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?

Thanks in advance.

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"}