Met Question - Cloud Chat

[VORTIME]

Hi guys,

Can someone explain how to read these charts?

http://pages.unibas.ch/geo/mcr/3d/meteo/

is it a case of taking the points where the dry/wet adiabatic rates converge and entering the millibar value into a pressure caliculator? Any tips?

VT

[IO540]

If you do a google on "tephigram" you get several pages explaining how to interpret them.

There is a lot of additional information to be gleaned from the various lapse rates but I never got that far

A few weeks ago I posted a rough guide to determining the type of cloud to be found at various levels, according to how close the temp and DP get. My knowledge on this is only basic.

Not many pilots know this stuff, which is a shame. Unfortunately, absolutely everybody I have ever come across who understands this kind of advanced aviation weather (upper atmosphere met, basically) is either working for the UK Met Office, or is involved in one or another commercial weather data repackaging company.

If you want to learn it, it may be an idea to book a day with certain people I can give you details of, and bring a few friends to spread the cost.

The key thing is that it needs to be learnt in the practical context i.e. getting the data off the internet.

[B Fraser]

Thats about right

When the environmental lapse rate is less than the dry rate, you have absolute atmospheric stability. When the ELR is between the dry and wet, you have conditional stability and when the ELR is greater that the saturated lapse rate, stay in the bar as it is Cu-Nim time.

IO540 guessed my former employer.

[IO540]

Some worked examples might be handy, BF

[B Fraser]

okey dokey

check out http://www.du.edu/~etuttle/weather/atphys.htm and start reading at paragraph "Stability of an Air Column".

I could have written a bit more but suddenly the lure of ironing a shirt followed by dishwashwer emptying/ filling and sock sorting was far more compelling.

[ShouldItDoThat]

Originally Posted by B Fraser

okey dokey

check out http://www.du.edu/~etuttle/weather/atphys.htm and start reading at paragraph "Stability of an Air Column".

I could have written a bit more but suddenly the lure of ironing a shirt followed by dishwashwer emptying/ filling and sock sorting was far more compelling.

Well on the face of it, it all looks hunkey dorey, but there's a glaring mistake that you've made, which means I'll have to work through more rigourously to make sure there aren't more errors. Not bad for an inter-laundering effort though

Oh forgot to mention the mistake, there should be a "I" at the start of the paragraph on "Lapse Rate"

SIDT

[Fuji Abound]

B Fraser

Thank you. That should be required reading for all pilots instrument flying!

[IO540]

Thank you for that, BT. Unfortunately, the paper contains a load of formulae, and when I graduated (in the days of big collars and flared trousers) I swore I would never look at another formula

What is needed is several examples of actual tephigrams, and the interpretation. You could write a nice little web article - I have never seen such a thing that was clear practical and readable.

BTW there is another form called a skew-t; you can get them from

http://weather.uwyo.edu/upperair/sounding.html

Select Europe, then GIF/Skew-T. It's a tephigram but slightly skewed. These are real baloon ascents; rarely useful due to being just twice a day.

Being an ex employee of a weather provider, there should not be a conflict of interest

[B Fraser]

Originally Posted by IO540

Thank you for that, BT. Unfortunately, the paper contains a load of formulae, and when I graduated (in the days of big collars and flared trousers) I swore I would never look at another formula

....and when I quit the Met Office, I swore I would never look at another tephigram.

if e = esw - 0.000646p(t - t')(1 + t'/1167) and you have an overdraft then go and find a more lucrative job.