diff --git a/homeassistant/components/weather/openweathermap.py b/homeassistant/components/weather/openweathermap.py
index b70413b9565..0e3a6f90b70 100644
--- a/homeassistant/components/weather/openweathermap.py
+++ b/homeassistant/components/weather/openweathermap.py
@@ -149,6 +149,15 @@ class OpenWeatherMapWeather(WeatherEntity):
     def forecast(self):
         """Return the forecast array."""
         data = []
+
+        def calc_precipitation(rain, snow):
+            """Calculate the precipitation."""
+            rain_value = 0 if rain is None else rain
+            snow_value = 0 if snow is None else snow
+            if round(rain_value + snow_value, 1) == 0:
+                return None
+            return round(rain_value + snow_value, 1)
+
         for entry in self.forecast_data.get_weathers():
             if self._mode == 'daily':
                 data.append({
@@ -159,7 +168,9 @@ class OpenWeatherMapWeather(WeatherEntity):
                     ATTR_FORECAST_TEMP_LOW:
                         entry.get_temperature('celsius').get('night'),
                     ATTR_FORECAST_PRECIPITATION:
-                        entry.get_rain().get('all'),
+                        calc_precipitation(
+                            entry.get_rain().get('all'),
+                            entry.get_snow().get('all')),
                     ATTR_FORECAST_WIND_SPEED:
                         entry.get_wind().get('speed'),
                     ATTR_FORECAST_WIND_BEARING: