Wind Chill Factor  
  There are two components when considering the implications of the out-door temperature: the actual air temperature and then the wind-chill factor.  
  Whether it's horses (particularly those getting on in years without any excess fat cover), children or indeed adults exercising with minimal clothing, wind-chill can be an extremely important factor.

With this is mind, the calculator below will give an approximate temperature after taking the wind into account. [These are in metric.]

While many people will not have the means to gauge air temperatures or wind speed, most weather Apps include these in their forecasts.  Those can be used for checking purposes.

  
   
   
     Temperature  °C    
     Wind speed  Km/hr    
     Adjusted temperature    
         
     Temperature  °F    
     Wind speed  M/hr    
     Adjusted temperature    
         
  Conversions          
 
   
 
   
  Horses
With an adjusted temperature of 10°C or less, serious consideration needs to be given to rugging a horse, especially one that is older or thin for any reason.
Humans
Hypothermia can set in with a body temperature drop of just 3°C.  Care needs to be taken in cold and windy conditions, especially with children.  Obviously the type of clothing is critical with a wind-proof jacket a must have in cold, breezy/windy conditions.