Category: Commentary

The thermometer peaked at 16.8C on Saturday, under the strong morning sunshine, before variable cloud drifted across in the afternoon. This high was a significant 6.1C above my long-term average and made it the warmest day since 24th November (17.1C). The day also gave us the highest solar radiation of 571W/m2 at 13.46 and the greatest loss of equivalent rainfall through evaporation from ground sources and plant life of 1.73mm.

Although the minimum of 4.9C overnight, logged at 06.13 early Sunday, it was the lowest for three days, however it was still 2.2C above the average.

The start to Sunday revealed a sky that was mostly cloudy, but high and thin. This cloud cover is thanks to the depression off the Bay of Biscay throwing a large sheet of cloud across southern England, but there is hope that it will thin and clear during the morning to give us the last of the very warm days. As the depression and recent high pressure relocate, the wind has backed further to come from the east, the indication of cooler weather to come after Monday. The barometric pressure is at its lowest today at 08.00 with a reading of 1002.9mb as the high pressure drifts away and the depression edges closer.

The forecast synoptic charts indicate that a cold front will travel south across the UK on Monday and be over our area around midnight Monday. This will herald the arrival of a much colder air stream that will see maxima during the week only rise to single figures, some 2C or 3C below the long-term average, and the wind coming from the much cooler northeast with a likely wind chill.

Although the peak temperature of 14.0C on Friday was a little below the maximum of Thursday it was still 3.3C above my long-term average, logged at 11.27, before the cloud built up. The minimum of 6.4C, logged at 06.29 early Saturday was also above average with +3.7C.

Another fine day dawned on Saturday with strong sunshine that had lifted the temperature to 8.2C by 08.00 with the prospects of another sunny day ahead but possibly a little cloud in the afternoon. The humidity of 77.2% at 08.00 was the lowest all month, partly due to the air stream backing into the east and the surface soil beginning to dry up after the sunshine and warmth this past week. The first week of March has been totally dry although the equivalent loss of rainfall, due to evaporation from ground sources and plant life, now totals 10.8mm.

The old anticyclone is now centred over Europe but still fending off the advances of the depression in the Bay of Biscay, which will affect the West Country today. Rain has been falling over the Penzance area and as far east as Plymouth this morning.

The SSW or sudden stratospheric warming that I referred to yesterday occurs when the stratosphere – the layer between 10 and 50km above Earth’s surface – heats up by 50 degrees in just two days according to the Met Office. They add that “We don’t feel this ‘warming’ ourselves because it happens so high up but it can have an extreme knock-on effect on our weather”.

The temperatures will begin to take a tumble on Monday with Tuesday the real start of the cold blast, with maxima in single figures. I note today that the Met Office and BBC both forecast that there might be light snow next Saturday. Time will tell!

Thursday gave us a very sunny morning but cloud from the associated depression in the eastern Atlantic drifted across around midday that thinned just before 14.00 allowing broken sunshine to return. However, the strong sunshine and southerly breeze, gusting to 19mph, the strongest all month, lifted the temperature to a maximum of 15.3C at 14.22 being 4.3C above the long-term average and was the warmest day all month. The cloud overnight that minimised loss of warmth into the atmosphere in contrast to the clear skies this past week, meant that the minimum of 8.4C made it the warmest night since 27th January and 5.8C above average. The maximum solar radiation of 515W/m2 was the highest all month.

The first couple of hours after dawn on Friday were mainly cloudy, however, just after 08.00 the cloud thinned and broke allowing a little sunshine to break through, the thermometer having risen to 9.3C by 08.00, the warmest start to day since 21st February.

A SSW event is a Sudden Stratospheric Warming. The Met Office are ‘very confident’ that such an event will occur next week. I mentioned yesterday that temperatures would tumble next week as a northeasterly wind will set in. A spokesperson said “The stratospheric polar vortex is now weakening rapidly. This is when the mid stratospheric wind is predicted to reverse from westerly to easterly. Sudden changes in the stratosphere can trigger a breakdown in the polar vortex, meaning cold air that is usually concentrated around the Arctic spills further south than usual.

The coming weekend will be very pleasant with temperatures beginning to drop on Monday then on Tuesday we begin to feel the colder, northeasterly wind with maximum temperatures dropping down to single figures, some 2 of 3C below average. There could be the return of night frosts, but not as severe as last week, so gardeners beware!

I was delighted to find a bee enjoying the sun and warmth yesterday when visiting a crocus in my garden.

Thanks to the wall to wall sunshine on Wednesday the thermometer rose to a maximum of 13.7C at 14.32 making it the warmest day since 22nd February and 3.0C above my long-term average. The UV level rose to a peak reading of 2.5, the highest since 8th October, still at the top end of “low’ in strength. The solar radiation produced a peak of 513W/m2, the highest since 25th October, as the sun gains strength.

It will have been the last of the nights that an air frost was recorded, the thermometer only dropped below zero (-0.1C) at 04.36 early Thursday. That was quite a contrast with only three hours of below zero temperatures against the previous nights when we had in excess of twelve hours of freezing temperatures.

After dawn the sun shone strongly on Thursday that had lifted the thermometer to 1.9C by 08.00 making it the warmest start to a day at that time since 27th February.

As the anticyclone loses its domination a depression in the eastern Atlantic will begin to influence our weather over the next few days with much less sunshine and probably a mainly cloudy day on Friday.

The weather after the weekend will likely be so different to the past few days. The forecast charts for the jet stream next week show a major change in strength, but especially direction, so the mild days of this week will be but a memory! The wind is forecast to come from the northeast, a cool direction, that is likely to depress the temperatures by day and the maxima will probably be below average for March.

The wall to wall sunshine on Tuesday, and especially the change in wind direction from north to southwest, gave us the warmest day since 22nd February with a maximum of 13.4C logged at 14.42, being 2.6C above my long-term average. The wind was for most parts light with a peak gust of 13mph, the highest for ten days. The thermometer was much slower to fall away in the late afternoon and evening, not reaching freezing point (-0.1) until 23.24, at least two hours later than the previous five evenings. The minimum of -2.6C, logged at 06.02 early Wednesday, was 5.0C below average but the least cold night since 27th February.

After the ground had thawed under the rising sun and a light breeze on Tuesday, the loss of equivalent rainfall due to evaporation from ground sources and plant life was 1.70mm, which was the highest loss since 5th October. The first four days of March have seen the equivalent of 6.4mm of rainfall lost through evaporation as the ground slowly begins to dry a little after the very wet end to February.

The recent anticyclone is easing eastwards with its two centres today over Italy and Turkey. This modest change in position will see the light breeze come from the south-southwest today before backing further into the south in the late afternoon. It is still acting as a blocking high to the advancing weather fronts and showers from the next depression that will see more cloud on Thursday`afternoon with the possibility of light showers early Friday. The barometric pressure has now dropped to 1023.0mb at 08.00, some 12mb below its peak on Sunday.