Wow cloudbase is high...

A friend and I were driving back from the airport the other day. He
remarked, "Wow, cloudbase is high today. I bet it's at least 6,000
feet."

He and I began musing - exactly how do we know that cloudbase is high?
What visual cues tell us that the Cu are high (or low). We're not
talking Temperature Dewpoint spread here - strictly visual.

Any ideas?

And yes, flying season is obviously drawing to a close :-)

Erik Mann
LS8-18 P3

I think it has to do with how many clouds you can see (more clouds,
higher bases), and the detail with which you can see the edges (less and
less as these eyes grow older).

I've found that my eyeballs are pretty darn accurate. Down here in the
southern US flying the vibrator, I was always interested in knowing how
high I had to climb to get above those pesky thermals. I could easily
tell the difference between 2500, 4000, 6000, and 8000. But I think
some of it has to do with just knowing how the sky generally looks with
those bases.

Big Sky musings; When I was driving out west to the Montana contests of
the 90s, I was trying to figure out what "Big Sky Country" meant. Is
the sky bigger there than in New Jersey? Driving the Madison River
valley, you definitely get a 'big sky' feeling, but what causes it?

I concluded it was the fact that you could see the peaks of mountains
where the mountain bases were beyond your horizon. In other words, you
could see objects and the implied space between you and that object,
that was beyond your normal horizon - Big Sky!

Keep on musing Papa3

Bill Watson
Foureyes, aka Mauledriver, '77

Papa3 wrote:
A friend and I were driving back from the airport the other day. He
remarked, "Wow, cloudbase is high today. I bet it's at least 6,000
feet."

He and I began musing - exactly how do we know that cloudbase is high?
What visual cues tell us that the Cu are high (or low). We're not
talking Temperature Dewpoint spread here - strictly visual.

Any ideas?

And yes, flying season is obviously drawing to a close :-)

Erik Mann
LS8-18 P3

Papa3 wrote:
A friend and I were driving back from the airport the other day. He
remarked, "Wow, cloudbase is high today. I bet it's at least 6,000
feet."

He and I began musing - exactly how do we know that cloudbase is high?
What visual cues tell us that the Cu are high (or low). We're not
talking Temperature Dewpoint spread here - strictly visual.

Any ideas?

I compare to nearby hills and mountains.

Of course, that doesn't work so well in the flatlands.

Jeremy

Bill,

You are talking about the seemingly vast "amount" of sky visible when
you get that 'big sky' feeling. I believe it's a combination of good
visibility (25 mi), lots of clouds in view and yes, high cloud bases.
There is a correlation between all three, you can only see all these
clouds in a clear sky and with high cloud bases.
Here on the edge of the great midwest in Chicago I have often gotten a
tease of that Montana scene (mostly when driving out to Iowa or through
Minnesota) when I would just have that feeling of wow, that's a big sky
today and I bet the cloud bases are at least 6-7k. Bill is also right
that we do develop a calibrated eye sight that is pretty accurate in
judging heights - from the ground as well as from the air.

Having worked my ways for many hours through the miserable haze of the
North Carolina summer skies I must admit it is easy to prefer the more
western longitudes. On one flight with Rob Ware when he still lived in
Apex NC, (pre GPS) I urged him to look at his compass after leaving a
thermal. We were happily cruising back to where we had come from. The
haze was so thick you could only see a 2-3 mile circle of nondestinct
ground features like looking into an upside down funnel.

Herb Kilian, J7

Maule Driver wrote:
I think it has to do with how many clouds you can see (more clouds,
higher bases), and the detail with which you can see the edges (less and
less as these eyes grow older).

I've found that my eyeballs are pretty darn accurate. Down here in the
southern US flying the vibrator, I was always interested in knowing how
high I had to climb to get above those pesky thermals. I could easily
tell the difference between 2500, 4000, 6000, and 8000. But I think
some of it has to do with just knowing how the sky generally looks with
those bases.

Big Sky musings; When I was driving out west to the Montana contests of
the 90s, I was trying to figure out what "Big Sky Country" meant. Is
the sky bigger there than in New Jersey? Driving the Madison River
valley, you definitely get a 'big sky' feeling, but what causes it?

I concluded it was the fact that you could see the peaks of mountains
where the mountain bases were beyond your horizon. In other words, you
could see objects and the implied space between you and that object,
that was beyond your normal horizon - Big Sky!

