Author: Eric Gilbert

Tuesday 29th September
The limited sunshine on Monday, especially in the morning and late afternoon, combined with an air flow from a mainly easterly direction, gave us the coolest day this month with a maximum of only 17.3C, logged in the early afternoon at 14.37, which was 1.7C below average.

At first the temperature began to fall away during the past evening and just before midnight, under relatively clear skies, however, an advancing warm front began to push cloud and moist, warm air across the country that then saw the thermometer make an about turn from the minimum of 9.9C, which was logged just after midnight at 00.49.

Tuesday after first light revealed very misty conditions that saw the visibility fall to about 300m by 07.30, forming fog, then slowly begin to lift. The light breeze has now veered from the east to southeast that is drawing warmth from Europe with the result the temperature has risen during the early hours to reach 14.7C by 08.00 that will give us a very warm day with a maximum well above average. Hopefully, as the weather front eases away, the cloud might break this afternoon allowing some sunshine to break through.

During the early hours of Wednesday the breeze will veer from southeast to south and later south-southwest that will continue a reduced flow of warm air. All the while two depressions in the North Atlantic will deepen that will see a weather front cross the country during the morning. There is increasing confidence that the cold front will produce some precipitation but quantities are uncertain at the moment. I have now four empty water buts, just one full, small one remaining, so I would welcome some precipitation as the ground is still very dry and I continue to water my flowers and runner beans using pots sunk into the ground to minimise evaporation.

All the while the recent anticyclone, now over eastern Europe, will act as a buffer to the advancing depressions trying to advance from
the Atlantic, that by Wednesday will have deepened significantly with a forecast centre barometric pressure of 955mb. By Thursday the pressure will begin to rise again as a minor ridge begins to push across the country from the southwest, giving us a dry and sunny day. This week is a topsy turvy weather week as almost daily the pressure rises and falls.

The images continue to be from Stourhead of early autumn colours.

Monday September 28th
After a bright start to Sunday the variable cloud produced a few spots of rain mid-morning and thickened after mid-day that saw a cold weather front cross mid-afternoon. The cold weather front produced a little drizzle at first then light rain at 15.30 that eventually totalled 1.6mm. The high of 20.3C at 13.59, before the cloud increased, was 1.3C above average.

The past night was cold. The back edge of the weather resulted in the cloud thinning early evening combined with the cooler air behind the weather front, resulted in a low of 5.3C at 07.38 early Monday, which was 4.2C below average. The low temperature was also as a result of calm conditions once again in the early hours as the anemometer fell stationary after 01.00.

The diurnal range was considerable over the past twenty-four hours with a difference of 15.0C between the high and low. The rainfall for the month currently stands at 25.7mm compared to my 42-year average of 67.2mm.

Once again radiation fog had formed in the early hours of Monday due to the very low temperature and precipitation the previous afternoon so the humidity was high, which limited visibility significantly in the River Og valley and to the north but not so intense to the east. By 08.00 the fog had slowly thinned to leave just misty conditions. The forecast radar map indicates that the high cloud from the recent weather front will persist for several hours limiting the sunshine.

A temporary ridge of high-pressure will produce a fine day on Monday that as it edges towards eastern Europe on Tuesday will produce a breeze from the Southeast, which will carry across from the near Continent a much warmer air stream that will result in a very warm day. The barometric pressure is rising and falling almost each day as the high pressure comes and goes.

A very deep depression continues to form in the North Atlantic that by Wednesday will sneak in behind the falling high pressure. We will likely see some useful precipitation in the morning and the wind picking up as another weather front crosses the area.

Sunday 27th September
Saturday was a splendid early autumn sunny day that eventually saw the thermometer climb to a peak of 20.6C at 15.14 before cloud began to thicken around 16.00. It was the seventh consecutive dry day with the UV level classed as Moderate. The cloud again began to thicken considerably after 22.00 that meant a less cold night than previously, however, a minimum of 8.6C, logged at 05.18, was 0.9C below my long-term record.

A thick bank of cloud blotted out any chance of sunshine after dawn on Sunday. In fact, two weather fronts are going to pass over the UK today, both cold fronts with cooler air behind them, that will see the cloud thicken towards mid-day, after some brightness mid-morning, with the possibility of light shower activity from around noon. The rain radar at 08.00 indicated scattered showers already falling over Dartmoor and Exmoor arriving from the southwest, while there track indicates that they will miss us. However, a line of developing shower activity, stretching from Brittany across the Channel towards southern England, is now being shown on the radar that could pass over our area. This significant change in our weather is the result of low pressure to the west of the UK that is producing very heavy rain over Ireland and North Wales. The air stream today will veer from southeast to south then west-southwest as the day progresses and pick up in strength after a calm night.

