For thousands of years, the working people of our country have summarized rich experience in "cloud watching and weather prediction" based on the changes in the shape, direction, speed, thickness, and color of clouds during production practices. They have also compiled these experiences into proverbs. Here we will gather these proverbs related to "cloud watching and weather prediction" together for those who are interested to observe and compare.
"Heavenly hook-shaped clouds, earthly drizzle": Hook-shaped clouds are called cirrus uncinus in meteorology. They usually appear before warm fronts and low pressure systems. The appearance of cirrus uncinus indicates that a front or low pressure system is about to arrive, which is a harbinger of rain. However, after rain or during winter, if hook-shaped clouds appear, there will be continuous clear days or frost, hence the sayings "hook-shaped clouds dissipate, clear and dry weather," and "winter hook clouds, dust storms."
"Fortress clouds, rainy weather": Fortress clouds refer to altocumulus castellanus or stratocumulus castellanus, often appearing before a low-pressure trough, indicating unstable air. There will be thunderstorms approximately 8-10 hours later.
"Clouds meeting clouds, rain pouring down": Clouds meeting clouds refer to upper and lower cloud layers moving in different directions, meaning inconsistent wind directions at different heights where clouds reside. This often occurs near fronts or low-pressure areas, predicting rain. If clouds move against the ground wind direction, there is a saying "clouds moving against the wind, the sky will change."
"River pigs crossing the river, heavy rain": River pigs refer to scud clouds below nimbostratus clouds. The appearance of such clouds shows that water vapor in the nimbostratus clouds is abundant, and heavy rain is imminent. Sometimes, scud clouds are blown by strong winds to places with clear skies, and at night, you can see clouds resembling river pigs floating across the 'Milky Way,' which is also a precursor to rain.
"Cotton-like clouds, rain coming soon": Cotton-like clouds refer to floccus altocumulus clouds. Their appearance indicates instability in the middle atmosphere. If the air contains sufficient moisture and rises, cumulonimbus clouds will form, leading to thunderstorms.
"Gray cloth hanging in the sky, continuous drizzle": Gray cloth clouds refer to nimbostratus clouds, often evolving from altostratus clouds becoming thicker and lower, covering large areas with thick layers. These clouds contain ample water vapor and frequently produce continuous precipitation.
"Clouds moving east, smooth travel; clouds moving south, rising water levels; clouds moving west, need for raincoats; clouds moving north, good for drying wheat": Predicting weather conditions based on the direction of cloud movement, clouds moving east or north indicate clear weather; clouds moving west or south predict impending rain. The direction of cloud movement generally represents the wind direction at their respective heights. This proverb explains the distribution of clouds at different locations within a low-pressure system. It applies to clouds densely covering the sky, being low and moving relatively fast.
"Clouds moving east, gusty winds; clouds moving west, need for raincoats": The clouds referred to here are low clouds in low-pressure areas. Low pressures move from west to east (often from southwest to northeast). Clouds moving west indicate that the area is ahead of the low-pressure system, and local rainfall is expected as the low-pressure system approaches. Clouds moving east indicate that the low-pressure system has already passed through, leaving the area behind it, and the weather will soon clear up, often accompanied by some wind before clearing.
"Dark clouds meet the setting sun, no rain today, tomorrow": Refers to when a dark cloud like a city wall rises under the horizon as the sun sets, indicating that the dark clouds are moving eastward, and the rainy weather from the west is approaching, bringing rain. Generally speaking, if the mid-level clouds are encountered, it will rain that night; if high-altitude clouds are encountered, it will rain the next day. However, if the dark clouds in the west appear in blocks or are disconnected, or if the local area was originally cloudy, then it is not a sign of future rain.
"Unlocking the sky in the northwest, bright sunshine tomorrow": Refers to when a crack appears in the clouds in the northwest during rainy weather, revealing a patch of blue sky, known as "unlocking the sky." This indicates that the local area is already in the rear part of the rainy weather system. As the rainy system moves eastward, the local area will stop raining and the clouds will dissipate, improving the weather.
"The sun makes an appearance, won't be seen for three days": Refers to spring and summer when, during a rainy day at noon, the clouds split open, allowing the sun to briefly appear, but the clouds quickly reassemble and thicken. This indicates that the local area is under the influence of a quasi-stationary front. Near the quasi-stationary front, airflow ascends strongly and variably. When ascending airflow strengthens, the clouds thicken and rainfall increases; when ascending airflow weakens, the clouds thin out, and rainfall decreases or stops. Around noon, due to intense solar radiation, the upper parts of the clouds evaporate, or the ascending airflow beneath the clouds weakens, causing the clouds directly overhead to split open. As the solar radiation weakens or the ascending airflow beneath the clouds strengthens, the split clouds reassemble and thicken. Therefore, "the sun makes an appearance" often predicts continued overcast and rainy weather. This saying is similar to others like "the sun smiles, temples get drenched" or "a brief shine, a yard of rain."
"Koi fish spots in the sky, no need to turn the grain tomorrow" (block clouds, scorching heat): Koi fish spots refer to altocumulus translucidus clouds. The air mass producing such clouds is stable. By evening, encountering descending airflow, the clouds rapidly dissipate, indicating fine weather the next day. However, if the clouds resemble small fish scales, they are cirrocumulus clouds, often occurring ahead of low-pressure troughs or on the periphery of typhoons, suggesting windy or rainy weather in the near future. Hence, there is also the saying "fish scale sky, either wind or rain."
