This function works if city is found, but how do I 'error handle' a 404 response?

JSONWeatherApp

function getJSONOuter(cityName) {

            if (!cityName) {
                var cityName = "Calgary";
            }

            if (cityName == "" || cityName == null) {
                cityName = "Calgary";
            }

            try {
                $.getJSON('https://cors.5apps.com/?uri=http://api.openweathermap.org/data/2.5/weather?q=' + cityName + '&units=metric&APPID=c3e00c8860695fd6096fe32896042eda', function (data) {

                    //Was not able to trigger this 404 code so I need to investigate more how to error handle a JSON call.
                    if (data.cod == 404) {
                        alert("404 initial if statement");
                        throw "city not found";
                    }

                    var windSpeedkmh = Math.round(data.wind.speed * 3.6);
                    var Celsius = Math.round(data.main.temp)
                    var iconId = data.weather[0].icon;
                    var weatherURL = "http://openweathermap.org/img/w/" +
                        iconId + ".png";
                    var iconImg = "<img src='" + weatherURL + "'>";

                    $('#location').html('Location: ' + data.name + ', ' + data.sys.country);
                    $('#sky-image').html(iconImg);
                    $('#weather-id').html('Skies: ' + data.weather[0].description);

                    $('#temperature').html(Celsius);
                    $('#toFahrenheit').click(function () {
                        $('#temperature').html(Math.round((9 / 5) * Celsius + 32));
                        $('#wind-speed').html(Math.round(windSpeedkmh * 0.621) + ' mph')
                    })
                    $('#toCelsius').click(function () {
                        $('#temperature').html(Celsius);
                        $('#wind-speed').html(windSpeedkmh + ' km/hr')
                    })

                    $('#wind-speed').html(windSpeedkmh + ' km/h');
                    $('#humidity').html('Humidity: ' + data.main.humidity + ' %');
                })
            }
            catch (e) {
                alert("Error: " + e);
            }

            try {
                getForecast(cityName);
            }

            catch (e) {
                alert("Forecast fail " + e);
            }          
        }

Line 20-42 not my code

see working code sample at https://gist.github.com/tadesegha/5378fb7cf24fe802cff5ebcb8df88f19