H******7
发帖数: 34403 | 1 What do forecasters mean when they say things such as, "There is a 30
percent chance of rain"?
A: The National Weather Service says, "The probability of precipitation is
the likelihood of measurable precipitation (0.01 inches or greater) for a
specified forecast time period, and occurring at any point for which the
forecast is valid."
A reasonable English translation of this bit of government speak is: The
probability gives the odds of any one place in the area covered by the
forecast getting wet, whether it's from rain or snow. The 0.01 inches or
greater comes from the fact that any less rain or water from melted snow or
ice can't be measured. If the bottom of the rain gauge is wet, but the water
isn't deep enough to measure, that's called a "trace' and really doesn't
count.
A forecaster assigns a precipitation probability that shows his or her
confidence in the forecast, how much of the forecast area is likely to have
precipitation, and low long the precipitation is expected to last.
The important point is that the odds are for the rain or snow to fall on any
place in the area covered by the forecast.
This means, that the probability could be low – say 30% – yet you have
hard rain for a few hours. In this case, the forecast isn't wrong, you're
just one of the unlucky people who happened to be in the small part of the
region that got wet that day. Or, if your lawn and garden needed the rain,
you were one of the lucky ones. And, your friend a couple of miles away who
needs the rain can't complain about the forecast not working out. Rain did
fall on at least one place in the area. |
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