Handbook of Meteorology/Folklore
FORECASTING THE WEATHER: WEATHER FOLKLORE
Two classes of people criticize Weather Bureau forecasts, the public and the Weather Bureau. Probably the Weather Bureau itself is the severer critic of the two. Its rules for purposes of verification are inflexibly definite. The practise is definite as to the character of the forecast, the time of occurrence, and the place of occurrence.
Rain—Fair.—By rain in this connection is meant any kind of precipitation in season. The general term precipitation is used to embrace rain, snow, sleet or hail; but in forecasts, “rain” may be used to cover any or all. To verify a “rain” forecast, precipitation must occur to the amount of 0.01 inch or more. The forecast may designate “rain,” “showers,” “thunder-storm,” “snow,” “sleet,” etc., but the meaning for verification does not vary. Even the term ”clearing,” when used in connection with a rain forecast, means that rain will fall during a part of the time covered by the forecast.
For purposes of verification, fair means only the absence of precipitation. The forecaster may differentiate the kinds of fair weather to be anticipated as partly cloudy, cloudy, unsettled, overcast, or threatening—these are all variations of the forecaster’s ”fair.” If precipitation occurs to the amount of o.oi inch or more, by the rules of the Weather Bureau the forecast fails.
Warmer—Colder.—The rules concerning temperature forecasts are also equally definite, but with certain limits in verification. If the forecast is ”warmer,” any rise of temperature is a verification; so also is ”cooler” if lower temperature is forecast. But if a change is not forecast, or if the words ”not much change,” ”slight change,” ”continued warm,” (or cool), or ”stationary temperature” are used, a definite number of degrees (6 in summer and 10 in winter) is required to vitiate the forecast. Modifying words, “slightly,” “much,” “probably,” etc., do not relieve the forecaster of the failure of his verification.
Time of Occurrence.— The forecasts most generally sent out for publication are based on the 8:00 a.m. observations and reports. The terms designating time are ”to-night” and the name of the following day. “To-night” covers the twelve-hour period from 8:00 p.m. of the current day to 8:00 a.m. of the following day. Therefore, whatever is forecast for “to-night” must occur within these time limits. “Rain to-night” would fail of verification if none occurred until after 8:00 a.m. the day following, even though a heavy downpour set in immediately thereafter. “The following” day begins at 8:00 a.m. and ends at 8.00 p.m. after the current day—that is, for purposes of verifying the 8.00 a.m. forecast on Monday, “Tuesday” covers only that portion of the day between 8.00 a.m. and 8.00 p.m.
Place of Occurrence.—Most forecasts are made to cover individual states. The larger states are subdivided into “north,” “south,” “east” and “west” sections. The daily forecast may be for the whole of a state or for any of its sections. If rain is forecast, say, for New Jersey, and none is reported from any of the stations in the. state, the verification fails, even though showers may have occurred at nearby stations in Pennsylvania and New York.
The Value of Safety.—Measured by their effect on commerce, production, and transportation, some weather changes are of no particular effect; they are neither beneficent nor hurtful. Other changes are classed as “critical”; if they occur unexpectedly—that is, without forewarning, they may result in loss by damage, or by destruction; they also may cause human suffering.
The “unexpected” may be unseasonable rains, snowstorms, floods, frosts, cold waves, hot spells, tornadoes, or other severe weather. These are the weather conditions to which the forecaster must be keenly alert; they are the possibilities that demand his chief care. Forecasters realize that it is wiser to warn against a killing frost that does not materialize than to fail in warning against one that does appear. The unverified forecast of frost may cause some trouble and some loss, but the killing frost that comes without warning is likely to result in loss infinitely greater.
In the raisin-growing regions of California, a shower on the fruit curing in the open air causes very great damage. The fruit grower, therefore, is closely observant of the forecast of showers. The expense of stacking his trays, however, is small compared with the loss of his crop or the impairment of its quality, resulting from a shower. It is to the credit of the district forecaster that in many years not a shower has occurred of which timely warning was not given.
Recently a West Indian hurricane threatened the Gulf Coast and warnings were duly issued. Precautions were taken as indicated; but, by the time the hurricane reached the Gulf Coast, not much energy was left in it. But what would have been the result had the warnings been omitted and the hurricane had possessed the violence of the storms which destroyed Galveston and Corpus Christi?
