Las Vegas winters are not very cold however, we do have days when the night time low is below freezing. Your exterior faucets, valves and vacuum breakers should be properly protected against freezing by adding foam cups, pouches or other devices.
In today's case, an old towel was used but it was not properly covered to remain dry. Besides the obvious corrosion issue, when the towel is wet, it does not insulate much at all and allowed the vacuum breaker to start freezing to the point where the top cap snapped off the unit and the vacuum breaker started to leak. Fortunately, it was not a big leak but over time if not found and repaired, this damaged device will waste thousands of gallons of water and possibly burst and cause a real disaster.
Home Watcher LV
Las Vegas, NV