"Dirty days hath September
April June and November
From January up to May
The rain it raineth every day
All the rest have thirty-one
Without a blessed gleam of sun
And if any of them had two-and-thirty
They'd be just as wet and twice as dirty."

This humorous rhyme has been attributed to various authors in various eras, perhaps indicating how generally true it is of winter on the west coasts of both Europe and North America. While not precisely true, it nonetheless predicts with fair accuracy what weather any given day between September and June is likely to bring to Vancouver or London.

A human desire

It has been a human desire for millennia to be able to predict the weather with a reassuring degree of accuracy, and oral and written history is full of rhymes, anecdotes, and adages meant to guide the uncertain in determining whether the morrow will bring weather fair or foul. For the farmer wanting to plant his crop, for the merchant about to send his ships on trade, foreknowledge of tomorrow's circumstances might mean the difference between success and failure.

Where does weather happen?

It is in Earth's middle latitudes, between roughly 30° to 60° North and South, that a significant portion of humanity's daily activities take place. It is also within these rough boundaries that "weather" can be said to happen, that is, where meteorological phenomena do not persist over the long term, and where it may be warm, sunny, and calm one day, and cold and stormy the next.

A great percentage of the world's population lives in the equatorial regions, but for the most part, these regions do not experience weather as it is understood by this definition. The Sahara Desert, for instance, is almost uniformly hot and dry, whereas weather trends on the Indian subcontinent and in the western Pacific, ie, the monsoonal belt, occur gradually over the very long term, and the diurnal weather patterns remain constant.

Weather lore, therefore, refers to this mid-latitude region of daily variability. While some of it may apply equally to the Southern Hemisphere, the Southern Hemisphere resident may need to take into account the fact that weather systems rotate opposite to those in the North, so, for instance, the "crossed winds" rule (see below) must be reversed for the Australian reader.

How accurate is weather lore?

Any sufficiently lengthy process of observation, combined with testing of hypotheses, will produce some useful information, and weather lore is no different. However, it may not take into account or be aware of larger circumstances which affect local conditions.

The rhyme above, for instance, describes circumstances which occur as the planet-girdling north Polar front slips south and meets warm, moist air pulled in from equatorial regions. Two hundred years ago, the concept of huge rotating air masses creating weather was not only unknown, but would have gotten one laughed out of a scientific establishment if ventured as an explanation.

As a consequence, even though there is some predictive value to much of the body of folklore, it is necessarily ignorant of why it predicts what it does, and of inconsistent reliability in how accurately it predicts what it does. However, a considerable body of weather lore is reliable enough that it can be said to be useful.

True lore, and why

Red sky at night, sailors delight.
Red sky in the morning, sailors take warning.

Weather systems typically move from west to east, and red clouds are the result of the sun shining on their undersides at either sunrise or sunset. If the morning skies are red, it is likely that the sun is lighting the underside of moisture-bearing clouds coming in from the west. Conversely, in order to see red clouds in the evening, sunlight must have a clear path from the west in order to illuminate moisture-bearing clouds moving off to the east. There are many variations on the red morning sky prediction.

Mackerel sky and mares' tails make lofty ships carry low sails.

The unmistakable herringbone pattern of mackerel sky and the long, wispy cirrus which is mare's tail are all high-altitude indicators that a moisture-bearing low pressure system is moving in from the west. This usually means an increase in wind speed, a shift to more easterly winds, and increased cloud and precipitation within the next 24 hours or so. Unless a captain wants to risk torn sails and damaged spars, he takes his sails in.

When clouds appear like rocks and towers,
the earth's refreshed with frequent showers.

The characteristic cauliflower shape of summer cumulus clouds is an indicator of moist surface air rising quickly into cooler, drier air aloft. When towers (cumulus castellanus) appear, they indicate a relatively higher degree of instability between warm, moist air at the surface and cool, dry air aloft. Such towers may well grow into local thundershowers as the day progresses.

