January 2012 Forecast

[Thundery wintry showers]

The forecast was as follows:

Changeable, frequent NW winds, dry in south

The polar vortex situated up in the Arctic is proving very difficult to budge- in short what this means is that we will continue to see the dominance of low pressure to the north of the British Isles and thus any cold snowy episodes will be short-lived.

The first week of January will see the weather slowly quieten down after a boisterous start (gales on the 3rd). The 4th will start off dry and sunny for most, but the next batch of wet and windy weather will spread east during the afternoon and evening. A few showers will follow behind on the morning of the 15th, but for the most part the 15th will be a sunny day with fairly chilly north-westerly winds. A mild dry cloudy day is expected for most parts on the 6th, followed by colder, brighter weather (but still with temperatures no lower than the seasonal average) on the 7th.

The current model outputs and teleconnections show very strong support for a mid-Atlantic ridge towards midmonth. The Atlantic ridge will often extend eastwards towards the British Isles bringing mild dry weather, some sunshine for the south, and rather dull damp conditions in northern and western Britain. However, from time to time Atlantic depressions will push south-eastwards across the North Sea introducing colder and more unsettled weather via north-westerly outbreaks, with some snow for northern hills but nothing especially cold or snowy at low levels. Temperatures will tend to be rather above average for most during this period, but in southern and south-western England they may be near average due to a weaker Atlantic influence.

The last third of January is open to question, but there is a continued signal for above average pressure in the mid-Atlantic. With the dominant low pressure to the north weakening, and low pressure over Europe at times, temperatures will probably be close to normal across most of the UK, with an increased chance of short-lived northerly or north-easterly outbreaks bringing some snowfalls to low ground. I think the chances of a widespread snowy outbreak during the last third of the month are about 30-40%, as opposed to near 0% during the first two-thirds. However, we will also continue to see some mild interludes due to mild air pumping around the mid-Atlantic high and arriving our way from the north-west.

Overview

January 2012 will be quite a mild month, I am envisaging a Central England Temperature (CET) of about 5.2C. Compared to 1981-2010 averages, the mean temperature will probably range from 1 to 1.5C above in north-east Scotland to within 0.5C of the average in southern England, though it must be noted that the 1981-2010 averages are generally somewhat higher than for any other 30-year period.

Most parts of southern and eastern England will end up with a dry month with rainfall shortages of around 30-50%, possibly more in some south-coast counties. Northern Scotland will be wet with excesses of 30-50% while other regions will have close to average rainfall.

Sunshine totals will be above average in south-west England, with excesses of 20-40%, but most other regions will have near or below average sunshine, with shortages of 20-40% likely across much of Scotland and Northern Ireland.

The first third of January went pretty much as forecast, but towards midmonth we ended up with an anticyclone situated on top of Britain, rather than sat to the south-west allowing a mix of mild westerlies and cold northerlies- this brought dry and notably sunny weather for many with some frost. During the last third of January we did indeed have a mid-Atlantic ridge and an advancing block over Russia, but the weather turned out differently to what I predicted, as our weather was dominated mostly by polar maritime north-westerlies and pressure did not fall significantly over Europe.

Overall I think I was close to identifying the correct synoptic patterns but some small but important differences resulted in significant differences in the weather. Rainfall and temperatures weren't far off what I expected, though most places were a little warmer than predicted. Sunshine was generally higher thanks to the sunny anticyclonic spell midmonth, with negative sunshine anomalies concentrated in the west (Ireland and W Scotland) rather than in the north- indeed eastern Scotland had quite a sunny month.