Potten End Newsletter Article 16

This article originally appeared in the Potten End Newsletter, May 2014.

Potten End Weather

“Water and air,
the two essential fluids on which all life depends,
have become global garbage cans.”
― Jacques-Yves Cousteau

In early April much of the country experienced periods of very high levels of air pollution caused, in part, by Saharan dust.

Storms in the Sahara whipped up a large amount of sand and dust into the upper atmosphere. Saharan dust settling in the UK is nothing unusual and can happen several times a year. Winds of around 20mph are required to lift sand into the atmosphere, and the Sahara had been experiencing wind storms in excess of 40mph at the time.

Normally the sand and dust settles in the countries of Southern Europe. In April however, winds from the south and east combined the sand and dust with industrial pollution from Europe. Our weather at the time was stable and calm which meant that the pollution gathered over the UK and was not dispersed.

According to The Department for Environment, Food and Rural Affairs (Defra), certain areas reached 10 out of 10 – or “very high” – on its air cleanliness scale for a few days.

When levels reach 7 to 9 on Defra’s scale, adults and children with lung problems and adults with heart problems are advised to reduce exertion.

When pollution levels reach 10, the general population is told to “reduce physical exertion, particularly outdoors, especially if you experience symptoms such as sore eyes, cough or sore throat”.
The deposit of fine Saharan sand on cars and buildings was just one visible effect of the event. The air was visibly hazy with some reporting a distinctly blue tinge to it. This resulted in some incredible sunsets.

Fortunately the event passed after a few days when wind and rain helped to disperse the pollution and remove the sand and dust from the air.

Recent studies suggest that air pollution can have wide-ranging effects on the weather. Parts of China and Asia have the highest levels of air pollution in the world and researchers have found that, especially during winter, these pollutants strengthen storms above the Pacific Ocean, which in turn feed into weather systems in other parts of the world.

The effects can be quite dramatic with the pollution causing thicker and taller clouds leading to heavier precipitation.

Potten End Newsletter Article 15

This article originally appeared in the Potten End Newsletter, April 2014.

Potten End Weather

Conquering the world on horseback is easy;
it is dismounting and governing that is hard.
– Genghis Khan

Recent reports suggest that Genghis Khan’s incredibly successful advance through Mongolia may have been helped by the mild, wet winters after a significant dry spell.

Scientists studying a 1,112 year tree ring record show that there was a fifteen year period of persistent moisture which was unprecedented in the previous 1,000 years.

This could have led to a rapid rate of growth of grassland which provided significant fodder for his war horses and favoured the formation of Mongol political and military power.

One other equally speculative consideration of a mild winter like the one we’ve just experienced is how insects, be they pest or delight, will fare. Common wisdom suggests that harsh winters decimate the insect population. But, to paraphrase a recent scientific study: “it depends”.

Insects relay on a huge number of strategies to survive the winter and it is more dependent on the availability of food than the actual minimum temperatures. It is thought that a mild winter can be more detrimental to the insect population than a harsh winter. During a mild winter, the hibernating insects may emerge earlier only to find that flowers have not developed sufficiently to provide them with enough food to sustain them and they will starve to death.

Soil moisture is another factor affecting insect survival. A damp mild winter may encourage the growth of fungal pathogens that kill insects. On the other hand, a dry winter may cause insects to dry out and die. Some insects are better than others at preventing water loss and may thrive in drier conditions.

Diseases, predators and parasites that have strong effects on insect populations are all affected by the weather in some way. And there is always the timing of reproduction when spring arrives and the local weather conditions at the time which will have more effect than any over-wintering issues the insects may have experienced.

So, as you can see, simply predicting insect populations from the type of winter we’ve experienced is about as straight forward and reliable as predicting the summer’s weather in March!

As I write this article, we’re experiencing some nice warm dry weather. It’s the first prolonged dry spell for England since the start of December. The aquifers and reservoirs are full to the brim (possibly the fullest they’ve ever been) and we’re almost certainly not going to experience a hosepipe ban this year and possibly next year which is good news for gardeners and car-washers alike.

Let’s hope the dry spell lasts long enough to enable those who have been flooded out to rebuild their lives and return to some sort of normality more quickly.

The temperature, wind, rain and many other weather measurements can be monitored live on the Potten End Weather web site.

Potten End Newsletter Article 14

This article originally appeared in the Potten End Newsletter, March 2014.

Potten End Weather

H:”What’s my temperature?”

L: “Wet and windy”

H: “That’s a barometer!”

– Laurel and Hardy

The country has been battered by fierce storms over the last few weeks. And as I write, despite it being a beautifully sunny day, there seems to be no end in sight. We have experienced the wettest December to January period since records began.

The latest theory is that our bad weather is a result of higher than normal temperatures in Indonesia and the tropical West Pacific. This has caused increased rainfall in that region and has caused major changes to the Pacific jet stream which, when linked to the unusually strong North Atlantic jet stream, has caused exceptionally bad weather both sides of the Atlantic.

As I have discussed before (Newsletter Article, October 2013), the highly variable nature of the British climate does not help when trying to link these extreme weather events with global warming. The Met Office say there is “… no definitive answer on the possible contribution of climate change to the recent storminess …”. They then go on to say that the increase in the intensity of daily rainfall rates is consistent with what is expected from a warming world.

Going back a few years in the Potten End Weather Archives, I’ve counted up the number of rain-free days we get in the months from November to February.

