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As part of the home dashboard I am developing, I get information about incoming rain. It is given in mm/min.

Is there a consensus on the precipitation rate that is called "light rain", or "heavy rain"? (I would like, if this is possible, to use some standardized naming)

WoJ
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2 Answers2

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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 this one (PDF page 66, page label 58):

Light rain: falling rate of less than 2.54 mm/h. This would be < 0.042 mm/min.

Moderate rain: falling rate of more than 2.8 mm/h, but less than 7.6 mm/h. This would be 0.042 mm/min - 0.127 mm/min.

Heavy rain: falling rate of more than 7.6 mm/h. This would be > 0.127 mm/min.

So clearly different standards compared to the DWD answer (note: 1 l/m² is equivalent to 1mm). Nowadays, automated weather stations use rain gauges with sensors, so a modern station with the computer inside has a clear and accurate computation of rain/snow falling rates. But there is no universal standards.

Spencer
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DanielC
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    Since you reference the other answer, you should point out that DWD's use of l/m^2 corresponds to 1mm in NOAA's definition. – Spencer Dec 10 '21 at 16:29
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The German Weather Service (Deutscher Wetterdienst, DWD) provides the following definitions:

Heavy rain is defined as large amounts of precipitation during a fixed period of time. [...]

The DWD issues warnings of heavy rain using three categories:

  • heavy rain: 15 to 25 l/m² within 1 hour or 20 to 35 l/m² within 6 hours
  • severly heavy rain: 25 to 40 l/m² within 1 hour or 35 to 60 l/m² within 6 hour
  • extremely heavy rain: above 40 l/m² within 1 hour or above 60 l/m² within 6 hour

Source: https://www.dwd.de/DE/service/lexikon/begriffe/S/Starkregen.html and https://www.dwd.de/DE/wetter/warnungen_aktuell/kriterien/warnkriterien.html?nn=508722#doc453962bodyText3, translation my own.

Heavy rain is distinct from constant rain by the period of time, over which the rain falls, as well as the total amount of rain per m². Still, heavy rain events may be part of constant rain periods.

Erik
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