ADVANCE ALERT (NO: 2, 6 Dec) Severe Wintry Weather

ADVANCE ALERT (issued 9am, 6 Dec, 2012) continued for the risk of severe wintry weather arriving around Tuesday night (11th-12th) and lasting several days towards the following weekend. Confidence in such an eventuality is now at 60%, up from 50-55% yesterday (5 Dec).

Much colder air will be massing over the Baltic regions after this weekend and will begin to make a westward push around Tuesday possibly overspreading most of Britain before arriving in Ireland with sub-freezing temperatures and the potential for snow mid-week, and this spell could last several days, a week or even longer

The latest guidance is not quite as intense as some maps we saw in the past day or so, but still a solid three or four days of wintry weather potential in northeast winds, likely some snow here and there from weak disturbances and the onshore flow of cold air across the Irish Sea.

The counties around Dublin, Wicklow and Meath as well as east Ulster would be more at risk but the south coast could see slight amounts and elsewhere the wintry precipitation is likely to be more elevation-based.

Current maps have potential for daytime readings of about 0-2 C and overnight lows -7 to -4 C from about Wed 12th to Sat 16th. As speculated yesterday, the cold spell appears likely to relax its grip after that with the blocked Atlantic flow finding ways of pushing back in from the southeast at first, so that near the end of this cold spell, mixed precipitation is likely for a while before a general thaw.

The moderately severe cold is about 60% likely on the current guidance, severe cold (days below -2 and nights around -10) about 20% possible.  The weakest solution we can envisage is for mixed sleety precip and highs 4-6 C in this period.

This surface pressure chart shows cold NE winds setting during Tuesday afternoon. Shower activity at this point is confined to eastern Britain and eastern parts of Ireland.
This GFS chart shows cold east-southeasterly winds feeding up over Ireland and Britain by Friday 14th with the risk of wintry showers becoming more widespread.
As for Britain, colder air arrives in the northeast during Tuesday. Severe cold and some accumulating snow possible in eastern England around 11th-16th. A stormy breakdown of the cold spell could lead to a nasty mix of heavy snow, freezing rain, flooding rains into parts of the southwest, and travel disruptions on several days. The Christmas holiday period could continue to be a travel nightmare in parts of Britain, especially in the northeast as milder air slowly pushes the cold air out with freezing rain or snow ahead of the warm fronts. This may take days to push all the way across the region.

The Meteo Times' (TMT) Peter O'Donnell is a Vancouver-based climatologist who specialises in providing long-range forecasts for Ireland and Britain.