1 Nov 2013

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!

1 Oct 2013

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).

1 Sep 2013

Potten End Newsletter Article 10

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

Potten End Weather

“The reason lightning doesn’t strike twice in the same place 
is that the same place isn’t there the second time.” 
― Willie Tyler

At last, after a run of wash-out summers, we’ve finally had a summer worth talking about. July may not have been the hottest on record, but it was close. The Met Office put it in the top three on record. In Potten End it was the second hottest on record with a high of 34.9°C. In our records, the hottest July was in 2006 with a high of 35.2°C.

The long July heat wave was aided by a jet stream located to the north of the UK which kept a nice stable high pressure area over most of the UK.

Spectacular thunderstorms around the country marked the end of the heat wave. It’s quite common for storms like this to form at the end of a heat wave. Water vapour rising with the warm air forms water droplets which combine and turn to ice crystals as the air rises higher. The ice crystals fall as hail and pick up a negative electrical charge by rubbing against smaller positively charged ice crystals. This results in a negative charge forming at the base of the cloud and a positive charge forming at the top of the cloud. The negative charge is attracted to the surface of the earth and other clouds and objects. When the negative charge becomes too strong, lightning is discharged which balances the charge within the cloud.

Some interesting facts about lightning:
  • On average, a lightning bolt lasts for about one 10,000th of a second.
  • A lightning bolt contains enough energy to light a 100 Watt light bulb continuously for three months.
  • Lightning speeds through the air at around 75 miles per second (around 270,000 miles per hour).
  • Lightning is hotter than the surface of the sun reaching temperatures of around 30,000°C.

September Outlook

September marks the beginning of the meteorological autumn. We can obviously expect the temperatures to drop a little and the evenings will start to darken earlier. We can expect average temperatures of between 10.1°C and 19.6°C and a little more rain than August – typically around 30-50mm over the month.

Weather Online

Don’t forget that you can check on the weather in Potten End wherever you are by going to http://www.pottenend.org where there is also an archive of all previous articles, historical weather data and other interesting information.

You can also subscribe to the Potten End Weather Twitter feed at @pottenend. Live weather information is tweeted several times a day.

Please note that if you send twitter messages to @pottenend about local information or events, they can be re-tweeted to all of the Potten End Weather twitter followers.

1 Mar 2013

Potten End Newsletter Article 9

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

Potten End Weather

“Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating;
there is really no such thing as bad weather, only different kinds of good weather.”


― John Ruskin

The sun seems to have been particularly absent this winter. If we go through our records and add up the number of days where the temperature has been at or below 0ºC (an arbitrary but useful measure of a cold winter) then we find that, as this article goes to press, this winter (Dec 2012 to Feb 2013) is the fourth coldest. The top five coldest winters on our records are:
  1. 2008/09:  47 days at or below 0°C
  2. 2009/10:   45
  3. 2010/11:    39
  4. 2012/13:    38 (incomplete at time of writing)
  5. 2011/12:    28
The remaining years on record average out at about 20 days below 0°C.

Solar Cycles and Their Effect on the Winter

The sun goes through regular cycles of activity in which sun spots, solar radiation and many other factors vary dramatically. These solar cycles have a duration of around 11 years and have been observed for hundreds of years.

Solar cycles were discovered in 1755 and we are now in cycle 24 which started in March 2012.
Recent research for the Met Office by Imperial College London and the University of Oxford suggests that the variability of ultraviolet radiation from the sun over the solar cycle may have a much larger effect on our climate than previously thought.

When the UV levels are low, unusually cold air forms high up over the tropics and is balanced by a more easterly flow of air over the mid-latitudes. This is a pattern that brings easterly winds and cold weather to northern Europe.

The opposite occurs when UV levels are high and westerly winds bring warmer air and milder winters.

Measurements of solar activity indicate that the minimum occurred around December 2008.

No coincidence then that this was the coldest winter we have recorded in Potten End.