Keep on musing Papa3

Bill Watson
Foureyes, aka Mauledriver, '77

Papa3 wrote:
A friend and I were driving back from the airport the other day. He
remarked, "Wow, cloudbase is high today. I bet it's at least 6,000
feet."

He and I began musing - exactly how do we know that cloudbase is high?
What visual cues tell us that the Cu are high (or low). We're not
talking Temperature Dewpoint spread here - strictly visual.

Any ideas?

And yes, flying season is obviously drawing to a close :-)

Erik Mann
LS8-18 P3

Born and raised in Southern California, Learned to fly in South Texas, and
living in Georgia the past 34 years, I was thrilled to go to Moriarty this
summer and fly. The "Big Sky" effect, to me, includes not having the view
blocked by 75' tall pine trees everywhere so you can see the horizon from
the ground. Being able to clearly see features a long way away is the other
part. High bases help a lot, too. From the air-distinct cloud shadows in the
distance add to the effect. In Georgia, the haze and irregular patches of
"Piney Woods" make you wonder--"is that a cloud shadow or woods 3 miles
away?"

Here, you can easily see individual water droplets in the clouds
sometimes--you know the bases are low! Otherwise, detail in the clouds is
the clue to height-but it can fool you. Size doesn't help much.

If winter comes, can spring be far behind?

--
Hartley Falbaum
DG800B "KF" USA


"Herb" wrote in message
ups.com...
Bill,

You are talking about the seemingly vast "amount" of sky visible when
you get that 'big sky' feeling. I believe it's a combination of good
visibility (25 mi), lots of clouds in view and yes, high cloud bases.
There is a correlation between all three, you can only see all these
clouds in a clear sky and with high cloud bases.
Here on the edge of the great midwest in Chicago I have often gotten a
tease of that Montana scene (mostly when driving out to Iowa or through
Minnesota) when I would just have that feeling of wow, that's a big sky
today and I bet the cloud bases are at least 6-7k. Bill is also right
that we do develop a calibrated eye sight that is pretty accurate in
judging heights - from the ground as well as from the air.

Having worked my ways for many hours through the miserable haze of the
North Carolina summer skies I must admit it is easy to prefer the more
western longitudes. On one flight with Rob Ware when he still lived in
Apex NC, (pre GPS) I urged him to look at his compass after leaving a
thermal. We were happily cruising back to where we had come from. The
haze was so thick you could only see a 2-3 mile circle of nondestinct
ground features like looking into an upside down funnel.

Herb Kilian, J7

Maule Driver wrote:
I think it has to do with how many clouds you can see (more clouds,
higher bases), and the detail with which you can see the edges (less and
less as these eyes grow older).

I've found that my eyeballs are pretty darn accurate. Down here in the
southern US flying the vibrator, I was always interested in knowing how
high I had to climb to get above those pesky thermals. I could easily
tell the difference between 2500, 4000, 6000, and 8000. But I think
some of it has to do with just knowing how the sky generally looks with
those bases.

Big Sky musings; When I was driving out west to the Montana contests of
the 90s, I was trying to figure out what "Big Sky Country" meant. Is
the sky bigger there than in New Jersey? Driving the Madison River
valley, you definitely get a 'big sky' feeling, but what causes it?

I concluded it was the fact that you could see the peaks of mountains
where the mountain bases were beyond your horizon. In other words, you
could see objects and the implied space between you and that object,
that was beyond your normal horizon - Big Sky!

Keep on musing Papa3

Bill Watson
Foureyes, aka Mauledriver, '77

Papa3 wrote:
A friend and I were driving back from the airport the other day. He
remarked, "Wow, cloudbase is high today. I bet it's at least 6,000
feet."

He and I began musing - exactly how do we know that cloudbase is high?
What visual cues tell us that the Cu are high (or low). We're not
talking Temperature Dewpoint spread here - strictly visual.

Any ideas?

And yes, flying season is obviously drawing to a close :-)

Erik Mann
LS8-18 P3

I forget where I read this... but it seems to apply. An author pointed out
that it is very hard to estimate the size (therefore the distance) of
typical clouds because their borders are fractal. (A fractal is a line or
shape that has a fractional dimension. Wikipedia defines it as 'a shape that
is recursively constructed or self-similar, that is, a shape that appears
similar at all scales of magnification and is therefore often referred to as
"infinitely complex".') The little swirls of the cloud are shaped exactly
like the big parts. That means that you can't tell objectively whether the
curlicues that make up the cloud are "small and close" or "big and far".
When you get closer to a cloud, the details look just like the broader view.

