But it's a dry heat....

"Doug Semler" wrote:

First off, it's psychRometric.

Do you understand relative humidity?

I thought so, but I foolishly trusted the spelling in the url.

Now, I am going to use the following readings:
104 degrees F for the temperature (the "official" high)
80 degrees F for the dew point.

According to the formula RH =~ 100((112 - .1T - Td)/(112 + .9T))^8,
where T = observed temperature and Td = dew point temperature, I get a
relative humidity of 88.32%.

We must be looking at different charts.

Dan Luke wrote:
I wrote:
Now, I am going to use the following readings:
104 degrees F for the temperature (the "official" high)
80 degrees F for the dew point.

According to the formula RH =~ 100((112 - .1T - Td)/(112 + .9T))^8,

(Note it should be +Td and not -Td...That's a typo)

where T = observed temperature and Td = dew point temperature, I get a
relative humidity of 88.32%.

We must be looking at different charts.

Noooo....I foolishly did not check my work. Mea Culpa. I did the
math in a calculator (using the relative humidity formula above) and
what happened was
1) I did not convert to Celsius (duh)
and 2) I did not raise the (112 - .1T + Td)/(112 + .9T) portion to the
eighth power. Unfortunately, that portion of the formula happens to be
..882, sooooo it comes sufficiently close to 90% that I thought I had
hit the right answer :-/

BTW, taking it one step further, to have a RH of ~.90 in 104 degrees F
(~40 degrees C), you would have a dew point temp of ~ 38 degrees C
which is ~100 degrees F