Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString objectForKey:]: unrecognized selector sent to instance 0x7f9298554560'

Printing description of self->metArray:
{
    weatherObservation =     {
        ICAO = YBBN;
        clouds = "few clouds";
        cloudsCode = FEW;
        countryCode = AU;
        datetime = "2014-11-24 03:00:00";
        dewPoint = 20;
        elevation = 5;
        hectoPascAltimeter = 1014;
        humidity = 61;
        lat = "-27.38333333333333";
        lng = "153.1333333333333";
        observation = "YBBN 240300Z 02019KT 9999 FEW029 SCT250 28/20 Q1014";
        stationName = "Brisbane Airport M. O";
        temperature = 28;
        weatherCondition = "n/a";
        windDirection = 20;
        windSpeed = 19;
    };
}

-(void)getMetar{

   // NSString *location = @"YBBN";
    NSString * const metarUrl =@"http://api.geonames.org/weatherIcaoJSON?ICAO=YBBN&username=demo";

    NSURL *url2 = [NSURL URLWithString:metarUrl];
    NSData *data2 = [NSData dataWithContentsOfURL:url2];

    metArray = [NSJSONSerialization JSONObjectWithData:data2 options:kNilOptions error:nil];

    //Create an NSDictionary for the weather data to be stored.
    NSDictionary *metarJson = [NSJSONSerialization JSONObjectWithData:data2 options:kNilOptions error:nil];

    //Loop through the JSON array
    NSArray *currentMetarArray = metarJson[@"weatherObservation"];

    //set up array and json call
    metarArray = [[NSMutableArray alloc]init];
   for (NSDictionary *metaritem in currentMetarArray)
    {
        //create our object
        NSString *nClouds = [metaritem objectForKey:@"clouds"];
        NSString *nObservation = [metaritem objectForKey:@"observation"];

        //Add the object to our animal array
        [metarArray addObject:[[metar alloc]initWithclouds:(nClouds) andobservation:nObservation]];

    }
}