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Old 05-08-2012, 11:15 AM
 
Location: Toronto
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Or at least I haven't noticed any. But people do feel cooler vs. warmer in the shade/cloud versus the sun, and direct sun vs. low sun.

There are indexes for humidity (heat index or humidex) used, to make the apparent temperature seem hotter and those for wind chill to make the apparent temperature seem colder. But what about sun? For instance, it feels warmer when there is direct sunlight vs. cloud. As well, sun angle also makes a difference.

Wind chill and humidity are based on the warm-blooded human body and have to do with the human body's heat loss responses and human perception alone (it can't make a physical object itself hotter or colder). However, the sun does have a real effect (eg. I've heard that it could be 6-7 degrees Celsius warmer in the sun vs. the shade), that's not just human perception, but on heating physical objects themselves. If it's a big enough effect to affect a weather station's recordings that would have otherwise been in the shade, then clearly it can affect a human too.

Perhaps, there's no index because the sun can be out one minute and then cloud comes over and covers it, making it less hot or warm, as well it changes over the day naturally too (but then again, that can also apply to wind -- wind chill isn't consistent either, and is just as fickle).
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Old 05-08-2012, 11:29 AM
 
Location: Buenos Aires, Argentina
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It should be. I always feel that a 38 celsius sunny day feels hotter than a 38 celsius cloudy day, IF you are walking under the sun in the street. Oddly enough, since the 38 celsius cloudy day is usually more humid than the other, it feels more uncomfortable than the sunny one if im in my house.

But, anyways, i understand your point.
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Old 05-08-2012, 12:21 PM
 
Location: Yorkshire, England
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I'm not sure if it's possible to measure the impact of sunlight on temperature due to the amount of variables involved (sun angle/clearness of sky/airmass etc). For example, I was in Leeds on Sunday evening in sunny but chilly conditions, and the low sun was certainly bright enough but oddly for the time of year didn't seem to be giving off hardly any warmth at all compared to shaded areas (more like midday in mid-winter). If we'd been under a warmer airmass I'd expect to feel some more strength in the sun even compared to a higher ambient temperature.
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Old 05-08-2012, 12:26 PM
 
Location: Near the Coast SWCT
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Quote:
Originally Posted by Stumbler. View Post
If there are "feels like" apparent temperatures for humidity, wind-chill etc., why isn't there one for sun? .
Yup, there is. Its called "real feel" unlike the"heat index" or"apparent"

The RealFeel® uses multiple factors including the temperature, humidity, cloud cover, sun intensity, and wind to explain how hot it feels outside.

Apparent temperature is the general term for the perceived outdoor temperature, caused by the combined effects of air temperature, relative humidity and wind speed.



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Old 05-08-2012, 12:55 PM
 
Location: Laurentia
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Perhaps there isn't any index solely for sun since avoiding this effect is as simple as being under shade or in sun, and people move back and forth between sun and shade every day. Thus it isn't as much of a weather phenomenon as wind chill or humidity, which are atmospheric phenomena. The general rule that temperature in sun is 10-30F hotter than in shade seems to suffice. There's also the RealFeel index.
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Old 05-08-2012, 01:14 PM
 
Location: Top of the South, NZ
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I think the feel of the sun would be too variable to use reliably. Humidity seems to be the big factor affecting sun feel.
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Old 05-08-2012, 08:49 PM
 
Location: Valdez, Alaska
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The solar angle is really important as a factor in "solar intensity" as well, at least in places where it differs significantly throughout the year. The same temperature will feel considerably warmer in March than in January here, even with all other conditions being equal. It's very noticeable around early March when you really start feeling the warmth of the sun again.
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Old 05-09-2012, 08:53 AM
 
Location: New York City
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Sun is more easily avoidable. On hot days, weather announcers will always advise to stay in the shade or at least wear light colored clothing. Any sensible person will know to stay out of the sun when it's hot.
Also, there is such a thing as UV index.
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Old 05-09-2012, 10:33 AM
 
Location: Melbourne AUS
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BOMs "feel like" temps are bull crap. Often, if there is a decent wind, a 30C temp with say 25% humidity will yield a "feels like" of something like 21-23C. Yeah whatever. 30C is 30C, even if there is a moderate wind.
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Old 05-09-2012, 06:58 PM
 
Location: Dalby, Queensland
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Quote:
Originally Posted by Flight Simmer View Post
BOMs "feel like" temps are bull crap. Often, if there is a decent wind, a 30C temp with say 25% humidity will yield a "feels like" of something like 21-23C. Yeah whatever. 30C is 30C, even if there is a moderate wind.
I completely agree with this. BOM's apparent temp seems to be nearly always lower than the actual temp, even when there is no wind! The only time the apparent temp is higher is on a warm humid day in summer, with light winds. On one day earlier this month the actual high was about 22C, but the apparent temp only got as high as 16C. It certainly didn't feel like 16C to me.
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