So unless you have an object near the cloud to compare it to, such as a
mountain or an aircraft, it's tough to objectively estimate the cloud size
and therefore its height. Watch a typical Cu, estimate how big it is... then
be amazed at how big it REALLY is (and therefore how high or far it must be)
when an airliner flies in front of it. If there are clouds near the
mountains, sometimes you can estimate their size and altitude and then
assume the rest of the visible clouds are at a similar altitude.

A cloud's motion can be another clue... but only if you know something about
the wind. Is that cloud "big and far and moving fast" or "small and close
and moving slow" ?

The white-to-gray gradient can also be a clue if you can see the side of a
cloud.

Not sure if this helps... but it explains why it's hard!

Roger


"Papa3" wrote in message
ups.com...
A friend and I were driving back from the airport the other day. He
remarked, "Wow, cloudbase is high today. I bet it's at least 6,000
feet."

He and I began musing - exactly how do we know that cloudbase is high?
What visual cues tell us that the Cu are high (or low). We're not
talking Temperature Dewpoint spread here - strictly visual.

Any ideas?

And yes, flying season is obviously drawing to a close :-)

Erik Mann
LS8-18 P3

....back in Poland, all of us glider pilots allowed to fly had to go
through a very rigoreus medical examination. The Goverment could not
risk the investment of training the glider pilots without having the
option of eventally using them in Air Force. One of the medical test
was a stereoscopic distance evaluation. You would have to look at two
very small wooden sticks from a distance of five yards and the future
of your flying cariere was to be determinated by the simple guess...
which of them was closer?. No reference point was available. Without
going into details, I think the idea behind this test was to eliminate
the prospect pilots who couldn't, by natural instincts determinate the
distance to the object. Was there any merrit to such a test, I don't
know. All I know is that if we were not be able to determinate the
distance, we would have to be given by God only one aye.
rk


Roger Worden wrote:
I forget where I read this... but it seems to apply. An author pointed out
that it is very hard to estimate the size (therefore the distance) of
typical clouds because their borders are fractal. (A fractal is a line or
shape that has a fractional dimension. Wikipedia defines it as 'a shape that
is recursively constructed or self-similar, that is, a shape that appears
similar at all scales of magnification and is therefore often referred to as
"infinitely complex".') The little swirls of the cloud are shaped exactly
like the big parts. That means that you can't tell objectively whether the
curlicues that make up the cloud are "small and close" or "big and far".
When you get closer to a cloud, the details look just like the broader view.

So unless you have an object near the cloud to compare it to, such as a
mountain or an aircraft, it's tough to objectively estimate the cloud size
and therefore its height. Watch a typical Cu, estimate how big it is... then
be amazed at how big it REALLY is (and therefore how high or far it must be)
when an airliner flies in front of it. If there are clouds near the
mountains, sometimes you can estimate their size and altitude and then
assume the rest of the visible clouds are at a similar altitude.

A cloud's motion can be another clue... but only if you know something about
the wind. Is that cloud "big and far and moving fast" or "small and close
and moving slow" ?

The white-to-gray gradient can also be a clue if you can see the side of a
cloud.

Not sure if this helps... but it explains why it's hard!

Roger


"Papa3" wrote in message
ups.com...
A friend and I were driving back from the airport the other day. He
remarked, "Wow, cloudbase is high today. I bet it's at least 6,000
feet."

He and I began musing - exactly how do we know that cloudbase is high?
What visual cues tell us that the Cu are high (or low). We're not
talking Temperature Dewpoint spread here - strictly visual.

Any ideas?

And yes, flying season is obviously drawing to a close :-)

Erik Mann
LS8-18 P3

Roger Worden wrote:
I forget where I read this... but it seems to apply. An author pointed out
that it is very hard to estimate the size (therefore the distance) of
typical clouds because their borders are fractal. (A fractal is a line or
shape that has a fractional dimension. Wikipedia defines it as 'a shape that
is recursively constructed or self-similar, that is, a shape that appears
similar at all scales of magnification and is therefore often referred to as
"infinitely complex".') The little swirls of the cloud are shaped exactly
like the big parts. That means that you can't tell objectively whether the
curlicues that make up the cloud are "small and close" or "big and far".
When you get closer to a cloud, the details look just like the broader view.

So unless you have an object near the cloud to compare it to, such as a
mountain or an aircraft, it's tough to objectively estimate the cloud size
and therefore its height. Watch a typical Cu, estimate how big it is... then
be amazed at how big it REALLY is (and therefore how high or far it must be)
when an airliner flies in front of it. If there are clouds near the
mountains, sometimes you can estimate their size and altitude and then
assume the rest of the visible clouds are at a similar altitude.

