But it's a dry heat....

"Doug Semler" wrote in message
oups.com...
"Dan Luke" spewed this drivel:
"Matt Barrow" wrote:
The same day it hit 104 in Chicago and ...the humidity was 90+/-
percent.
Baloney.
Look at a psychometric chart:
http://www.rfcafe.com/references/gen...tric_chart.htm
Ever hear of "Heat Index"?
Yes.

What's that got to do with your made-up statement that the temperature
was
104 F. and the humidity was 90%?

Did you attempt to understand the chart?

First off, it's psychRometric.

Do you understand relative humidity?

According to NOAA, July of 1995 (about which I presume Matt is talking)
had the following (from
http://www.crh.noaa.gov/lot/science/jul1395/jul1395.htm)
quote
In the immediate Chicago region, surface dew points held in the upper
70s to near 80 however the temperature exceeded 100 degF for several
hours. Heat Index values were greater than 115 degrees for much of the
midday and afternoon hours...reaching 125 degrees for the 2145UTC
observation from Midway (MDW). In fact, the mercury remained at or
above 100 degF at MDW for seven hours, from 13/1800UTC to 14/0100UTC.
This extraordinary length may be partially due to the more urban
location of the field.
/quote

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%.

P.S. A heat index of 125!?!? That's definitely "stay at home and hope
the AC doesn't go out on me" weather!

One aspect is that for people outdoors (homeless, for example) cannot get
out of the heat during the day (shade doesn't work) nor at night (temps stay
high). I suspect that can add to a death toll.


--
Matt
---------------------
Matthew W. Barrow
Site-Fill Homes, LLC.
Montrose, CO

Or even 46.9% .....First I don't hit the exp(8), and then I fudge up
and forget to convert to deg C the second time around...

My brain is fried today. Must be the humidity....Too bad it's so humid
out that I don't feel like taking the rest of the day off and
golfing... g

Matt Barrow wrote:
One aspect is that for people outdoors (homeless, for example) cannot get
out of the heat during the day (shade doesn't work) nor at night (temps stay
high). I suspect that can add to a death toll.

Of course. And of course, I was talking about for *me*. I have lived
in the desert, where the temperatures routinely rose above 100 in the
summer. However the humidity was low enough that air conditioning was
not required (well, for ME at least). Then one July 4th, there was a
95 degree day with something like a HI of 105...That was one of the
worst days...I did run the AC that day. Not so much because it felt
like it was 105, but because if you didn't, you would lose 5 pounds in
sweat.

There's a wikepedia article on the July 1995 chicago heat wave that
reads, in part:

quote
Because of the nature of the disaster, and the slow response of
authorities to recognise it, no official "death toll" has been
determined. However, figures show that 739 additional people died in
that particular week above the usual weekly average. Further
statistical analysis analyzed by Eric Klinenberg (author of Heat Wave:
A Social Autopsy of Disaster in Chicago) showed that blacks were more
likely to die than whites, and that Hispanics had an unusually low
death rate. This has been explained by the fact that many blacks at the
time lived in areas of sub-standard housing and were quite dispersed,
while Hispanics at the time lived in places with higher population
density. Thus demographics, rather than ethnic values, were shown to be
the reason for this disparity in deaths.
/quote

Note that I take wikepedia articles with a grain of salt; I don't know
the reference for the "figures" regarding the death toll, but it is
probably from the same book mentioned.

"Doug Semler" wrote in message
ups.com...
Matt Barrow wrote:
One aspect is that for people outdoors (homeless, for example) cannot
get
out of the heat during the day (shade doesn't work) nor at night (temps
stay
high). I suspect that can add to a death toll.


There's a wikepedia article on the July 1995 chicago heat wave that
reads, in part:

quote
....
/quote

Note that I take wikepedia articles with a grain of salt; I don't know
the reference for the "figures" regarding the death toll, but it is
probably from the same book mentioned.

