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Rain, or as it is called in Japanese, /ame/ 雨 is formed from liquid droplets of water that have condensed from atmospheric water vapor that then fall from the sky under gravity. It has been the source of worship and reverence from cultures across the world due to both its nurturing and destructive powers. 

Wherever you are in the world, the air contains some amount of water vapor. This water vapor may originate from evaporation (蒸発) off the oceans (海洋), lakes (湖), or the ground (地面) or it may be provided by transpiration (蒸散) from plants (植物). Rain falls from the sky out of clouds (雲), but rain is also not the only form of precipitation. Furthermore, the process of water going from liquid to gas to liquid/solid and so on creates a cycle known as the "water cycle." 

Though words associated with rain such as 雨 (rain), 雨雲 (raincloud), 雷雨 (thunderstorm), etc. may seem simple, the Japanese language is rich with rain-related words. Just the words to describe the various of aspects of precipitation thus far requires an extensive knowledge of weather vocabulary, much of which you would naturally learn from watching weather reports (天気予報).  

On other planets, what falls as "rain" may not be made of water, but in this discussion, we'll mostly be talking about the H2O that falls out of our sky. 

※雨季 refers to the rainiest portion of the year, which although that translates to "rainy season," this word itself is not limited to any region's particular rainy season. The rainy season in Japan is still known as 梅雨, although this word may also be read with its ON readings as バイウ, especially in compounds such as 梅雨前線 (seasonal rain front). 

※雨露 may be read as ウロ or あめつゆ. The former is restricted to the written language whereas the latter is used in the spoken language. 

※雨水, when used to mean "rainwater," is read as あまみず in the spoken language. 

※Many words created with the ON reading ウ are literally in nature such as 白雨, which although directly means "rain which appears white," is a literary euphemism for "rain shower," which would be typically expressed with more common words in the spoken language like 俄雨（にわかあめ）or 夕立（ゆうだち）.

※When read as じう, 時雨 is a rare literary word meaning "read when falls at a good time." However, these same Kanji are usually read exceptionally as しぐれ, which is a set phrase meaning "rain shower" during late autumn to early winter. しぐれ comes from the verb 時雨（しぐ）れる, which carries the verbal meaning of a such a shower falling. 
※雨模様 may alternatively be read as あまもよう. Though 模様 is a Sino-Japanese word, in this expression もよう is likely a corruption of 催（もよ）い as 雨催（あまもよ）い happens to be an older form of the phrase. Other synonyms to these expressions include 雨気（ウキ・あまけ）and 雨気色（あまげしき）.

Not only is important as a standalone Kanji, but it is also used as a radical (部首) in a myriad of other Kanji related to weather phenomena. Its colloquial radical name is 雨冠（あめかんむり）, but its technical radical name is 雨部 as seen in the prior chart. This radical has 8 strokes (8画) and is the 173rd traditional radical in the Kangxi Dictionary (康煕字典・こうきじてん).

The generic word for precipitation is 降水, which is a Sino-Japanese compound literally meaning "falling water." Indeed, precipitation in a broad definition is water vapor (水蒸気) which condenses (凝結) into either liquid (液体) or solid (固体) form and then falls (落下) down due to gravity (重力). 

There are various morphologies (形態) of precipitation that are distinguished in Japanese meteorological terminology. The chart below lists these terms as well as other important vocabulary related to precipitation. 

The Many Words for "Precipitation"

Although translating 降水 as "precipitation" is accurate, it can be understood in two different ways. It can either refer to the phenomenon of precipitation falling to the surface, or it can refer to precipitation that has fallen. In the latter case, it would be colloquially understood a "rainfall," but the macro interpretation which encompasses any form of precipitation is what is used in any meteorological context. For instance, 降水確率 (chance of precipitation) on your phone doesn't just refer to rain. 

In more technical weather reports, the Kanji 水 will be switched out for the Kanji of the precipitation being particularly referenced. Thus, "rainfall" is 降雨（こうう）, "snowfall" is 降雪（こうせつ）, and "hailfall" is either 降雹（こうひょう） or 降霰（こうさん） depending on the size of the hail (see above for size differentiation). 

