Weather Forecasting by the Clouds

[maverick]

Can you predict incoming weather by the clouds? You should be able to, it could save you life!


Altocumulus clouds: are mid-level, grayish-white with one part darker than the other. Altocumulus clouds usually form in groups and are about one kilometer thick. Altocumulus clouds are about as wide as your thumb when you hold up your hand at arm's length. If you see altocumulus clouds on a warm, humid morning, there might be a thunderstorm by late afternoon.

Altostratus clouds: are mid-level, gray or blue-gray clouds that usually covers the whole sky. The Sun or moon may shine through an altostratus cloud, but will appear watery or fuzzy. If you see altostratus clouds, a storm with continuous rain or snow might be on its way. Occasionally, rain falls from an altostratus cloud. If the rain hits the ground, then the cloud has become a nimbostratus.

Cirrocumulus clouds: are small rounded puffs that usually appear in long rows high in the sky. Cirrocumulus are usually white, but sometimes appear gray. They are the same size or smaller than the width of your littlest finger when you hold up your hand at arm's length. When these clouds cover a lot of the sky, they can look like the scales of a fish, which is it is called a "mackerel sky.” Cirrocumulus are common in winter and indicate fair, but cold, weather.

Cirrostratus clouds: are high, thin sheet-like thin clouds that usually cover the entire sky. The clouds are so thin that the Sun or moon can sometimes shine through and appear to have a halo as light hits the ice crystals and bends. The halo is the width of your hand held at arm's length. Cirrostratus clouds usually come 12 to 24 hours before a rain or snowstorm

Cirrus clouds: are made of ice crystals and look like long, thin, wispy white streamers high in the sky. They are commonly known as "mare's tails" because they are shaped like the tail of a horse. Cirrus clouds are often seen during fair weather. But if they build up larger over time and are followed by cirrostratus clouds, there may be a warm front on the way

Cumulonimbus clouds: also have vertical growth and can grow up to 10 km high. At this height, high winds will flatten the top of the cloud out into an anvil-like shape. Cumulonimbus clouds are thunderstorm clouds and are associated with heavy rain, snow, hail, lightning, and sometimes tornadoes.

Cumulus clouds: have vertical growth. They are puffy white or light gray clouds that look like floating cotton balls. Cumulus clouds have sharp outlines and a flat base at a height of 1000m. They are generally about one kilometer wide which is about the size of your fist or larger when you hold up your hand at arm's length to look at the cloud. Cumulus clouds can be associated with fair or stormy weather. Watch for rain showers when the cloud’s tops look like cauliflower heads.

Nimbostratus clouds: are dark gray, have ragged bases and sit low in the sky. Nimbostratus clouds are associated with continuous rain or snow. Sometimes they cover the whole sky and you can't see the edges of the cloud.

Stratocumulus clouds: are low, lumpy, and gray. Sometimes they line up in rows and other times they spread out. Only light rain (usually drizzle) falls from stratocumulus clouds. To distinguish between a stratocumulus and an altocumulus cloud, point your hand toward the cloud. If the cloud is about the size of your fist, then it is stratocumulus.

Stratus clouds: are low and have a uniform gray in color and can cover most or all of the sky. Stratus clouds can look like a fog that doesn't reach the ground. Light mist or drizzle is sometimes falling when stratus clouds are in the sky.

[The Other Tom]

....and don't forget one of my favs, the lenticular cloud. I guess this is a variation of a cumulus cloud, but, man, they make for nice photographs. To stay on topic, I believe these type clouds indicate very high winds at altitude.

[AaronRDavis]

This is very insightful and worth committing to memory or at least saving as a reference.

[maverick]

....and don't forget one of my favs, the lenticular cloud

They fall into the cumulus cloud category and depending on their altitude: stratocumulus, altocumulus, cirrocumulus

[freestone]

From what direction the clouds are coming from can be helpful too. During the summer, puffy morning clouds in the southern sky always makes me nervous but less so if I see them to the northeast.

[sekihiker]

From what direction the clouds are coming from can be helpful too.

Cloud movement indicates wind direction and I always get wary when winds are from the SW through SE quarters.

[dave54]

The Forest Service issued a pocket sized guide years ago on this very topic (it was old when I started in 72). It included presence or absence of dew, changing wind direction, clouds, and other indicators. I have been trying to find an old copy of that booklet for years, posting on old timers websites etc. I am willing to digitize and post it, if I could only lay my hands on one.

[commonloon]

This is a little off topic, but I'd like to add that I find the cloud type to be just a part of weather "prediction" in the Sierras. I'm kind of being master of the obvious, but I after a close call with lightning up high, I've made of point of making sure I think about:

1) The day's pattern: are clouds slowly building throughout the day, and am I seeing any cumulonimbus clouds.
2) What has the temperature being doing? Did it flip cold to warmer or vice versa? Are there cold or warm breezes?
3) Timing: T-storms mostly happen in the late afternoon in the summer in the Sierra.
4) What have the clouds been doing the last few days? Many times there will be a cycle of worsening weather for 3-4-5 days then it will recede.
5) Is the pressure dropping? (likely bad weather approaching).

In my case, I never really could make out the cumulonimbus clouds (they were blocked by a ridge) until it was a few minutes from hail coming down like cats and dogs ;-) I did have the good sense to bail on a summit and start descending though. It was a learning experience.

[dave54]

Look for castellatus clouds in the morning -- a row of columns, or 'chess rooks'. If they build in the morning then dissipate, there is an increased chance of thunderstorms in the afternoon.

[Sierra Miguel]

Growing up in the Midwest, I used to predict the weather three days in advance by the cloud types. In the mountains here, that doesn't work for me at all. I instead pay attention to what time of day the clouds start forming, and whether they're coming from a typically monsoonal direction. So like the others are saying, if it's coming from the Gulfs of Mexico or California.