Estimating the height of clouds
Richard Bielak
I've tried to guess the height of clouds above the ground, just by
looking. Occasionally I compare my results with actual weather
reports. My estimates are often in the ballpark (within a 1000 feet).
Here are some criteria that I use:
1. Wispy looking clouds (i.e cirrus) are made of ice crystals, so
they must be high - in the 20,000 foot range.
2. White puffy clouds, with white bottoms are usually within 3000
to 8,000 foot range. You can kind of guess the height by angular
height over the horizon.
3. White puffy clouds, with grey bottom are probably low near 2000
feet. I think the bottoms are grey, since they are not lit up
by the sun.
4. Solid grey overcast is usually high (5000 - 8000 feet) if it looks
in "focus" (I don't know how to describe it better).
5. Solid grey, without any sharp features is probably low stratus
at 200 feet :-(.
Are there more "scientific" rules-of-thumb to eyeball the cloud
ceiling?
...richie
P.S. One way to verify my guesses is to watch jets coming into Newark
or JFK. They are at about 5000 feet or so over my house.
P.P.S. What about wind estimates?
--
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Yiannis Papelis
>Since I've become a pilot, I have been looking at the sky a lot :-).
Know exactly what you mean ...
> useful comments about detecting ceiling deleted
>P.P.S. What about wind estimates?
The most useful thing I have found for wind estimate is watching the flag
outside a building on the way to the airport.
A flag hanging down is good news. (0-4 knots)
Small waves are also ok (4-8 knots), where small means you can't really
see the area of the flag.
Intense waves, where the flag is actually fully visible (but not
stretched) are not good, but can still fly if using a runway aligned with
the wind (10-20 knots).
A flag that is almost flat and strechted is bad news ( >20 knots).
Note that this will vary with the type of flag and where it is located.
You need to adjust the signs for bigger, heavier flags, and must ignore
flags that are stranded in closed areas that are susceptibel to turbulence.
--
Yiannis E. Papelis, - Electrical & Computer Engineering, U of Iowa
Center for Computer Aided Desing - Home of the Iowa Driving Simulator
e-mail: yia...@ccad.uiowa.edu
Paul Raveling
> Since I've become a pilot, I have been looking at the sky a lot :-).
> I've tried to guess the height of clouds above the ground, just by
> 2. White puffy clouds, with white bottoms are usually within 3000
> to 8,000 foot range. ...
>
> 3. White puffy clouds, with grey bottom are probably low near 2000
> feet. ...
>
> 4. Solid grey overcast is usually high (5000 - 8000 feet) if it looks
> in "focus" (I don't know how to describe it better).
...
> P.S. One way to verify my guesses is to watch jets coming into Newark
> or JFK. They are at about 5000 feet or so over my house.
Milage (or altitude) may vary depending on local conditions.
While soaring thermal lift in the west you can find clouds of
types 2, 3, and 4 at altitudes up to the high teens, say
15,000'ish. Differences relative to New York & New Jersey
might be natural due to different humidity, pressure, & temp.
------------------
Paul Raveling
Rave...@Unify.com
Steve Wolf
A flag that is seen being ripped off the pole by the wind is probably a
good indicator that you shouldn't fly today. :-)
--
Steve Wolf
Hewlett-Packard UUCP: hplabs!fc.hp.com!woof
Fort Collins, CO ARPA: wo...@fc.hp.com
Ken Brown
>Since I've become a pilot, I have been looking at the sky a lot :-).
>I've tried to guess the height of clouds above the ground, just by
>looking. Occasionally I compare my results with actual weather
>reports. My estimates are often in the ballpark (within a 1000 feet).
As a former Weather Observer for the Air Force during the 1970's,
let me say that if you are getting within 1000 feet, you're doing
about as well as the people who get paid to estimate cloud height.
In weather school, they emphasized that of all of the ways to determine
cloud heights, Estimating was the least reliable (after pirep, radar,
measured and balloon). The lower the clouds are, the more important
it is to a pilot, and there are accurate ways of measuring low clouds.
On the other hand, if you estimated a cirrus layer at 20,000 feet and
a pilot finds it is really at 22,000...so what?
>
>Here are some criteria that I use:
>
>1. Wispy looking clouds (i.e cirrus) are made of ice crystals, so
> they must be high - in the 20,000 foot range.
