Precipitation field in OpenWeatherMap API 2.5

Question

I'm using the Open Weather Map API for weather forecast. Current available version is 2.5 Here is a snippet of XML

...
<time day="2013-09-07">
<symbol number="500" name="light rain" var="10d"/>
<precipitation value="2.5" type="rain"/>
<windDirection deg="8" code="N" name="North"/>
<windSpeed mps="1.16" name="Calm"/>
<temperature day="14.56" min="12.79" max="14.56" night="12.79" eve="14.56" morn="14.56"/>
<pressure unit="hPa" value="973.09"/>
<humidity value="98" unit="%"/>
<clouds value="broken clouds" all="68" unit="%"/>
</time>
...

Here is the API request.

Does anyone know the unit of the field precipitation?

2.5 are mm of rain? perhaps a probability?

Answer 1

Their description for protocol of weather station data transmission describes data for upload in millimetres for both snow and rain. And their JSON API v.1.0 (previous one) states Precipitation volume i.e. not probability.

All in all, it is precipitation volume in mm.

Answer 2

You can get precipitation probability with a forecast (not history as far as I know) from forecast.io

{"time":1421080800,"precipIntensity":0.0401,"precipIntensityError":0.0099,"precipProbability":0.47,"precipType":"rain"}

Answer 3

according to their API documentation (http://openweathermap.org/weather-data), this value represents rain (Precipitation) in the last 3 hours in mm (milimeters).

It would be great if rain probability was provided, but I don't think so.

Answer 4

From 2020-08-13: https://openweather.co.uk/blog/post/new-probability-precipitation-openweather-forecasts

... we have added the Probability of precipitation parameter to our weather forecasts.

The meteorological definition of “probability of precipitation” is:

“The chance that measurable precipitation (0.1 mm of rain or snow) will fall on any random point of the forecast region during the forecast period.” Simply put, this parameter shows the “chance of rain or snow” forecast.

You can find information about the probability of precipitation in each API response in the pop field. This is available to our users in the following OpenWeather APIs:

• One Call API – in “hourly” and “daily” parts of API response
• Hourly Forecast 4 Days
• Daily Forecast 16 Days
• 5 Days / 3 Hours Forecast

Look for e.g. hourly.pop in "One Call API 2.5" (https://openweathermap.org/api/one-call-api#parameter) or the newer "One Call API 3.0" (https://openweathermap.org/api/one-call-3#example)

Probability of precipitation. The values of the parameter vary between 0 and 1, where 0 is equal to 0%, 1 is equal to 100%