Help: Formula for Windchill Factor

Subject: Formula for Windchill Factor
From: wdyat12
Date: 02 Mar 01 - 10:48 PM

Now that the windiest month is upon us and the temperature still hasn't given us a break in Maine, windchill factor is very much on our minds. I have seen many charts for windchill factor, but I can't for the life of me lay my hands on one now. My son is making a weather station with sensors inputted into his old computer. He needs the formula for calculating windchill in Fahrenheit or Celsius so he can have that displayed in real time on screen. We searched the net this afternoon with no results for the formula. We retreived many fancy sites that automatically calculate windchill factor for you, but none that tell you how to do it. Is there anyone at Mudcat who possesses this knowledge?

wdyat12

Subject: RE: Help: Formula for Windchill Factor
From: katlaughing
Date: 02 Mar 01 - 10:59 PM

I found the following at http://weather.miningco.com/science/weather/library/weekly/aa120198.htm:

Calculating Windchill

The National Weather Service uses the following formula to calculate the windchill:

Windchill Temp. (§F) = 0.0817(3.71(V)^0.5 + 5.81 - 0.25V)(T - 91.4) + 91.4

where V is the wind speed in miles per hour and T is the outside temperature in degrees Fahrenheit.

In SI units, the windchill is calculated using the following formula:

Windchill Temp. (§C) = 0.045(5.27(V)^0.5 + 10.45 - 0.28V)(T - 33.0) + 33.0

where V is the wind speed in kilometers per hour, and T is the outside temperature in degrees Celsius.

To simplify the calculations using the formulas above, the windchill temperature can be determined using the calculator below (you'll have to go to that site for this, as it didn't copy correctly.) After you enter a new wind speed or temperature, tab or click outside the box and the windchill temperature will be automatically updated.

Temp (§C)If you deplore calculations and want the information tabulated, USA Today provides an excellent reference table. Find your wind speed on the vertical axis, air temperature on horizontal axis, and follow the column and row until intersection to determine your windchill temperature.

If you live in the United States, you can look for your state and associated windchill at the Ohio State or Weather Underground windchill graphics site.

Limitations to Windchill

Various scientists around the world have presented issues and concerns regarding the validity of the windchill calculation. These issues include the complexity of interaction between the wind and people, measurement heights of wind speed, clothing insulators, and sunshine warming effects. These issues are well founded and worth considering when performing calculations and analyzing windchill.

Quiz Time

Do you think you fully understand the concepts discussed above? Try the quiz below to test your knowledge. Jot your answers down on a piece of scratch paper and check them after your have completed the quiz.

Q1 Skiing down your favorite winter slope, you view a thermometer reading 20§F. At 12 miles per hour, what is the effective temperature on your face (the only uncovered part of your body)? Feel free to use the calculator above.

Q2 If the outside temperature is 5§C, the wind speed is 15 kilometers per hour, and you place a glass of water outside, will the water freeze?

Q3 At 0§C and no wind, what is the windchill temperature and why is it different than the reading on the thermometer?

Q4 You recently replaced the antifreeze in your car because the TV weather forecaster predicted winter windchill temperatures dropping into the 10s (degrees F) and ambient air temperatures in the 20s. Your old antifreeze was rated to 20§F, while the new antifreeze is rated to 10§F. Assuming that the old antifreeze was still good, was the change necessary?

(Answers are at a link at that website.)

Subject: RE: Help: Formula for Windchill Factor
From: wdyat12
Date: 03 Mar 01 - 01:08 AM

Thanks kat,

You have saved the day! Now Ben can move on with his project. I think he was talking about the formula for predicting the tides in the Gulf of Maine for his next application. Any thoughts on this one?

wdyat12

Subject: RE: Help: Formula for Windchill Factor
From: katlaughing
Date: 03 Mar 01 - 03:02 AM

Well....no thoughts, but plenty of searching has turned up several sites with LOTS of info. Doesn't look as though there is any one set formula, there are so many factors involved from what I can tell. Maybe one of our sailors will come in here and give us a hand. In the meantime, these ought to give Ben food for thought:

22 pages of info on tides

Make a tide prediction (noaa)

Tide predicting machines- hitory of (noaa)

Main page for NOAA's Tide Site

WWW Tide & Current Predictor

Good luck!