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Re: [Phys-L] depicting uncertainty on maps



In my local area (near Baltimore, MD) the local weather station is now putting out "contour area maps" with a range of snow falls specified within each area (e.g. 1 - 3 in, 3 - 5 in, etc.). This same procedure could have been used with the experimental NWS page, since the specified overall area stayed the same with only the internal contour lines changing from map to map. As a user of the information, it's simpler for me to just have to look at one map rather than three, and I should get the same predicted snowfall range for my particular location. Averaging the low and high values to get the expected value is pretty simple to do in one's head. Of course putting all the information on one map also saves the weather person and the TV station expensive presentation time.

Don
-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@mail.phys-l.org] On Behalf Of John
Denker via Phys-l
Sent: Tuesday, March 14, 2017 9:33 AM
To: Forum for Physics Educators <Phys-L@Phys-L.org>
Cc: John Denker <jsd@av8n.com>
Subject: [Phys-L] depicting uncertainty on maps

Hi --

Here is a timely example of uncertainty handled in an intelligent way.
Note the contrast:
++ For a point forecast, the National Weather Service routinely expresses
the uncertainty in the amount of snowfall by quoting a range, e.g. 12
to 18 inches. In physics it might be more conventional to write that
as 15±3 inches, but quoting the range is perfectly reasonable also.
-- On a map, the contours and color-coding don't lend themselves to
representing a range.
++ You can do a lot better by putting out *three* maps: lower limit,
nominal, and upper limit. The NWS has an experimental page that
does just that. Here is a screen grab:
https://www.av8n.com/physics/img48/snowfall-map-brackets.png



By way of contrast, note that as usual in the real world, the uncertainty is
neither calculated nor communicated using sig figs or anything like that.
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