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A question about wind chill

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RayProudfoot
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A question about wind chill

Post by RayProudfoot » Wed Feb 28, 2018 9:26 am

Wind chill is a constantly changing value depending on the strength of the wind in cold conditions. My Davis VP2 console shows Wind Chill but it's not being updated with each update of the wind - every 2.5 secs.

But on my WUnderground site it is being recalculated with each change of wind. Why isn't the the Davis VP2 console updating more frequently?

https://www.wunderground.com/personal-w ... =ISTOCKPO4
Cheers,
Ray, Cheshire.

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mcrossley
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Re: A question about wind chill

Post by mcrossley » Wed Feb 28, 2018 9:30 am

I thought it was normally calculated on the average wind speed, which doesn't change rapidly. Sounds like WU may be calculating it on the instantaneous speed?

RayProudfoot
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Re: A question about wind chill

Post by RayProudfoot » Wed Feb 28, 2018 9:36 am

That would explain the lack of updates on the console. Bit disappointing because gusts could create a new record which will be missed if only average wind is used. :(
Cheers,
Ray, Cheshire.

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mcrossley
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Re: A question about wind chill

Post by mcrossley » Wed Feb 28, 2018 9:52 am

It would bounce around all over the place though if it used the instantaneous speed.

RayProudfoot
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Re: A question about wind chill

Post by RayProudfoot » Wed Feb 28, 2018 10:06 am

Yes but it would correctly show the actual wind chill. And it's only shown to a whole number so no more so than the wind value constantly changing.
Cheers,
Ray, Cheshire.

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mcrossley
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Re: A question about wind chill

Post by mcrossley » Wed Feb 28, 2018 10:21 am

You could argue that the average speed is a better value, body chill takes effect over a period of time of exposure, you aren't instantly chilled in a few seconds. Though you may feel an icy blast! :lol:

RayProudfoot
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Re: A question about wind chill

Post by RayProudfoot » Wed Feb 28, 2018 10:30 am

Good point Mark. :D
Cheers,
Ray, Cheshire.

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jdc
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Re: A question about wind chill

Post by jdc » Wed Feb 28, 2018 11:53 am

It's always described as an 'indicator' as to the effects of wind at low temps and varies depending on sunshine too, so seems fairly imprecise to start with. I think it is primarily for use in regions where temperatures are less than -10 and where the wind is probably more linear.
Extract (part) from 'Marine Observers Handbook' :
It can be measured by the rate of heat loss per unit area, the "windchill factor" or more commonly by the "windchill equivalent temperature" (WET). No allowance is made for precipitation or sea spray. Windchill does not apply to inanimate objects, even heat producing engines. In "full" sunshine, a correction of about +7°C at low wind speeds and +3°C at gale force should be made.

RayProudfoot
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Re: A question about wind chill

Post by RayProudfoot » Wed Feb 28, 2018 12:32 pm

Thanks John. I don't have any sunshine recording hardware but even if I did it seems unlikely the Davis software could use it.

Most of the time WC is not an issue in the British Isles at sea-level or thereabouts. Just for a few days in the year when we have very unusual conditions.
Cheers,
Ray, Cheshire.

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