In the spoken language, 降水, 降雨, and 降雪 are fairly common as they're often used by weather reporters. However, 降雹 is rarely heard and 降霰 would only be understood in the written language. To combat this, the native phrasings of these words are used in everyday conversation instead. 

Also, if one's goal is to use "precipitation" in the sense of "amount of...that fell," you'll need to add 量, whether you're using formal Sino-Japanese vocabulary or colloquial native vocabulary. As for the Sino-Japanese vocabulary, those compounds can be understood in the same two ways as 降水. Thus, 降雪 may refer to the act of snow falling or it can refer to snowfall, and to emphasize "amount," you just add 量. 

※Though there are Sino-Japanese morphemes present in the second column as well, the percentage is drastically different. 

※Snowfall is also talked about in terms of how much snow accumulates on the ground, which may not be the same amount of snow which falls from the sky. The "accumulation of snow" is 積雪（せきせつ） and the "amount of accumulated snow" is 積雪量. Colloquially, these words may be replaced with 雪が積もること and 積もった雪の量 respectively. 

※As can be seen from it having been added to this second chart, "frost" may also be thought as precipitation as deposits of ice crystals which form directly from water in its gas state may "fall," but frost may also occur from water vapor that is already on some surface. 霜's readings are as follows: ソウ (ON) and しも (KUN). 

On Earth (地球), the water cycle (水循環)is driven by solar energy (太陽エネルギー) in a continuous cycle of water changing between its solid phase (固相), liquid phase (液相), and gas phase (気相).  The general flow of the water cycle is evaporation/transpiration (蒸発散) → condensation (凝結) → cloud formation (雲の形成) → precipitation (降水) → discharge (流出). Below are the various phenomena that occur in the water cycle.  

The greatest contributor to the formation (生成) of clouds is the existence of updrafts (上昇気流). When air masses (空気塊) contains water vapor carried up higher into the atmosphere (大気) expand (膨張) due to drop (低下) in air pressure (空気圧) and then adiabatically cool (断熱冷却), the result is that humidity (湿度) rises (上昇) as the amount (量) of water vapor doesn't change. 

Though the dew point (露点温度) will change according to air temperature (気温) and the amount of water vapor prior to being lifted upward, when the dew point is exceeded, that results in supersaturated vapor (過飽和蒸気). When normal air containing particulates (微粒子) reaches a supersaturation degree (過飽和度) of 1%, the condensation process (凝結過程) begins in which water vapor continues to coalesce into cloud condensation nuclei (雲粒), which in turn produce cloud droplets (雲核), whether they be formed with water vapor that liquifies (液化) or freezes (凝固). 

Now that we've gone over a little bit about how clouds are formed, let's look at the Japanese names for all the kinds of clouds one can find in the sky.

※In addition to the 'kinds' of clouds listed above, there are also other nonacademic descriptions of clouds such as 笠雲 (cap cloud) and 吊るし雲 (roll/rotor cloud). 

Rain falls from the sky in the form of raindrops. Although we've learned about the meteorological difference between the kinds of "rain" based on the diameter and temperature/freezing nature of rain, we have yet to actually go over the words for "raindrop" aside from the generic word 雨粒 and a brief mention of 雨垂れ. In total, there are four words to distinguish.

・雨粒（あまつぶ）: Refers to each individual droplet of rain that falls from the sky.  
・雨滴（うてき）: A literary word which typically refers to large drops of rain (大粒の雨) falling from the sky.
・雨垂れ・ 霤（あまだれ）: Refers specifically to rain following from the eaves (軒) of buildings.
・滴・雫（しずく）: Literally, "drop of water," when used in reference to rain, it has a poetic sound to it.

※The antonym of 大粒 (large drop) is 小粒 (small drop). 

