Connection string is defined in SQLExpressInfo. Logging to server as user 'admin' that has dbcreator role. Database is created automatically if it doesn't exist.
Service can be installed with admin developer console opened from visual studio. It can be started manually. Service project can also be tested in console with argument --test that simulates one api call and saving of weather data (if installed service is not running) Data is fetched and saved every 8 minutes. OpenWeatherMap updates data with variable frequency depending on time of the day, smetimes every 10 minutes, later in the evening every 1 hour or so from my testing experience.
The cache is deleted after 5 minutes. I had problems with SqlDependency notifications implementation so I couldn't improve it even more.