Best Clouds for Colorful Skies
by Michael DeYoung
When you live in predominantly cloudy place it is easy to crave those clear days with only blue skies and predictable light on our favorite terrestrial subjects. Even though I enjoy a vitamin D day as much as anyone, I don’t like plain blue sky in my images. I have learned through much trial and error and meteorological knowledge that bad weather produces great images, usually at the leading and trailing edge of a storm system.
Though any cloud type comprised of ice crystals can turn colorful, there are two cloud types that are the most predictable for producing orange and pink skies at the ends of the day. They are cirrus and altocumulus clouds. The type I look for the most are fair weather clouds associated with the fair weather side of the jet stream. They form in upper level high pressure systems. A mostly dry flow across a mountain range in the mid and upper levels of the atmosphere can cause lee side altocumulus and cirrus clouds, the kind I like the most. Lingering fair weather mid and high clouds are also common near the tail and of clearing storms.
Cirrus, cirrostratus, and cirrocumulus are high clouds. Regardless of where you are on earth, cirrus clouds are always comprised of ice crystals. In the tropics and mid latitudes, cirrus commonly forms at 25000-30000 feet above ground level (AGL). In Alaska where the stratosphere is thinner than in lower latitudes, cirrus clouds are found in the 17000-20000 range near the top of some of our highest peaks. They can be thin and wispy looking like hooks and filaments or be dense patches with ragged edges, thick enough to make the edges of the sun indistinct.
Altocumulus clouds are considered mid clouds and form in the 7000-15000 foot AGL range. Altocumulus clouds come in many varieties. Thin altocumulus clouds that are cellular or look like fish scales or washboards are always pleasing in images and can turn dramatic color. My favorite altocumulus cloud is mountain wave or altocumulus standing lenticular clouds. Most of Alaska’s ranges and the Rockies, Cascades and High Sierra all create their own weather and produce mountain wave clouds. In Alaska, altocumulus clouds are almost always ice crystals. In the mid latitudes they may not be. It depends on the season and their height.
Mountain wave clouds form under a stable atmosphere with a shallow layer of moist air in the mid levels along with a long stretch of strong winds that are perpendicular to the mountain range. Mountain ranges force air to rise creating a series of waves with alternating rising and sinking air along and downstream of the crest. This is similar to a river when the river bed changes from a smooth bottom to big boulders resulting in a wav train. When this takes place under a mid level temperature inversion, commonly referred to as a subsidence inversion, mountain wave clouds in the shape of almonds or flying saucers form. They can appear nearly stationary (just like a wave train in a river is always in the same place at the same flow level) and won’t change until upper atmospheric flow and moisture changes. If there is nothing blocking their view they can turn fantastic colors.
Ice crystals are the key to the colors we see. They bend and reflect light, especially the warmer colors of the visible light spectrum with their longer wavelengths while the colder colors with shorter wavelengths just pass through the ice crystals off into space. In arctic air masses you can see beautiful pink colors in clear skies pre-sunrise and post-sunset. Ice crystals can remain suspended aloft without forming a cloud, and can precipitate out of clear air. They reflect light back to the source, the rising or setting sun, called back scattering. This creates the rich alpenglow and pink bands opposite of where the sun was during twilight.
Colorful skies lit by cirrus and altocumulus clouds are more difficult to forecast in Alaska than in the mid latitudes of the western U.S. There are two reasons for this. First, Alaska can have a lot of persistent low level moisture and clouds that frequently obscure colorful high clouds above. Secondly, Alaska is not always in the prevailing westerlies, remaining north of them much of the time. Sometimes, weather approaches Southcentral Alaska from an easterly direction. Thus, in an easterly flow, the rules of thumb that work in the mid latitudes for a predictable colorful sunrise or sunset are reversed. In an easterly wave, I’ve seen blazing red sunsets followed by morning rain/snow gloom and doom-the exact opposite of what typically happens down south.
The fact remains though that thin high and mid clouds comprised of ice crystals are the most likely to produce beautiful pre-sunrise and post-sunset colors. This indirect warm soft light, a color wash from clouds is my favorite landscape light and has resulted in some of my most successful commercial sales of landscape images.
I look for days when there is nothing but scattered (20% to 50% sky coverage) and even broken (60% to 90% sky coverage) thin layers of altocumulus and cirrus. I keep an eye on what’s happening during the day. If there is clear air or even just thin clouds where the sun will rise or set, then there is a good chance these clouds will turn colors. When I see these conditions I get jazzed about making images.
Remember, in the northern latitudes, the sun rises and sets at shallower angles than it does further south. The time between sunset and civil twilight is longer in Anchorage than it is in Albuquerque. At 36 North, the time between sunset and clouds turning color is about 10-15 minutes. At 63 North, in Denali, it is more like 20-30 minutes, sometimes longer, enough time for people to run out of patience and put their cameras away! Don’t get caught off guard. Be patient! My favorite app for telling me where the sun is and where it will be and what elevation it will be, including below the horizon to help plan when the color will explode is Roger Moffat’s Golden Hour app. You can see all this information, on any day you choose at any location (it is GPS enabled and doesn’t need a cell signal to work) with a simple slider and compass graphic.
Here are a few suggestions on how to identify clouds and better predict a colorful sunrise/sunset. Williwaw Publishing, who puts out the Alaska Weather Calendar, also produces the Alaska Cloud and Weather Field Guide in a laminated foldable card.
Many sites have a detailed weather observation called a METAR. They even decode the cloud layers for you. Sometimes you will see obvious clouds from the camera but the METAR reports “clear” (CLR). This means that all clouds are above 20,000 feet - favorable for color. It they are reporting a cloud layer above 7000 feet you know you have altocumulus, above 16000 feet, then cirrus. What I look for when examining FAA Cams are scattered to broken layers only at 7000 feet or above and some sort of clearing where the sun will rise or set.
I know this is a lot of technical information and that meteorology and how it affects our light can be a lot like an onion. Every time you peel a layer back, more layers just keep coming. But with a little practice you will begin to learn more about high and mid clouds. When you travel to the mid latitudes, particularly the semi-arid and arid areas of the west, you will discover a fair number of days with pretty high clouds that blaze with color.
All images provided were taken in Alaska.
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