Is the met office having a laugh

John Wallis · Post by **John Wallis** » Sat Dec 12, 2009 10:57 am

If you click on the link and scroll down to the 36 hours synopsis for Sunday you will see a Christmas tree sat over southern England. Are the boys from the met office having a seasonal giggle here? Anybody know what it signifies? The only thing I can see from the previous charts are 2 troughs heading that way, maybe that's the symbol for an occluded trough....Any ideas?

http://www.meteonet.nl/aktueel/brackall.htm

brian day · Post by **brian day** » Sat Dec 12, 2009 12:06 pm

Must be windy down there, the xmas tree has fallen over!

dave-mclaughlin · Post by **dave-mclaughlin** » Sat Dec 12, 2009 2:03 pm

It's a convergence line

A slow-moving trough, which is parallel to the isobars and tends to be persistent over many hours or days. They are quite common in cold northerly outbreaks down the Irish Sea, affecting west Wales, Devon and Cornwall in particular, but can be found in other areas also. This convergence line can gives hours of persistent precipitation over very localised areas, whilst a few miles down the road it is relatively dry, leading to some heavy snowfall/rainfall. In summer the convergence lines are not as easy to forecast, but then can still occur due to sea-breeze convergence, and are over the land, whilst in winter they are over the sea.

See http://www.metoffice.gov.uk/weather/uk/guide/key.html