It is the desire of the Weather Bureau to prevent loss by forewarning. The district forecasters do not strain points for high percentages of verification. A row of failures may be discouraging; a mistake against the forecaster may make him a target of derision; but a mistake which results in loss of life is irreparable. Therefore, in making forecasts, it is “safety first.”
Those who make intelligent use of Weather Bureau predictions realize that forecasts are not insurance policies. They merely are expressions which represent the experience and judgment of the best-trained meteorologists. In one particular the dissemination of weather forecasts might be made even more valuable—namely, by issuing a map and forecasts based on the 8:00 p.m. reports, to be published in the morning papers. When the public decides that it really wants this information, the information will be forthcoming. As a rule, the public gets what it deserves, but not always what it needs.
Popular Weather Prediction—Folklore[1]
Weather prediction is probably as old as human history and some of the sayings popular to-day passed current more than three thousand years ago. They survive because they are true. Mariners at sea and shepherds on land learned their lessons well; neither the one nor the other was possessed of a daily weather map. The wind was a fair barometer; the blinking of the stars was an excellent hygrometer. The discovery of the underlying principles of barometric pressure was the beginning of modern meteorology. The use of the barometer quickly appealed to sailors, and practically every deep-water vessel in the world is equipped with one. Transportation companies, lighting companies, farmers and manufacturers find it a necessity. The invention of the aneroid barometer has popularized its use tremendously.
In the hands of one without experience, or without training in the use of it, the barometer is usually a disappointment. To the trained observer, or to the observer who has gained wisdom by experience, it is an instrument of the highest value. To be serviceable in forecasting weather conditions it must be watched—not casually but systematically. The experience that comes from intelligent study of pressure changes will enable an observer to command most gratifying results.
General Pressure Indications.—As a rule, pressure changes should not be considered by themselves; they should be studied in conjunction with changes in temperature, humidity and wind direction. There are, however, certain general weather conditions indicated by changes in barometric pressure which hold good:
A gradual rise of the barometer indicates settled fair weather.
A rise from a very low pressure indicates wind and clearing weather—the more rapid the rise, the stronger the wind. Rapid changes in pressure indicate early and marked changes in the weather.
A sudden rise in pressure indicates as great a change as a sudden fall.
The wind is apt to blow hardest when, after having been very low, the barometer begins to rise.
Should the pressure continue to remain low after the sky has cleared, expect more rain within twenty-four hours.—Prince.
If the pressure falls two or three tenths of an inch in four hours or less, expect gale winds.—Prince.
In summer a sudden fall in pressure indicates a thunder-storm; if it does not rise when the storm ceases, unsettled weather may be expected.
A fall in pressure not accompanied by stormy conditions indicates a severe storm at a distance.
A steady but very slow fall in pressure indicates that the low and its storm conditions is moving slowly. “Long falling, long last; short notice, soon past.”—Fitzroy.
During a period of low pressure, fine weather may be regarded with suspicion; a change may he expected at any time and most likely it will be sudden.
The barometer falls lower for high winds than for rain, but torrential rains may accompany a very low pressure. In winter, if high temperature accompanies very low pressure, heavy rain followed by a cold wave may be expected.
A rising barometer usually indicates winds having a westerly element—southwest, west, or northwest. A falling barometer usually indicates winds having an easterly element—southeast, east, or northeast. The rule is not infallible, however. Occasionally there occurs a dry east wind with a rising barometer.
A gradual but steady fall of the barometer indicates unsettled weather, increasing moisture and rain. A slow fall from a very high barometer indicates unsettled and rainy conditions rather more certainly. A sudden and rapid fall indicates a sudden downpour and high winds, or both. In summer a thunder-storm is preceded usually by a drop in pressure.
Wind Indications of Weather Conditions.—Throughout the eastern half of the United States[2] winds with a westerly element—northwest, west, and southwest winds—indicate fair weather. Winds with an easterly element—northeast, east, and southeast winds—indicate unsettled weather, rain or snow.
A straight north wind is apt to be a clear- weather wind. “The north wind driveth away rain.”—Prov. xxv, 23; but this is not always true, especially if it veers into the northeast.
