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.
Another way to think about this is in terms of PV.The short wave trough is a PV anomaly -a
tropopause depression-which induces ascent ahead of itself depending on it's structure.As it
approaches the surface baroclinic zone development can take place-depending on timing and diabatic
factors.If this PV anomaly 'phase locks' with the surface low ie develops an optimal westerly tilt
structure then explosive development can take place.
Let's not forget Browning's 'Sting-in the tail' of the back bent occlusion and the strong jet.

BTW how popular is PV thinking currently with you operational forecasters ?

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regards,
david
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