Thursday, September 29, 2011

Weather Forecasting

It's Rebecca again, I've been fielding questions on how a weather forecast is made and what it takes to make a forecast. So I thought I would do a few installments on weather forecasting. Now this is not intended to make you a meteorologist. However, it will give you a good idea on what it takes to make the type of forecast you see on WTEN. I will cover how weather models, skew-T/log-P diagrams, severe weather indicies are used to make a forecast. I thought a good place to start would be how you can make your own backyard forecast, just by observing what going on around you.

Not too long ago all the technology we take for granted didn't even exist. Therefore, people had to predict the weather based on observation, patterns, cloud types, folk lore, and even the behavior of animals. These warning signs for bad weather are not fail proof. But, it's much more accurate than you might think. If you're outdoors a lot being able to forecast foul weather with simple observation is a valuable skill. You will be able to make an educated guess on doing things like: hiking, horseback riding, or going for a boat ride. A lot of what I'm going to tell you was taught to me by my grandparents. I will tell you the folk lore, then show the science that backs it up. Also, I will show you common clouds and how they can help you make a short term forecast. I hope you find it interesting.

The Mechanics of Bad Weather

Most of you have heard a cold front or a warm front is moving in. Or, we have high or low pressure dominating overhead. However, how many of you know what they are.

A cold front is the leading edge of a moving mass of air. It is heavier, colder, and drier than the air it is pushing into. Whereas a warm front is the leading edge of a mass of lighter, warmer, and moister air. Cold fronts push underneath warmer air. Which forces the warmer air to lift. This in turn causes it to condense into clouds.

A high-pressure system is generally the result of the dense air of a cold air mass falling toward the earth, whereas a low-pressure system is the result of a warm air mass rising. As the warm air rises, it cools and forms clouds and possibly storms, so low pressure systems are usually associated with rain.

Making a weather prediction by seeing what's going on around you

You can predict short term weather with something as simple as smoke coming out of a  chimney. If the smoke is flowing down or laying close to the ground;  it means it most likely going to rain soon.  This is caused by an approaching cold front or because high humidity is absorbing smoke particles.

At night if it seems there's fewer stars out than normal it might mean a storms is on the way. This is because, when there is a lot of turbulence ( wind shear) in the air it's harder to see the stars.

If you see a rainbow and the wind is coming from the same direction, it means the rain is moving toward you.

Weather folklore and wives tales.

Weather lore has been around since people needed to predict the weather to plan their activities. I'm sure most of you have heard the weather predicting rhyme:  "red sky in the morning, sailor’s warning; red sky at night, sailors delight". There are variations of this rhyme in such places as Shakespeare's  play "Venus and Adonis" and even the Bible.  But, is this true or just a wives tale?  The answer is it's true in the Northern Hemisphere. In order to understand why this is true, we must understand how weather systems move and the colors in the sky. In the northern hemisphere the weather is influenced by the westerly trade winds . Therefore, weather systems normally move from west to east. The colors we see in the sky are a result of how the light rays are being split. The thicker the atmosphere, the more water vapor,  and the higher the amount of other particles in the atmosphere the more the light is scattered. with all of this in mind let's take another look at the poem.
Red sky in morning, sailor’s warning.

 A red sunrise reflects the dust particles of a system that has just passed from the west. This indicates that a storm system is most likely moving to the east. the deeper the red color in morning sky the higher the water content in the atmosphere. So, rain is on its way.

Red sky at night, sailors delight.

 When we see a red sky at night, there is a high pressure system with dry and stable air  to our west. The high pressure system is stirring up dust particles in the air. Therefore,  the setting sun is sending its light through a high concentration of dust particles. So, basically good weather will follow.

“Mares’ tails and mackerel scales
Make lofty ships carry low sails.”