"Cloud hooks point in one direction, wind comes from that direction": Cloud hooks refer to the tails of cirrus uncinus clouds, appearing high in the sky, sometimes with small hooks at the top, or arranged in rows. The direction pointed by the small hooks at the top indicates the direction of high-altitude winds, which are often linked to ground-level winds. Therefore, the general direction of the cloud hooks can roughly predict the origin of the wind.
"Dark clouds cover the morning, even without rain, wind arrives": Refers to black clouds covering the southeast direction in the morning, predicting rain. Because the southeast wind blowing in the morning is warm and humid, its temperature is higher than the local air, creating a cold upper layer and hot lower layer, making it easy for water vapor to rise and form clouds. With daytime heating of the ground, the air rises more, prompting the clouds to lift higher, and the water vapor cools into droplets, possibly changing the weather to either windy or rainy conditions.
"Yellow clouds flipping up and down, hailstones coming": Yellow clouds are mostly caused by strong warm and humid air rising, resulting in showers and hail.
"Mountains wearing hats, heavy rain coming": Mountains wearing hats refer to low atmospheric pressure and abundant water vapor forming cloud layers at the mountaintops. Whether it rains or not generally depends on the situation. If the clouds gradually lower and thicken, the possibility of rain increases; conversely, if the clouds rise and thin out, the chance of rain decreases.
"Morning red sky, stay indoors; evening red sky, travel far": Indicates that red skies in the morning predict rain, while red skies in the evening predict clear weather.
"Cloud eating fog means rain, fog eating cloud means clear": Seeing fog followed by clouds suggests the possible arrival of low pressure, which is a sign of rain. Conversely, if the clouds disappear and fog arises, it indicates that the low pressure has passed, and clear weather is approaching.
"Sunset rays, rain within three days": Refers to sunlight shining through gaps in the clouds, called "sun rays." Evening appearances of sun rays indicate strong convection, predicting rain.
"Morning red sky, stay indoors; evening red sky, travel far": Morning red skies in the east and red skies in the west mean sunlight scattering off clouds, indicating abundant moisture in the air or an incoming rain system. Combined with generally unstable daytime air, the weather will likely turn to overcast and rainy; if evening red skies appear, it signifies that the western sky has cleared. Evening convection typically weakens, causing the eastern clouds that form the red skies to move further east or dissipate, predicting clear weather.
"Long sunny weather followed by fog means overcast, long overcast weather followed by fog means sunny": Refers to fog after prolonged sunny weather, indicating the approach of warm and humid air, making the air moist and signaling overcast and rainy weather. After prolonged overcast weather, fog indicates that the cloud layer is thinning and splitting, with surface temperatures dropping, causing water vapor to condense into radiation fog. After sunrise, the fog will dissipate, leading to clear weather.
In warm seasons, if castle-like clouds appear in the morning, it indicates that the moist air layer at this height is already very unstable. By afternoon, once the lower level convection develops, the combination of upper and lower unstable layers will generate strong convective movements, forming cumulonimbus clouds and causing thunderstorms. Hence the saying "early castle clouds, afternoon heavy rain."
Additionally, clouds with weather forecasting signs often exhibit certain continuities, seasonal characteristics, and regional features during their evolution. When clouds appear in the order of cirrus, cirrostratus, altostratus, and nimbostratus, moving continuously from afar and gradually increasing in quantity, lowering in height, and thickening, it predicts the imminent arrival of overcast and rainy weather. Conversely, if the clouds rise in height, thin out, and disintegrate from layered formations into scattered ones, there will be no overcast or rainy weather. In warm season mornings, if flat-bottomed, convex-topped, isolated cloud masses (cumulus humilis) or fast-moving white broken clouds (fractus cumulus) appear, it indicates stability in the middle and lower air layers, predicting clear weather.
Moreover, the color of clouds can also forecast certain weather conditions. For example, hail clouds initially appear with white tops and black bottoms, then red appears in the clouds, forming chaotic clouds of white, black, and red with yellow edges. Black results from sunlight not penetrating the cloud body; white is due to non-selective scattering or reflection of sunlight by the clouds; red-yellow is due to selective scattering of sunlight by some cloud droplets (with diameters ranging from one-thousandth to one-hundredth of a millimeter). Sometimes rain clouds appear pale yellow, but the color is uniform and does not wildly fluctuate. Many proverbs predict hail based on cloud color and shape. For instance, Inner Mongolia has proverbs like "not afraid of black clouds, afraid of black clouds mixed with red, most afraid of yellow clouds with white bugs underneath," and Shanxi has proverbs like "yellow clouds flipping, hail weather; chaotic clouds, hails in groups; clouds fighting, hail falling," "black clouds, yellow clouds, earth-red clouds, flipping and churning clouds, mostly severe hail disasters," etc. Also, "afternoon black clouds rolling into lumps, wind, rain, and hail coming together," "yellow sky, sultry heat, clouds flipping, prevent hail," etc., all indicate that when air convection is strong, clouds develop rapidly, like dense smoke rushing upwards, and the clouds roll violently up and down, it's easy to have hail.