Clouds - Can they be used to hunt thermals?

[aeajr]

Can clouds be used to identify likely areas of thermal activity?

Can they be used to identify areas to avoid?

[Doc Data]

Some of my best rides have been right under a big fluffy cumulus cloud.... just don't get up into it!

Dave

[rcav8r2]

I usually rely on the cumulus (along the edges), but I've also had some good thermal flights on a crystal clear day (not a cloud from horzon to horizon) and right after a rain where there is total cloud cover. I quit trying to read the sky, and just watch the plane :)

[viti]

the support system for a cloud is a thermal,its your guess as the were to be,,i almost always look slightly up wind of the cloud as most thermals tilt backwards from wind drift etc

days of cloud streets remind me of seaweed in a river basin,they remain as columes but wander around alot

yes clouds are a great indicater of lift but sink is what tells me of lifts presence;) ;) ;)


viti

[Ollie]

When a cumulus cloud is building it is being fed by a thermal. When the cloud is decaying the thermal is history.

As Viti says, the thermal's origin is generally up wind of the cloud but the wind can change direction and strength with altitude, causing the shape of the thermal to wander some.

[davidleitch]

The other day I was at an electric comp and it was raining very slightly. Put the Organic up for some landing practice before the start of the comp at 9:00 am and lo and behold noticed pelicans circling like they were thermalling.... In the rain.... Anyhow went over to join them and could have stayed there for 15 minutes if I'd wanted to just 30-50 metres off the ground thermalling in the rain.

I'll never understand the weather. But birds do.

[aeajr]

Wow!

This is exciting stuff. Thanks guys!

[ASK]

The most obvious thermal indicator is a flat-bottomed cumulus cloud. The bottom is flat while the cloud is developing, and the bottom marks the dew point elevation.

The cloud bottom loses flatness and shows virga (rain that doesn't reach all the way to the ground) when the cloud is over-developed (is a source of precipitation). A cloud can also just disappate, and the bottom will not be flat at that time.

Though lift is generally under and inside the cloud, occasionally you will find lift alongside the cloud, usually on the windward side. This can be like ridge lift! For a big scale example, look for little lenticular clouds forming and disappating over the top of a cumulo-nimbus cloud. Not really for any sane (or legal) flying, full-scale or RC, but interesting none the less.

Another fun cloud/lift indicator (and very useful for RC flying) is the small, wispy, puffy "almost not there" kind of clouds. On some days these are the first indicators of a forming cumulus cloud, and on other days they don't progress any farther. Still, they usually indicate an area of the sky with thermal activity. You can see blue sky through the cloud, it is translucent, almost transparent.

Aradhana Singh Khalsa

[flyonline]

Don't forget too that clouds can be formed by the uplift of air not through thermals (for example orographic formation from air lifted up over mountains), for example thunderstorm heads are a good example, though for RC purposes there is lift present and that's all that matters really.

Steve

[ASK]

Orographic clouds include lenticular clouds and rotor clouds. They do not form heads, or thunderstorms. Here is a web page showing pictures of orographic clouds:

http://atschool.eduweb.co.uk/kingworc/departments/geography/nottingham/atmosphere/pages/orographic.html

In RC we aren't likely to use the lift that results in orographic cloud formation, as this lift is too high above the ground for us to still see our planes. However, if there is orographic cloud formation caused by a higher gradient of air rising over a mountain, we can fly in the lift of a lower gradient that is close to the slope, provided the lower gradient is moving in a effective direction relative to the slope.

The heads or anvils on thunderstorm-spawning clouds, more correctly known as cumulonimbus clouds, are formed by ground heating resulting in convective updrafts or "thermals", not by orographic effect. On another web page are some pictures of these:

http://atschool.eduweb.co.uk/kingworc/departments/geography/nottingham/atmosphere/pages/cumulonimbus.html

Here are pictures of developing cumulus clouds, with those flat bottoms that indicate that thermals are feeding them. If a cloud is round on the bottom, chances are that the lift has shut down.

http://atschool.eduweb.co.uk/kingworc/departments/geography/nottingham/atmosphere/pages/fairweathercumulus.html

[aeajr]

Thanks for the links and the insights.

[aeajr]

Good information here. Worth bringing it back.

What tips can you share about cloud watching?

[rogerflies]

Cumulus clouds are an indication of conditions favorable for thermals, but they usually form much higher than we usually fly our models.

This formula will give an idea of how the cloud base is:
Cloud Base Altitude = ((((temperature - dew point) / 4.5) * 1000) + measure station altitude)

For a typical day here we have 62-40/4.5 * 1000 + 250 = 5139. Can you see you plane well enough to fly it at that distance? I can't. Even at half that distance, I'd be afraid to take my eye off the plane for more than a blink.

I'd say the clouds over the field only tell us what's happening far upwind from where we're flying. You're just guessing about where the remnant of the rising air mass is with respect to the cloud.

I'd rather just watch the plane, and depend on my familiarity with the field or my experience in reading the terrain.

Roger

[Miami Mike]

I suspect a lot of glider fliers think their plane is under a cloud when in reality the cloud is much farther away than they think it is.

http://static.rcgroups.com/forums/attachments/1/5/7/8/9/a2428331-25-cloud.gif

[PizzaHunter]

))) nice))

[Hossfly72]

a lot of glider fliers think their plane is under a cloud when in reality the cloud is much farther away


I made the mistake of thinking the cloud was a lot farther away (ie- above) once. Lost a great Electra in a small, mean little cumulous cloud. The cloud monster ate it and spit it out in pieces. Made me think twice when I took my IFR lessons in a full scale plane!

[rogerflies]

I used to fly my 42% Spacewalker into low clouds. It was a very stable plane, but the turbulence in the cloud would often spit it out in a different direction in an unusual attitude.

Roger

[Libelle201B]

I suspect a lot of glider fliers think their plane is under a cloud when in reality the cloud is much farther away than they think it is.

http://static.rcgroups.com/forums/attachments/1/5/7/8/9/a2428331-25-cloud.gif Mike, RIGHT ON :)