Let's talk Arizona weather: How meteorologists predict rain
How do meteorologists figure out an area's chance for rain? It is wizardry, or some kind of mystical foresight? Not really. Here's how weather forecasters really predict a chance of rain.
What does it mean when the forecast calls for a 10-percent chance of rain? How is that determined?
That number expresses the probability, or likelihood, of measurable rain (the National Weather Service defines that as one 100th of an inch) in a given area during a certain period of time.
Austin Jamison, meteorologist with the National Weather Service in Phoenix, explains.
“We have computer models that provide us with some information and there are some statistical techniques that have been derived to come up with numbers like that,” Jamison said. “What we’re trying to get at is the likelihood for a given area during a given time getting at least one 100th of an inch of rain.
What is wetting rain?
"For instance, if in the Phoenix area there is a 20-percent chance of measurable rain, that doesn’t mean all day rain and it doesn’t necessarily mean that all parts of the area will get rain. There is a 20-percent chance that some part of the area will get measurable rain.”
Precipitation of .10 inches or more over most of the area specified.
National Weather Service meteorologist explains what is meant when they say there is a 20-percent chance of rain.