Peter O'Donnell's Winter 2012-13 Forecast Summary

Based on my usual methodology and a consideration of the unusual ice-free anomaly expected to start the season, the following is my expected temperature and precipitation trend for DEC-JAN-FEB (following a November with expected mild temperatures 1-2 C deg above average, and near normal in precipitation ... October expected to be near normal for temperature and somewhat on the wet side of normal).

DECEMBER looks fairly close to normal (on the whole) with a roughly equal mixture of mild and cold days. There may be one relatively severe cold spell of 2-4 days around the middle of the month towards the 20th. This might not produce much snow as it could be a shallow incursion but some snow would be likely given the temperature anomalies indicating below zero temperatures briefly. Before that, the period 7th to 13th is expected to be quite mild (highs could reach 11-13 C), and the run up to Christmas increasingly mild with rain replacing any earlier sleet or snow in most areas but there would be a better chance for snow in north-central parts of Britain around Christmas. A stormy interval may develop just around or after Christmas Day. Numerical index values suggest a windy day on the 26th so there's one specific daily forecast to test out. 
JANUARY looks relatively mild but with severe cold forming gradually off to the north and east of Ireland and the U.K., some intervals of modified cold could intrude, perhaps less forcefully in south and west regions of Ireland. The month may also become rather stormy at times especially in periods around the 10th and 25th. Some damaging winds would not surprise me given the developing thermal gradient across the Atlantic and a likely very strong zonal jet stream at times. A trend to much colder weather getting closer to Britain at least is likely near the end of the month although mild weather could hold on in Ireland and the southwest parts of England.

FEBRUARY is expected to be much colder than average by 1.5 to 3.5 degrees with considerable snow or sleet and frequent easterly winds. This will develop because of massive blocking to the north of Ireland and the U.K. extending from Iceland to Scandinavia. There is some indication of a very severe period of wintry weather. This severe cold may last some time beyond the end of the month.

I may update this seasonal forecast if I have any further results from ongoing research, but this is the output of the current research model with some consideration given to the ice anomaly. I suspect it will intensify the pattern that would have existed otherwise, so I have tended to amplify the numerical output on either side of normal. Once severe cold is established over snow cover it is hard to dislodge during the depth of winter, but would also warn that February is the least reliable of the three monthly forecasts not only because it's further out but also because it is more anomalous.

Peter O'Donnell is a Vancouver-based climatologist who specialises in providing long-range forecasts for Ireland and Britain.