For a future weather forecast, let's say these values are present:
precip: .2in
precipchance: 50%
Is that saying that there's a 50% chance of *any* rain falling? Or, is it saying that there's a 50% chance that the area will see at least .2 inches of rain?
Thank you for your question. You are correct. The precipchance element is the chance of any measurable precipitation occurring in the forecast grid cell. The precip element is the estimated amount of precipitation.
To calculate these we use 'ensemble models'. These models run the weather forecast model multiple times with slightly different initial conditions to see how stable the weather forecast is. If all the runs indicate that precipitation will occur, then the precipchance will be close to 100%. If few runs indicate precipitation will occur, the chance will be close to 0%. Similarly with the precipitation amount, the average amount of forecast precipitation will be used. Some of the ensemble runs will indicate different amounts of precipitation but if they indicate measurable precipitation, they will be counted in the chance element.
For more information, please see https://www.visualcrossing.com/resources/documentation/how-do-we-create-our-weather-forecast/
Regards
Visual Crossing Support