Now  what do mares tails and Mackerel Scales have to do with the weather?  Mares tails are cirrus clouds, which are high clouds composed of ice crystals, called this because they often look like flowing tail of a horse. Mackerel scales are actually  altocumulus or cirrocumulus clouds. They often appear to resemble fish scales. They exist lower in the atmosphere than cirrus clouds, and are formed by small convective currents and instability in the atmosphere Cirrus clouds taken by themselves normally indicate  fair weather. However, If they are soon followed by mackerel scale clouds, they could indicate bad weather. Now while these types of clouds don't drop precipitation.  They do, often precede an approaching storm front by 24-48 hours. However, it is  possible that  the bad weather might pass near but not over where you're observing from. I will include pictures of both of these clouds at the end of this post.

“A summer fog for fair,
A winter fog for rain.
A fact most everywhere,
In valley or on plain.”

There a two ways fog form. The first way,  is for the temperature to fall to the dew point, in which the humidity rises to 100 percent. This happens on clear and calm summer nights. A cloudy sky acts like a blanket and holds in the heat of the day, so fog won’t form because the air temperature can't reach the dew point. So a summer fog means clear and calm weather is ahead.

Fog can form if there is warm and moisture air flowing  over a cold surface. This is how most winter fogs form.  In this cast the Warm and moist air is a forerunner of rainy weather.

Here is another one that talks about the same thing, it just talks about dew instead of fog.

“When the dew is on the grass,
Rain will never come to pass.
When grass is dry at morning light,
Look for rain before the night.”

If there is no dew on the grass, it either means the sky is cloudy or there is a strong breeze, both of which may mean rain is on the way.

“Rainbow in the morning, Shepherds take warning.
Rainbow at night, Shepherd’s delight.”

Rainbows always occur in the part of the sky that's opposite the sun. When you see a  rainbow in the morning; it means the light from the rising sun is refracting through the water droplets in a rain cloud to your west. Therefore, a rainbow in the eastern sky would happen in the evening. It would mean the rain has pasted you and is to your east.

 “When leaves turn their back ‘tis a sign it’s going to rain.”

Trees like the oak and maple have leaves that will curl when the humidity is very high; high humidity can  indicate an approaching storm. Also, the way the leaves on a tree grow is determined by the prevailing winds. Storm winds are naturally non-prevailing, blowing the leaves backward from their normal orientation thus showing their backs.

 " The higher the clouds, the better the weather."

When the clouds are high, you have high pressure and dry air overhead.

“Pale moon rains; Red moon blows.
White moon neither rains or snows.”

As I've said in past post, raindrops form around a dust particle or other small object,  the more dust particles there are in the air, the greater the chance that moisture will have something on which to form raindrops. When there are a lot of dust particles in the air, the moon will appear pale or reddish. It looks white when the air is very clear.

“When the wind backs; and the weather glass falls
Prepare yourself for gales and squalls.”

A backing wind is a wind that changes its direction in a counterclockwise manner; for the most part it will start in the west, then change to the southwest, south, and then southeast.  When you have a backing wind it indicates that low pressure is approaching from the southwest.

The Weather glass was an early form of barometer. When the weather glass falls, the atmospheric pressure was lowering, signaling the approach of a storm. 

Pictures of  clouds
Clouds tell us much of what is happening and when. Fluffy cumulous clouds tell us the weather is fine and clear sunny skies usually host those. Dark stratus clouds block the sun and spell rain or snow. Cumulus Congestus clouds also known as towering cumulus form when the atmosphere becomes unstable and there are upward air currents. Cumulus clouds can develop into thunderstorms by evening.

                                                              Low Clouds

Stratus clouds
Stratus is from the Latin for layer or blanket. Stratus clouds form a low layer that can cover the entire sky like a blanket. Rain and drizzle often come from stratus clouds. If they lift quickly in the morning, they often indicate a nice day ahead.

Nimbostratus Clouds

Nimbostratus clouds are dark sheets of clouds which blot out the sun and are often followed by long-lasting precipitation within a few hours.

