I have been monitoring the weather since 1979. It has become apparant that the weather is changing in recent years in a number of ways.

We are experiencing more frequent cold dry spells during the winter. Historically most of the weather in the UK comes up from the SW from the Atlantic from a series of depressions. This brings relatively mild and wet conditions. What seems to be happending is that this feed is cut off either as a result of high pressure in mid Atlantic bringing down colder and dryer air from the NW or even the arctic. Alternatively high pressure over Northern Europe blocks off the SW flow and a cool easterly flow is established.

Recent examples of this occurred in January 2008, January 2009, January 2010 and in December 2010.

I am not sure why this has occurred but it is more than chance. A significant shift is occuring in the paturns and therefore we can expect more of the same dry, cold spells until the trend stops.

There is a scientific set of data that supports this shift which is know as the North Atlantic oscillation (NAO). This can be positive and negative. THe cool dry weather seems to line up with an increased incidence of negative oscillation.

The latest NAO chart can be found here. Note the blue sections in the recent history.

NAO charts
UPDATE

Since the autumn of 2011 the atlantic flow has re-established itself resulting in 2012 being the wettest year on record. This along with increased cloud cover also depressed the maximum temperature in 2012 and this looks like continuing in to 2013.

RAINFALL

The climate in Bristol has become wetter in recent years. Very few years have more than 1000mm of rain but the number of these are increasing.

1910's - 6
1920's - 4
1930's - 2
1990's - 2
2000's - 5

The number of months with a >30mm event is also increasing with 22 recorded in the decade starting with Jan 2000 and three alone in 2012.