Author Topic: Heat Index vs Apparent Temperature  (Read 3753 times)

rexross

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Heat Index vs Apparent Temperature
« on: June 14, 2015, 06:14:38 PM »
I am having trouble understanding the difference between the tags for HeatIndex and Apparent Temperature

Here are the details:

The tag for Apparent Temperature being used is
STAT$AT_US:CURRENT$


The tag for Heat Index being used is
STAT$HEATINDEX:CURRENT$


Data Returned Are:
Apparent Temperature   93.1
Heat Index             104.6
Actual Temperature            87.8

By the way, I am using a Davis Vantage Pro station.

Anyone have any thoughts here?

Thanks

elagache

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Definition and scepticism (Re: Heat Index vs Apparent Temperature)
« Reply #1 on: June 14, 2015, 09:38:49 PM »
Dear rexross and WeatherCat numerologists, . . . .

I am having trouble understanding the difference between the tags for HeatIndex and Apparent Temperature

Huh?  I didn't even know WeatherCat supported such a thing.

However, if you check the WeatherCat manual not only does WeatherCat support the United States definition of "Apparent Temperature" it also can compute the Australian version!

That just leaves one matter - what in the blankety, blank is "Apparent Temperature" in the first place.  Well, putting Goggle on the case I came up with this definition:

https://www.ncdc.noaa.gov/societal-impacts/apparent-temp/at

It appears to be another computed value based on some attempt to evaluate how the human body responds to weather extremes.

I've gone on record in the past discouraging people from trying to use these computed values.  I strongly feel that you cannot convert the complexity of experienced weather into a single number - especially a pseudo temperature.  We all have weather stations, so we have all the raw data.  We do better explaining to people the complexity of how our body responds than to try humor them with a single number.

In the end it reminds me of the saying: "A man with a watch knows the time. A man with two (or more) is never sure."

Cheers, Edouard  [cheers1]

xairbusdriver

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Re: Heat Index vs Apparent Temperature
« Reply #2 on: June 14, 2015, 10:38:29 PM »
[rant]
In my opinion, and we all know what that's worth, "Apparent" temperature is like "unexpected" crash. I suspect it is not used (around here, anyway) because "Heat Index" is so much higher and 'extreme' sells better than 'technical'. [rolleyes2] I'd much rather NOAA come up with various colors for the dangers of heat, similar to their system for ozone. The use of these various terms may lead to results similar to crying wolf too often. Excessive heat can be a killer, but I am too cynical to believe most media are really concerned about my health.

We have an inop exhaust fan in our attic and I specifically asked the company send someone only in the earliest hours of the day, it's an inconvenience, not an emergency and no ones health needs to be threatened by working in 120+ temps... apparent, real, pseudo or actual! [sweat2]
[/rant]
My wife is gone for 15 days. Do you think my attitude might be slightly affected? ;D

Blicj11

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Re: Heat Index vs Apparent Temperature
« Reply #3 on: June 15, 2015, 06:34:21 AM »
According to one expert, me, Apparent Temperature reflects the effect of wind speed and relative humidity on the temperature, whilst Heat Index calculates the discomfort felt taking into consideration the effect of humidity on temperature. I know this is true because it is what I have posted on my website.  :)
http://timberlakesutah.com/weather-gauges-explained/
Blick


xairbusdriver

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Re: Heat Index vs Apparent Temperature
« Reply #4 on: June 15, 2015, 01:47:30 PM »
Quote
I know this is true because it is what I have posted on my website.
Well, that's good enough for me!  [tup] ;)

I guess if there's no wind, we should just run around more to get the Heat Index down to what the "Apparent" temp would be? :o :P

LesCimes

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Re: Heat Index vs Apparent Temperature
« Reply #5 on: June 15, 2015, 06:10:55 PM »
Hmm, what the apparent temperature is right now, or the heat index, I don't know, but it is apparent to me that it is too hot and it is higher than my heat index can take. Am staying inside today with the A/C running.  [sweat2]

xairbusdriver

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Re: Heat Index vs Apparent Temperature
« Reply #6 on: June 15, 2015, 09:36:45 PM »
I have a small pond/water garden that will probably show, when I eventually get a camera that works... Anyway, even though it gets 10+ hours of Sun, it still cools me off when I get in it to remove dead water lily leaves/blooms and replace the filter material. I do wear long waders, the bottom is slick as... stuff... but I can still feel the cool(er) water when I stick in my arms up to my shoulder. ;) I would assume that water counts as 200% humidity?! [rolleyes2] Currently (°F): Actual: 90.8, "Apparent": 97.0, "Heat Index": 100.1, Humidity (outside the 'pond'): 56%, light winds mostly from the S/SE.

elagache

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Hot is what you feel. (Re: Heat Index vs Apparent Temperature)
« Reply #7 on: June 15, 2015, 10:36:41 PM »
Dear X-Air, Blick, LesCimes, and WeatherCat station caregivers,

I still haven't gotten my station fully reconfigured from the desperate effort to avoid the sensor errors.  At the moment I've got my second temperature/humidity probe stuck against a wall on a small deck that gets really beaten on by the sun.  When I did the work on that small deck, most of the work was done with some cloud cover.  However, toward the end of the installation, the sun came out and even if it was February, I started sweating like a pig.  Now I have that second temperature/humidity probe to back up what I was feeling.  When the sun is beating on it, it can be 20 degrees hotter than the probe that has proper shielding.  With all the fancy analysis, none of these indices I think are capable to going over 20 degrees the measured air temperature.  Yet, if you have to work in a situation were the sun's heat is being reflected upon from all sides - it does feel like it is 20 degrees warmer than the air temperature!

I can respect the attempt to come up with these indices and I suppose they do help people in some areas to calibrate their activities.  Nonetheless, the plethora of these indices is proof enough that this is an inexact science.

Cheers, Edouard  [cheers1]