Typically, we would report all cirrus type clouds as 20,000 feet in the
winter, and 25,000 feet in the summer. I was stationed at Kincheloe AFB
(long since closed down and now used as a civilian airport) near Sault
Ste. Marie, Michigan. Observers further south I believe would report
them at 25,000 and 30,000 feet respectively.
>
>2. White puffy clouds, with white bottoms are usually within 3000
> to 8,000 foot range. You can kind of guess the height by angular
> height over the horizon.
>
>3. White puffy clouds, with grey bottom are probably low near 2000
> feet. I think the bottoms are grey, since they are not lit up
> by the sun.
The height of Cumulus type clouds are usually estimated by the size
of the individual clouds. The assumption (right or wrong) is that
the clouds are roughly the same diameter, and so the smaller the
elements, the higher the clouds. Cumulus and Stratocumulus are
large and are reported anywhere between 2,000 and 6,000 feet,
altocumulus are medium sized and reported as 8,000 to 16,000 feet, and
cirrocumulus are small (they are the ones that look like fish scales)
and reported to be 20,000 to 25,000 feet. It just depends on the
size and your level of experience.
>
>4. Solid grey overcast is usually high (5000 - 8000 feet) if it looks
> in "focus" (I don't know how to describe it better).
>
>5. Solid grey, without any sharp features is probably low stratus
> at 200 feet :-(.
>
The stratus types are the hardest to estimate because the lack of
features prevent the eye/brain depth perception mechanism to lock on.
Fortunately, the higher stratus (as and cs) are usually thin and offer
other clues as to their height (the ring around the sun caused by the
ice crystals in cs for example would cause the 20,000/25,000 foot rule
to kick in).
As I said earlier, the estimated cloud heights were considered the least
reliable and when they got low enough, we would turn on our (rather
primitive) cloud measuring device. Our base did not have wx radar
because we were rather close to two other bases that did have radar
(K.I. Sawyer AFB and Wurtsmuth AFB).
But we did have a Rotating Beam Ceilometer! This device consisted
of two units (a transmitter and a receiver) a known distance apart.
The transmitter would sweep an infrared beam from horizontal to
vertical (like a ladder being raised on a fire truck). When the
beam hit a cloud that was over the receiver, the reflected energy
would be detected. Since the horizontal distance and the angle of
the beam are known - trigonometry gave us the height of the base of
the clouds. Simple, but it worked. Memory tells me that resolution
got very poor above about 4,000 feet AGL at our installation.
The way to hone your cloud estimating talent is to do what you have
been doing - make a guess and then check it against a nearby station's
report. That's how we did it:
Trainee: "I estimate those clouds to be 3,000 feet. What did Wurtsmuth
report last hour?"
Trainer: "16,000."
Trainee: "I estimate those clouds to be 16,000 feet."
>
>P.S. One way to verify my guesses is to watch jets coming into Newark
>or JFK. They are at about 5000 feet or so over my house.
>
Another way to get the height of low clouds is if they obscure the
very top of a mountain or building of a known height. This method
was reported as Measured as I recall.
Ken Brown - Weather Observation Specialist (AFSC 25271)
Systech Corp. {ucsd,uunet}!systech!ken
San Diego, CA
P.S. Being a Weather Observer sure was weird - being paid to look out the
window 8 hours a day, but it sure made the weather questions on the
Private Pilot Written Exam a piece of cake :-).
Mark Cousins
>Are there more "scientific" rules-of-thumb to eyeball the cloud ceiling?
I'm amazed no one has mentioned this, but one handy method is the convergence
of the temperature and dewpoint. From _Aviation Weather_:
"You can estimate the height of cumuliform cloud bases using surface
temperature-dew point spread. Unsaturated air in a convective current cools
at about 5.4 deg F (3.0 deg C) per 1,000 feet; dew point decreases at about 1
deg F (5/9 deg C). Thus in a convective current, temperature and dew point
converge at about 4.4 deg F (2.5 deg C) per 1,000 feet as illustrated in
figure 44. We can get a quick *estimate* of a convective cloud base in
thousands of feet by rounding these values and dividing into the spread or by
multiplying the spread by their reciprocals. When using Fahrenheit, divide
by 4 or multiply by .25; when using Celsius, divide by 2.2 or multiply by .45.
This method of estimating is reliable only with instability clouds and during
the warmer part of the day."
Mark
--
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