"Phil Layton" wrote in message
...

"PJB" wrote in message
...
As the low moves NE it will encounter this
jet, it is the interaction of this jet and a shortwave upper trough
moving
out of canada that will determine how this feature develops. If the
Surface
Low, Jet and upper trough happen to engage at the right time (typically
if
the surface low moves into the left exit on the cold side of the the
jet)
the low could deepen very quiclkly.

The Forcing is provided on the forward side of the shortwave, and also
by
the powerful upper air dynamics.

Thanks Paul, I'm OK on the low level baroclinic zone. Could you just
amplify
the last sentence. What is a 'shortwave Upper Trough' is this just a
'trough' of low pressure, but at altitude and not necessarily at the
surface?

Phil

Yes Phil a shortwave is a trough of low pressure at a certain height (say
300mb) it is called a shortwave becuase it is much smaller than a typical
"long wave" upper trough which stretch for thousands of miles (such as when
we are in an omega block - that is the longwave pattern) a shortwave is a
much smaller feature, but it can provide the required forcing to deepen a
low very quickly.