Is there scientific difference between chance and possible?

[bluemingidiot]

What are the scientific definitions of chance and possible?

This is today's weather forecast from your National Weather Service which is part of your National Oceanic and Atmospheric Administration:

"A chance of showers, with thunderstorms also possible after noon. Cloudy, with a high near 70. South wind 10 to 15 mph, with gusts as high as 20 mph. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms."

This is a fairly typical forecast.

This forecast has two chances.  One is for showers and one is for precipitation.  What is the difference?  If precipitation consists of something more than showers, shouldn't there also be a chance for that?

Do you think your National Weather Service should be more transparent?  Do you think the National Oceanic and Atmospheric Administration is intentionally trying to be confusing? 

[Deleted]

Precipitation is anything more than fog mist. Showers come and go for a period of time. In Oregon we have light showers in late spring. Showers or rain in winter. Rain can go on for days. Forecasters give us a heads up, up to 50% is a good showers day, 100% is a good rain, but it don't mean nuttin', just a guess. If there are clouds there is a more than slight chance of precipitation, clear sky at the moment, possible, you might be good....without a slicker, possible....James

[Bear Foot Farm]

"A chance of showers, with thunderstorms also possible after noon. Cloudy, with a high near 70. South wind 10 to 15 mph, with gusts as high as 20 mph. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms."

"Chance" tells you how likely it is to rain where you are. (50%)

"Possible" (in the context given) tells you atmospheric conditions will be right for the formation of thunderstorms, and those conditions will be more likely after noon, since daytime heating adds to the intensity of storms.

So what they are saying is "It may or may not rain, but if it does and it's after 12 PM, it could be a thunderstorm with heavy downpours."

[bluemingidiot]

Most of the time when rain is in the forecast, if we get precipitation at all, it is drizzle. That is more likely to occur in the am.

Weather patterns vary across the country.   Urban people seem less conscious of this than rural people.  Television station general managers seem to have a low weather threshold.  They hire weather forecasters from different parts of the country.  Weather forecasters keep trying to project the weather patterns where they are from on the area where they now are.

Weather forecasters are like politicians.  They like attention and are constantly trying to tell people what they think people want to hear.  They often don't know a lot about what they are saying but that doesn't seem to bother them.

[Deleted]

In Oregon, Percentage=good chance, Showers come in April, bring May flowers. Sun, right now=no precipitation for 15 minutes, maybe. If you go out without gear between Oct 1 and July 4 your chances of getting wet, went up....James