Straight south winds along the Atlantic and Gulf Coasts are apt to bring unsettled weather, inasmuch as the south wind blows from the sea, it usually brings warm air and excessively humid weather. Occasionally it brings storm conditions.
West winds are dry winds; in the eastern half of the United States they are apt to be dust-laden also. In midsummer they blow many miles over sun-heated ground and they are therefore apt to be hot winds.
East winds almost always precede rain and snow by twenty-four hours or more. Along the Atlantic Coast the east wind is pretty certain to be a storm-breeder.
Northwest winds are the prevailing winds of the greater part of the United States. They are also the clearing winds for most of the cyclonic storms that sweep the country; they constitute practically all the cold-wave winds.
Southwest winds are the prevailing winds during the summer months in the eastern part of the United States. With a falling barometer, they bring rain.
Northeast winds are storm-winds; almost always they are cold and raw.
Southeast winds are rain winds along the entire coast and much of the interior of the United States, for the greater part of the year. The time varies from twelve to eighteen hours in winter and from eighteen to thirty-six hours in summer.
Barometer and Wind Indications.—When pressure and wind-direction are both considered and interpreted according to their mutual relations, local forecasts can be made with a much greater degree of certainty. During the colder months, throughout the United States, the western highlands excepted, precipitation begins with falling pressure. In the summer months, and in the western highlands it is apt to begin with the rising barometer. The following indications have been compiled for the Weather Bureau by Garriott.
29.80 or below, rising rapidly |
w | Clearing and colder.
|
30.00 or below, rising slowly |
s to sw | Clearing within a few hours; fair for several days.
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30.10 to 30.20, rising rapidly. |
sw to nw | Fair, followed in two days by warmer and unsettled weather.
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30.10 to 30.20, steady |
sw to nw | Fair, with stationary temperature for one or two days.
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30.20 and above, steady |
sw to nw | Continued fair; steady temperature.
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29.80 or below, falling rapidly |
e to n | Severe northeast gales; heavy rain or snow.
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29.80 or below, falling rapidly |
s to e | Severe storm probable, followed by clearing and colder weather.
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30.00 or below, falling rapidly |
se to ne | Rain with high wind, followed within 24 hours by clearing and colder weather.
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30.00 or below, falling slowly |
se to ne | Rain likely to continue 48 hours.
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30.10 or above, falling rapidly. |
e to ne | Rain or snow probable within 12 to 24 hours. In winter, snow and high winds.
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30.10 or above, falling slowly. |
e to ne | In summer, light winds and rain after 48 hours; in winter, rain within 24 hours.
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30.10 to 30.20, falling slowly. |
se to ne | Rain in 12 to 18 hours.
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30.10 to 30.20, falling rapidly. |
s to se | Increasing wind; rain in 12 to 24 hours.
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30.10 to 30.20, falling slowly. |
s to se | Rain within 24 hours.
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30.10 to 30.20, falling rapidly. |
sw to nw | Warmer; rain in 18 to 24 hours.
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30.10 to 30.20, falling slowly. |
sw to nw | Warmer; rain in 24 to 36 hours.
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Barometer and Temperature Indications.—The following are noted by P. R. Jameson. They apply chiefly to that part of the United States and Canada east of the Rocky Mountains, approximately from the latitude of the Ohio River to that of the Saskatchewan River.
Pressure Rising
Below 30 F |
Cold wave |
Between 30° F and 40° F |
Freezing temperature |
Between 40° F and 50° F |
Frost or freezing temperature probable |
Between 50° F and 60° F |
Cooler |
Above 60° F |
Warm; cool nights |
Pressure Falling
Below 30° F |
Overcast; snow |
Between 30° F and 40 F |
Rain, sleet or snow |
Between 40° F and 50° F |
Unsettled; rain |
Between 50° F and 60° F |
Heavy rains |
Above 60° F |
Showery conditions; unsettled |
Humidity Indications.—The gathering moisture of the air or, technically, its increasing humidity, is an indication of unsettled weather. Ordinarily, the air which may be at the dewpoint at daylight becomes relatively dry at midday because its higher temperature gives it what is popularly termed “a greater capacity for moisture.” But if the relative humidity remains high in the middle of the day it is evident that the absolute humidity has increased, and unsettled weather may be expected.
