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Weather updates from site founder Brian Gaze that keep you in the know.

January shrouded in uncertainty

Posted Mon 7th January 2019 13:25

There continue to be indications of a more potent and lengthy cold spell developing in late January. However, it is only a possibility and before then a more changeable and mixed period of weather with fluctuating temperatures is likely.

Mixed outlook despite SSW

Despite the Sudden Stratospheric Warming (SSW) event which has been taking place, the path to cold and snowy weather is far from clear during the rest of this month. A lot of people are asking about SSWs and assume they more or less guarantee cold weather in the UK. The evidence I have seen suggests that isn't the case. What they do is lead to a an increased chance of colder periods of weather developing in our part of the world. The reason is that cold blocks of air are pushed out of the Arctic down to mid latitude locations such as the UK. However there is no guarantee at all that one of those blocks will make a beeline for the a small island in the North Atlantic.

Bringing things back to the latest medium range model output, I have annotated today's London GEFS 06z plot below. The key things to note are:

1) The transition to colder conditions early this week. Upper air temperatures fall from 4C to -7C between now and Wednesday. The same general pattern applies to all of the country as colder air sweeps down from the north. Unfortunately if you're hoping for snow there won't be much precipitation and wintry showers will mostly be restricted to the north and eastern coastal counties. 

2) Later this week it turns milder again and 850hPa temperatures rise well above the 30 year average. 

3) Towards the middle of the month 850hPA temperatures trend down towards the average. The number of rain spikes on the lower half of the plot increases, so there is a clear suggestion of it becoming more unsettled.

4) By January 20th mean 850hPa temperatures drop below the 30 year average and a few of the individual runs (GFS op and GFSP are examples) show it becoming very cold by the last week of the month. 

TL;DR

Computer models are painting a mixed picture. In the short term it turns colder but temperatures recover later this week. Towards mid January more unsettled weather is favoured and temperatures dip down towards the 30 year average. During the last third of the month there continues to be evidence to suggest a longer and and sharper wintry period is possible, but it remains very uncertain.

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geordiesrgr8 6 years ago Show replies(0)

The weather this month continues to tease wiil it or won't it get propper cold ??? anyone have a crystal ball?

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