132 votes
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How can a storm drop 40 inches (1 metre) of rain?

You were right to question whether the atmosphere really held that much water. It comes nowhere close! We use precipitable water to track this, which is the measure of all moisture in the entire ...
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47 votes

What does a mm of rain mean?

It's confusing to measure liquid in units of length instead of volume, isn't it? Here's how it works. "One millimeter of rain" is actually one cubic millimeter per square millimeter. On average, over ...
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  • 748
28 votes
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At what humidity does it start to rain?

Short answer: humidity is not a proxy for rain starting and no, it does not start raining automatically when 100% humidity is reached (haze or clouds can form though). The onset of rain is dependent ...
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25 votes

How can a storm drop 40 inches (1 metre) of rain?

I invite correction if I missed any details, the column of air above you, at any one time, at 100% humidity can hold maybe 3-6 inches (75-150 mm) of water depending on temperature and it's likey to ...
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  • 5,667
20 votes

What does a mm of rain mean?

It is the amount of rain that it takes to cover the ground X milimeters deep. It is normally measured in 24 hours and is measured each morning at a fixed time like 0900. But now the measurements are ...
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  • 1,820
17 votes

What does a mm of rain mean?

Does it mean that 3mm per square meter was experienced in a specific area, or does it mean that the total amount of rain had a volume such that if it was spread over all of Hong Kong the height ...
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17 votes

Ways to make a "How hard is it raining?" detector for personal use?

If you're open to a more mechanical solution, I'd suggest building a "tipping bucket rain gauge", best explained by a picture (source: https://www.researchgate.net/figure/Sideview-of-tipping-...
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  • 271
15 votes

If it rains harder, does it mean the rain's duration will be shorter?

The intensity of a rainstorm does not actually cause the duration of the precipitation to be shorter. There is a strong correlation, but not in the sense you may be implying here (let me get back to ...
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14 votes

Ways to make a "How hard is it raining?" detector for personal use?

Upon reading the question my first thought was, please define what is meant by "how hard is it raining?". My initial tangent thought was "what about the impact energy of the rain" -...
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13 votes

How can a storm drop 40 inches (1 metre) of rain?

Harvey is almost stationary and is rotating new gulf moisture up the "dirty" side (east of the center). I am outside the main path and have 10+ inches (250 mm) in 30 hours (emptied the rain gauge ...
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13 votes

Ways to make a "How hard is it raining?" detector for personal use?

One way to do that is to estimate how much water is changing. If you can ignore the spill over, then that is approximately how much the puddle is changing. Another idea you can use is to measure the ...
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13 votes

Ways to make a "How hard is it raining?" detector for personal use?

It's not perfect, but a simple solution to the issue of a puddle building up on the resistance plate is to tilt the plate a bit, so that instead of the water building up on the plate it runs off. Your ...
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  • 231
11 votes
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Do forests affect local rainfall and climate significantly?

For rain to fall, water vapour must exist in sufficient quantities in the atmosphere. The main source of atmospheric water vapour is evaporation from oceans. However, evaporation from large bodies of ...
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11 votes
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How do rivers last so long in dry weather?

The rivers are generally fed by water that percolated into the ground, it takes longer for that water to work its way down to the stream so the streams and rivers keep flowing long after the initial ...
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  • 6,465
9 votes
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TRMM rainfall measurement for synoptic systems

The Tropical Rainfall Measuring Mission (TRMM) satellite is a single satellite, carrying multiple instruments on board, as described here. It makes a total of 16 orbits/day at a low altitude of 400 km,...
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8 votes

If it rains harder, does it mean the rain's duration will be shorter?

Robert Cartanio's answer makes very good points, and I'll accentuate them with some examples. Thunderstorms tend to produce "hard rain" and larger scale organized convection will have areas of hard ...
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8 votes
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Could a reported rainfall pH of 3.1 actually be realistic?

A quick literature search seems to confirm Gordons estimation, even at the scale of a whole bucket: [T]he annual mean pH, based upon samples collected weekly during 1970-1971 and weighted ...
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  • 476
8 votes

Why is northern Australia unsuitable for agriculture?

Erratic Climate Lets take Broome, Australia as our example. Broome gets 615mm of rain a year (24 inches), including 58/182/180/102mm in Dec through March. Coupled with average highs in the low 90s, ...
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  • 3,294
8 votes

What does a mm of rain mean?

Given any container with straight sides, 3 millimeters of rainfall will fill up that container to 3 millimeters in depth. The size of the container does not affect this. It holds whether the ...
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7 votes
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The sun sometimes appears pure white after rainfall, how can this be explained?

When it rains the raindrops nucleate around aerosol particles of salt, dust, clay, soot, dimethyl sulphide, etc. In addition a falling raindrop may pick up any particulate matter that may be in its ...
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7 votes

How does evapotranspiration affect rainfall?

Without water in the air, clouds cannot form and evaporate quickly if they do and so a sudden drop in evapotranspiration that resulted in low humidity could decrease the prevalence of rain. But, in ...
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  • 419
7 votes

Could a reported rainfall pH of 3.1 actually be realistic?

Raindrops gain a small amount of acidity as they fall through carbon dioxide in the air, but that's not what this question is about. Raindrops commonly start off as ice crystals which have to nucleate ...
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7 votes
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Why is thunder and lightning rare, even though it rains frequently?

Rain in a climate such as Ireland is most often stratiform. That is, it is created when moist air is lifted by a front, or by divergence in the upper troposphere. Thunderstorms involve buoyant air, ...
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  • 96
6 votes

How can there be a hot summer with rain and no thunderstorms and lightning?

This is an El Nino summer, and a very strong one and a very weird one at that. Weather patterns are messed up world-wide. Apparently a stable high pressure cell has set up that oscillates back and ...
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6 votes

Is there an upper bound to the amount of rain that can fall in an hour?

From http://www.srh.noaa.gov/eax/?n=holtmorecrain1947 A very moist airmass was in place across Missouri during the afternoon and evening of 22 June 1947, as evident by dewpoint temperatures in the ...
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6 votes

Where can I find the record for the heaviest single-day rainfall ever recorded on any date at a specific location?

Sounds like your question, like most questions about historical data, might be a little challenging to find the right source, as it often is around the world. But seeing you said Atlanta brightened ...
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6 votes

How can a storm drop 40 inches (1 metre) of rain?

The atmosphere can "hold" only maximum 75mm worth of precipitation at any given locality, this is true. However, this particular hurricane Harvey was a very slowly moving structure. The vortex would ...
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6 votes

What does a mm of rain mean?

It literally means that the water depth will be 0.5mm. For example, if you place a container under the rain and it fills up to 0.5mm, then the precipitation is 0.5mm. Despite the fact that a wide ...
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6 votes

Is there a consensus on the "heaviness" of rain?

If there was a worldwide standard, then WMO would have imposed it to its members. Here are the definitions in the American (NOAA/NWS) standard (summarized at NJWeatherScan, initially from manuals like ...
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