TWO Buzz

Weather news and views from Brian Gaze.

Settled weather favoured

How will temperatures respond?

Posted 12th January, 12:44

Computer models are consistently showing high pressure being the dominant feature of the UK's weather through the middle third of January. That means mainly a lot of dry periods, but pinning down the outlook for temperatures is more difficult.

High pressure dominates

The GEFS 00z ensemble plot below for London shows forecast 850hPa temperatures (about 1500m above sea level) and precipitation. To begin with 850hPa temperatures are above the 30 year average (thick black line), but they then dip and are often close to or a little below it through the rest of the 16 day period. 

However, 850hPa temperatures don't tell the whole story at the moment. The temperatures we experience down at the ground level can become detached from those above when high pressure is controlling things. The resulting calm means the air which is cooled by contact with the colder surface, at this time of the year, isn't mixed out with the warmer air above it. 

GEFS 00z 850hPa temperatures and precipitation, London init 12th January 2022

The opposite scenario is also possible : lower 850hPa temperatures could actually lead to it being milder higher at the ground level due to more cloud and breeze. 

At the moment the favoured scenario is for colder upper level air to push down from the north towards the UK at times. It may affect the east and northeast, but high pressure probably builds back quickly and cuts off the flow. That means it could turner colder at times in the north east and there is a risk of wintry showers. In the south temperatures may tick up on those days due to it becoming windier.

Dry, dry, dry!

The GEFS also shows strong support for a continuation of the settled theme. A few small rain spikes appear  on the lower half of the plot, particularly later on and on plots for locations in the north of the UK. Nonetheless, it looks very dry for the time of the year. The caveat I will add is that sometimes the computer models are not very good at identifying a pattern change and things can creep in at quite short notice. 

So will it be cold?

There is uncertainty about how air mass temperatures will impact those that we experience at the ground level as I discussed. However, the London GEFS 00z 2m temperature plot suggests that temperatures will often be close to or below the average.

In the short term it appears somewhat milder on the plot, but the GEFS tends to struggle forecasting temperature inversions of the sort I discussed above.  Other models, such as the UK Met Office Global (view UK Met Office Global charts)  are showing lower maximum values in southern and central regions. 

GEFS 00z 2m temperatures, London init 12th January 2022

TL;DR

Settled weather is expected to continue for quite a long time. The GEFS ensemble model shows things staying mostly dry, especially in the southern half of the UK, for much of the next 16 days. There are indications of it turning more changeable in the north and there is a tendency for transitions to "creep in under the radar" and appear at quite short notice.

The temperature outlook is quite uncertain. Calm conditions under high pressure, particularly in southern and central regions, could lead to it being cold. Also, there are hints of colder air from the north sweeping southwards and flirting with the UK at times. That would bring lower temperatures to the north, but it could mean that daytime values in the south actually increase a little.  

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Add chart. Must be from TWO forecast models

paulbkinsella 7 days ago
Any sign of SSW? If so, how Strong will the SSW be? How Long will it last? When would it Start?

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