Soundings -  Page 3

This tutorial is probably the most difficult so far. Take a deep breath.
spacer 
This was a midnight sounding on the right. 
It looks dreadful, doesn't it? 
spacer 
Lets blow up the bottom bit
spacer 
 

With some difficulty, it can be seen that the dry and the dewpoint lines are very close or even coincide near the surface.
The surface dewpoint Tdew and dry temperature Tdry are both about 14C.
Tdew probably won't change much during the day.  But Tdry will rise to an expected 20C (obtained from various forecast sources).
spacer
spacer 
From the expected surface temperature of 20 follow the dry adiabatic line upward diagonally to the left until it meets the environmental line. 
This occurs at about 880 mbs.
spacer 
However, now we must consider the moisture content of the air.
From the surface dewpoint of about 14, follow (or parallel) a purple/brown  line upwards to the right.

This will intersect the dry adiabatic from 20 surface at about 920 mbs.  This is the expected cloudbase.
spacer
A cross check using the Bradbury 400 ft / degree rule would come up with the same result - ie 6 difference means cloudbase of 2,400 feet.  So we have confirmed expected cloud base.
Remember that the 400 ft / degree rule is only appropriate if cumulus develops and cannot be used to determine thermal depth on blue days.
spacer

The relevant part of the sounding is shown
spacer 
The maximum temperature is assumed to be 20C
spacer 
Earlier, we saw how to work out the cloud base.
spacer 
But the convection does not stop at cloud base.  It continues at the SALR until reaching the ELR at around 400 mbs (~23,000 feet).



Blue Haze caps or Cumulus?
On a later page, we will see how it can be determined (with, it must be said, a certain degree of uncertainty) whether or not it will be a blue day.



How tall will the clouds grow?
It is important to have an idea how tall the cloud might grow as this gives an indication of potential shower activity (or otherwise).
Showers are unlikely if the cloud tops do not penetrate the height at which  -10C occurs.
In this example, clouds do indeed go to heights where the temperature is -25C
The later midday sounding shows that we were correct with the earlier interpretations.  Indeed, the airmass looks even more likely to result in heavy showers - there is a bigger area between the black and the red line. 
(to be technical, larger CAPE).
spacer 
And it all went to plan:
spacer