Wait for DispatchQueue

Question

I'm working on a project where I am supposed to compare two weathers, but I'm kind of stuck.

I'm entering the name of two cities which I'm appending to my array. Creating a for-loop to loop through the array and then sends then I'm passing the data to a function called downloadJsonData which are retrieving data from an API.

@IBAction func compareTemperature(_ sender: Any) {
    if city1.text!.isEmpty || city2.text!.isEmpty{
        //Empty
        print("Empty")
    }
    else{
        cities.append(city1.text!)
        cities.append(city2.text!)
        
        for(index, _) in self.cities.enumerated(){
             self.downloadJsonData(path: self.cities[index]) {
                 print("Completed: Downloaded JSON data")
                 print(self.dataArray.count)
             }
         }
    }
}

So the for-loop is supposed to run twice, but the prints inside the completion blocks is only running once.

var dataArray:[ResponseData] = []
func downloadJsonData(path: String, completed: @escaping () -> ()){
    
        let mainUrl = "http://api.openweathermap.org/data/2.5/weather?q="
        let city = path
        let endUrl = "&appid=9e73e77789b74d085856e30d5dda6285&units=metric&lang=se"
        let urlString = mainUrl + city + endUrl
    
       guard let url = URL(string: urlString) else {return}
       
       URLSession.shared.dataTask(with: url) { (data, response, err) in
           guard let data = data else{
               return
           }
           
           do{
               self.dataArray.append(try JSONDecoder().decode(ResponseData.self, from: data))
               
               //Complete task in background
               DispatchQueue.main.async {
                   completed()
               }
           }
           catch let jsonErr{
               print(jsonErr)
           }
       }.resume()
   }

So when I'm trying to print the self.dataArray.count it always returns 1. I've tried for hours but cannot find a way to fix this issue.