White Christmas

A north-westerly flow has become a semi-permanent feature of the UK weather over the past couple of years. Combined with an enhanced North-Westerly Jet, this flow gave rise to a polar-maritime type heavy rainfall scenario, with enhanced cyclonic activity leading to flooding in the Summers of 2007 and 2008.

The cause of this weather feature, is thought to be either (1) related to the La Nina, a cool water phase of the Pacific, which tends to cause an intense polar jet in the northern hemisphere, which interacts with upper level vorticity near Greenland, causing a northwesterly flow into the UK.
(2) A slight weakening of the north-Atlantic drift / Gulf Stream circulation, could induce a stronger polar jet. Literature tends to suggest that the Meridional Overturning Circulation (MOC) is weakening, which could be part of a longer term cycle, (3) Diminished solar activity and ionization by solar particles, or changes in northern hemisphere cloud cover particularly near the Arctic, (4) Arctic Oscillation / North Atlantic Oscillation changes due to ocean cycles.
Since the ocean and atmosphere are intrinsically coupled, it is unlikely that the atmospheric changes are not related or linked to changes occurring simultaneously in the Ocean. (5) Ice melt in the Arctic causing some feedback on the climate, which I don't understand (6) Other feedback process of unknown origin ....

Projecting the northwesterly flow / sinking Rossby waves pattern scenario into Winter 2008, I provided a forecast (Seasonal 2008) at OnlineWeather.org.uk. This was based on increased storminess, and changes to the mean (prevailing) airstream arriving into the UK.
In "normal" conditions, a Tropical Maritime flow dominates the weather of the UK (mT on figure 1.), yet during the past couple of years, the flow has been shifting gradually to a semi-permanent returning polar maritime (rPm) or polar maritime (Pm) flow, which coincided with a super-La Nina phase.