"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