It would end up being something like this:

public interface WeatherService {
   @GET("v1/public/yql")
   Call<String> getWeather(@Query("q") String query);

}

Then create the object like this:

Retrofit retrofit = new Retrofit.Builder()
            .baseUrl("https://query.yahooapis.com")
            .addConverterFactory(ScalarsConverterFactory.create())
            .build();

      WeatherService wService = retrofit.create(WeatherService.class);

And run it like this:

String query = "select * from weather.forecast where woeid in (select woeid from geo.places(1) where text=\"Leeds\")&format=json";

Call<String> weather = wService.getWeather(query);
         try {
            Response<String> resp = weather.execute();

You should change the ConverterFactory to json and properly parse the weather output.

I have not tested this, just giving you an idea of how to use the Retrofit query.

Looking at the API specification for Yahoo weather, it doesn't mention anything about a 7 day forecast, and from the example responses it appears to only be the imminent forecast.

Your best option is to try an alternative, such as WorldWeatherOnline, they have a free API which does allow you to specify a number of days.

You need to register for a free API key, but once you've done that you could request using:

http://api.worldweatheronline.com/free/v1/weather.ashx?q=London&format=json&num_of_days=5&key=

You'd get a response such as

{
    "data": {
        "current_condition": [{
            "cloudcover": "75",
            "humidity": "87",
            "observation_time": "01:48 PM",
            "precipMM": "0.0",
            "pressure": "998",
            "temp_C": "4",
            "temp_F": "39",
            "visibility": "8",
            "weatherCode": "116",
            "weatherDesc": [{
                "value": "Partly Cloudy"
            }],
            "weatherIconUrl": [{
                "value": "http:\/\/cdn.worldweatheronline.net\/images\/wsymbols01_png_64\/wsymbol_0002_sunny_intervals.png"
            }],
            "winddir16Point": "WSW",
            "winddirDegree": "250",
            "windspeedKmph": "17",
            "windspeedMiles": "11"
        }],
        "request": [{
            "query": "London, United Kingdom",
            "type": "City"
        }],
        "weather": [{
            "date": "2013-12-26",
            "precipMM": "0.1",
            "tempMaxC": "6",
            "tempMaxF": "43",
            "tempMinC": "3",
            "tempMinF": "37",
            "weatherCode": "113",
            "weatherDesc": [{
                "value": "Sunny"
            }],
            "weatherIconUrl": [{
                "value": "http:\/\/cdn.worldweatheronline.net\/images\/wsymbols01_png_64\/wsymbol_0001_sunny.png"
            }],
            "winddir16Point": "WSW",
            "winddirDegree": "248",
            "winddirection": "WSW",
            "windspeedKmph": "20",
            "windspeedMiles": "13"
        }, {
            "date": "2013-12-27",
            "precipMM": "3.4",
            "tempMaxC": "10",
            "tempMaxF": "51",
            "tempMinC": "4",
            "tempMinF": "40",
            "weatherCode": "113",
            "weatherDesc": [{
                "value": "Sunny"
            }],
            "weatherIconUrl": [{
                "value": "http:\/\/cdn.worldweatheronline.net\/images\/wsymbols01_png_64\/wsymbol_0001_sunny.png"
            }],
            "winddir16Point": "SW",
            "winddirDegree": "214",
            "winddirection": "SW",
            "windspeedKmph": "43",
            "windspeedMiles": "27"
        }, {
            "date": "2013-12-28",
            "precipMM": "0.4",
            "tempMaxC": "8",
            "tempMaxF": "46",
            "tempMinC": "1",
            "tempMinF": "34",
            "weatherCode": "116",
            "weatherDesc": [{
                "value": "Partly Cloudy"
            }],
            "weatherIconUrl": [{
                "value": "http:\/\/cdn.worldweatheronline.net\/images\/wsymbols01_png_64\/wsymbol_0002_sunny_intervals.png"
            }],
            "winddir16Point": "SW",
            "winddirDegree": "216",
            "winddirection": "SW",
            "windspeedKmph": "16",
            "windspeedMiles": "10"
        }, {
            "date": "2013-12-29",
            "precipMM": "0.0",
            "tempMaxC": "6",
            "tempMaxF": "42",
            "tempMinC": "3",
            "tempMinF": "37",
            "weatherCode": "113",
            "weatherDesc": [{
                "value": "Sunny"
            }],
            "weatherIconUrl": [{
                "value": "http:\/\/cdn.worldweatheronline.net\/images\/wsymbols01_png_64\/wsymbol_0001_sunny.png"
            }],
            "winddir16Point": "WSW",
            "winddirDegree": "259",
            "winddirection": "WSW",
            "windspeedKmph": "22",
            "windspeedMiles": "14"
        }, {
            "date": "2013-12-30",
            "precipMM": "4.3",
            "tempMaxC": "9",
            "tempMaxF": "49",
            "tempMinC": "5",
            "tempMinF": "42",
            "weatherCode": "113",
            "weatherDesc": [{
                "value": "Sunny"
            }],
            "weatherIconUrl": [{
                "value": "http:\/\/cdn.worldweatheronline.net\/images\/wsymbols01_png_64\/wsymbol_0001_sunny.png"
            }],
            "winddir16Point": "SW",
            "winddirDegree": "227",
            "winddirection": "SW",
            "windspeedKmph": "36",
            "windspeedMiles": "23"
        }]
    }
}

That should do what you want :)

I made a wrapper for Yahoo Weather API on android. Check it here: https://github.com/zh-wang/YWeatherGetter4a

After visiting So many sites, I got to know that Yahoo does not support multiple languages for the weather API response.