New Butterfly Vario

On Feb 19, 10:12*am, Chris Nicholas wrote:
In my experience lift in cloud is stronger only if the cloud has a lot
of vertical development – say several thousand feet, which of course
developing CBs do have, and provided you can stay centred in the lift,
which as Jim points out is harder if you can’t see the real horizon. I
have found that expanding the GPS scale helps a lot in keeping in good
lift, in VMC or in IMC. (I still do not advocate people teaching
themselves to do the latter these days – if it goes wrong in a
slippery glider, it can do so very quickly and very badly.)

In the more usual “good” conditions in the UK when we get them, an
inversion stops vertical cu development and they are often only a few
hundred or 1-2000 feet deep. Then, as Jim says, it is usually faster
to keep in the energy where you can see it, in VMC. With very shallow
clouds, it is not even worth going up to cloud base – the lift weakens
before getting there. Even if it does strengthen briefly at and into
cloud, I usually lose more in the fumble of coming out on the wrong
heading, or on the right one but into another cloud and in its sink,
than staying below, if achieved speed is what you are after.

Chris N

It is very common in Arizona to have at least a slight inversion at or
below cloud base. What happens in these cases is that the rising
airmass in a strong thermal continues going up under its own
momentum. It's not uncommon in these circumstance to find the lift
cutting off a thousand feet below the clouds and very nice looking
clouds have no lift under them. I sometimes refer to these clouds as
resulting from the last dying gasp of a rising thermal!

With instability of the atmosphere rising above cloud base, thermals
will often increase with strength as you approach the cloud and this
increase continues into the cloud. These are the circumstances when
you might get too close to the cloud - it's not uncommon here to find
a ten-knot thermal strengthening to 12 to 15 knots! At these vertical
speeds, you can go from a safe distance below into cloud in about half
a turn. It's very easy to do and a not uncommon experience out west.

Mike