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#1
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Just what does a 60% chance of rain mean?
Does it mean that somewhere within 100 miles of me there is a 60%
chance of rain falling, or does it mean that there is a 60% chance that I'm going to get rained on (assumimg that I'm outside)? I'm not a big fan of biking in the rain, although being around 90F today I sort of am looking forward to it. |
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#2
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Just what does a 60% chance of rain mean?
"dgk" wrote in message ... Does it mean that somewhere within 100 miles of me there is a 60% chance of rain falling, or does it mean that there is a 60% chance that I'm going to get rained on (assumimg that I'm outside)? I'm not a big fan of biking in the rain, although being around 90F today I sort of am looking forward to it. In my experience it means there is a 60% chance that they will change the forecast just before you leave. Seriously, it seems every date this summer I penciled in for a ride the long range forecast switched. I was almost hoping to get thunderstorm forecasts as I knew by ride time it would have flipped. The only problem was that the reverse worked too. |
#3
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Just what does a 60% chance of rain mean?
"dgk" wrote: (clip) being around 90F today I sort of am looking forward to it. ^^^^^^^^^^^^^^^^^^ Normal body temp is 98.6F. You may be dying. |
#4
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Just what does a 60% chance of rain mean?
"dgk" wrote in message
... Does it mean that somewhere within 100 miles of me there is a 60% chance of rain falling, or does it mean that there is a 60% chance that I'm going to get rained on (assumimg that I'm outside)? I'm not a big fan of biking in the rain, although being around 90F today I sort of am looking forward to it. I ran into a story about this a few months back and learned something new from it. Apparently it is intended to indicate neither the _percentage of different locations_ within the named area which are expected to get wet that day, nor the _percentage of time_ any given location might get wet on that day. Rather, it is intended to indicate the _percentage of different days_, each having the same atmospheric conditions, when rain will fall somewhere within the named area. And apparently then that means that on (100 minus _that percentage of days_) no rain will fall anywhere within that area. See: http://www.sciencedaily.com/releases...0414130623.htm ------------ Begin quote from article linked to above: ....new research indicates that only about half the population knows what a forecast means when it predicts a 20 percent chance of rain, according to researchers at the University of Washington. Writing in the Bulletin of the American Meteorological Society, the researchers said the confusion comes because people don't understand what the 20 percent chance of rain actually refers to. Many people think it means that it will rain over 20 percent of the area covered by the forecast or for 20 percent of the time period covered by the forecast, said Susan Joslyn, a UW cognitive psychologist and senior lecturer. "When a forecast says there is 20 percent chance of rain tomorrow it actually means it will rain on 20 percent of the days with exactly the same atmospheric conditions," she said." ------------ End quote. |
#5
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Just what does a 60% chance of rain mean?
On Wed, 5 Aug 2009 09:17:59 -0700, "Terry Neff"
wrote: "dgk" wrote in message .. . Does it mean that somewhere within 100 miles of me there is a 60% chance of rain falling, or does it mean that there is a 60% chance that I'm going to get rained on (assumimg that I'm outside)? I'm not a big fan of biking in the rain, although being around 90F today I sort of am looking forward to it. I ran into a story about this a few months back and learned something new from it. Apparently it is intended to indicate neither the _percentage of different locations_ within the named area which are expected to get wet that day, nor the _percentage of time_ any given location might get wet on that day. Rather, it is intended to indicate the _percentage of different days_, each having the same atmospheric conditions, when rain will fall somewhere within the named area. And apparently then that means that on (100 minus _that percentage of days_) no rain will fall anywhere within that area. See: http://www.sciencedaily.com/releases...0414130623.htm ------------ Begin quote from article linked to above: ...new research indicates that only about half the population knows what a forecast means when it predicts a 20 percent chance of rain, according to researchers at the University of Washington. Writing in the Bulletin of the American Meteorological Society, the researchers said the confusion comes because people don't understand what the 20 percent chance of rain actually refers to. Many people think it means that it will rain over 20 percent of the area covered by the forecast or for 20 percent of the time period covered by the forecast, said Susan Joslyn, a UW cognitive psychologist and senior lecturer. "When a forecast says there is 20 percent chance of rain tomorrow it actually means it will rain on 20 percent of the days with exactly the same atmospheric conditions," she said." ------------ End quote. Ok, so all it is telling me is that there is a 60% chance of rain somewhere in the area. Actually, it has dropped to 40%. I'm very likely not to get wet, at least by rain. |
#6
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Just what does a 60% chance of rain mean?
dgk wrote:
Does it mean that somewhere within 100 miles of me there is a 60% chance of rain falling, or does it mean that there is a 60% chance that I'm going to get rained on (assumimg that I'm outside)? I'm not a big fan of biking in the rain, although being around 90F today I sort of am looking forward to it. What I remember from an explanation I heard a long time ago was that 60% chance meant that 60% of the area in question would get rain, not that the entire area had a 60% chance of rain and a 40% chance of no rain. |
#7
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Just what does a 60% chance of rain mean?
dgk wrote:
Ok, so all it is telling me is that there is a 60% chance of rain somewhere in the area. No, it means that there is 100% chance of rain in 60% of the area, but they don't know which 60% that is. So you do have a 60% chance of getting rained on. This makes sense if you think about it. Those moving clouds are going to dump their water somewhere over the area, it's just not clear exactly where. |
#8
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Just what does a 60% chance of rain mean?
On Aug 5, 1:29*pm, SMS wrote:
dgk wrote: Does it mean that somewhere within 100 miles of me there is a 60% chance of rain falling, or does it mean that there is a 60% chance that I'm going to get rained on (assumimg that I'm outside)? I'm not a big fan of biking in the rain, although being around 90F today I sort of am looking forward to it. What I remember from an explanation I heard a long time ago was that 60% chance meant that 60% of the area in question would get rain, not that the entire area had a 60% chance of rain and a 40% chance of no rain. Wrong. http://www.utexas.edu/depts/grg/kimm...forecasts.html - Frank Krygowski |
#9
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Just what does a 60% chance of rain mean?
On Aug 5, 1:31*pm, SMS wrote:
dgk wrote: Ok, so all it is telling me is that there is a 60% chance of rain somewhere in the area. No, it means that there is 100% chance of rain in 60% of the area, but they don't know which 60% that is. So you do have a 60% chance of getting rained on. This makes sense if you think about it. Those moving clouds are going to dump their water somewhere over the area, it's just not clear exactly where. Wrong. http://www.utexas.edu/depts/grg/kimm...forecasts.html - Frank Krygowski |
#10
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Just what does a 60% chance of rain mean?
On Aug 5, 8:36*am, dgk wrote:
Does it mean that somewhere within 100 miles of me there is a 60% chance of rain falling... Yes, practically speaking, that's pretty close to it, although the 100 mile radius is too large. Actually, it means 60% of the time the weather is exactly like this, it's going to rain _somewhere_ in "the area." I've never found a good definition of "the area" but I'm sure it's not as big as a 100 mile radius. ,,, or does it mean that there is a 60% chance that I'm going to get rained on (assumimg that I'm outside)? Unfortunately, that's not what it means. And it's too bad, because that information would be a lot more useful! I've never liked the way they define probability of precipitation. For one thing, "the area" that a forecast applies to seems poorly defined, or at least has never been explained to me. What are the area's boundaries? For another thing, if (say) the area consisted of one county, and 0.01" of rain fell in only one extreme corner of the county, the definition allows the weather man to say "See? It rained, just like I predicted." - Frank Krygowski |
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