The Heat Index formula is complicated
June 17th, 2023 at 12:26:58 AM
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I'm sure you've all head of the Heat Index, which is how hot it *feels* once you factor in humidity. I wondered about the formula so I looked it up, and it's crazy long:
...where t = temperature and rh = relative humidity percentage.
I got on this track because I'm working outside these days so I looked up the hottest eight hours of the day, which turns out to be 1-9pm (heat index of 101-113°F), so that's when I'll be sleeping. I'll work 8 of the hours between 10pm-10am, for which the range is "only" 84-96°F. That's for Austin, TX. We're planning on moving in a couple years, partially because of the heat. It's always been hot in the summers here, but the last few years have been RIDICULOUSLY hot.
Quote:HI = -42.379 + 2.04901523*T + 10.14333127*RH - .22475541*T*RH - .00683783*T*T - .05481717*RH*RH + .00122874*T*T*RH + .00085282*T*RH*RH - .00000199*T*T*RH*RH
...where t = temperature and rh = relative humidity percentage.
I got on this track because I'm working outside these days so I looked up the hottest eight hours of the day, which turns out to be 1-9pm (heat index of 101-113°F), so that's when I'll be sleeping. I'll work 8 of the hours between 10pm-10am, for which the range is "only" 84-96°F. That's for Austin, TX. We're planning on moving in a couple years, partially because of the heat. It's always been hot in the summers here, but the last few years have been RIDICULOUSLY hot.
I run Easy Vegas ( https://easy.vegas )
June 17th, 2023 at 1:34:43 AM
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I found a rare chart that goes below 40% humidity. I know Los Angeles is subject to strange noon-time readings of 100 degrees, but the humidity is much less than 40% in some parts, so it's a dry heat that feels cooler than the air temperature. I'd worry more about sunburn than getting overheated in the Caution Zone.
June 17th, 2023 at 7:40:51 AM
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looks like 140 feels like 125, no matter what?
the next time Dame Fortune toys with your heart, your soul and your wallet, raise your glass and praise her thus: “Thanks for nothing, you cold-hearted, evil, damnable, nefarious, low-life, malicious monster from Hell!” She is, after all, stone deaf. ... Arnold Snyder
June 17th, 2023 at 8:39:56 AM
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Quote: odiousgambitlooks like 140 feels like 125, no matter what?
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"It's a dry heat."
May the cards fall in your favor.
June 17th, 2023 at 9:32:40 AM
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You only need to get the skin to 131/f to get second degree burns. So, you’re pretty much in the death zone high 120’s. Your body would attempt to stay cooler than the air, but it wouldn’t be fun for long if you don’t have any means to get cooler.
Sanitized for Your Protection
June 17th, 2023 at 10:17:14 AM
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Quote: rxwineYou only need to get the skin to 131/f to get second degree burns. So, you’re pretty much in the death zone high 120’s. Your body would attempt to stay cooler than the air, but it wouldn’t be fun for long if you don’t have any means to get cooler.
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That is what the pool is for. Been 94 here with 70% humidity. I don't spend much time outside the house so it only bothers me when the air conditioner breaks.
At my age, a "Life In Prison" sentence is not much of a deterrent.
June 17th, 2023 at 11:02:51 AM
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if the relative humidity is 25% or less, looks like the temperature often feels cooler than it is, often by quite a bit. On that chart, anyway
for weather I usually look at weather.com and the "hourly graphical forecast". I un-click heat index as I find it interferes with the display, and unless conditions are really bad it just adds maybe a degree or two, not that interesting. In any case, I feel I can say that it never displays something lower than the real temperature. I'll have to look and see if the relative humidity really drops ... I bet it just shows no change with them
for weather I usually look at weather.com and the "hourly graphical forecast". I un-click heat index as I find it interferes with the display, and unless conditions are really bad it just adds maybe a degree or two, not that interesting. In any case, I feel I can say that it never displays something lower than the real temperature. I'll have to look and see if the relative humidity really drops ... I bet it just shows no change with them
the next time Dame Fortune toys with your heart, your soul and your wallet, raise your glass and praise her thus: “Thanks for nothing, you cold-hearted, evil, damnable, nefarious, low-life, malicious monster from Hell!” She is, after all, stone deaf. ... Arnold Snyder
June 19th, 2023 at 10:59:01 AM
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The Weather Channel has their little car heats up chart for Austin at 103°. After 10 minutes the car will be 122°, and after 30 minutes, the car will be 137°.
Then there's the dew points of the mid to upper 70's in most of central and eastern Texas with a dry line of dew points in the 30's & 40's coming in from the northwest but heat indices will still be over 100°.
Construction workers may consider exiting the state after rest breaks for heat stress were just outlawed, effective in a few months.
There's also 100's of thousands of homes without power in the heat affected areas. Not sure if it's from storms or just overloaded circuits or unpaid bills. Prices for electricity could spike very high if it isn't windy enough outside, and that could lead to load shedding, or blackouts.
Then there's the dew points of the mid to upper 70's in most of central and eastern Texas with a dry line of dew points in the 30's & 40's coming in from the northwest but heat indices will still be over 100°.
