Retrieve current weather observation.

async def observation(self):
        """Retrieve current weather observation."""

        try:
            observations = await self.api.observations()
        except:
            return self._last_observation

        closest = self._filter_closest(self.station.latitude,
                                       self.station.longitude,
                                       observations)

        if closest is not None:
            self._last_observation = closest.currentObs
             
        return self._last_observation