Does anyone know what “27% chance of precipitation” means in weathermanese?
Does it mean that the probabilty of some measurable preciptation during the day is 27%, or does it mean that, at any given moment durng the day, there is a 27% probability that it is then raining?
I’m not sure inquiring minds want to know this, but I need to pack for a trip.
Update First reply is in:
My understanding is that it means that during the time for which the forecast is supposed to be good, 27% of the area covered by the forecast
will experience precipitation. In other words, if a forecast is for a one-hundred square mile area, 27 of those square miles will get rained upon.
Second update A reader points me to the Environment Canada website with the following explanation:
Probability forecasts cannot be used to predict when, where or how much precipitation will occur. For example, a 60% probability of snow today does not mean that it will snow during 60% of the day. However, the probability figure does mean that there is a 60% chance of a measurable amount of snow falling at that location.
If that’s right, and if there’s a 27% chance of some rain this afternoon, then in most places the probability that it will be raining at any given moment must be much smaller than 27%. I’m leaving my raincoat home.