Construction workers may consider exiting the state after rest breaks for heat stress were just outlawed, effective in a few months.
There's also 100's of thousands of homes without power in the heat affected areas. Not sure if it's from storms or just overloaded circuits or unpaid bills. Prices for electricity could spike very high if it isn't windy enough outside, and that could lead to load shedding, or blackouts.
Last edited by: ChumpChange on Jun 19, 2023
June 19th, 2023 at 6:14:52 PM
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Quote: DRichQuote: rxwineYou only need to get the skin to 131/f to get second degree burns. So, you’re pretty much in the death zone high 120’s. Your body would attempt to stay cooler than the air, but it wouldn’t be fun for long if you don’t have any means to get cooler.
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That is what the pool is for. Been 94 here with 70% humidity. I don't spend much time outside the house so it only bothers me when the air conditioner breaks.
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To me that isn't living, it's hiding and I can't live like that. Life is really too short to spend half your time hiding from the weather. But people will say, the winter, the winter, it's worth it living here. Screw the winter, the days are short the weather is always totally undependable, I lived in that kind of climate for almost 8 years and winters did not impress me. In Michigan we have mostly really nice weather for seven or eight months of the year, who cares about the rest of it. I worked outside all day today it was 80° and 45% humidity absolutely gorgeous. I'm putting in a patio tomorrow and it's going to be another gorgeous day.
"It's not called gambling if the math is on your side."
June 19th, 2023 at 9:44:46 PM
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Just an update on my work situation: My brilliant idea of sleeping during the hottest part of the day and working overnight and in the mornings is still tough, because when it hits 92% humidity it's just impossible to feel anything but miserable. I then bought a pricey ice vest thinking it would be a game changer, but that makes it only slightly more tolerable. I then cooled a small room with a window AC down to 67°F and hung out there with a wet shirt for 30 minutes, but then when I went outside to work (early morning), I lasted only 10 minutes before I was uncomfortable and sweating profusely. I had a plumber here today around 3pm to run a camera in the drain, in the shade, but when he stood up he nearly passed out. So, I'm gonna spend a few days finishing the essential outside work and then push all the non-essential stuff to October.
I run Easy Vegas ( https://easy.vegas )
June 20th, 2023 at 11:18:18 AM
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Some reports in the online news media of people & pets sitting in cool bathtubs for hours to keep cool.
The Weather Channel says there's an average of 15 100°+ days per year since 1942, but there've been 15 100°+ days in Texas just this month alone.
Seems I remember Texas having heat waves for decades now, but with global warming, they're getting much more pronounced.
I've been on this global warming trend since 1997, but that's from a Minnesota perspective. It's supposed to be near 90° in Minneapolis for the rest for the week. I don't go outside unless it's below 85° outside unless I just want some fresh air or go on a road trip. A gallon of milk will spoil in 10 minutes in a 90° trunk.
Ski season in the Sierras has been extended to the end of July. There's still several feet of snow on the ground.
The Weather Channel says there's an average of 15 100°+ days per year since 1942, but there've been 15 100°+ days in Texas just this month alone.
Seems I remember Texas having heat waves for decades now, but with global warming, they're getting much more pronounced.
I've been on this global warming trend since 1997, but that's from a Minnesota perspective. It's supposed to be near 90° in Minneapolis for the rest for the week. I don't go outside unless it's below 85° outside unless I just want some fresh air or go on a road trip. A gallon of milk will spoil in 10 minutes in a 90° trunk.
Ski season in the Sierras has been extended to the end of July. There's still several feet of snow on the ground.
Last edited by: ChumpChange on Jun 20, 2023
June 20th, 2023 at 11:22:52 AM
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Quote: EvenBob
To me that isn't living, it's hiding and I can't live like that. Life is really too short to spend half your time hiding from the weather.
What makes you think that I am hiding from the weather. I wouldn't be doing anything different 99% of the time if the weather was different. On average I leave the house for about two hours per week no matter what the weather is. I went to the pharmacy to pick up a prescription on Saturday and today I will go to a doctors appointment. I probably won't leave the house the rest of the week.
At my age, a "Life In Prison" sentence is not much of a deterrent.
June 20th, 2023 at 11:50:35 AM
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Quote: MichaelBluejayJust an update on my work situation: My brilliant idea of sleeping during the hottest part of the day and working overnight and in the mornings is still tough, because when it hits 92% humidity it's just impossible to feel anything but miserable. I then bought a pricey ice vest thinking it would be a game changer, but that makes it only slightly more tolerable. I then cooled a small room with a window AC down to 67°F and hung out there with a wet shirt for 30 minutes, but then when I went outside to work (early morning), I lasted only 10 minutes before I was uncomfortable and sweating profusely. I had a plumber here today around 3pm to run a camera in the drain, in the shade, but when he stood up he nearly passed out. So, I'm gonna spend a few days finishing the essential outside work and then push all the non-essential stuff to October.
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You can get a box fan (Walmart $20) and run it outside with an extension cord. Put it on a chair or stool if you need to. Even if you're moving around you can go back and stand in front of it. Might help.
