It's easy to forget, but the first ten days of December maintained
the cyclonic regime which had continued unbroken since Oct 31.
A short anticyclonic interlude followed, and the remainder of
the month was cyclonic/northerly/easterly.

Mean pressure charts will soon be uploaded to:
Charts: http://www.climate-uk.com/monpre/0912.htm
The Monthly Review will shortly be made available at:
http://www.climate-uk.com/monthly/0912.htm
Graphs: http://www.climate-uk.com/graphs/0912.htm and
http://www.climate-uk.com/graphs/200912.htm
Not The Long Range Forecast should be available by Jan 5 on:
http://www.climate-uk.com/page4.html

The mean sea-level pressure distribution over the Atlantic/Europe
sector during December 2009 was dominated by a large but flat
area of low pressure centred 1002mbar at 49N 25W -- far south
of its normal position. It's flatness is the result of being a compromise
between a location much further north during the first half, and a
position near the Azores during the second half. The Azores high
was absent. Pressure was high over Greenland and to a lesser
extent over northwest Russia. The mean flow over the British
Isles was weakly southwesterly except in northern Scotland
where it was weakly southeasterly.

Aloft, there was a broad diffluent trough at about 20degW.

The sea-level pressure anomaly field showed below average
pressure across the Atlantic/Europe sector south of approx
latitude 55-60degN, and above average further north.

The main anomaly centres we
-15mbar near the Azores
+16mbar over the Barents Sea
+14mbar over northeast Greenland

Over the British Isles pressure anomaly ranged from -1.5mbar
over Shetland to -9mbar over southern England. The anomalous
flow over the British Isles was easterly..

CET (after Manley) 3.1°C (2.0degC below the 1971-2000 mean)
CET (after Hadley) 3.3 or 3.4°C (1.7 or 1.8degC below)
E&W Rain (provisional): 106.9mm (106% of 1971-2000 mean)
E&W Sunshine (prov): 73.0hr (153% of 1971-2000 mean)

The Manley CET was the lowest for December since 1996.

CScotT: 1.8°C (-2.7degC)
ScotRain: 78mm ( 76 %)
ScotSun: 40hr (127 %)

NIT: 4.1°C (-2.1degC)
NI Rain: 60mm ( 62 %)
NI Sun: 60hr (164 %)

Rainfall totals ranged from 212mm at Capel Curig (Snowdonia)
and 195mm at Valentia (Irish Rep) to 41mm at Murlough
(Co Down) ... however, the large number of unattended sites
means that few stations in Scotland actually have a correct
rainfall for this month as snowfalls have not been melted
manually.

Percentages ranged from 193 at Manston (Kent) to an estimated
40-50 at several sites in northwest Scotland.

Sunshine totals ranged from 97h at Bramham (nr York)
[KZ sensor] to 20h at Fair Isle (CS recorder).

Percentages ranged from 233 at Church Fenton (nr York)
to 82 at Dyce (Aberdeen). [The usual caveat about
the change in sunshine recorders applies]

(c) Philip Eden