In most medical facilities, there are nurse staffing patterns that need to be watched and measured.  The key is to contstantly follow key metrics that will allow you to see yearly cyclical patterns that you can prepare for.  Depending upon with region you are in, you will be able to identify months that will see your staffing needs rise based upon your needs and the needs of the facilities within your region. 

You can also measure the average and median time of nurses that are employed at your facility.  This will help you prepare for situation when you have multiple new hires during a single quarter.  It will also allow you to try and work on increasing these averages.