heat index defined

[mitchell]

Here is the NWS definition of heat index:

"Heat index (HI) is sometimes referred to as the "apparent Temperature". The HI, given in degrees F, is a measure of how hot it feels when relative humidity (RH) is added to the actual air temperature. For Example, using the chart below, if the air temperature is 90 F. and the relative humidity is 60% it will feel like 100 F."

My question is this...feels like 100 F. AT WHAT RELATIVE HUMIDITY?

[WindRunner]

I'm not exactly sure of what you are asking, but I'll try my best.



This chart shows the relationship between temperature and relative humidity (RH). As you can see, a temperature with a high RH or a high temp with most any RH can be dangerous, even if you are only exposed to it for a short amount of time. I'm not sure what you mean by "at what relative humidty?", but if you look at the chart, you can see that a HI of 100 could be a combination of several situations, such as 84° and 95%, 86° and 80%, 88° and 70%, 90° and 60%, or 94° and 45%. Any one of these setups could cause a HI of 100°, as well as many others with numbers in between and beyond those.

[mitchell]

I'm not sure what you mean by "at what relative humidty?", .

Re-read the quote from the NWS website I posted above...When they say "For example, using the chart below, if the air temperature is 90 F. and the relative humidity is 60% it will feel like 100 F." I'm asking feels like 100 F. AT WHAT RH? It makes all the difference in the world..at if they mean 100 F. at 0% RH then that seems kind of dumb.

[senorpepr]

I'm not sure what you mean by "at what relative humidty?", .

Re-read the quote from the NWS website I posted above...When they say "For example, using the chart below, if the air temperature is 90 F. and the relative humidity is 60% it will feel like 100 F." I'm asking feels like 100 F. AT WHAT RH? It makes all the difference in the world..at if they mean 100 F. at 0% RH then that seems kind of dumb.

It is at 0%. In other words, 90°F at 60% = 100°F at 0%. To adjust for an average humidity would make the formula too difficult to calculate than it already is.

Anyway, heat index isn't a very accurate measurement to what it feels like, but it's one of the easiest formulas to calculate.

Heat index only calculates the relationship between temperature and humidity. It disregards wind speed, which provides a cooling effect. It also disregards solar radiation, which provides a heating effect.

[mitchell]

It is at 0%. In other words, 90°F at 60% = 100°F at 0%. To adjust for an average humidity would make the formula too difficult to calculate than it already is.

Anyway, heat index isn't a very accurate measurement to what it feels like, but it's one of the easiest formulas to calculate.

Heat index only calculates the relationship between temperature and humidity. It disregards wind speed, which provides a cooling effect. It also disregards solar radiation, which provides a heating effect.

Thanks...seems like during the hot spell this summer, more time was spent talking about the "heat index", "real-feel temperature", "feels-like temperature", "apparent-temp" (every local met/news outlet seems to feel the need to coin a term) than the actual temperature.

[AussieMark]

Heat index only calculates the relationship between temperature and humidity. It disregards wind speed, which provides a cooling effect. It also disregards solar radiation, which provides a heating effect.

Can't a hot wind have a heating effect?