This research won’t help with short term forecasts (measured in a small number of days) but it will probably help the Met Office improve seasonal forecasts for months and even years ahead.

The effect of the solar cycles should not be blamed on general global warming. Joanna Haigh, Professor of Atmospheric Physics at Imperial College London, says:

Compared with the effect of man-made emissions over the last century, solar variations still have a very minor effect on long-term global climate trends, but this study shows they may have a detectable influence on winter climate.

March Averages

It is said that March comes in like a lion but goes out like a lamb. These are March’s averages over the first and last week for all years on our records:
  • Temperature: starts at 3.3ºC, ends at 8.2ºC.
  • Daily rain: starts at 1.5mm, ends at 1.3mm.
  • Peak rain rate: starts at 0.5mm/hr, ends at 2.9mm/hr.
  • Wind gust: starts at 11.1mph, ends at 12.8mph.
Temperature and daily rain concur with the saying, peak rain rate and wind gusts would differ. Feel free to interpret them individually or all together at your leisure!

Hope you all have a great spring in spite of or because of the weather!

1 Feb 2013

Potten End Newsletter Article 8

This article originally appeared in the Potten End Newsletter, January/February 2013.

Potten End Weather

Teacher: “What is a blizzard?”
Stanley: “A blizzard?! … A blizzard is the inside of a buzzard”.
– from the Laurel and Hardy film “Pardon Us”, 1931

A Review of 2012’s Weather

2012 was certainly a year to remember. Apart from the phenomenal Olympic Games when the weather really excelled itself along side our athletes, it felt like most of the year was more like the washout that accompanied the Diamond Jubilee weekend.

The Met Office say that 2012 was the second wettest in the UK on record (the wettest was 2000 by 6.6mm). In Potten End however, it was by far the wettest year on our records (though admittedly 2006 is our earliest complete year of data). I’m pretty sure we’re not going to see a hosepipe ban this year!
Potten End Rain Totals and Wettest Months

Temperatures

Last year may not have had record hot temperatures, but it made up for it with the coldest day on our records which was 11th February 2012 with a temperature of -9.5ºC.

The hottest temperature we have on record is 35.2ºC on 19th and 25th of July. The hottest in 2012 was 31.4ºC on 19th August

Wind

Another record breaker last year was the highest recorded windspeed. On 15th June a gust of 21.9mph was recorded. 2012 was also the windiest year we have on record with 8 days where wind speed was 15mph or more

Winter and Spring

Past performance is no guarantee, but from our records we note that: February and March have about 9 or 10 days of rain on average; The minimum average temperature in February and March is around 2ºC with maximum averages of around 8ºC for February and 11ºC for March.

18 Jan 2013

Snow!

It’s been snowing in Potten End continuously for 5 or 6 hours now. Just measured the depth and it’s around 5.5cm.
Snow, Potten End, 2pm, 18th Jan 2013

Snow continuing to fall as I type. May update later.

2 Jan 2013

2012 – The Wettest Year on Record?

While preparing an article for our local parish magazine reviewing the weather for 2012 and comparing it with other years, I’ve been digging through the database to get some interesting statistics.

Was 2012 the wettest year on (our) record ?

Yes! And by some margin!

We recorded a total of 821mm (32.3″) of rain in 2012. The previous high was 722mm (28.4″) in 2008 and it’s nearly double the lowest recorded amount of 430mm (16.9″) in 2006.

Though please bear in mind our records only go back to 2005 (which is a year for which we only have partial statistics and is therefore not included in the analysis).

These are the figures:
  • 2006: 430mm
  • 2007: 572mm
  • 2008: 722mm
  • 2009: 665mm
  • 2010: 500mm
  • 2011: 545mm
  • 2012: 821mm
There’ll be a slightly more detailed analysis and more comparisons in the full article which will appear in print towards the end of January and on line on 1st Feb.

And more snippets of information may appear here as I dig around a bit more.