What's the weather like today?

private async Task GetWeatherInfos()
{
    try
    {
        var position = await PositionManager.GetPosition();
        WeatherForecastObject weather_infos = await WeatherAPIManager.GetWeather(position.Coordinate.Latitude, position.Coordinate.Longitude);

        await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal,
                                () =>
                                {
                                    main_page.SwitchToWeatherGrid();
                                    main_page.PrintWeatherInfos(weather_infos);
                                });

        await GUIOutput("The weather forecast for " + weather_infos.name + " are: " + weather_infos.weather[0].description +
                        " with temperature between " + ((int)weather_infos.main.temp_min).ToString() + " °C and " + ((int)weather_infos.main.temp_max).ToString() + " °C." +
                        " The humidity rate is equal to " + ((int)weather_infos.main.humidity).ToString() + " % and the wind speed is " + ((int)weather_infos.wind.speed).ToString() + " meters per second.", true);

        await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal,
                                () =>
                                {
                                    main_page.SwitchToDefaultGrid();
                                });
    }
    catch
    {
        await GUIOutput("I'm sorry, I couldn't retrieve the informations from the web.", true);
    }

    state = AssistantState.BACKGROUND_DEFAULT;
}

public class WeatherAPIManager
{
    public async static Task<WeatherForecastObject> GetWeather(double lat, double lon)
    {
        var http = new HttpClient();
        var response = await http.GetAsync("http://api.openweathermap.org/data/2.5/weather?lat=" + lat.ToString() + "&lon=" + lon.ToString() + "&units=metric&APPID=0bf33bf113a3c37dea2ddbb52272ea90");
        string response_str = await response.Content.ReadAsStringAsync();
        var serializer = new DataContractJsonSerializer(typeof(WeatherForecastObject));
        var stream = new MemoryStream(Encoding.UTF8.GetBytes(response_str));
        return (WeatherForecastObject)serializer.ReadObject(stream);
    }
}