Rain is quantified for meteorological agencies such as the 気象庁 of Japan by the amount (雨量) that falls over specific periods of time. Rain meters (雨量計) are placed throughout the country to record rainfall accurately, and in Japan, totals are shown in millimeters--the counter being ミリ（メートル）. Rain intensity (雨の強さ) is typically given by the hour, but when precipitation within a short period of time is too intense, rainfall amounts may be given in increments of 10 minutes to emphasize the severity of the downpour (土砂降り). 

※At first glance, 少雨（しょうう）, 強雨（きょうう）, and 弱雨（じゃくう） are literary equivalents of 小雨, 強い雨, and 弱い雨 respectively. Although they are completely synonymous with their respective counterparts, these 'literary' words are very rare and only seen in contexts in which a writer is trying to write more concisely. However, for official meteorological reports, only 小雨, 強い雨, and 弱い雨 are used as being understood clearly by the public is of utmost importance. On the other hand, 強雨 is starting to become more common thanks to the relatively newly coined phrase 短時間強雨, which is equivalent to "short-span heavy rain." 

※Anything 強い雨 or greater may also be colloquially described as 大雨（おおあめ）. Whenever this word is used in meteorological reports, it is further described as being 集中豪雨（しゅうちゅうごうう） or 局地的大雨（きょくちてきおおあめ）--see below. 
※猛烈な雨 may also be referred to as 豪雨 in weather reports--see below.

※雨強し: This expression refers to heavy rainfall, which in meteorology would be rain greater than 15 mm an hour. However, the meteorological definition of 強い雨 is 20-30 mm. 

～降（ぶ）りになる

When referring to rain becoming either of the states above, alternative expressions may be found utilizing ～降（ぶ）りになる. 

The terms above are used as the standard expressions for rain intensity in weather reports made in Japan, but there is an array of terminology used colloquially to describe the nature of rainfall. 

In addition to the slew of words we just covered regarding rain intensity, Japanese is also full of words which describe rain in terms of season. 

Though it may feel like we have already gone over enough words related to rain, the world of Japanese literature provides us even more descriptive rain-related words to brighten up a passage. Though none of the words below are particularly common, their meanings should be more than evident so long as you have a strong knowledge of Kanji and can recognize the ON readings of said characters.

The word 雨季 refers to "rainy seasons" irrespectively of any particular region. As for the Japanese archipelago, the "rainy season" is known as 梅雨, read either as バイウ or つゆ, and lasts from May to July. 

The reason for the use of the Kanji 梅 is due to the start of the rainy season being aligned with when plums ripened. This led to the coining of the phrase 入梅（にゅうばい） which refers to the "start" of the rainy season. This may also be expressed by 梅雨入（つゆいり）, which may be seen shortened to ついり. 梅雨, regardless of reading, may also be alternatively spelled by using the Kanji 黴 meaning "mold" instead as it, too, has the ON reading バイ, and the moist conditions of the rainy season are perfect for mold growth. 

If there are so many rain-related words in Japanese, it makes sense that there are even more set phrases--idioms, proverbs, four-character idioms, etc.--about rain. As we have already seen an extensive list of expressions, let's leave off here with just a handful of expressions limited to those that are, in fact, well-known and common.

• 雨男（あめおとこ）: Man who brings rain with him wherever he goes.
• 雨女（あめおんな）: Woman who brings rain with her wherever she goes.
• 一雨ありそう（な）: To have the feeling that some sort of commission is about to happen.
• 雨垂れ石を穿（うが）つ: Literally "rain drops will drill through rock (over time)," this proverb refers to no matter how little one's strength may be, if one perseveres, benefits will be reaped. 
• 雨後（うご）の筍（たけのこ）: Literally "bamboo shoots after rain," this is a euphemism for the same sort of thing appearing over and over again.
• 櫛風沐雨（しっぷうもくう）: Four-character idiom referring to undergoing hardships as if one were struggling through the wind and rain.
• 晴耕雨読（せいこううどく）: Four-character idiom referring to working in the field when the weather is fine but reading at home when the weather is rainy, this may also be extended to referring to living in quiet retirement in which one's time is divided between work and intellectual hobbies.
• 遣（や）らずの雨: Rain which falls that is seemingly trying to prevent you from having people go home, or simply just preventing people to leave in general.
• 雨夜（あまよ）の月: Literally "moon on a rainy night," this is a euphemism which relates to something which cannot be seen outside of imagination. 
• 黒風白雨（こくふうはくう）: Four-character idiom referring to heavy, harsh wind with the strong, whitish rain of a sudden shower.
• 篠突く雨（しのつくあめ): Heavy rain that looks as if it is bamboo bound together and dropped. 
• 雨降って地（じ）固まる: Literally interpreted as "the ground hardens after it rains," this proverb speaks of how adversity strengthens a foundation. It is equivalent to the English proverb "what doesn't kill you makes you stronger." 

