Tuesday, February 4, 2014

Colorado Cloud Atlas: Riding the Orthographic Lift!

Are you a sky watcher?
I sure am!

Day or night, the sky provides a free show ~
always changing and never the same.

Sometimes the sky in Colorado 
can look downright scary!

I jumped out of the car
and snapped this photo
one recent Friday evening.

Evening Sky, 
Aurora, Colorado 

Pretty scary-looking cloud formation!
Then I shot overhead and to the right.

Was I worried?

Not long after I moved to the eastern slopes of the Rockies,
I learned that this type of cloud formation
is a harbinger of good things!
Snow-eating, warm Chinook winds!

I was fascinated with the snow-eating winds
when I first heard about them as a child.
I tried to imagine a Chinook arch
stretching across the sky.

This was long before the days 
of Google Search, Wikipedia, 
and instant knowledge gratification.

In my imagination, 
I saw a black, rainbow-shaped arch
hanging above the Rockies.
I distinctly remember attempting to draw one,
and my drawing looked something like this.

It was decades later,
when I was living in Calgary,   
that I got to see the Real Deal.
And was I surprised!
Definitely not a rainbow,
black or otherwise.

Chinook Arch
Calgary, Alberta, Canada
Source:  Wikipedia 

At sunrise or sunset,
a Chinook arch can produce stunning colors.

Chinook Arch
Calgary, Alberta, Canada
Source:  Wikipedia

And that is precisely what I was seeing
that recent Friday in January:
the western edge of a Chinook arch at sunset.

Chinook Arch
Aurora, Colorado, U.S.A.

The map below shows a driving route 
between Aurora and Calgary.
The route parallels the eastern front 
of the Rocky Mountains,
one of the places in the world
where Chinook-type winds occur.

The US/Canadian border
is the solid horizontal line
directly under the letters "ouver"
in the upper left of the map.

Driving from Aurora to Calgary
Source:  Google Maps

Pacific Northwest
Source:  go northwest

As a child, I wondered:
What made a wind eat snow
and paint black rainbows in the sky?

And, of course, I found out!
It's just the neatest thing!
Take a ride with me on 
The Orthographic Lift!!!!!

The arch occurs 
when Chinook winds form
at the juncture of mountains and plains.

Meteorologists refer to Chinook winds
as foehn or föhn winds.

When warm moist air
is forced up and over a mountain range, 
it drops most of its moisture
on the windward side of the range,
as the air rises, expands, and cools.
Precipitation occurs as rain, snow, or fog. 

The forcing of air 
up the side of a mountain range
by raising terrain
is orthographic lift.

How a Chinook or Foehn Wind is Produced
Source:  Wikipedia

As the now dry air flows 
down the leeward side of the mountain range,
it is compressed 
by increasing atmospheric pressure, 
and it warms up.
It is this downward flow of warming dry air
that forms the Chinook wind.

Chinook Wind
Source:  Wikipedia

Don't let those words 
Adiabatic Heating 
scare you,
like they used to scare the heck out of me
in hydrology class!

They just mean that
an air mass (a gas) 
warms up in temperature 
and shrinks in volume
because the atmospheric pressure 
on the air mass increases
as the air mass flows down the mountain.

Voilà!  Snow-eating wind!!!!!

The opposite,
Adiabatic Cooling happens during 
orthographic lifting.
When an air mass 
moves up a mountain range,
atmospheric pressure decreases,
so the air mass (a gas) expands
and its temperature drops.

Chinook Arch
Source:  fineartamerica ~ Duyunova

During the winter,  
Chinook winds 
can increase temperature dramatically,
from -20°C (-4°F) 
to as high as 10-20°C (50-68°F).
Source:  Wikipedia

The distinctive look of the Chinook cloud formation
is caused by air turbulence.
The fast-flowing wind
moving down the mountain slopes
causes waves in the atmosphere,
like river water hitting a rock mid-stream.
The high crest of the wave forms
a band of stationary stratus clouds
parallel to the mountains,
the Chinook arch!
Source:  crownofthecontinent
Source:  Wikipedia

Chinook Arch
Aurora, Colorado, U.S.A.

