🚀 go-pugleaf

In article <181610@ipl.jpl.nasa.gov> pdb059@ipl.jpl.nasa.gov (Paul Bartholomew)
writes:
>As to what these percentages mean, let me quote a pertinent passage from
>Cecil Adams (better known as the author of the column, "The Straight Dope")
>when he was asked a similar question (quoted without permission from the
>book, "More of the Straight Dope"):
>
>"The National Weather Service (and various other weather services around the
>world, under the guidance of the World Meteorological Organization, a UN
>agency) sends up measuring devices called radiosondes in helium balloons
>twice a day.  These collect weather data continuously as they rise through
>the atmosphere--wind speed and direction, temperature, barometric pressure,
>and humidity.  The information is radioed to the ground and eventually ends
>up at the National Meteorological Center near Washington, D.C., where it's
>fed into a computer.  (There are other centers in other parts of the world
>that do the same thing.)  Other data from satellites and ground reporting
>stations are also fed in, and what you end up with, metaphorically speaking,
>is a complete three-dimensional picture of atmospheric conditions around the
>world.  The computer program then applies various laws of fluid mechanics
>to predict future conditions."
>
>"Unfortunately, there is only so far you can go with this.  While it's
>possible to predict the temperature, say, with a reasonable degree of
>certainty, precipitation is much chancier.  The best forecasters can do is
>to give the probabilities, which they do by having the computer compare
>present conditions with historical data.  When you hear there's a 10 percent
>chance of rain, that means that out of the last 100 times the weather con-
>ditions were just like they are now, it rained 10 times.  (More or less--I
>am obliged to oversimplify a bit, you understand.)"
>
>Ms. Bryan, if you care to continue this argument, I suggest you find a
>reputable source to bolster your case.  The explanation above, in addition
>to being correct, is the only logical interpretation of the facts.  Your
>explanation, while being charming, bears no resemblance to reality and does
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>not reflect *my* memory of weather forecasting in D.C. during the five years
>that I lived there.

Well, I don't really want to get involved in this (particular) flame war,
but I will say this much: I lived in Minnesota for 9 years and observed that
when the weather forecasters there predicted 20-30 % chance of rain, it rained
at some point (measurable) >50% of the time.  When they predicted 50% or
greater, it rained at least 95% of the time.  Never having heard an authorita-
tive explanation of what they meant, such as you offer, I had come to the
conclusion that they must have meant an X% chance of rain meant that I would
find it raining X% of the time, that day.  I wish you or someone else would
offer some sort of explanation for the difference (other than alcohol,
hallucinogenic drugs, or other "diminished capacity" descriptions of my
powers of observation, if you please).   I know that's not a fair challenge
but I'm curious as to what a possible explanation might be.

If you're right about the explanation of what the percentage means, I sure
wish someone would open a bookie joint and allow me to bet on the odds the
forecasters give for rain - I could retire on the winnings.  :-)

Fred
------------------------------------------------------------------------------
Fred Scott             |    "...And last year, their rationale for their pay
Protocol Engines, Inc. | raise?  They 'needed it on order to attract a better
Mountain View, CA      | class of people.'  Well, apparently.  But they do try
E-mail: fred_s@pei.com | their best, and maybe that's scariest of all."
                       |                  --- Will Durst on Congress