Inside the SerializeWeatherForecast Instantiate a new JsonSerializer and name it serializer. Then, add a using statement

using System;
using System.IO;
using System.Collections.Generic;
using Newtonsoft.Json;


namespace Treehouse.CodeChallenges
{
    public class Program
    {
        public static void Main(string[] arg)
        {
        }

       public static WeatherForecast ParseWeatherForecast(string[] values)
       {
            var weatherForecast = new WeatherForecast();
            weatherForecast.WeatherStationId = values[0];
            DateTime timeOfDay;
            if (DateTime.TryParse(values[1], out timeOfDay))
            {
                weatherForecast.TimeOfDay = timeOfDay;
            }
            Condition condition;
            if (Enum.TryParse(values[2], out condition))
            {
                weatherForecast.Condition = condition;
            }
            int temperature;
            if (int.TryParse(values[3], out temperature))
            {
                weatherForecast.Temperature = temperature;
            }
            double precipitation;
            if (double.TryParse(values[4], out precipitation))
            {
                weatherForecast.PrecipitationChance = precipitation;
            }
            if (double.TryParse(values[5], out precipitation))
            {
                weatherForecast.PrecipitationAmount = precipitation;
            }
            return weatherForecast;
        }

        public static List<WeatherForecast> DeserializeWeather(string fileName)
        {
            var weatherForecasts = new List<WeatherForecast>();

            using (var reader = new StreamReader(fileName))
            using (var jsonReader = new JsonTextReader(reader))
            {
                var serializer = new JsonSerializer();
                weatherForecasts = serializer.Deserialize<List<WeatherForecast>>(jsonReader);
            }

            return weatherForecasts;
        }
        public static void SerializeWeatherForecasts(List<WeatherForecast> weatherForecasts, string fileName)
        {
            using (var writer = new StreamWriter(fileName))
            using (var jsonwriter = new JsonTextwriter(writer))
            {
                var serializer = new JsonSerializer();
                serializer.Serialize<List<WeatherForecast>>(fileName);
            }
        }

    }
}

using System;
using Newtonsoft.Json;

namespace Treehouse.CodeChallenges
{
    public class WeatherForecast
    {
        [JsonProperty(PropertyName = "weather_station_id")]
        public string WeatherStationId { get; set; }
        [JsonProperty(PropertyName = "time_of_day")]
        public DateTime TimeOfDay { get; set; }
        public Condition Condition { get; set; }
        public int Temperature { get; set; }
        [JsonProperty(PropertyName = "precipitation_chance")]
        public double PrecipitationChance { get; set; }
        [JsonProperty(PropertyName = "precipitation_amount")]
        public double PrecipitationAmount { get; set; }
    }

    public enum Condition
    {
        Rain,
        Cloudy,
        PartlyCloudy,
        PartlySunny,
        Sunny,
        Clear
    }
}