This term is frequently bandied
about in gliding circles. I HATE IT as it is used to describe two
distinct phenomena.
Convection starts in a promising
manner with excellent cumulus. On occasions, it can remain excellent
all day.
But all too often, things
go wrong by the early afternoon. Two common problems are spreadout
and shower formation
Both these are frequently
referred to by that word "overdevelopment" but the causes are totally different.
However, the effect can
be very similar - the sky becomes covered with cloud and with the sun cut
off, thermals die
spacer
Spreadout
- the ominous beginnings spacerspacer Spreadout occurs when the
convection cannot go any higher and hits a "lid". This lid is commonly
referred to as an inversion, but strictly speaking, an inversion implies
that the temperature of the air increases with height.
A lid or cap, even when
the temperature is isothermal (the same through several thousand feet)
has the same effect.
A typical sounding is shown
on right and the very moist layer (where the two lines coincide) almost
guarantees spreadout.
spacer
-Shower
development - typical sky
spacer The sounding on right was
a typically showery situation.
But it was equally easy
to forecast.
Huge showers were expected
and duly arrived.
spacer One pilot reported in excess
of 10 knots in one cloud-
spacer
I was forecasting for competitions
on both these days - it was easy! (for me)
