[at-l] Wash

Mara Factor mfactor at gmail.com
Sat Feb 25 07:46:41 CST 2012


To paraphrase from Wikipedia <http://en.wikipedia.org/wiki/Wind_chill>, The
felt air temperature is determined by convection, or how quickly the wind
speed over our skin draws heat away.  The human response is to maintain
surface temp so the higher the wind, the faster our actual temperature
drops and the lower the perceived temperature.

Here's the formula from
Wikipedia<http://en.wikipedia.org/wiki/Wind_chill#Formulae_and_tables>used
to calculate windchill:

[image: T_{wc}=35.74+0.6215 T_a-35.75 V^{+0.16}+0.4275 T_a V^{+0.16}\,\!]
where [image: T_{wc}\,\!] is the wind chill index, based on the Fahrenheit
scale [image: T_a\,\!] is the air temperature, measured in °F, and [image:
V\,\!] is the wind speed, in mph.

And NOAA's chart and
converter<http://www.nws.noaa.gov/os/windchill/index.shtml> because
the chart doesn't cover the high wind speeds on Washington today.

Humidity doesn't play a role in the North American formula which is only
defined for temps less than 50 F.  The heat index does incorporate humidity
and starts above 80 F.

Mara
Stitches, AT99

Visit my Travels and Trails web site at:
http://friends.backcountry.net/m_factor


On Sat, Feb 25, 2012 at 7:41 AM, Felix J <AThiker at smithville.net> wrote:

>   [image: Current Summit Conditions]<http://www.mountwashington.org/weather/conditions.php>
> Temperature 9.6°F  Wind 81.5 mph  Direction 269° (W)  Gust 88.6 mph  Wind
> Chill -22.3°F  Saturday 7:30 AM
>
> How can the windchill be -22  with 80 mph winds at 9 degrees?
>
>
> --
> Felix J. McGillicuddy
> ME-->GA '98
> "Your Move"
> ALT '03 KT '03http://Felixhikes.tripod.com/
>
>
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