Author: Eric Gilbert

The warmer air won on Tuesday as the ground also became less cold with the thermometer rising to a maximum of 9.4C at 14.27 being the first above average maximum since the 5th at + 2.3C. Cloud began to increase after midday, from a weather front moving south over our area, that also brought the misty conditions in the late afternoon an fog overnight.

The humidity began to rise from a low of 92% after 13.30 and reached 100% at 21.50, holding that value into Wednesday morning.

As a result of the thick cloud overnight, once again providing a duvet to minimise loss of warmth into the atmosphere, the thermometer did not drop below 7.7C logged at 07.58 on Wednesday, which was a significant 6.4C above my long-term average. The precipitation from the mist and very light drizzle amounted to 0.3mm after five consecutive dry days.

There was one very significant change in the weather data on Tuesday as the UV sensor gave a maximum value of 0.7, still very low as we are in January, but the highest value since 30th November.

Wednesday after first light revealed the misty and murky conditions had deepened into a fog limiting visibility to 200m.

The high pressure seems reluctant to move away with little variation in pressure over the past twenty-four hours, down just 0.4mb, with a reading of 1035.2mb at 08.00, and now centred off the coast of Brittany. It is likely to influence our weather until the weekend. This slight relocation, and it is forecast to move east over Germany, will see the calm conditions continue with the wind varying as the day progresses from west-souuthwest to southwest and then south-southwest.

It was a degree warmer on Monday than Sunday although it didn’t feel like it as there was more of a breeze. The thermometer reached a maximum of 5.8C at 12.09 in the morning brightness but cloud then began to arrive that stopped any further sunshine and increase in temperature. The breeze picked up around midday with quite a flurry that produced a gust of 18mph at 12.15, the strongest air movement since Monday 6th. Very little warmth, such as there was, seeped into the atmosphere overnight thanks to the cloud cover with the thermometer only dropping 2C producing a minimum of 3.8C at 07.22 early Tuesday so the first night without a ground frost or air frost.

Tuesday arrived with total cloud cover as a weather front is tracking southwards with the cloud building during the late morning. The temperature had risen a little to 4.3C by 08.00.

The recent high pressure is still maintaining calm conditions with the recent cool air trapped beneath it although the warm air is slowly winning. The barometric pressure dropped just 4mb in the last twenty-four hours with a reading of 1035.6mb at 08.00, still very high.

Last week I logged how the continuing cold was slowly seeping into the ground. The last four days has seen the situation reverse with the ground temperature at a depth of 5cm rising slowly over the last four days with -1.8C, 0.3C, 0.4C and 1.1C today as the cold comes out of the ground but still having an effect on the air temperature. It was only two weeks ago, on the 1st, that the ground temperature at 08.00 and depth of 5cm read 9.4C.

Sunday was the first day when the very cold air began to give way to slightly milder air arriving from the west. As a consequence the temperature rose to a high of 4.8C at 14.45, the highest since the 6th, however, this was still 2.3C below my long-term average. It was a dry day under the influence of the high pressure, centred overhead, but thick cloud meant no UV light triggered the UV sensor. Overnight the thermometer slowly fell away to reach a minimum of 0.9C at 02.44 before rising slightly to reach 1.7C at 08.00 on Monday.

Monday after dawn revealed a sky with much less cloud, which was higher and thinner, that should result in weak sunshine as the day progresses. The wind direction, such as it is, has veered a few degrees from south yesterday into the south-southwest.

I mentioned yesterday that the centre of the high pressure was migrating south to be in a position over Southern England for much of the day. The maximum barometric pressure of 1041.6mb was logged at 20.56 Sunday evening, the highest pressure since 5th February 2023 when a reading of 1048.1mb was recorded. The intense high pressure has brought us the very calm conditions for the past few days as there is little pressure gradient to originate much air movement. The maximum air movement on Sunday was one incidence of just 5mph and 8mph overnight, although for many hours the anemometer was virtually still.

The pool of cool air trapped under the high pressure is slowly giving way to warmer air inching in from the west but it will take a another day before temperatures return to near normal for mid-January.

Saturday was slightly less cold than the previous three very cold days as the thermometer slowly rose to a maximum of 4.1C at 13.16. There was no sunshine but the high pressure was slowly relocating and beginning to cut off the flow of very cold air and allow the slightly warmer air to edge in from the west with its associated cloud. Thick cloud cover overnight, acting as a duvet that minimised loss of warmth into the atmosphere, meant no air frost but with a minimum of 0.8C at 00.31 early Sunday that we did have a slight ground frost. The maximum was 3.0C below my 40-year average and likewise the minimum was below average, just, with -0.2C. Once again, under the centre of the high pressure, there were hours when the anemometer dod not turn with a maximum movement of just 5mph on one occasion.

Sunday after first light revealed the total cloud cover. The centre of the high pressure is slowly drifting south over Brittany that will produce a significant change in wind direction to come from the south all day, a much warmer direction, at the same time the warmer air to the west is slowly edging closer.

Being under the centre of the anticyclone means there is little variation in gradient between the high and low-pressure, hence the calm conditions with little or no air movement. The barometric pressure reading at 08.00 was 1039.7mb being the highest pressure since 11th January 2024.

In the shade there is still a coverage of frozen snow that will slowly melt away over the next day or two. Automatic rain gauges are great for live monitoring of precipitation, also rate of fall, but not accurate on timing when snow or sleet falls. After a snow event I bring in my Met Office type copper rain gauge at 08.00 and slowly melt the snow before measuring accurately. With near freezing weather during many hours, as we have experienced this week, any snow in an automatic rain gauge will only melt under the influence of sunshine or when the temperature recovers significantly thus it will only register the precipitation slowly many, many hours later or even days after the event.

Friday yet again was a very cold day under the very light easterly air stream although we enjoyed a few hours of welcome sunshine. The thermometer eventually reached a maximum of just 1.9C at 14.18 being 5.2C below my 40-year average. From that time the thermometer began to slowly fall away reaching freezing again, taken as -0.1C, at 18.06, even earlier than on Thursday. The minimum of -7.5C, due to the clear sky overnight with no cloud to provide a duvet to minimise any loss of warmth, was logged at 07.17 early Saturday being once again a significant below average temperature at -8.8C. Friday was dry with little air movement, sometimes calm for many hours, with my anemometer registering the strongest air movement of just 8mph on one occasion.

Saturday after first light revealed the sky was still clear with the temperature at 08.00 having recovered slightly to reach -6.9C.

Automatic rain gauges are great for live monitoring of precipitation but not accurate on timing when snow or sleet falls. After a snow event I bring in my Met Office type copper rain gauge at 08.00 and slowly melt the snow before measuring accurately. With near freezing weather during many hours, as we have experienced this week, any snow in an automatic rain gauge will only melt under the influence of sunshine or when the temperature recovers significantly thus it will only register the precipitation slowly many hours later or even days after the event.

The centre of the high pressure today will leave Scotland and emigrate to England and continue the calm conditions and dry weather, with sunshine. The warmer air has begun to spread over the West Country and will slowly move eastwards with Sunday in Marlborough being cool, but thankfully not so cold as the past week and on Monday closer to average.

The Jet Stream is on course to arch to the north of the UK from Sunday thus leaving the UK on the warmer southern side thus cutting off the flow of cold air