Stratocumulus Clouds

Stratocumulus clouds are low, rolling mass of thin, lumpy gray to white clouds. They may produce light precipitation but usually dissipate by the end of the day.

 Middle Clouds

Altocumulus Clouds

Altocumulus clouds are larger than cirrocumulus clouds and, they are patterned white to gray clouds that are often rippled or appear in waves. Altocumulus are considered fair weather clouds, they often follow storms.
Altostratus Clouds

Altostratus clouds are formless gray to bluish clouds that form a thin veil over the sun and moon. If the clouds gradually darken and blot out the sun or moon, precipitation will follow.
                                                                   High Clouds
Cirrus clouds 
In Latin, the word cirrus means curl. Cirrus clouds are very high in the atmosphere where the air is very cold. These clouds are made of ice crystals. They are usually associated with fair weather, but may sometimes indicate that storms are on their way.

                                                                   Mares Tails
Cirrostratus Clouds

                                                         Above  Mackerel Scales

                                                          Halo around the sun

Halo around the Moon

Cirrostratus clouds are milky, white-veined clouds that produce a halo around the sun or moon. Often called 'bed-sheet' clouds, Halos are another warning sign that bad weather is on the way. A halo around the sun or the moon is caused by light reflecting off ice crystals, generally found in cirrostratus clouds. This  type of cloud can indicate a warm front is coming, and that rain or snow might be expected in 24-48  hours. The brighter the halo, the more likely it will rain.
Cirrocumulus Clouds 

Cirrocumulus clouds appear in layers that look like rippled sand or fish scales. Nicknamed mackerel sky, they are considered an omen of good weather.

Cumulus clouds

I've talked about cumulus clouds before. They are flat-bottomed and have growing, cauliflower-like towers. They often form around midday and precede cumulonimbus clouds.
Cumulonimbus Clouds

Cumulonimbus clouds nicked named thunderheads, are towering storm clouds that can reach as high as 60, 000 feet. As most of us know they bring heavy rain, sleet, hail, thunder, lightning and Even tornadoes.
A site on clouds

Well that's it for part 1. I have always found weather lore interesting. The question of the day is: sometime in the future will the complicated equipment  meteorologists use today ever be considered in the same light?  The folklore I've talked about here is not always accurate. But, if you  observe and use it, you may be surprised how accurate it is. I hope you've enjoyed this segment.

Before I go I thought I would share this, As a horse owner I've always found this useful

If the tail is dry -- the weather's clear
If the tail is wet -- it's raining
If the tail is white -- it's snowing
If the tail is burning -- it's hot
If the tail is horizontal -- it's windy
If the tail is gone -- there's a hurricane
If the horse is gone -- there's a tornado!


Rebecca Ladd

P.S. From Andy: I thought I would add an additional thought or two to this awesome blog post from Rebecca. You can also use wind directions and your barometer for( if you have one) to predict your local weather for a period of 24-36 hours in advance with reasonable accuracy. Here is a link to a wind-barometer table:

Wind-Barometer Table

Also the sequence of cloud types can also give you a clue as to what type of a weather system will be heading your way. You can also use wind direction and cloud type to aid you in your forecast too. I'll add all this over the next few days!



  1. I found this very easy to read. I also enjoyed the Wind-Barometer Table. Have you ever heard of the weather rock?
    rock is the perfect weather indicator, it
    never fails. It is more accurate than your local
    weather person. This rock is the living word and
    is 100% correct. This is how it works:

    a dry rock means fair weather.
    a wet rock means it's raining.
    a dusty rock means a dust storm.
    a swaying rock means it's windy.
    a shadow under the rock means it's sunny.
    a white rock means it's snowing.
    if the rock is jumping up and down, an
    earthquake is upon us.
    if the bottom of the rock is under water it's a

  2. I'm glad you enjoyed it..........yes I've heard of the weather rock.


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