On 11/03/17 18:56, Harry Bloomfield wrote:
David was thinking very hard :
I have several thermometer cum weather prediction (barometer) cum
humidistats dotted around the place.

I did fancy something more accurate as the readings all seem suspiciously
low (but then they are indoors).

Just taken the most long term reliable one outside to check. It was
showing 30% humidity indoors and outside it has already dropped to 28%.

Both values are unlikely. I have a weather station logging both values
contantly. 40 to 45 is normal indoors, outdoors will be around the 70 to
95% most of the time at this time of year. It tends to dip in really
cold weather, because the cold air cannot support much humidity.

It doesn't work like that.

What does tend to happen is that really cold weather freezes out the
moisture at night and when it warms up its temporarily low humidity.

Today humidity at my local RAF airfield (Lakenheath) has been around 88%
- since dark its 100%.

Inside if you take 100% saturated air at say 5C and heat it to 20C its
gonna be around 40% or less - roughly halves for every 10C

Winter internal humidity can be alarmingly low in frosty weather

Meanwhile the Met Office local forecast is showing around 80% which seems
quite high; I would expect it to be nearly turning misty if the air was
that saturated. Probably wrong of me, though.

No: mist forms at 100% by definition.



--
No Apple devices were knowingly used in the preparation of this post.