POP and SNOWFALL FORECAST
 
METEOROLOGIST JEFF HABY
POP stands for probability of precipitation. It ranges from 0 to 100%, with 0 being no chance for precipitation in the designated time
frame to 100 being certain. A snowfall forecast will often include how much accumulation to expect. This will be given in a range such
as for example 13 inches or 6 to 12 inches. What is interesting is that you will run into situations where the POP is well less than
100% yet an accumulation forecast is given. Many times in a snow situation the snow will be widespread across the forecast region. Mesoscale
influences and dynamics will determine where the heaviest snow occurs. This is why the snowfall forecast is given in a range of values
instead of just one number. The accumulation forecast also assumes snow will occur in the first place. You may see a situation such
as a POP of 60% and 1 to 3 inches of snow expected. It would seem that if a range of snowfall is given then snow will be a certainty. The
assumption being made is that if snow occurs then 1 to 3 inches is expected. In many cases the POP can seem too low since it does usually
snow in the forecast area when an accumulation is given that is 1 inch or greater. It seems POP should be at least 80% when a range of
snowfall amounts in forecasted. As mentioned though, there is a hidden assumption in the accumulation forecast that snow will occur
in the first place.


