"Martin Rowley" wrote in message
...

... in major forecasting centres (such as Exeter), they will overlay water
vapour imagery in particular against other imagery and model fields -
modern NWP suites can produce 'pseudo WV' fields - and such errors are
quickly picked out and can be allowed for.

An example of the pseudo water vapour field that Martin mentioned with 300mb
GPH overlaid for midday today.
http://www.metbrief.com/Images/psuwv.gif

Jon.