Key winter forecast takeaways
•El Nino dominated winter
•Warmer than average winter
•Severe cold spell with snow and frost most likely in January following SSW
•Average rainfall after wetter start
•Settled end to winter
•Possible record warmth later in Feb
December is likely to be a very unsettled month dominated by an area of low pressure to the northwest of the country. This is likely to act as a driver for Atlantic depressions to cross the country. This will lead to above average temperatures with wet and often windy spells of weather to cross the country. The centres of these depressions are likely to edge further south as the month progresses - they follow the jet stream that starts the month across the north of the country but finishes it to the south. As this occurs, there is the possibility of a damaging storm hitting the UK. Temperatures closer to average are likely towards the end of the month in the north and an increasing chance of hill snow likely, but temperatures to the south will remain above average and lowland lying snow either short lived or not at all. It is likely to be a wetter than average month particularly to the south by the end of the month. Flooding possibilities are most likely during this month.
January is likely to start in a similar vein to the end of December but this month is likely to see a sharp turnaround to far colder conditions which could last for a couple of weeks. The period of cold is likely to be triggered from stratospheric breakdown in the form of a Sudden Stratospheric Warming. Low pressure that was previously to the north of the country will be replaced by high pressure that will act as a block to December's Atlantic depressions. In turn, cold Arctic air will flood south from the North or East, depending upon the orientation of the high pressure, and this will likely lead to a period where snow, ice and frost - even to lower levels and to the south of the UK may disruptively occur. A slow transition to more average conditions is likely by the end of the month as the high pressure drifts west. Overall, temperatures will be near average or slightly below with precipitation near average or slightly below. A more settled month when compared to December with an increased risk of fog and one where any flooding risk will recede.
Once the cold of January has faded then February is likely to be a more benign month. High pressure is likely to settle towards the west of Greenland and possibly towards the East of Scandinavia, with weak low pressure crossing the Atlantic and separating these two high pressure ridges. This will allow a warmer and weak southwesterly airflow to filter across the UK as the block across Western Greenland and Hudson Bay in Canada will not be strong enough to prevent the westerlies returning, and, the SSW in January will have reduced the strength of the residual polar vortex dramatically. This will leave February warmer than average, with periods of misty weather especially over Westerly exposed coasts. There is a possible risk of record warmth being experienced later in the month. Drier weather is likely towards the south east of the country, but overall the rainfall is expected to be near average. Frost and lying snow are unlikely and any residual snow will thaw rapidly.
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