Trouble retrieving JSON Data?

public static final String TAG = MainActivity.class.getSimpleName();

private CurrentWeather mCurrentWeather;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    String apiKey = "c52e1d1ae23ca2a0b45a95023f752699";
    double latitude = 37.8267 ;
    double longitude = -122.423;
    String forecastUrl = "https://api.forecast.io/forecast/" + apiKey + "/" + latitude + longitude;

    if(isNetworkAvailable()) {
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(forecastUrl)
                .build();

        Call call = client.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                try {
                    String jsonData = response.body().string();
                    Log.v(TAG, jsonData);
                    if (response.isSuccessful()) {
                        mCurrentWeather = getCurrentDetails(jsonData);
                    } else {
                        alertUserAboutError();
                    }
                }
                catch (IOException e) {
                    Log.e(TAG, "Exception caught: ", e);
                }
                catch (JSONException e) {
                    Log.e(TAG, "Exception caught: ", e);
                }
            }
        });
    }
    else {
        Toast.makeText(this, R.string.network_unavailable_message, Toast.LENGTH_LONG).show();
    }
    Log.d(TAG, "Main UI code is running ");


}

private CurrentWeather getCurrentDetails(String jsonData) throws JSONException {

    JSONObject forecast = new JSONObject(jsonData);
    String timezone = forecast.getString("timezone");
    Log.i(TAG, "From JSON: " + timezone);

    return new CurrentWeather();
}

private boolean isNetworkAvailable() {
    ConnectivityManager manager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = manager.getActiveNetworkInfo();
    boolean isAvailable = false;
    if (networkInfo != null && networkInfo.isConnected()){
        isAvailable = true;
    }

    return isAvailable;
}

private void alertUserAboutError() {
    AlertDialogFragment dialog = new AlertDialogFragment();
    dialog.show(getFragmentManager(), "error_dialog");
}