Some here would be REALLY UPSET that you didn't check it against
SNOPES.COM!!

Others want long, detailed notes...and then disappear without a word. :~(

"Matt Barrow" wrote:

Yes.

What's that got to do with your made-up statement that the temperature was
104 F. and the humidity was 90%?

How was that made up? Check the weather records from June, 1990. Do a
google
search on heat related deaths in Chicago.

I meant the part about 90% RH. If you look, you'll see that's off the chart
at 104 deg. F.

Did you attempt to understand the chart?


Yes, and I understand your point, thank you. I assume your point is that
one
would perspire more at 120 than at 104. If so, that wasn't my point.

No, my point is that 90% RH at 104 deg. F. is not a set of conditions one
will find in the surface atmosphere. People often assume that the humidity
is much higher than it actually is when the weather is warm. At 104 deg. F.,
50% RH would be awfully uncomfortable; 90% RH would be, if not impossible,
damned near it.

Relative humidity is the humidity you feel. Given constant absolute humidity
(no front, rainstorm), the highest relative humidity occurs at the coolest
part of the day, usually around dawn.

One thing...When the desert gets how it still cools substantially during
the
evening and night. When humid air gets hot (like the 104-105 that Chicago
had, the heat effect holds. I suspect that a couple days of this is what
kills so many and did back in 1990.

The heat holds because of the high dewpoint. The dewpoint acts as a low
limit to temperature fall because of the heat of condensation--as atmospheric
water condenses it gives up heat and warms the air. The higher the dewpoint,
the higher the overnight low. Cloud cover can also affect this by slowing
radiaton cooling.
--
Dan
C-172RG at BFM

"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.

"Matt Barrow" wrote:
Matt and I don't tread too lightly on each other's feelings. The last
thing
he told me in another thread was "kiss my bass." It's not meant with ill
will.

I also told you to quit carping.

Are you trying to drum up another pun cascade?

This board could put together a World Championship team for "Triva
Pursuit".
Unfortunately, many of us have the sensitivity (not to mention _tact_) of a
Abrams tank with a stuck cruise control.

Yes, but we're lovable, anyway.

--
Dan
C-172RG at BFM

"Dan Luke" wrote in message
...


No, my point is that 90% RH at 104 deg. F. is not a set of conditions one
will find in the surface atmosphere. People often assume that the
humidity
is much higher than it actually is when the weather is warm.

Which is probably how the folks in Chicago were describing it to us. Having
been there in the summer just a few times, I do know you just get wringing
wet just standing outside.

On the other end, I also recall a few episodes of shoveling snow, here in
Colorado, wearing only a light jacket. And, no, it wasn't that the exercise
was keeping me warm. We get nice fluffy powder, the easterners/northerners
get slush.

At 104 deg. F.,
50% RH would be awfully uncomfortable; 90% RH would be, if not impossible,
damned near it.

Sometimes, the "near impossible" happens :~)

My in-laws live in Scottsdale, and I've been there a few times during the
summer (dragged kicking and screaming). It's so amazing to be in such heat
and your shirt is bone dry, contrasted with the wringing wet mentioned
earlier, in the high 80's, low-mid 90's.


Matt
---------------------
Matthew W. Barrow
Site-Fill Homes, LLC.
Montrose, CO

"Dan Luke" wrote in message
...

"Matt Barrow" wrote:
Matt and I don't tread too lightly on each other's feelings. The last
thing
he told me in another thread was "kiss my bass." It's not meant with
ill
will.

I also told you to quit carping.

Are you trying to drum up another pun cascade?

Well, we can roll with that.


This board could put together a World Championship team for "Triva
Pursuit".
Unfortunately, many of us have the sensitivity (not to mention _tact_)
of a
Abrams tank with a stuck cruise control.

Yes, but we're lovable, anyway.

All warm and fuzzy we are.


--
Matt
---------------------
Matthew W. Barrow
Site-Fill Homes, LLC.
Montrose, CO

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