Those in the south of Britain who woke to steady (and notable) rainfall
this morning might have been surprised to look at the Exeter analysis

http://www.weather.org.uk/charts/UKCpf000.png

and find no fronts in association with this rain .... however,
inspecting the upper air charts, particularly:-

http://www2.wetter3.de/Animation_00_UTC/06_1.gif

shows the culprit: a broad 'pool' of cold air aloft (slightly 'bluer'
colours on this output) and if you follow it through the sequence, the
feature actually intensifies. This indicates potential for
instability-based vertical motion and if the atmosphere is moist enough
(which it obviously is), then thick cloud and rain can result. These
things can result in surprisingly significant icing for aircraft
operations, which are not what the surface/mslp pattern might indicate.

Surface charts don't always show the whole story, particularly with
blocked anticyclonic features.

Martin.


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