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Friday, June 6, 2008 at 7:32 am

Robert D. Jordan

No Title I’m writing to ask for help with an argument that I am having with a friend in Atlanta. We are both members of an organization of sight-hound fanciers. We hold lure coursing field trials where our sight-hounds demonstrate their hunting skills chasing an artificial lure. He and I are arguing about the heat index. He posted to our discussion list what seemed to me to be rather unusually high heat indexes for some past trials that we held in northern Virginia during  the month of June. I went to the Almanac web site and found a weather history archive where I could get the weather obversations for Leesburg Virginia for the dates in question. http://www.almanac.com/weatherhistory/index.php   This page had a lot of information but it didn't have a Heat Index. So I looked and found a NOAA page that had a "Heat Index Calculator" on it. http://www.srh.noaa.gov/elp/wxcalc/heatindex.html  I found in order to use the Heat Index calculator I needed to know the "Relative Humidity". So I found another NOAA page that had a Relative Humidity Calculator on it. http://www.hpc.ncep.noaa.gov/html/dewrh.shtml   Using the two form tools I got significantly lower heat indices than my friend did. I wondered why my figures were different than Johns so I played around with the numbers and found that when I entered the “average humidity” and temperature into the form tool, where it asked for relative humidity, I got significantly higher readings. When I explained all this to my friend he replied that average humidity and relative humidity were the same. He says that all humidity readings are relative so it doesn’t matter which reading he uses. Below are the figures that I used and my results. I know it’s a lot to ask but if anyone that understands how to complete these calculations could review them and offer their opinion as to their accuracy and also whether John’s statement that all humidity statments are relative humidity, I might name a child after them: Saturday June 5, 1999 (Leesburg VA.) Min Temp 51.8 Mean Temp 67.9 Max Temp 82.4 Dew Point 53.7 Relative Humidity 37.3 Heat index 81.4 Sunday June 6, 1999 (Leesburg VA.) Min Temp 55.4 Mean Temp 72.0 Max Temp 89.6 Dew Point 57.8 Relative Humidity 34.41 Heat index 88.4 Saturday June 4, 2005 (Kelly's Ford VA.) Min Temp 60.8 Mean Temp 68.7 Max Temp 78.8 Dew Point 64.7 Relative Humidity 62.09 Heat index N/A (A heat index value cannot be calculated for temps less than 80 degrees) Sunday June 5, 2005 (Kelly's Ford VA.) Min Temp 60.8 Mean Temp 74.6 Max Temp 87.8 Dew Point 69.3 Relative Humidity 54.47 Heat index 92.2 Saturday June 2, 2007 (Leesburg VA.) Min Temp 64.4 Mean Temp 77.4 Max Temp 89.6 Dew Point 66.2 Relative Humidity 45.94 Heat index 91.8 Sunday June 3, 2007 (Leesburg VA) Min Temp 66.2 Mean Temp 71.7 Max Temp 82.4 Dew Point 65.1 Relative Humidity 56.0 Heat index 84.2 Thanks in advance Bob Jordan

Saturday, July 12, 2008 at 3:20 pm

Jessica Arguinzoni

Will try to find equation for you Are you calculating the correct field? I mean last year I was doing an experiment to determine, affect of distance from lake (lake ontario) on temperature, humidity, and so forth. I ended up using that calculator and to my surprise I think I did that same thing, and my values where different. I will try to find the equation for you, but I know I did it manually and it should give you a much different figure. I feel like your relative humidity is way to low.