In the Pacific Northwest,
the same flowing air mass 
can drench the coast in rain,
hammer the windward Rockies with snow,
and dramatically warm the leeward Rockies.
Source:  Wikipedia

Chinook Arch Over Calgary
Source:  Wikipedia

Many people mistakenly think that Chinook
means snow-eater
because a warm Chinook wind
can melt a foot (30 centimeters) of snow in a day.

But Chinook is taken
from the name of the indigenous people
who lived along the lower Columbia River,
where the term was first used
to describe a warming wind
moving from the Pacific Ocean
into the Pacific Northwest.

The word Chinook
used to describe the warm winds, 
was carried into Alberta, Canada by fur traders.
Source:  Wikipedia

Location of the Chinook People
Lower and Middle Columbia River Basin
Source:  Wikipedia

Chinook Arch Over Aurora

How lucky we are to live in a world
that is endlessly fascinating!


  1. Replies
    1. Thanks, Adam! I think they are beautiful too! Have a great day!

  2. Fascinating it can be most times, even when the bad comes around, like winter weather

    1. Hi HGW! We're having a little bit of fascinating winter weather along the Front Range right now ~ we seriously could use a Chinook, because it is a meat locker outside! Have a good one!

  3. What a fascinating post with such gorgeous, eye-popping photos! I studied meteorology for a while, and this post makes me homesick! (Can you believe I briefly considered being a weather girl?!?)

    1. Thank you, Snowcatcher! Let me think about your question. You call yourself Snowcatcher, you craft stunning snowflakes, and you ride your bike every month of the year, even in snow! I'm not the least bit surprised to hear there is a meteorologist hidden in your heart! I think we all consider and discard various possible careers. The first career I considered for several years was princess. I was going to grow up and marry Prince Charles (Is that Canadian or what! LOL). You probably would have made a fun weather girl! Stay warm today ~ Burrr!

  4. Wow, those are some phenomenal clouds..I do enjoy sky watching but, have never seen clouds
    quite like the ones you have on display here. Thanks for sharing...the weather fascinates me and I do
    know a bit about weather and clouds. They hold a mystique about them as you watch them from a distance.
    When I fly I always like to grab a window seat if possible so I can look down at the clouds as well.

    1. Hi Truedessa! Thank you for your kind words! Clouds do hold a mystique that never lets go of me. We often have exciting weather in the Denver area because we live where mountains and plains meet. That makes it fun for skywatchers like me. Like you, I'm always racing for a window seat on a plane, although I'm torn between watching the gorgeous clouds or the incredible landscapes below. Have a great day!

  5. It is the same sky but different all around as one can spy, yet kinda the same too. Wonderful shots at your zoo.

    1. Thanks Pat! It gives me a lot of pleasure when someone enjoys my photographs or writing. Have a great day at your bay!

  6. The cloud formation is just beautiful. I can't imagine a Chinook wind bringing warm air to you. The sky is amazing. Very great photos today.

    1. Thank you, Peggy! Chinooks are awesome, because you can go from bitter to balmy in an hour! We could sure use one here today ~ When Terry drove to work this morning the outside thermometer on his car was registering -18 degrees F. I hope it's warming up where you are! My sisters and I jokingly referred to sudden increases in body temperature as Chinooks! I'm glad that you enjoyed the photos!

  7. Hi Louise! I have not seen this type of cloud formation nor did I know anything about it. In Switzerland we used to have "foehn"......everything was so much more beautiful afterwards (very, very clear) but foehn never failed to give me a headache (a lot of people got them actually). Thanks for sharing ~ I'd be rather intimidated by those clouds!

    1. Hi Audrey! Aside from the "foehn" induced headaches, I'll bet it was wonderful to live in Switzerland! Have you ever read "Heidi" to yourself or to Sophie and Clara? It was one of my favorite books when I was a little girl. I would read a simplified version to my third graders, and then we would watch the 1993 version of the movie starring Jason Robards. (I just had to build so much background knowledge in some of my kiddos, that I sometimes used movies to help me). I did the same kind of thing with Anne of Green Gabales.

      The Alps have "Chinooks" too, but they are called different names in different European countries; "foehn" is one of the names. These kinds of winds occur in a number of places around the world. The clouds do look intimidating until you learn to recognize them and know what they portend.