A hygrometer is useful in detecting increase of moisture, but it is not wholly essential. Where a hygrometer is available it is apparent that the less the difference between the wet bulb and the dry bulb the greater the moisture content of the air and the greater certainty of unsettled weather
The effects of increasing moisture in the air are so well known that the literature of them is great, and popular sayings concerning them are found in all ages.
When the locks turn damp in the scalp house most surely it will rain.—Indian Tradition.
If metal plates sweat it is a sign of foul weather.—Pliny.
The tightening of cordage on ships is taken by sailors as a sign of approaching rain.
A red sun has water in his eye.—New England Tradition.
When it is evening, ye say it will be fair weather, for the sky is red; and in the morning it will be foul weather, for the sky is red and lowering.—Matthew xvi, 2-3.
Rainbow in the morning, shepherds take warning;
Rainbow at night, shepherds’ delight.
Circles around the sun or the moon indicate increasing moisture.
Salt absorbs moisture quickly. Its becoming coherent is a sign of increasing moisture.
The sunflower lifts its head when the moisture of the air increases.
The perfume of flowers becomes stronger when the air becomes damp; so also does the odor of a tobacco pipe.
It is well to bear in mind that these traditions apply to a more or less sudden change from dry to moist air, and not to the long-continued spells of moisture that come with steady sea winds.
Moist weather of long duration may be clear, as is commonly the case along the Atlantic Coast in summer; but a rapid change from dry to moist air almost always brings hazy conditions, and this is the sort of change that precedes rain.
And if through mists Sol shoots his sullen beams,
Frugal of light in loose and straggling streams,
Suspect a drizzling day and southern rain
Fatal to fruits, and flocks and promised grain.
The foregoing are only a few of the traditions and folklore sayings concerning the humidity of the air. Nearly all of them may be reduced to one or the other of two general principles— the hygroscopic character of many common substances, or the mistiness of the air which tends to scatter all but the red rays of the sun.
The varying conditions of humidity usually afford indications more or less characteristic. These are more noticeable at morning and evening when the humidity is high. They are apt to be most pronounced on the horizon when vision penetrates a layer of air of greatest density. The following are proverbs of seamen:
A whitish -yellow western sky indicates rain.
Unusual hues of the sky forming a background of sharply edged clouds indicate heavy rains and gusty winds.
A white, yellow or greenish-yellow sunset indicates a storm.
A diffuse or hazy sunset indicates a coming storm.
A purple sky foretells continued fine weather.
A blur or haziness at the horizon indicates unsettled weather.
This may be correct if the haziness is due to misty air; but it is not true if the hazy or distorted outlines are caused by the refraction of air currents.
If the sun draws water in the morning expect rain by night.
This may be true in some localities, but it is not generally true. The appearance is due to the reflection of straggling rays of sunlight from dust motes or from mist.
Red evening sky, a fine to-morrow.
A red morn betokens a tempest.
Cloud Indications.—Cloud matter is the first step in condensation. If precipitation is feeble in energy and slow in process, only cloud is formed; if it is more energetic the cloud matter forms rain or snow.
Because cirro-stratus clouds, higher than others, consist of the first precipitation on the advancing low, they are among the best indications of an approaching storm. In a majority of instances they are the overflow from the upper part of the approaching cyclone; they may be more than one hundred miles in advance of the storm center.
Not all cirrus and cirro-stratus clouds are storm clouds, however. If they rise to a higher altitude, or if they disappear, fine weather is likely to follow. If they accompany a rising barometer, fair weather is likely to continue.
Cirro-stratus clouds covering the western horizon to a height of 30 degrees or more indicate rain within twelve hours as a rule. This is a still more certain indication if the lower edge of the cloud is wavy. A cirrus patch with streamer edges, which increases in size, indicates snow.
Clouds moving apparently against a surface wind in reality are moving with an upper current of the air. That is, crosswinds are blowing, and cross-winds very commonly precede rain or snow; a departing storm may also clear with crosswinds.
When ye see a cloud rise out of the west, straightway ye say: There cometh a shower; and so it is.—Luke xii, 54.
The greasy, gray clouds which are characteristic of tropical skies during the rainy season are sometimes seen during summer in northern latitudes. They are pretty certain to indicate a heavy downpour.
Greenish-tinted masses of cloud collecting in the southeast indicate heavy rains.
A mackerel sky—twelve hours dry.
