Category Archives: Weather

A white or green Christmas 2018?

The GFS model is now within range of the big day on the 25th. From now until Christmas Eve I will be having a look to see what is on offer.

The first operational run suggests something of interest but please bear in mind there is a long way to go yet. While operational runs are often exciting, the below suggests a potent northerly with snow for many, the right hand average is much more realistic though admittedly boring.

My own guess at this stage is for something benign, a high of 6C with a low of 2C, perhaps some frost early or late on?

10th: Op run this morning is showing quiet weather. A high of 4C after overnight frost.

11th: Op run now shows a slack north-easterly and possible snow.

13th: An anticyclone to the north of Scotland continues to keep things seasonal on the op run this morning. The average again benign.

14th: More interest on today’s midnight run. The op shows a cold pattern. Frost early and late and a high of 2 or 3C. A chance of flurries. Even the average looks less mild!

You can find out what every Christmas Day in London was like weatherwise here.

 

 

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November 2018: average and rather sunny

November was most notable for the amount of sunshine. Some 79 hours were recorded, that’s 135 per cent of average, the sunniest November for two years.

The mean temperature finished 8.4C, 0.4C above average, the mildest November for three years.

Some 72.5mm of rainfall was recorded, 122 per cent of the 1981-2010 average, the wettest November for two years.

To view full stats follow this link:http://1drv.ms/1kiTuzv

november 2018

London winter forecast 2018-19

Long range modelled forecasts have been all over the place of late and, looking at the underlying signals, it is easy to see why.

When I’ve produced these forecast in the past, in terms of QBO and ENSO data, there’s usually a lot of analogues to compare with. This year, however, seems to be an exception.

Considering QBO first I looked back over data to 1950 and found nothing similar for October. However, looking over the whole series the cyclical nature of this circulation may give some clue.

bestfit

Some 20 months were revealed, ranging from June 1959 to June 2015.  Using NOAA’s  Niño 3.4 region I narrowed this list down to the few that had an ENSO value of around +1 with a rising trend. With NOAA’s forecast of a Modoki El Nino (one that occurs in the central Pacific) this narrowed the list to just 1 period: June 2015. Considering maxima anomalies this would give the following winter.

winter 2018-19 max anomaly.PNG

The above would suggest there being a general cool down through December with a cold spell starting just before Christmas into the new year? And another cold spell end of January into the first week of February?

winter 2018-19 precip anomaly

The above precipitation anomaly chart would suggest a wetter than average December,  January and February, though February by much less so.

It’s been a very busy autumn so I’m keeping this short.

The below figures, particularly January and February, may be different in the event of an SSW occurring. In all then.

The mean:
December: +0.8C
January: -1.2C
February: -1.7C
Overall: -0.3C (broadly average)

Precipitation:
December: 158%
January: 155%
February: 120%
Overall: 134%

 

How cold will November end?

Twitter and other forums have been at fever pitch with excitement for a ‘nailed-on’ cold spell. 

But with many getting carried away over tales of a repeat of March’s ‘Beast from the East’ it is important to remember that snow in November is extremely rare in the south-east; despite predictions of the incoming upper air being very cold the ground is still very warm and will take time to cool.

However, as seen in November 1993, a week of hard frosts were enough to chill the ground enough for a decent week-long cold spell. Similarly, although the snow didn’t arrive in London until December, November 2010 was also cold enough.

The weather of late has been in an ‘average mood’ with the mean temperature in September and October both finishing at 0.2C below. The mean for the this month is currently (on the 15th) running 1.8C above average, therefore for the mean to finish the same as September / October would require a big cool down, as hinted by the models.

Will we see another an average, 1993 or a 2010 end to the month. My hunch is it will be something between the three.

Below is a graph that shows this November so far with average, 1993 and 2010 ends.
2018: 0.4
1993: -0.8
2010: -1.4

East London’s highs and lows of the last 60 years

The chart below shows every maximum and minimum temperature recorded in this area since January 1st 1959, some 21,860 days!

The extremes range from -12.7C recorded on January 31st 1972 to 37.5C on August 10th 2003.