      I hope that you are enjoying a good week!

  8. WOW! Now those clouds would have made me run for cover!! I never imagined that they could be so dramatic, Louise! Great photos and 'lesson' about this weather phenomenon. thanks.

    1. They are dramatic looking, Jim! Thanks for your kind words! I meant only to post a few pictures and say what type of cloud formation they were. Obviously that didn't work. I got going and couldn't stop myself! Supper was late for two nights! Poor E-P! "You're never going to change, honey," says he! I'm so fortunate to have found someone who "gits" me! Have a great day!

  9. Those clouds are majestic! Thank you so much for sharing. Great post.

    1. Thanks, Linda! I hope that you are enjoying your day!

  10. Indeed we are lucky to live in such a fascinating world! I am always in awe of it. Those are amazing clouds. I love taking photographs when the sky is so dramatic. The power of it all is astounding!

    1. Hi Martha! You and I both love taking photos so much! Have a happy day!

  11. I am most definitely a sky watcher! I love the sky in all its forms, whether it be an amazing cloud formation, a serene sunset, or a beautiful sunrise. These pictures are amazing :)

    1. Thank you, Keith! There is just so much to see in our wonderful world! Hope all is well with you!

  12. Snow eating winds - I learned something new today. Absolutely amazing photos. Those clouds would be a little bit scary here. Might mean a bad thunderstorm - or worse.

    1. Thanks, Alex! We get some awesome thunderstorms here too! I hope that you are enjoying a happy day!

  13. Calgary could use a good Chinook right now - it is freezing (-24c with windchill below -30c)

    1. Hey Sis! I'm wishing for a Chinook too. Yesterday Terry went to work at -18F/-27C. Today is a little warmer -11F/-23C. I've given up on the degree symbol! LOL Stay warm!!!!!

  14. These are beautiful! Thank you so much for sharing these pictures.


  15. Thanks, Gina! I love the blogging world because of all the amazing things that people share! Have a happy day!

  16. Some great pictures! I enjoyed reading. Good luck with your endeavours.

    Thank you. Love love, Andrew. Bye.

    1. Thank you, Andrew! I'm glad that you enjoyed my post! Take care!

  17. Wow-- amazing cloud photos-- talk about being in the right place at the right time!! You captured some spectacular images!!


    1. Thanks, Vicki! Sometimes you just get lucky! Have a great evening!

  18. You always have the most beautiful pictures. And today you taught me something I didn't know. Thanks:) And have a good one.

  19. Gorgeous pics! That's one part I miss about living near the mountains--the variety. I always look at the sky as a still of the ocean, the amazing variety of white peaks if we could only freeze it for a moment... Nature is amazing, isn't it?

    1. Thanks, Crystal! I so agree ~ nature is fabulous! Take care!

  20. Hello Fundy!
    First of all, a warm thank you for your kind, and fun comment on my blog!
    Your were not far off about feather, actually it is part of Mallard duck's wing!
    The answer has just been posted! ;-)
    Now, back your pictures and this very interesting article of yours about Chinook arch.
    You must have been flabbergasted at this sight! WOW!!
    Strangely enough, sometime the Australian sky looks quite similar but for very different reasons... When happens there, it is SAND storms moving from the central parts to the East coast!!
    The Wikipedia pics enhance yours and this post with your explanations is truly fascinating!
    I can go to sleep tonight a little moor enlightened!!!
    Keep well!

  21. Hi Noushka! I should have thought of a mallard! That was fun! Thank you for your kind and encouraging comment! I like to write about science topics, and I am so happy that this post has been well-received. I'm headed over to your blog now! Take care!

  22. That is so so fascinating!! And beautiful but also a little scary!!! Clouds are an endless source of fascination for me too! Many long car journeys spent cloud watching! They're always most special when combined with light like your Aurora here! X

    1. Thanks, Kezzie! I think there are a lot of cloud watchers like us in the world! Have a good week!

  23. Hi,
    I just found your blog while looking for a picture of a Chinook arch cloud formation. The pictures are impressive.
    Would it be acceptable if I were to copy your 6 of 16 for my own blog? I'd be happy to give you credit.
    Thank you, Karen Wills


Thank you for your comments! I appreciate them very much.