A cloud's motion can be another clue... but only if you know something about
the wind. Is that cloud "big and far and moving fast" or "small and close
and moving slow" ?

The white-to-gray gradient can also be a clue if you can see the side of a
cloud.

Not sure if this helps... but it explains why it's hard!

Roger


Interesting. Our premise was actually slightly different; although it
is "hard", we seem to be able to do a remarkably good job of estimating
cloud base visually even without reference objects such as hills,
airliners, etc. That said, I tried this yesterday (a day with
extensive OD here in NJ) and failed pretty miserably. I was guessing
4,000 feet or so, until a 777 came by well below cloudbase. Where I
am, that means about 6,000 minumum...

I'm still of the opinion that people can generally guesstimate +/-
1,000 feet AGL at least in the eastern US where bases typically only
vary from 3,000 to 8,000 AGL. I still can't explain why.

P3

For what it's worth, stereoscopic depth perception (that is, depth
perception judgments derived from the parallax created due to intrapupillary
distance, or how far apart your eyes are) is essentially useless beyond a
few feet. Beyond that we all learn to estimate what's closer to us based on
other, non-stereoscopic cues.

Respectfully,
Bullwinkle


On 10/25/06 12:55 AM, in article
,
" wrote:

...back in Poland, all of us glider pilots allowed to fly had to go
through a very rigoreus medical examination. The Goverment could not
risk the investment of training the glider pilots without having the
option of eventally using them in Air Force. One of the medical test
was a stereoscopic distance evaluation. You would have to look at two
very small wooden sticks from a distance of five yards and the future
of your flying cariere was to be determinated by the simple guess...
which of them was closer?. No reference point was available. Without
going into details, I think the idea behind this test was to eliminate
the prospect pilots who couldn't, by natural instincts determinate the
distance to the object. Was there any merrit to such a test, I don't
know. All I know is that if we were not be able to determinate the
distance, we would have to be given by God only one aye.
rk


Roger Worden wrote:
I forget where I read this... but it seems to apply. An author pointed out
that it is very hard to estimate the size (therefore the distance) of
typical clouds because their borders are fractal. (A fractal is a line or
shape that has a fractional dimension. Wikipedia defines it as 'a shape that
is recursively constructed or self-similar, that is, a shape that appears
similar at all scales of magnification and is therefore often referred to as
"infinitely complex".') The little swirls of the cloud are shaped exactly
like the big parts. That means that you can't tell objectively whether the
curlicues that make up the cloud are "small and close" or "big and far".
When you get closer to a cloud, the details look just like the broader view.

So unless you have an object near the cloud to compare it to, such as a
mountain or an aircraft, it's tough to objectively estimate the cloud size
and therefore its height. Watch a typical Cu, estimate how big it is... then
be amazed at how big it REALLY is (and therefore how high or far it must be)
when an airliner flies in front of it. If there are clouds near the
mountains, sometimes you can estimate their size and altitude and then
assume the rest of the visible clouds are at a similar altitude.

A cloud's motion can be another clue... but only if you know something about
the wind. Is that cloud "big and far and moving fast" or "small and close
and moving slow" ?

The white-to-gray gradient can also be a clue if you can see the side of a
cloud.

Not sure if this helps... but it explains why it's hard!

Roger


"Papa3" wrote in message
ups.com...
A friend and I were driving back from the airport the other day. He
remarked, "Wow, cloudbase is high today. I bet it's at least 6,000
feet."

He and I began musing - exactly how do we know that cloudbase is high?
What visual cues tell us that the Cu are high (or low). We're not
talking Temperature Dewpoint spread here - strictly visual.

Any ideas?

And yes, flying season is obviously drawing to a close :-)

Erik Mann
LS8-18 P3

"Papa3" wrote in message
ups.com...
A friend and I were driving back from the airport the other day. He
remarked, "Wow, cloudbase is high today. I bet it's at least 6,000
feet."

He and I began musing - exactly how do we know that cloudbase is high?
What visual cues tell us that the Cu are high (or low). We're not
talking Temperature Dewpoint spread here - strictly visual.

Any ideas?

And yes, flying season is obviously drawing to a close :-)

Erik Mann
LS8-18 P3

When you're moving, the apparent speed at which the clouds "move" relative
to you can help give you a clue.

Tim Ward