After peaking in 2003, summer maxima seems to be in decline. Winter minima, by comparison, has been increasing since 2012

maxmin

October 2018: average and rather sunny

October was most notable for the amount of sunshine. Some 136 hours were recorded, that’s 127 per cent of average, the sunniest October for six years.

The mean temperature finished 11.6C, 0.2C below average, the same anomaly as September. And 1.6C cooler than October last year.

Some 52.1mm of rainfall was recorded, 78 per cent of the 1981-2010 average, the wettest October for four years.

To view full stats follow this link:http://1drv.ms/1kiTuzv

October 2018 max.JPG

November: an Indian summer before turning cold?

With the mean temperature of both October and September finishing 0.2C below average it is probably safe to say that the weather is in an average kind of mood.

Conditions during the first part of November look changeable, according to the Met Office’s 30-day forecast . After mid month, however, the agency says the forecast is uncertain.

Now that much of the UK has had its first frost any warm spell in November will, correctly, be called an Indian summer. A singularity called the St Martin’s Summer occurs in 66 per cent of years, occurring between 15th and 21st and peaking on the 18th.

And, as if by magic, the GFS model today has this chart for the 16th, an Atlantic ridge of high pressure with daytime temperatures about 6C to 8C above average. Though warm during the day I would imagine there being a risk of fog forming at night

16th

Beyond that there could be a tendency for much more unsettled weather at the end of the month. The early December storms singularity occurs in 98 per cent of years, starting between November 24th and December 14th, often peaking on December 9th.

November, the last autumn month, can often surprise with its extremes, though it can also often be characterised by days of anticyclonic gloom. The warmest, coldest and wettest November conditions in London back to 1959 can be found here.

 

 

Perfectly average months are extremely rare

Readers of this blog know that I often described a month as fairly average – a look at local statistics shows that many months come in very close to the monthly mean.

But when you combine mean temperature with rainfall that is 100 per cent average it becomes very rare and non-existent with 100 per cent sunshine hours considered.

Of the 2650 months since 1797 just one, February 1972, saw a mean temperature and rainfall precisely average. However, sunshine hours were just 40 per cent of the 1981-2010 average.

To extend the data I included monthly rainfall totals that were between 90 per cent and 110 per cent of average. Even then just five more months were revealed: September 1806, February 1876, January 1883, October 1886 and March 1972.

Although on paper February 1972 was perfectly average a look at the weather for the month reveals typically variable weather. The website London Weather explains:

The maximum temperature was only 3C on the 1st as mild Atlantic air slowly displaced the very cold continental air eastwards. There were outbreaks of rain, and during the remainder of the first week, although mild, it was often dull and wet. During the second week, active frontal systems crossed the country bringing strong winds but with sunshine between the rain bands. After mid month, east winds returned, and although not cold, it was frequently dull.

Considering the Met Office forecast the mean for this month, October 2018, is set to finish precisely average. However, rainfall looks set to finish well under the average for the time of year.

First frosts in East London since 1959

Although many parts of the UK have already recorded their first air frost this part of the capital, being so built up and close to the City, remains frost free.

Although many may think that frosts are getting later a look back through local statistics to 1959 shows these events are very random.

The scatter graph below illustrates this.

first frost in east london a

Taking out the winters of 1974/75 and 2002/03, which didn’t see frosts until February and January respectively, the scatter can be seen better here.

first frost in east london b

The median for the first frost is November 6th with an average minimum of -1.4C.

October frosts can be a precursor to a mild winter much in the same way that heavy October snowfall in the Alps has lead to an awful season. But there are exceptions, as happened in 2008/09.

* To record an air frost the temperature must fall to -0.1C or lower.

September 2018: average, dry and sunny

September was most notable for the amount of cold nights. The record minimum was matched together with three further new entries into the top ten list of extremes back to 1959 – a rare occurrence.

The mean temperature finished 15.2C, 0.2C below average, ending a run of 5 months where the mean has been, at times, well above average.

Some 32.6mm of rainfall was recorded, 63 per cent of the 1981-2010 average. Some 183 hours of sunshine were recorded, 132 per cent of average and more than August!

For the first time in years the autumnal equinox period was very stormy, as shown by this graph.

wind run

To view full stats follow this link:http://1drv.ms/1kiTuzv

Summary for September 2018 to follow…