EXC_BAD_ACCESS with worldweatheronline API

Question

In my iOS app I'm using the weather APIs of worldweatheronline.com but I get a random "EXC_BAD_ACCESS" error oh this row (not always but sometimes) :

temperature.text = [NSString stringWithFormat:@"%@ °C", tempC];

Here is my code:

- (void)showWeatherFor:(CLLocation *)newLocation
{
NSString *myRequestString = [[NSString alloc] initWithFormat:@"http://api.worldweatheronline.com/free/v1/weather.ashx?q=%f,%f&format=json&num_of_days=5&key=ydvgep8jn5m846upd8kb2qp6", newLocation.coordinate.latitude, newLocation.coordinate.longitude];
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:myRequestString]];
NSData *response = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
NSString *JsonString = [[NSString alloc] initWithData:response encoding:NSUTF8StringEncoding];
NSError *error = nil;
NSDictionary *theDictionary = [NSDictionary dictionaryWithJSONString:JsonString error:&error];
NSDictionary *data = [theDictionary objectForKey:@"data"];
NSArray *currentDictionary = [data objectForKey:@"current_condition"];
NSDictionary *temp = [currentDictionary objectAtIndex:0];

if ([temp objectForKey:@"temp_C"] == nil || [temp objectForKey:@"temp_F"] == nil)
{
    return;
    termometro.alpha = 0;
}
else
{
    if (temp != nil)
    {
        if ([mainDelegate.gradi isEqualToString: @"°C"])
        {
            NSNumber *tempC = [temp objectForKey:@"temp_C"];
            temperature.text = [NSString stringWithFormat:@"%@ °C", tempC];
            mainDelegate.temperature = [[temp objectForKey:@"temp_C"]intValue];
        }
        else
        {
            NSNumber *tempF = [temp objectForKey:@"temp_F"];
            temperature.text = [NSString stringWithFormat:@"%@ °F", tempF];
            mainDelegate.temperature = [[temp objectForKey:@"temp_F"]intValue];
        }
        termometro.alpha = 1;
    }
}

}