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 

1/3/2014

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

Was I worried?
NOT!!!!! 

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!