How do weather forecasters calculate the percentage risk of rain, snow, storms, flooding etc.?

Hi,



What formulae are used for these calculations? How do you interpret what these percentage risks actually mean for your specific area on the actual day being forecast?



Thanks,

Wayne.How do weather forecasters calculate the percentage risk of rain, snow, storms, flooding etc.?
Dart board. (Not really but my friends are all convinced this is true...)



This can really vary from forecaster to forecaster and there is really no set formula for calculating precip risk. It can almost be more of a gut instinct/shooting from the hip thing.



Some things that can effect the risk that the forecaster will assign can be:

--What type of weather is being forecast such as airmass thunderstorms vs cold/warm front moving through.

--What size of an area are you forecasting for. TV Weather-people and the National Weather Service will generally have a much larger area that they are responsible for as opposed to an airline forecaster that is forecasting for a single point on the map.