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Old 08-14-2007, 08:59 PM
 
Location: Austin, TX
1,231 posts, read 3,531,663 times
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Quote:
Originally Posted by moot View Post
Yes, the urban heat island effect is warming Phoenix. It can be especially felt at night. The average low for July is 81F. That low hasn't even been reached this whole month. It's always upper 80s/low 90s.
The warmer overnight lows in cities are due more to the irrigation rather than the "heat island" effect. The type of heat trapped by the buildings holds heat well into the night but the higher humidity from watering the desert is what prevents the temperatures from being cooler by morning.

One study estimated that this added-humidity effect is the main reason why the overnight lows in Los Angeles have risen almost 10 degrees on average over the past century. Pretty stunning numbers.

Water is extremely effective at trapping heat but it's equally effective in holding down high temperatures because it takes more time to heat moist air than dry air. Hence, Phoenix gets much hotter than Dallas, and Death Valley makes Phoenix feel like an air-conditioned indoor mall.

Loved the opening post with its clear explanation of the monsoons. This year has been a good one for the interior southwest. Unfortunately, So Cal is burning and looks destined to have its worst fire year on record unless a freak storm dumps a ton of rain on them.
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Old 08-15-2007, 08:04 AM
 
Location: Perth, Western Australia
9,594 posts, read 25,190,667 times
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Quote:
Originally Posted by TheHarvester View Post
The warmer overnight lows in cities are due more to the irrigation rather than the "heat island" effect. The type of heat trapped by the buildings holds heat well into the night but the higher humidity from watering the desert is what prevents the temperatures from being cooler by morning.

One study estimated that this added-humidity effect is the main reason why the overnight lows in Los Angeles have risen almost 10 degrees on average over the past century. Pretty stunning numbers.

Water is extremely effective at trapping heat but it's equally effective in holding down high temperatures because it takes more time to heat moist air than dry air. Hence, Phoenix gets much hotter than Dallas, and Death Valley makes Phoenix feel like an air-conditioned indoor mall.

Loved the opening post with its clear explanation of the monsoons. This year has been a good one for the interior southwest. Unfortunately, So Cal is burning and looks destined to have its worst fire year on record unless a freak storm dumps a ton of rain on them.
Interesting post TheHavester...

Perhaps that's partly the reason dewpoints into the 70's are being experienced in the Phoenix area.

If you had me to guess, I'd figure that except during freakish storms that dewpoints never went past 60 F.
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Old 08-15-2007, 08:35 AM
 
Location: Austin, TX
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Quote:
Originally Posted by ColdCanadian View Post
Interesting post TheHavester...

Perhaps that's partly the reason dewpoints into the 70's are being experienced in the Phoenix area.
This morning I realized I had posted partially erroneous information. While it's true that water vapor holds heat very well, heating and cooling more slowly than dry air, the study I was relying on was only pertinent to Los Angeles and I don't know the literature regarding the general effect.

After all, the highest overnight lows in the USA (often over 100 degrees) are usually in Death Valley, which isn't exactly a golfing resort.

But the other thing I've known from at least 20 years ago was that Phoenix does, indeed, have higher dew points now that water has been imported and so many people irrigate. Lawns are probably the main culprit, and sprinkler systems often waste much of their output in the form of mist that drifts into the air rather than landing on the target. Obviously, more plants = higher dew points. The highest dewpoints in the USA are usually recorded in the mid-Mississippi Valley during conditions where air circulation is suppressed and the amazing amouns of water pumped into the air by corn, soy, and trees remains trapped at ground level, making places like Omaha very miserable during those extreme heat events.

The rest of my previous post contained some generalizations that might not be accurate. Sorry about that.
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Old 08-17-2007, 02:10 AM
 
Location: Salt Lake City, Utah
396 posts, read 1,195,513 times
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Quote:
Originally Posted by ColdCanadian View Post
*95 F with a dewpoint of 70 F doesn't feel damp, it feels like puddles will dry with some quickness, probably humidity around 40%, however the air feels kind of thick and almost creamy.
It would to me; a 62 degree dewpoint feels sticky. Since I don't have air conditioning (very few older homes do here), and the swamp coolers become useless at that humidity, it gets uncomfortable once it reaches the upper 80s with a 60+ degree dewpoint. In a dry heat, I'm uncomfortable by 95.

However, I also heard that because of the high elevation, a dewpoint in the mid-60s here would be equivalent to a dewpoint in the low 70s at sea level. I'm not sure about all the specifics of it, but I was told this by a professional meteorologist.
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Old 08-17-2007, 09:16 AM
 
Location: Perth, Western Australia
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Quote:
Originally Posted by bob rulz View Post
It would to me; a 62 degree dewpoint feels sticky.

Since I don't have air conditioning (very few older homes do here), and the swamp coolers become useless at that humidity, it gets uncomfortable once it reaches the upper 80s with a 60+ degree dewpoint. In a dry heat, I'm uncomfortable by 95.

However, I also heard that because of the high elevation, a dewpoint in the mid-60s here would be equivalent to a dewpoint in the low 70s at sea level. I'm not sure about all the specifics of it, but I was told this by a professional meteorologist.
Okay when I meant it doesn't feel damp, I met the air doesn't feel like their are puddles around, so there's it doesn't seem wet anywhere, but it's thick anyways. Maybe we're both confused since maybe where you live when it rains the surrounding air still can be dry, like under 80% humidity. (dry for rainy weather) Where I'm from we can't get humidity under 60% unless it doesn't rain.