Sanitized for Your Protection
June 20th, 2023 at 1:51:52 PM
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A bit off topic, but I have a friend who keeps fans running all over her house. I asked why and she said it was to cool it down and it's cheaper than air conditioning. I said it doesn't help at all to have a fan running unless you're near it and even then it doesn't lower the temperature. It only helps because the breeze helps transfer heat from the body to the air. She doesn't believe me. Who is right?
"For with much wisdom comes much sorrow." -- Ecclesiastes 1:18 (NIV)
June 20th, 2023 at 2:00:35 PM
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My air purifier is blowing seemingly cooler air at me. My window fan, which is always in the window this time of year, lets in warmer air when it's not on, but I use it to blow cooking smoke out of the room, or to cool the room when it's cooler outside than inside. Sometimes I come in and I'm sweating and have a medium size fan blowing on me when I sit down.
As for running box fans throughout the house, it might lower the heat buildup within rooms. If the sun is shining on one part of the house, the fans can recirculate air around to lessen heat buildup. So instead of one side of the house heating up to 85°, you can recirculate the air so it's only 81° around the house. But heat rises, and higher floors will have higher temperatures in the summer. So it might be 74° in the basement, 81° on the bottom floor, 86° on the 2nd floor, and 105° in the attic.
As for running box fans throughout the house, it might lower the heat buildup within rooms. If the sun is shining on one part of the house, the fans can recirculate air around to lessen heat buildup. So instead of one side of the house heating up to 85°, you can recirculate the air so it's only 81° around the house. But heat rises, and higher floors will have higher temperatures in the summer. So it might be 74° in the basement, 81° on the bottom floor, 86° on the 2nd floor, and 105° in the attic.
June 20th, 2023 at 2:06:08 PM
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You’re right. I wrote about this over 20 years ago. Scroll towards the bottom, “How ceiling fans work”. https://michaelbluejay.com/electricity/cooling.htmlQuote: WizardWho is right?
I run Easy Vegas ( https://easy.vegas )
June 20th, 2023 at 5:50:48 PM
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Quote: MichaelBluejayYou’re right. I wrote about this over 20 years ago. Scroll towards the bottom, “How ceiling fans work”. https://michaelbluejay.com/electricity/cooling.htmlQuote: WizardWho is right?
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The moving air does seem to enhance comfort, which is more important to me than temperature.
I like 60°F (or less) with still air, but 71°F is ok with the air moving. (I'm a wimp.)
Wizard, is it possible your friend is conflating "feeling more comfortable" with "cooling off the house"?
May the cards fall in your favor.
June 21st, 2023 at 5:49:40 AM
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Indeed! In fact, running fans will make her house hotter. Most ceiling fan motors are less than 50% efficient. This means that over half of the fan's electrical energy consumption is converted directly into heat.Quote: MichaelBluejayYou’re right. I wrote about this over 20 years ago. Scroll towards the bottom, “How ceiling fans work”. https://michaelbluejay.com/electricity/cooling.htmlQuote: WizardWho is right?
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Also, if it is hotter outside than inside, the higher air velocities inside the house will cause an increase in the heat transfer rate through the walls. (Although, I would imagine this additional heat would be relatively insignificant in a well-insulated house.)
Back to the OP, I have never liked the Heat Index as a meaningful metric for how hot it "feels." I suppose it has merits in giving some insight as to how a human body reacts to the specified conditions, but how it "feels?" Not so much. I have experienced both 85°F / 75% RH, and 100°F in the desert. Both have the same Heat Index value, but they feel nothing alike.
Hope you are able to stay cool, MBJ!
Fun fact: Humid air often feels oppressive as MBJ had described, and people tend to associate this with the air being "thick" or "heavy." However, humid air is actually less dense than dry air at the same temperature.
"Dealer has 'rock'... Pay 'paper!'"
June 21st, 2023 at 6:44:56 AM
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Headline: A blackout in Phoenix during a heat wave could be a catastrophic combination, sending more than 50% of the population to the hospital, according to a recent study.
June 21st, 2023 at 9:03:29 AM
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Quote: ChumpChangeHeadline: A blackout in Phoenix during a heat wave could be a catastrophic combination, sending more than 50% of the population to the hospital, according to a recent study.
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I’d go sit in my car with the AC on.
Sanitized for Your Protection
June 21st, 2023 at 10:04:44 AM
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Quote: rxwineQuote: ChumpChangeHeadline: A blackout in Phoenix during a heat wave could be a catastrophic combination, sending more than 50% of the population to the hospital, according to a recent study.
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I’d go sit in my car with the AC on.
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Until the gas ran out. An extended blackout in any city would be a nightmare, but one in Phoenix in the summer would be a disaster.
Even the Apaches avoided Phoenix in the summer.
It's 83 in Bisbee as I type this. 91 in Tucson and 93 in Phoenix. It will hit 105 this afternoon with an air quality alert. An extended blackout/heat wave with poor-quality air would send a lot of people both fleeing and being hospitalized.
The older I get, the better I recall things that never happened