Though we have focused entirely on rain composed of just H20, there are other expressions that utilize 雨 which not (entirely) be actually rain made of water. Below are such expressions.

When counting "rain," one must consider whether "rain" incidents or raindrops are being counted. 

When counting incidents of rain, you may find the counters ～雨（あめ） and ～降り listed. Though 一雨（ひとあめ）and 一降（ひとふ）り do refer to individual instances of rain, these counters are not typically used beyond 1, and even if they were, native numbers would only be used for 1-2. Typically, instances of rain are counted with either ～度 or ～回. 

As for counting "raindrops," you may find the native counter ～粒（つぶ） used in figurative contexts for small numbers, but the use of native numbers typically stops by 4. Typically, to count raindrops, the counter ～滴（てき） is used with ～点 being a rare alternative.  

There is also an array of onomatopoeia used to describe how rain sounds. These onomatopoeias are heavily tied to how intense the rain is. 

The etymology of the native Japanese word /ame/ has been the subject of intense scrutiny. Why is there an intrusive /s/ in words such as 春雨? Also, where is there a number of onomatopoeia which share this /s/ sound? On top of this, although most native rain-related vocabulary utilizes some form of /ame/, the word 樋（とい） meaning "gutter" is a major exception to this norm. 

These factors have driven some linguists to posture whether rain-related vocabulary from other language families might have contributed to the Japanese lexicon. Though such hypotheses require a major pinch of salt, let's look at some potential ties that have been posited. 

Since Old Japanese, there have been /s/ initial rain-related words such as そぼ降る (gentle rain falling), which would have been pronounced as /sopopuru/ at that time. Ignoring the actual quality of the o-vowels of the language at the time, derivative expressions such as どぼん (onomatopoeia for to "plop") , ぽとぽと (onomatopoeia of large drops), ほとばしる (to gush out) and 潤（ほと）びる (to swell from absorbed moisture) abound with /s/ being exchanged out for /t/ or /h~p/. 

Additionally, onomatopoeia such as ざぶざぶ (onomatopoeia for gushing), さばさば (candid), さっぱり (refreshing). ざぶん (splash/plop), etc. exist which don't deviate as much as the previous examples. What's more, the onomatopoeia in さめざめ (crying sorrowfully) is also likely related.

Drop the /s/ and have /b~p/ solidify to /m/ and then one gets /ame/. Thus, /ame/ can be viewed as just one of many derivatives of the initial onomatopoeic expressions. To some scholars, these word forms are thought to potentially have been borrowed from the Austronesian language family in which /sebu/ is a potential reconstruction of a rain-related word. 

As for potential Korean influence, we would need evidence of rain-related words that ultimately don't relate to the そほ morpheme found in Old Japanese, but considering how this morpheme would have already given rise to its derivatives including 雨 by that period, such influence would have to be far more ancient. 

In Modern Korean, the word for "rain" is /pi/. The only rain-related word with this sound in Japanese is 樋. In Classical Japanese, it had the reading とひ, and the  ひ would have been pronounced as /pi/ in Old Japanese. Even if this were viewed as an embedded morpheme, the word itself would be an amalgamation of a random borrowing into the language and not indicative of rain terminology being shared with Korean. 

In this lesson, we have thoroughly gone over all sorts of rain-related terminology that exists in Japanese from various angles. When you open up a new novel and encounter beautifully written weather descriptions, hopefully no word will be left as a mystery upon mastering the content shown here.