Weather Question

[DiscGo]

My brother and I were camping this weekend and we were debating the mean of "30% chance of rain". Does that mean "3 our of 10 times it will rain in this situation" or "30% of this area WILL receive rain"? I added a pole here, but if anyone has a source I'd really appreciate it.

[shlingdawg]

Yet there is a 50% chance the weatherman got it wrong.

[Scott P]

[i]Q: 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

[Mooseman70]

I've always understood it as 30% of the forecasted area could receive precipitation. I'm not a weatherman, but that's what I learned growing up.

[DiscGo]

Thanks Scott. I had just read the same article. I read elsewhere:
http://pajk.arh.noaa.gov/info/articl...ey/poptext.htm

That basically it means 3 out of 10 times will have rain, but that many meteorologists use it as 30% of the area (and that in the end you need to understand how your local weatherman uses it).


But as I now have it understood when the National Weather Broadcast list 30% chance of rain it implies "a chance of rain" as opposed to 30% of the area will receive rain.

Probability Percentage
10% slight chance, isolated, few
20% slight chance, widely scattered
30%, 40%, 50% chance, scattered
60%, 70% likely , numerous
80%, 90%, 100% (none used)


http://pajk.arh.noaa.gov/info/articl...ey/poptext.htm

[BruteForce]

Good question. I checked today's forecast and there was no rain/thunder in the forecast. We went ATV'ing from Chimney Rock to Eureka and back. On the way home (Saratoga Springs), the lightning kicked in, heavy rain quickly followed by massive hail.

By the time I hit Bangerter, there was nothing. My house in South Jordan didn't even get a sprinkle!

[offpiste]

after having taken some courses from Clayton Brough and Mark Weltie and they tell you they have 50% chance of being right in the next 24 hours and after that it drops to 15%, and the seven day forcast is just a guess. I take it all in stride and hopefully have what I need for the day.

[sparker1]

It means one of two things. If you are going to be outdoors, it is a certainty that you'll get wet. If you are staying in, but you garden is dying from lack of water, no way will it rain. And, in either case, the weatherman chalks it up as another accurate forecast.

[offpiste]

but true