use below for loop to iterate through forecastdays to get each forecastday
else if (xmlForecast.SelectSingleNode("/response/forecast/simpleforecast/forecastdays") != null)
{
XmlNodeList forecastdays = xmlForecast.SelectSingleNode("/response/forecast/simpleforecast/forecastdays").ChildNodes;
foreach (XmlNode forecastday in forecastdays)
{
}
}