Rain Free Days

We can see that so far this year January and February have been exceptionally rainy with only a small number of days where rain has not fallen. It is difficult to find any other increasing or diminishing trend in the table. But the sample size is very small compared to the data that the Met Office works with.

When I started out saying there was “no end in sight” to the current poor weather, that really refers to the more accurate five-day weather forecast at the time of writing. The longer range forecasts show that while the weather may remain unsettled in to the middle of March, we should be expecting longer spells of drier weather with temperatures slightly above the seasonal average. Whether that will be enough to bring relief to the flooded areas of the UK remains to be seen. I sincerely hope it will.

The wind, rain and many other weather measurements can be monitored live on the Potten End Weather web site.

Potten End Newsletter Article 13

The article from the December 2013/January 2014 Pottten End Newsletter can be found here in a slightly modified form.

Potten End Climate

Potten End Climate

“It always rains on tents. Rainstorms will travel thousands of miles,
against prevailing winds for the opportunity to rain on a tent.”
– Dave Barry

Annual climate for Potten End, based on live data, is available here:

• Potten End Annual Climate 

Potten End Newsletter Article 12

This article originally appeared in the Potten End Newsletter, November 2013.

Potten End Weather

“October extinguished itself in a rush of howling winds and driving rain and November arrived, cold as frozen iron, with hard frosts every morning and icy drafts that bit at exposed hands and faces.”
― J.K. Rowling, Harry Potter and the Order of the Phoenix


After a calm, mild start, this October turned blustery, cold, and wet. At the time of writing we’ve yet to experience frost. I’m sure we’ll get some frost before October ends and we’ll definitely get it in November.

Forecasting frost more than a few days in advance is incredibly difficult due to the wide range of conditions that affect air temperature. For example, on cloudy nights the cloud can act like a duvet, trapping warmer air near the surface which makes it unlikely that frost will occur.

Did you know there are three types of frost that form in very different ways?

Air Frost

An air frost occurs when air which is at least one metre above the ground cools below the freezing point of water.

Ground Frost

When the surface temperature of the ground, trees, hedges or other objects falls below the freezing point of water, frost forms on the surface of these objects. Some surfaces are more prone to frost than others. For example, grass is more prone to frost than concrete or tarmac surfaces because concrete and tarmac hold on to heat more than grass.

It is possible for ground frost to occur even if the air temperature is above freezing. The ground and other objects radiate heat away at night and can cool significantly even in late spring and early summer. This is why gardeners need to be wary of frosts until at least the end of May and perhaps slightly beyond.

Hoar Frost

Hoar frost occurs when dew freezes. Hoar frost is either a ‘feathery’ or a plain white frost of a more globular form.

When the temperature of the surface is below freezing before dew forms, the ‘feathery’ variety of hoar frost is created on the surface.

When the temperature of the surface falls below zero after the dew forms, the dew droplets freeze and the white globular hoar frost is created.

November Expectations

November temperatures can vary as wildly as they can in October. In 2010 November had a record high of 17.7°C at the start of the month and a record low of -6.1°C at the end of the month. The average November temperature is around 7°C.

We’ve recorded an average of just over 80mm rain in past Novembers with a high of 148mm in 2009 and a low of 29mm in 2011 which precluded our 2012 drought.

Have fun sweeping and raking up the leaves … or just wait until the wind blows them over to your neighbour!

Potten End Newsletter Article 11

This article originally appeared in the Potten End Newsletter, October 2013.

Potten End Weather

“Don’t knock the weather. If it didn’t change once in a while, 
nine out of ten people couldn’t start a conversation.”
― Kim Hubbard


Weather Fronts

Weather fronts bring a change in the weather and are frequently mentioned in weather forecasts. But what are they?

Weather fronts mark the boundary between two air masses. When the two air masses have different properties; for example, one air mass may be warm and moist while the other might be cold and dry, they produce a reaction in the zone where they meet known as a front.

This reaction is the principal cause of significant weather like showers, thunder showers and related unstable weather. It is caused by air being lifted and condensing in to clouds by the movement of the cold front under the warmer moist air.

The two main types of front are a warm front and a cold front. On weather maps these appear as a line with semi-circles and a line with triangles respectively. The semi-circles and triangles indicate the direction in which the front is moving.

Cold fronts can produce sharper changes in weather and move up to twice as quickly as warm fronts, since cold air is denser than warm air and rapidly replaces the warm air preceding the boundary.

A warm front moves more slowly than the cold front which usually follows because cold air is denser and harder to remove from the Earth’s surface. This also forces temperature differences across warm fronts to be more significant. Rainfall gradually increases as the warm front approaches. Fog can also occur at the head of a warm front.

When a cold front catches up with a warm from, it produces an occluded front. Occluded means hidden. On weather maps this is shown a line with both semicircles and triangles. In an occluded front, warm air is lifted up from the surface, and therefore ‘hidden’. An occluded front can be thought of as having the characteristics of both warm and cold fronts.

In the UK our unique weather is a result of us being an island nation between a large ocean to the west of us, a large land mass to the east of us and our position north of the equator. This means we experience a large number of frontal systems and their associated weather. It is one of the reasons why it is only really possible to forecast up to five days ahead with any degree of confidence.

October Expectations

October is a changeable month weather-wise. In the past, according to our records, we have seen temperatures as high as 25.3ºC (2011) and as low as  -1.7ºC (2008). On average we can expect to see temperatures between 7.5ºC and 15ºC. October can be a wet month with total rainfall between 20mm (2011) and 110mm (2006).