We are now in an unsettled period of weather as the recent high pressure has moved over eastern Europe allowing low pressure systems to arrive from the Atlantic that will edge towards the UK. The barometric pressure is currently falling rapidly with a reading of 1015.0mb at 08.00.

Tomorrow will see another major change in wind direction, from west, through north to east that will give us a sunny day behind the departing Sunday weather fronts. As Tuesday progresses, the wind direction will change further, to come the south-southeast, that will mean a much warmer air stream arriving from the near Continent, resulting in the temperature climbing higher again, probably several degrees above the late September average.

By Wednesday a very deep depression in the Atlantic, will have edged closer, its centre heading between Scotland and Iceland, that will bring possible sunshine and shower activity. At the moment the forecast charts indicate that the large area of high pressure over central Europe will block any further movement of the depression over the UK, thus any heavy rain and strong winds will keep to the west of England.

Saturday 26th September
After a slow start, due to variable cloud on Friday morning, the sun became quite hot in the afternoon that lifted the temperature to a peak of 22.6C at 16.07, which was again above the September average at +3.6C. However, the opposite occurred overnight with the temperature slowly falling away during the early hours and then quickly dropping to a minimum of 5.1C in the hour before dawn that was a significant 4.4C below average, which made it the coldest night this month and in fact since 12th May. The cold front that passed over around midday had cleared in the evening that resulted in a clear sky, there was also a lack of any breeze to stir up the atmosphere after 01.00.

Radiation fog formed in the River Og and River Kennet valleys before dawn that only began to thin after the sun rose above the horizon at 06.59 and had totally evaporated just after 08.00. Today will be the best day of the weekend with a sunny morning and variable cloud limiting the sunshine this afternoon. The high pressure is hanging on today, hence the fine weather.

Two weather fronts will arrive later on Sunday afternoon that might produce a little precipitation, however, it will be a cloudy day with the advance cloud in the morning thickening after around midday.

Monday will see a return to fine dry weather as the high pressure makes a brief reappearance, centred over the English Channel. However, brewing to the west of Ireland, with more certainty now, will be a very deep low pressure system that will see winds strengthening considerably, especially to the west of the UK, heralding the start of a more unsettled period. The centre of the low is forecast to have very low-pressure of 957mb. The thinking at the moment is that the depression might be blocked from crossing the country by the high pressure still to the east over Scandinavia and near Continent.

The Harvest Moon is the full moon that happens closest to the start of autumn. It is so called because traditionally this time of year was when crops were harvested and a nice bright full moon meant that you could work well into the evening.

Friday 25th September
Thursday saw the cloudier conditions in the morning begin to thin with strong sunshine in the afternoon that boosted the temperature to a maximum of 21.8C, being 2.8C average. The past night was relatively mild with a minimum of 12.3C at 07.21, just after sunrise in Marlborough.

The air was clear after dawn on Friday, however, the hour or so before sunrise saw mist form that quickly evaporated as the sun grew in strength. Another cold weather front will cross the UK today that will see an increase in variable cloud this afternoon but we are unlikely to see any precipitation.

The fine weather continues on Saturday as the high pressure eases back westwards and will be centred over the UK, hence a fine, calm and sunny day ahead. The slight relocation of the anticyclone will continue the calm conditions however, a slight change in direction to come from the west-northwest, which will result in a degree or two down on Friday’s peak temperature, but still above average. By Sunday the high pressure will be falling away as low pressure systems in the Atlantic edge closer with another front crossing late on Sunday.

The forecast charts indicate a possible very deep low pressure system forming from two depressions to the west of Ireland on Tuesday. There is great uncertainty at this time as to how close the depression will get to the UK, or will even cross the UK, if the latter we could be in for a wet and stormy day or two mid-week. I will be watching these possible developments closely over the weekend.

Today is the day of the Equilux. An equinox is the exact moment the sun crosses the earth’s equator, while an equilux is the actual day when daylight and darkness last for equal 12 hour periods. For the UK the times are 06.58 and 18.58.