Fix OpenWeatherMap forecast timestamp (#45124)

homeassistant/components/openweathermap/sensor.py

@@ -1,7 +1,10 @@
 """Support for the OpenWeatherMap (OWM) service."""
+import datetime
+
 from .abstract_owm_sensor import AbstractOpenWeatherMapSensor
 from .const import (
     ATTR_API_FORECAST,
+    DEVICE_CLASS_TIMESTAMP,
     DOMAIN,
     ENTRY_NAME,
     ENTRY_WEATHER_COORDINATOR,
@@ -95,5 +98,10 @@ class OpenWeatherMapForecastSensor(AbstractOpenWeatherMapSensor):
         """Return the state of the device."""
         forecasts = self._weather_coordinator.data.get(ATTR_API_FORECAST)
         if forecasts is not None and len(forecasts) > 0:
-            return forecasts[0].get(self._sensor_type, None)
+            value = forecasts[0].get(self._sensor_type, None)
+            if self._device_class is DEVICE_CLASS_TIMESTAMP:
+                value = datetime.datetime.fromtimestamp(
+                    value, datetime.timezone.utc
+                ).isoformat()
+            return value
         return None

homeassistant/components/openweathermap/weather_update_coordinator.py

@@ -138,7 +138,7 @@ class WeatherUpdateCoordinator(DataUpdateCoordinator):
 
     def _convert_forecast(self, entry):
         forecast = {
-            ATTR_FORECAST_TIME: entry.reference_time("unix") * 1000,
+            ATTR_FORECAST_TIME: entry.reference_time("unix"),
             ATTR_FORECAST_PRECIPITATION: self._calc_precipitation(
                 entry.rain, entry.snow
             ),