Environment Humidity

[stevothedevo]

Can someone explain to me 'humidity'. And I don't won't the math behind it cause I've already read up on it and although it seemed to make sense, my experience with humidity isn't adding up.

Example : Last Friday in Geelong was one of the muggiest days I could recall. It was around the 30* mark and overcast. Nothing weird about that I know but when a simple walk to the letterbox results in you dripping in pools of sweat then I thought I'd start asking questions. So later that day I checked the humidity online just to see how high it got. It told me that for pretty much the whole day, Geelong had a relative humidity of only 30%.
That to me doesn't seem right. How come it felt like I was in Bangkok yet with such a low humidity? What other factors should I be taking into account?

 

[PowerKat]

I suspect that you are looking at a 'Relative Humidity' measure which is not a pure % of moisture content in the air. Effectively, the reasonably high temperature of 30, drops the 'relative' measure/percentage.

Often in southern australia, humid weather precedes a 'cool change'. Humidity feels similar throughout the day (high) or may even feel like it's falling, although as the temperature drops the 'relative humidity' increases.

I found this definition (Dew Point is a factor also - I didn't know that):

Relative Humidity: Is a ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature. Relative Humidity is derived from the associated Temperature and Dew Point for the indicated hour.

 

[stevothedevo]

Thanks Powercat. So I guess 'Relative Humidity' doesn't really tell us much then. I mean for a really humid day to only have a Relative Humidity of 30% isn't really giving me a guide to anything.

After reading your reply I did some more reseach and found all kinds of humidity scales. 'Specific Humidity', 'Absolute Humidity', plus also 'Heat Index'. Sadly though none of these seem to be represented on my online weather pages I use.

Looks like I'll have to come up with my own 'Muggyness Scale' and simply judge it by feel. Last Friday I'll give it about a 7 and a half out of 10.

 

[PowerKat]

It's all relative

 

[Frodo]

Absolute humidity is of no real importance to the individual.

Relative Humidity is the one we refer to as being 'Humidity'.

It is relative to temperature because air can hold more moisture at higher temperatures.

Now I think your data was wrong. Humidity changes throughout the day, not constant. That's often why it rains on an evening.
For example:
If there was a constant amount of moisture in the air of say 0.1
Then at 30C the humidity would be 30%
At 20C it would be 50%
and at 12C it would be over 100% so it would rain.

If you google a psychometric chart you will see it.


And if you were sweating like you said, maybe you had a fever!

 

[Scotland]

If you google a psychometric chart you will see it.

Psychrometric.

You'd have a devil of a time trying to explain humidity with psyschological theory...

 

[Brad Goodman]

psyschological theory...

Which would be?

 

[Scotland]

Which would be?

Psychometric - psychology.

Psychrometric - properties of gas/vapour mixtures.

Fingers crossed dyslexia my OK now is.