Section author: Rodney Persky
Using your weather station can be fun, and reporting daily to various weather data sites can be very useful for your neighbours to check out the weather. However, at some point you may want to know how the weather effects your body, and if there is a way to tell when it’s good or not to work outdoors.
Here enters a whole realm of calculations based on energy transferring though walls, and the resistance offered by them. It can be a great learning adventure, and can save you a great deal of money, finding out how energy moves around.
Humidex is a tool to determine how an individuals body will react to the combination of Wind, Humidity and Temperature. The background of which is a heat balance across from your midriff to your skin, and is complimentary to ISO 7243 “Hot Environments - Estimation of the heat stress on working man”. A few important notes,
There are a number of assumptions that have been made to make this work which will directly affect its useability. These assumptions however have not been made available from Environment Canada, who are the original developers of the Humidex used in the PYWWS function cadhumidex. It is safe enough however to say that the following would have been some assumptions:
However, there are a number of assumptions pywws needs to make in calculating the Humidex:
There are also assumptions about the individuals body type and ‘acclimatisation’
Being Prepared for Summer - http://www.ec.gc.ca/meteo-weather/default.asp?lang=En&n=86C0425B-1
The function is descriptively named cadhumidex and has the parameters temperature and humidity, essentially the function operates as a conversion and can be used in a straightforward manner:
<ycalc>cadhumidex(data['temp_out'],data['hum_out'])</ycalc>
Putting it together, I have added colours that follow basic warning colors and the different brackets to produce a decent graph:
<?xml version="1.0" encoding="ISO-8859-1"?>
<graph>
<title>Humidity Index, Bands indicate apparent discomfort in standard on-site working conditions</title>
<size>1820, 1024</size>
<duration>hours=48</duration>
<xtics>2</xtics>
<xformat>%H%M</xformat>
<dateformat></dateformat>
<plot>
<yrange>29, 55</yrange>
<y2range>29, 55</y2range>
<ylabel></ylabel>
<y2label>Humidex</y2label>
<source>raw</source>
<subplot>
<title>Humidex</title>
<ycalc>cadhumidex(data['temp_out'],data['hum_out'])</ycalc>
<colour>4</colour>
<axes>x1y2</axes>
</subplot>
<subplot>
<title>HI > 54, Heat Stroke Probable</title>
<ycalc>54</ycalc>
<axes>x1y2</axes>
<colour>1</colour>
</subplot>
<subplot>
<title>HI > 45, Dangerous</title>
<ycalc>45</ycalc>
<axes>x1y2</axes>
<colour>8</colour>
</subplot>
<subplot>
<title>HI > 40, Intense</title>
<ycalc>40</ycalc>
<axes>x1y2</axes>
<colour>6</colour>
</subplot>
<subplot>
<title>HI > 35, Evident</title>
<ycalc>35</ycalc>
<axes>x1y2</axes>
<colour>2</colour>
</subplot>
<subplot>
<title>HI > 30, Noticeable</title>
<ycalc>30</ycalc>
<axes>x1y2</axes>
<colour>3</colour>
</subplot>
</plot>
</graph>
If you are not running the latest update / do not want to, then this can be implemented using a longer <ycalc> as follows:
<ycalc>data['temp_out']+0.555*(6.112*10**(7.5*data['temp_out']/(237.7+data['temp_out']))*data['hum_out']/100-10)</ycalc>
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