Are you uncomfortable at a dry 95 F outdoors or indoors?

I can feel uncomfortably cool at 74 F so I love weather in the high 70's, 80's, 90'sF and low 100's F.

Outdoors 98 F with heat index at 115 F is no problem for me,
however indoors I like it 78-84 F with no more than 50% humidity.

Last edited by ColdCanadian; 08-17-2007 at 09:24 AM..
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Old 08-17-2007, 10:06 AM
 
Location: Austin, TX
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Quote:
Originally Posted by bob rulz View Post
...a 62 degree dewpoint feels sticky.
Spoken like a true Utah resident. What I'd give for a dewpoint that low right about now, it sounds positively dreamy!...

Reality check: our dewpoint is around 75 today in central Texas.

But the tropical breeze is delicious and refreshing!
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Old 08-17-2007, 10:27 AM
 
Location: Perth, Western Australia
9,594 posts, read 25,190,667 times
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To me 62 F dewpoint might feel sticky at say 75 F, but at 95 F it would still feel toasty-dry or downright arid to me, as that would make the humidity level around 30%.

To me regular humidity is when a puddle in the street, say deepest parts 1/8th inch of water and over a foot in diameter would take all day, or at least most of the day to evaporate.

My guess is that out West it usually happens much faster than that.

Last edited by ColdCanadian; 08-17-2007 at 10:39 AM..
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Old 08-17-2007, 10:42 AM
 
Location: Perth, Western Australia
9,594 posts, read 25,190,667 times
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Quote:
Originally Posted by TheHarvester View Post
Spoken like a true Utah resident. What I'd give for a dewpoint that low right about now, it sounds positively dreamy!...

Reality check: our dewpoint is around 75 today in central Texas.
But the tropical breeze is delicious and refreshing!
Funny!

Your dewpoint at 75 F and tropical breezes sounds dreamy to me.
I wish we had a high somewhere in the mid-90's F today.

Right now it's in the low 70's and my bare-toes are a little cold.
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Old 08-17-2007, 12:40 PM
 
Location: Austin, TX
1,231 posts, read 3,531,663 times
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Quote:
Originally Posted by ColdCanadian View Post
To me 62 F dewpoint might feel sticky at say 75 F, but at 95 F it would still feel toasty-dry or downright arid to me...
You're smart. One of those rare individuals who understands the complexities of heat, cold, wet, and dry. Most weather forecasters don't even bother telling us about dewpoints because it's a difficult concept to grasp (apparently.)

And beyond those simple measures, there are a few dozen added components that comprise the weather as we experience it. But because most of us are not smart, weather forecasts are dumbed-down to the median comprehension of those who can only deal with 2 variables at a time in their brains. Hence, the meteorologists only tell us about "wind chill" in winter and "heat index" in summer, neglecting all the other variables that contribute to the reality of experiencing weather in any given place at a given moment. Elevation, pressure, wind, sun intensity, and localized ambient factors all contribute to the real feel of being in a place.

I chose the words "real feel" because AccuWeather's website uses "Real Feel" as a better indicator of how hot or cold it feels to be a human outdoors in a place, rather than simply relying on the miserably inadequate measurements that are used by National Weather Forecast indicators.

[rant] -- I wish our government and the institutions it funds would stop treating us like morons. If you treat a person like they're stupid, it contributes to their stupidity. But government has no faith in people. Government encourages sheep-like behavior. Follow the leader, believe in what you see on TV, hear on your radio, and read on websites or in newspapers. The Web is a hopeful medium for breaking through this wall of ignorance, but the government is constantly trying to clamp down on this medium because it provides too much information that might undermine the credibility of The Authorities. [/rant]
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Old 08-17-2007, 10:16 PM
 
Location: Salt Lake City, Utah
396 posts, read 1,195,513 times
Reputation: 198
Quote:
Originally Posted by ColdCanadian View Post
Okay when I meant it doesn't feel damp, I met the air doesn't feel like their are puddles around, so there's it doesn't seem wet anywhere, but it's thick anyways. Maybe we're both confused since maybe where you live when it rains the surrounding air still can be dry, like under 80% humidity. (dry for rainy weather) Where I'm from we can't get humidity under 60% unless it doesn't rain.
It's possible to rain with humidity under 80%, but it won't rain hard. Humidity regularly gets below 10% on summer days. Since it's rarely ever humid here, I don't even know what high humidity feels like, or, since it's been so long since I've been to the Midwest or East, I can't remember properly.

Quote:
Are you uncomfortable at a dry 95 F outdoors or indoors?

I can feel uncomfortably cool at 74 F so I love weather in the high 70's, 80's, 90'sF and low 100's F.
Both. Outdoors 95 is where I really start getting uncomfortable, even in a dry heat. I just have low heat tolerance overall; it's not like most people here are like that. I don't start getting cold until it's in the 40s, at least right when it starts getting cooler. In winter it's not jacket weather until the freezing point (unless it's windy).

Quote:
Outdoors 98 F with heat index at 115 F is no problem for me,
however indoors I like it 78-84 F with no more than 50% humidity.
115 heat index would be unbearable for me. Indoors I think everyone likes it down around that temperature. I don't know exactly how hot it gets indoors here, or what the temperature usually is.
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