Category: Commentary

Monday was the last of the days, until next week, when the maximum rose above the average for March with a peak of 12.8C at 13.37 being 2.1C above the long-term average. After around 13.00 the cloud, associated with the depression over France, built up producing misty conditions.

The first of the rain in March fell as a very light shower just after 09.00 on Monday but more registered on the automatic rain gauge between 02.00 and 04.00, that totalled 1.1mm, being the first precipitation this month.

The forecast cold front passed our way in the early hours of Tuesday crossing the south coast around 08.00. Behind it the temperature fell to a low of 4.3C at 06.37 being 1.6C above average, however, the arrival of the Arctic air, on a northeasterly breeze, produced a wind chill that meant outside at 08.00 it felt more like 3.1C rather than the air temperature of 4.6C.

The clearer air currently behind the cold front will likely produce some modest, short-lived sunshine, between variable cloud, but the temperature will be noticeably depressed compared to the unseasonal warmth of last week. However, there is another band of thicker cloud streaming south behind the front thus blocking out the early sunshine for much of the day.

Currently the air is streaming across the country from the north on a northeasterly breeze having originated around Greenland. It is being propelled towards us by a low pressure system over Scandinavia, with the air circulating anticlockwise, and a high pressure system over Iceland with its associated air mass rotating clockwise, so therefore squeezed between the two weather systems thus its direction and increased speed over recent days.

The glorious sunshine on Sunday raised the temperature to a maximum of 17.4C at 14.16 before cloud drifted across late afternoon. This high was a significant 6.4C above my long-term average and made it the warmest day since 17th October (17.4C).

Overnight the cloud continued to drift across, becoming thicker and lower, thanks to a large depression off the Iberian coast. As a result it limited the loss of warmth into the atmosphere so the minimum of 8.0C, logged at 06.45 early Monday, was 5.3C ave the average.

The warmth and sunshine on Sunday resulted in an equivalent loss of rainfall of 2.03mm, due to evaporation from ground sources and plant life, the highest this month, taking the toll loss for March to 14.6mm when the last nine days have seen no precipitation, a very dry start to the new month.

The rain radar on Monday morning showed a broken batch of thick cloud drifting across our area from northern France and associated with the depression off the Iberian coast, arriving just before 05.00. Spots of rain were observed just after 06.00 with light rain noted at 07.30.

A cold front is currently passing over the north of Scotland, by midday it is forecast to have moved south over northern England and by midnight will have arrived over southern England. Behind the front is the much colder air that will have travelled from around Greenland. This colder air, brought on a northeasterly airstream, will be with us for most of the week. As a result, maxima will be depressed and most likely be a couple of degrees below average with an accompanying wind chill.

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.