are preceded by a variety of higher altitude cloud types. Those types of clouds can be used by pilots to determine what the macro level weather pattern may suggest for the coming hours or days.

Mare’s tails:

Thin, white to light-gray streamer clouds high in the sky (cirrus clouds). Iso- lated mare’s tails aren’t a strong portent of bad weather to come, but dense and wide- spread mare’s tails can indicate the approach of a front from as far as 24 to 48 hours away.

Cirrostratus:

Uniform, featureless, white or gray clouds at high altitude covering most or all of the sky. These clouds usually mean that a significant amount of moisture is moving into the area. They aren’t spectacular, but they are important. Monitor the sky for a change in the weather.

Halos:

Rings of light around the sun or moon caused by light refracted through high altitude ice crystals. The old adage about halos preceding storms by 24 to 48 hours generally holds true in the wetter regions of the United States, but sometimes in drier climates halos can pass with no ill weather side effects.

Altostratus:

Gray, water-droplet clouds at medium altitude. A solid coverage of these gunmetal-gray clouds usually precedes major weather systems by less than ten hours.

Nimbostratus:

A layer of dark clouds with noticeable blurring below the cloud bases. These clouds bring rain or snow, and in the warmer months can develop into thunder- storms. Typically associated with the arrival of a front. The weather is likely to stay bad for 24 hours.

Summary of Clouds

This information is by no means all there is to know about clouds and how they can help us as pilots. There are many other common types of clouds that are good to familiarize yourself with simply to help enhance your understanding of the sky and the signs that any cloud formation might be providing. Stratus and Cirrus clouds are perfect examples. There are many varieties of these clouds depending on how high in the atmosphere they are forming, but they help paint a picture of the larger weather patterns that may help increase your forecasting abilities. We all know how important it is to check the forecast on a regular basis, but ultimately you never know unless you go.

 
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