Rain from high clouds or from thin clouds does not last long.
If detached clouds increase in size the moisture of the air also is increasing; if they decrease in size and disappear the moisture is decreasing. While the former condition in itself does not indicate an approaching storm, it is instructive in connection with other local indications.
A sky overcast with high clouds does not indicate stormy conditions if the clouds remain high. If the pressure falls and the clouds lower, stormy weather may be expected.
Rapidly increasing cumulus clouds indicate thunder-storms. A thunder-head or high cauliflower top to a cumulus cloud denotes a rapid updraught, which in itself is the beginning of a thunder-storm.
Still and very slowly moving cumulus clouds indicate a continuance of fair weather.
A cloud layer against the side of a mountain range, if rising to a greater height, indicates increasing pressure; if dropping lower, decreasing pressure.
Cirro-stratus together with alto-stra,tus clouds indicate precipitation with a probability of about 90 per cent.—McAdie.
Animal and Plant Indications.—To assert that four-footed animals, birds, and insects sometimes foretell approaching weather conditions is to make a very radical claim which cannot be established. But to assert that they do not recognize existing conditions and respond to them, and to weather changes in progress, is to fly in the face of the experience of four thousand years.
To most animal life weather conditions are of even greater importance than they are to humanity. If the experience of naturalists, and of those who are in close contact with herds and with bees is worth anything, one must admit that nature has provided them, not with “prophetic instinct,” but with keener sensitiveness to changes in weather conditions than is possessed by human beings. The bison is especially sensitive to weather changes.
All shepherds agree that before a storm, sheep become frisky, leap and butt one another.—Folklore Journal.
When horses and cattle become restless and uneasy, a change to unsettled weather may be expected.
When fowls oil their feathers and are unusually noisy, unsettled weather may be expected.
A bee was never caught in a shower.
When bees hover about their hives and refuse to take flight, unsettled weather may be expected.
When house flies bite, expect rain.[3]
When spiders strengthen their webs rain may be expected.
The song of the robin bringeth rain.
The odor of plants of the nightshade family becomes very rank with the approach of rain.
Milkweed closing at night indicates foul weather.
The convolvulus derives its name from the fact that its flower closes when a rapid increase of moisture occurs. This is true also of the pimpernel. The pitcher plant, on the other hand, opens to receive the coming shower. The leaves of the sugar maple, the Cottonwood and the sycamore turn so as to show the under side on the approach of a shower. Occasionally this is noticeable in the case of clover.
Experience will teach the observer the value of popular weather signs and traditions. The experience of out-of-door men whose employments are affected by weather conditions should not be tossed lightly aside. Perhaps the explanation of their reasoning may not bear critical analysis; the results, on the other hand, are apt to have a high value. Weather science now has treatises of inestimable value, but no book from which weather knowledge may be obtained surpasses wind and sky.
Indications of Heavenly Bodies.—It is hardly necessary to note that such indications are due to the effects of the varying moisture content of the air, together with slight refractions and diffractions caused by the moisture of the air.
Red sun in the morning, let the shepherd take warning.
A circle around the sun foretells foul weather.
The circle of the sun wets the shepherd.
A mock sun brings rain.
The moon with a circle brings water in her beak.
A lunar halo indicates rain; the larger the halo the sooner may rain be expected.
A large ring around the moon, and low clouds, rain will follow in twenty-four hours; a small ring and high clouds, rain in several days.
The halo around the sun or the moon is neither more nor less than a very faint rainbow caused by the refraction of light rays as they pass through mist or very thin cloud matter. It is therefore a phenomenon of humidity.
Before the rising of a wind the fainter stars are not visible, even on a clear night.—Pliny.
Mixed air currents cause so much refraction of light that feeble points of light are not perceived. With clear, still air the stars are very bright. In astronomical observatories, observations made on windy nights have but little value, so great is the blurring from refraction. The higher, the power of the telescope, the greater the impairment of visibility.
- ↑ The material for much of this chapter is inspired by Professor Edward Garriott’s Weather Folklore, published by the U. S. Weather Bureau.
- ↑ The narrow strip along the Gulf Coast should be excepted from the general rule. In summer it is within the Trade Wind belt.
- ↑ This is not true of the house fly. The biting stable fly, however, seeks shelter indoors on the approach of stormy weather.