When rain comes before the wind, dories, gear and vessel mind;
When wind comes before the rain, soon you'll make the set again

When rain comes before wind, it is often the result of an approaching front, which frequently means unsettled weather for a day or two. If wind comes before rain, it is often just the downdraft from an approaching local rainshower, which will likely blow over in a few hours.

When the wind is blowing in the North
No fisherman should set forth,
When the wind is blowing in the East, '
Tis not fit for man nor beast,
When the wind is blowing in the South
It brings the food over the fish's mouth,
When the wind is blowing in the West,
That is when the fishing's best!

This description of wind direction is an excellent illustration of how a low pressure area, typically bringing active weather, presents itself. With the approach of an active low, easterly winds typically pick up. These gusty winds can be unpleasant for a number of reasons; they are often unpleasantly warm in the summer or bitterly cold in the winter, they readily produce what is known as upslope or ''orographic'' cloud where the geography is suitable, and they are much drier and therefore dustier than a westerly wind. Northerly winds, which follow around a low, are cold and blustery. Sailing in conditions of northerly winds requires expertise and a good boat. Southerly winds bring warm temperatures, and though they may not necessarily feed the fish, they do provide pleasant fishing weather. The best circumstance, however, is to have a westerly wind blowing; the wind condition is likely to persist for some time, the weather should remain fair and clear, and the wind should be relatively constant.

No weather is ill, if the wind be still.

Calm conditions, especially with clear skies, indicate the dominance of a high pressure area. Because highs are regions of descending air, they discourage the formation of things typically associated with weather, such as clouds, wind, and precipitation. Calm conditions, though, may also result from a circumstance known as "the calm before the storm," in which a large thunderstorm cell to the west may be updrafting the westerly wind before it can arrive locally. This situation is readily identifiable by looking to the west. Such an approaching storm will be unmistakable. The only time this lore might be considered misleading is if it's February and you're sitting under the dome of an Arctic high at -35°C.

Seagull, seagull sit on the sand.
It's never good weather when you're on the land.

Seagulls are not especially fond of standing or walking. They are naturally at home in flight, and where they can, they sleep on the water. However, seagulls, like people, find gusty, turbulent wind difficult to contend with, and under such circumstances, the water is also choppy and unpleasant. Seagulls huddled on the ground are not likely a predictor of bad weather as much as they are a sign that the weather is already bad.

When halo rings the moon or sun, rain's approaching on the run

A halo around the sun or moon is caused by the refraction of that body's light by ice crystals at high altitude. Such high-level moisture is a precursor to moisture moving in at increasingly lower levels, and is a good indicator that an active weather system is on its way.

When windows won't open, And the salt clogs the shaker,
The weather will favour the umbrella maker!

Moisture in the air causes wood to swell, causing doors and windows to stick, and salt is a very effective absorber of moisture. With a high level of moisture in the air, the likelihood of precipitation is increased.

A cow with its tail to the West makes the weather best,
A cow with its tail to the East makes the weather least

Cows, like people, prefer not to have the wind blowing in their faces, and so typically stand with their backs to the wind. Since westerly winds typically mean arriving or continuing fair weather and easterly winds usually indicate arriving or continuing unsettled weather, a cowvane is as good a way as any of knowing what the weather will be up to for the next little while.

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

Fog is formed when the air cools enough that the vapor pressure favors condensation over evaporation. In order for the air to be cool on a summer night, the sky must be clear, so excess heat can be radiated into space. Cloudy skies act like a blanket, keeping the heat in. So if it is cool enough (and clear enough) for fog to form, it will probably be clear the next day. Winter fog is a consequence of two entirely different sets of circumstances. Above the ocean or a large lake, air is typically more humid than above land. Humid air moving over cold land will form fog and precipitation. (Near Canada's Great Lakes, thius is known as the "lake effect.") In northerly climates, ice fog may form when the temperature drops substantially below freezing. It is almost entirely an urban phenomenon, when the air is so cold that any additional vapor produced by automobiles, homes, and industry remains in condensation.

