Some help for you, u/sziehr!

ViewController.swift

import UIKit
import Alamofire
import SwiftyJSON

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // We'll be using forecast.io, as I'm unfamiliar with Weather Underground.
        // This is the api key you'd get from developer.forecast.io
        let apiKey = "<YOUR API KEY HERE>"
        
        // These are the coordinates for Alcatraz Island, in case you need hyper-local
        // weather forecasting to aid in an escape. ;)
        let coordinates = "37.826979,-122.422962"
        
        // Here, we're building the URL to get our data out of our defined constants.
        // Refer to the apidocs for more info. https://developer.forecast.io/docs/v2
        let forecastURL = "http://api.forecast.io/forecast/\(apiKey)/\(coordinates)/"
        
        // For networking, we'll use Alamofire. https://github.com/Alamofire/Alamofire
        // It provides a nice, clean networking interface, allowing you to focus on handling
        // your data.
        //
        // We'll use the URL we made above, using .GET and handling the response data in the
        // closure.
        Alamofire.request(.GET, forecastURL).response { request, response, rawData, error in
            // Checking to make sure there wasn't any networking error
            if error == nil {
                
                // Here, we'll use SwiftyJSON https://github.com/SwiftyJSON/SwiftyJSON
                // It makes accessing JSON data super easy.
                let data = JSON(data: rawData!)
                
                // Now, we're checking if we can get the temperature from the returned data.
                if let temperature = data["currently"]["temperature"].float {
                    // If yes, print it!
                    println(temperature)
                } else {
                    // If no, say so and print all the data so we can investigate.
                    println("Error in retrieving current temperature")
                    println(data)
                }
            } else {
                // If there does happen to be an error, print it out so we can have a look.
                println(error!)
            }
        }
    }

}