On Thu, 12 Feb 2004 23:45:43 -0000, J.Poyner wrote in

snip
Not come across this before.....what causes it, interested in exactly what a
short wave upper vortex is..

The flow in the middle to upper troposhere usually takes on a wave pattern,
seen best by the colours on say the 500 mb chart. This is the latest from
the GFS analysis.

http://www.wetterzentrale.de/pics/Rtavn001.html

You can think of the upper winds blowing along constant colour - just as at
the surface they blow along isobars, and the sinusoidal pattern is clear to
see. But, note the very small area of yellow moving into NW Scotland.
That is the feature I was referring to. It is up at about 16,000 to 17,000
feet and is moving into the deep high. That pool of cold air will cause
some mid level instability and cause cloud precipitation to be produced at
quite high levels. A band of rain crossed here during the night, as that
feature made its presence felt high up.

It looks as if it is going to be a persistent feature (posing problems for
the forecasters) and is still around in two days time. Here is the same
chart for Sunday and the yellow area - the upper low - is still clear to
see.

http://www.wetterzentrale.de/pics/Rtavn481.html

I'd refer you also to Martin Rowley's good explanation in MID



That is in the thread "Low in the High" started by Phil Layton.

--
Mike 55.13°N 6.69°W Coleraine posted to uk.sci.weather 13/02/2004 09:43:14 UTC