When sounds travel far and wide,
A stormy day will betide.

This piece of lore is true in summer but, depending on one's location, false in winter. Moisture-laden air is a better conductor of sound than dry air, so sounds travel further. In winter, however, cold air is denser and a better sound conductor than warm air, and when sounds are clearly audible from a distance, the cold, clear weather is likely to remain a while.

A coming storm your shooting corns presage,
And aches will throb, your hollow tooth will rage.

There have been some medical studies done which indicate some people experience this effect. The likely reason is that, with the fall in air pressure brought by an advancing low, blood vessels dilate slightly in reaction. This has the effect of aggravating already-irritated nerves near corns, cavities, or arthritic joints.

False lore, and why

If on February 1 the groundhog sees its shadow, thirty days of winter remain. If not, spring will follow immediately.

Annual records show that the groundhog is correct half the time and incorrect half the time. In other words, there is an equal, random chance of the groundhog's forecast being correct. Perhaps groundhogs can be taught to flip coins.

If spring comes in like a lion, it will go out like a lamb.

The degree of gentleness of which a lion is capable, and the degree of fierceness a lamb can show notwithstanding, statistically, spring comes in and goes out equally as often in either guise.

Rain before seven, clear by eleven.

Late-night rains and early-morning rains may simply be the last precipitation of a passing weather front. However, since fronts pass at night as often as they do in the day, morning rain is no predictor of a dry afternoon.

When March blows its horn,
your barn will be filled with hay and corn.

"Blows its horn" refers to thunderstorms. While March thunderstorms indicate that the weather is unusually warm for that time of year (thunderstorms can occur only with a sufficiently large temperature difference between ground and sky and sufficient amounts of moisture to produce charge differential within a cloud), it is no indicator of the long-term weather trend. It is still unwise to plant your annuals before the long May weekend.

If clouds move against the wind, rain will follow.

This rule is true under only one circumstance, otherwise it is false. If one stands with his back to the ground-level wind and observes the movement of the clouds, it is possible to determine whether the weather will improve or deteriorate. If the upper-level clouds are moving from the right, a low-pressure area has passed and the weather will improve; if from the left, a low pressure area is arriving and it will deteriorate. This is known as the "crossed-winds" rule. Clouds moving in parallel to the surface winds indicate no immediate change in the weather.

Cats and dogs eat grass before a rain.

While it is true that cats and dogs eat grass, a harmless activity, it has nothing to do with the weather and probably due more to the fact that cats and dogs are not purely carnivores.

Onion skins very thin
Mild winter coming in;
Onion skins thick and tough
Coming winter cold and rough.

This verse, and so many others like it, attempts to predict long-range conditions. These predictions have stood the test of time only because they rely on selective memory: people remember when they have predicted correctly and forget when predictions don't hold. One possible factor which could provide these predictions with a thin edge of credibility is that there is some degree of consistency in weather from year to year. Drought cycles or El Nino winters are a perfect example of such consistency. A pattern of cool summers and warm winters, for instance, may produce patterns in other natural events sensitive enough to be affected by changes in temperature or precipitation.

A guaranteed prediction

This ode to the weatherman

And in the dying embers
These are my main regrets
When I’m right no one remembers;
When I’m wrong no one forgets.

is one which never fails.

Source links

Folk Lore Weather Forecasting => http//www.shoal.net.au/~seabreeze/wea/weather.html
Coldal => http//www.coldal.org/weather.htm
Number 31 => http//richardphillips.org.uk/number/Num31.htm
Skywatch - Signs of the Weather => http//wilstar.com/skywatch.htm

Additional reading

"The Story of Weather" - Bill Giles (ISBN 0-11-400355-6)
"Instant Weather Forecasting in Canada" - Alan Watts (Library of Congress #68-9173)

This is a WE2 project.

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