Last September I flew from Santa Rosa to Renton and photographed an
interesting cloud which reminded me of what a jet contrail might look
like if somebody flew an arc over a river. Pictures posted here:

http://www.flying20club.org/streamer.html

Anybody seen anything like this before? Any idea what might make it?

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

"Jose" > wrote in message
...
> Last September I flew from Santa Rosa to Renton and photographed an
> interesting cloud which reminded me of what a jet contrail might look like
> if somebody flew an arc over a river. Pictures posted here:
>
> http://www.flying20club.org/streamer.html
>
> Anybody seen anything like this before? Any idea what might make it?

Could you clarify the question?

I can't tell from looking at the photos what cloud it is you're asking
about. There are cirrus, contrails, low-level stratus, and even some
cumulus-wannabe clouds in there. If I had to guess, I'd suspect you're
asking about the low-level cloud that is skinny through the right two-thirds
of the photo, expanding into a larger formation to the left one-third. But
you also say the cloud reminds you "of what a jet contrail might look like",
and that cloud doesn't look anything like a contrail to me (and of course
isn't where one would see a contrail).

Maybe you could provide a photo with the cloud in question highlighted
somehow (outlined, or maybe use Photoshop or GIMP to darken the areas
outside your interest).

Pete

> If I had to guess, I'd suspect you're
> asking about the low-level cloud that is skinny through the right two-thirds
> of the photo, expanding into a larger formation to the left one-third.

Yep, that's the one.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

Winds aloft and a little venturi effect.



"zatatime" > wrote in message
...
| On Sat, 4 Nov 2006 18:17:41 -0800, "Peter Duniho"
| > wrote:
|
| >Maybe you could provide a photo with the cloud in
question highlighted
| >somehow (outlined, or maybe use Photoshop or GIMP to
darken the areas
| >outside your interest).
|
| Look for the black arrow with the words "This Cloud" over
it.
|
| z

On Sat, 4 Nov 2006 18:17:41 -0800, "Peter Duniho"
> wrote:

>Maybe you could provide a photo with the cloud in question highlighted
>somehow (outlined, or maybe use Photoshop or GIMP to darken the areas
>outside your interest).

Look for the black arrow with the words "This Cloud" over it.

z

> Winds aloft and a little venturi effect.

So the winds essentially blow down the canyon, the pressure drops
because they are moving faster through the canyon than elsewhere, the
drop in pressure causes the moisture to condense?

Interesting that the affected area is so thin.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

Fly long enough and you'll see a river covered with fog and
you can see the fog flowing down stream with ripples just
like it was the water. My guess in the picture you posted,
there was a front with wet and dry air, moderate to strong
winds and terrain effects.
Lenticular clouds, roll clouds, wall clouds, all are
effected by or caused by the terrain.




"Jose" > wrote in message
m...
|> Winds aloft and a little venturi effect.
|
| So the winds essentially blow down the canyon, the
pressure drops
| because they are moving faster through the canyon than
elsewhere, the
| drop in pressure causes the moisture to condense?
|
| Interesting that the affected area is so thin.
|
| Jose
| --
| "Never trust anything that can think for itself, if you
can't see where
| it keeps its brain." (chapter 10 of book 3 - Harry
Potter).
| for Email, make the obvious change in the address.

> Fly long enough and you'll see a river covered with fog and
> you can see the fog flowing down stream with ripples just
> like it was the water. My guess in the picture you posted,
> there was a front with wet and dry air, moderate to strong
> winds and terrain effects.
> Lenticular clouds, roll clouds, wall clouds, all are
> effected by or caused by the terrain.

I've seen that, but this wasn't that. There was a river down there, but
there was no front that I recall, and the winds were light (eight knots
from the south - a tailwind). This cloud was maybe a thousand feet
above the valley, and curved smoothly around.

It looked to me as if it were the path of the wind coming down the
valley in the manner of a stream.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

"zatatime" > wrote in message
...
> Look for the black arrow with the words "This Cloud" over it.

Uh...thanks. That wasn't there when I looked at the picture. Presumably
Jose added that at my request. I'm sure I would have noticed it had it been
there when I took a look. :p

"Jose" > wrote in message
...
> [...]
> It looked to me as if it were the path of the wind coming down the valley
> in the manner of a stream.

It might have been. Take my comments with a grain of salt, since I'm no
expert on low-level wind structure or cloud formations. However, I'll note
what I do know. :)

Oh, and also keep in mind that I'm having a very hard time seeing with
certainty the actual 3D structure of the clouds in the picture. In
particular, I can't tell if the curve in the cloud is a change in elevation,
or is a lateral curve. I'm guessing the former, but can't rule out the
latter from the picture alone. It's also hard to see how the cloud is
positioned relative to the terrain underneath.

On to guessing... :)

While we talk about "the jet stream", there are in fact several
high-altitude jet streams, and countless smaller ones at low levels. The
cloud in your picture looks *to me* as though it could be some isolated jet
stream pulling moisture through the air. Over the hilly areas, orographic
lifting causes extra condensation, making for a fuller cloud formation,
while over the valley things thin out.

Alternatively, perhaps there's a bit of an inversion going on (not uncommon
in connection with hazy, low-stratus conditions as seen in the photo), in
which the winds aloft are picking up a bit of the extra moisture evident in
the larger part of the cloud, and carrying it as a thin "smear" downwind
from that area.

In both cases note that the winds you experienced in the airplane may or may
not be the same as in the area where the cloud is.

Ah well...as you can see, I don't really know. I have to admit, this is one
of the things I enjoy about flying, and especially of having an instrument
rating. It's not uncommon to run across strange cloud formations that are
beautiful and enigmatic at the same time. :) You may not get a confirmed
answer here, but at least you were able to share one such formation.
Thanks!

Pete

> I can't tell if the curve in the cloud is a change in elevation,
> or is a lateral curve.

It's a lateral curve, with no change in elevation. The cloud smoothly
follows the valley beneath and to the right.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

> I can't tell if the curve in the cloud is a change in elevation,
> or is a lateral curve.

It's not a change in elevation. It curves (smoothly) to follow the valley.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.