The Met Office’s outlook for UK winter 2013-14

21 02 2014

There are some headlines in the media today discussing the Met Office long range forecast for this winter.

Firstly it’s important to remember that it’s our short and medium term forecasts that are relied on by emergency responders to help them manage the impacts of severe weather.

The Met Office’s five-day forecasts and severe weather warnings have provided excellent guidance throughout the period of exceptionally stormy and wet weather we have experienced this winter. This advice has helped everyone from the emergency services, to government organisations and the public plan ahead for the conditions we’ve seen.

The news stories are based on information taken from our three month outlook for contingency planners, issued at the end of November 2013 so, what can our three month outlooks tell us?

These outlooks are not like our other forecasts because, as we have discussed previously, it’s not currently scientifically possible to provide a detailed forecast over these long timescales.

Instead, the outlook assesses the level of risk connected to five different scenarios for both temperature and rain/snowfall for the UK as a whole; they do not mention specific areas such as the West Country or the Somerset Levels. It’s a bit like the science-equivalent of factoring the odds on a horse race.

However, as with any horse race, it’s always possible that the favourite won’t win – so these probability scenarios have to be used in the right context. This is why they’re useful for contingency planners who plan ahead based on risk, but not that useful for the general public.





Winter so far – 20th February rainfall update

20 02 2014

The latest rainfall update from the Met Office National Climate Information Centre shows that this has been the UK’s wettest winter on record in the national series going back to 1910.

These provisional rainfall statistics for the winter so far (from 1 December 2013 to 19 February 2014) show new records for the UK, Wales, east Scotland, southwest England & south Wales alongside the record already set for southeast & central southern England.

Rainfall precentage of average 1 Dec 2013 - 19 Feb 2014

Rainfall precentage of average 1 Dec 2013 – 19 Feb 2014

With just over a week to go until the end of the season:

  • The UK has now received 486.8mm of rain, narrowly above the previous record of 485.1mm set in 1995.
  • Wales has seen 691.8mm of rain, beating the previous record of 684.1mm in 1995.
  • East Scotland has seen 514.5mm of rain, beating the previous record of 482.2mm in 1915.
  • Southwest England and south Wales has seen 632.5mm of rain beating the previous record of 610.7mm in 1990.
  • Southeast and central southern England has seen 492mm beating the previous record of 437.1mm set in 1915.

All countries and areas are also on target for a warmer than average winter.

Current record wettest winters:

Country Year Rainfall Winter 2014 to date*
UK 2014 486.8mm New record
ENGLAND 1915 392.7mm 370.4mm
WALES 2014 691.8mm New record
SCOTLAND 1995 649.5mm 634.3mm
NORTHERN IRELAND 1994 489.7mm 434.5mm

*These are provisional figures from 1 December 2013 to 19 February 2014 and could change after final quality control checks on data.





Met Office rainfall records – how far do they go back and what can they tell us?

14 02 2014

As we have seen over recent weeks and months, observations for the UK are essential to put recent weather into context and to detect variations and possible long-term trends in UK climate. So, when the Met Office quotes “the wettest on record” what does that mean?

Station records
All our time-series of rainfall come from observations made by rain gauges and their length is determined by how long the recording stations have been open.

Stations with long records are a very important part of the UK’s weather station network. These time series provide an accurate picture of rainfall for that particular location, provided there are no significant changes in instrument type or station exposure. One of the longest in the UK is the weather station at Oxford Radcliffe Observatory, which holds nearly 250 years of rainfall observations from 1767 to the present day and is maintained by Oxford University School of Geography and the Environment.

This will give an accurate picture of rainfall for the city and will be broadly representative of the year-to-year variations of rainfall across Oxfordshire or even central England, but it won’t be useful when looking more widely across England and Wales or the UK.

Regional records
So, to accurately make comparisons across regions and countries we need to create a different time-series.

One way of doing this is to calculate the average of different weather stations across an area – for example England and Wales. The England and Wales Precipitation series (EWP) is such a series of monthly rainfall totals from 1766 to the present day. For the most recent decades, the EWP series is based on over 100 stations, although this number decreases as you go back through the 20th, 19th and 18th Centuries.

The EWP series is much more reliable than a single station at representing rainfall for England and Wales overall and, because it extends back to 1766, it is very important climate series.

However, it does not cover the whole of the UK or take full advantage of the complete network of several thousand stations currently recording rainfall across the country.

National records
Met Office national records are created using gridded datasets which interpolate observations from the full network of stations onto a 5km by 5km grid covering the UK. The gridding method is a more sophisticated approach for analysing rainfall than simply taking an average of station data. However, because it is a digital series it is shorter than the EWP – the number of rain gauges with data in our electronic archive decreases rapidly by the early 20th Century.

So, the UK’s national climate series – the records you will see quoted when the Met Office releases statistics – is a comprehensive gridded rainfall analyses back to 1910. This series provides the best estimate of overall rainfall and its distribution across the UK.

The gridded rainfall analysis also enables us to produce maps showing UK rainfall patterns, for example January 2014:

Rainfall anomaly January 2014

Rainfall anomaly January 2014

How do the series compare?
Here are the headlines for January 2014:

  • For the England & Wales areal series, January 2014 (173.5mm) was the wettest January since 1948 (176.8mm) and the second wettest January in the series from 1910
  • For the EWP series, January 2014 (185.0mm) was the wettest January in the series from 1766, marginally wetter than 1948 (176.8mm)
  • For Oxford, January 2014 (146.9mm) was the wettest January in the series from 1767, wetter than 1852 (138.7mm)

You can see from the graph below that the EWP and the national England & Wales series both represent the same area and are very similar. Rainfall totals for the Oxford Radcliffe Observatory series are generally lower.

For any individual year there can be significant differences between series. For example we would probably conclude that January 1988 was climatologically more extreme for England and Wales than for Oxford, similarly 1997 is the driest January for England and Wales by a reasonable margin, but there are a number of similarly dry or drier Januarys than 1997 for Oxford.

January rainfall comparison

January rainfall comparison

So which is the best series to use?
Well, the answer is that we need to use them all. The Met Office routinely quotes rainfall statistics based on the gridded data, because these are considered the most reliable estimates, are based on the full network of observations, and can provide the regional pattern of rainfall.

The EWP series is an invaluable climate series because it provides a much longer near 250-year perspective but has less regional detail.

However, our climate analyses would not be possible without the long running high quality individual station series such as Oxford. These are the foundations of historical climate analysis.





How wet has 2012 been? Is it a record breaker?

27 12 2012

Provisional figures from the Met Office from 1 January to 26 December 2012 show that some parts of the UK have already had their wettest year on record.

New records have been set in England (1095.8 mm), northern England (1253 mm), E and NE England (1042.1 mm), Midlands (1048.2 mm), and East Anglia (788 mm), in a series that goes back to 1910.

A further 46 mm of rain is needed from 27 to 31 December for this to be the wettest year on record for the UK overall – the UK has had 1291.2 mm of rain from 1 January to 26 December. The wettest year on record for the UK is 2000 with 1337.3 mm.

2012 rainfall anomaly 1 Jan to 26 Dec

2012 rainfall anomaly 1 Jan to 26 Dec

In terms of temperature and sunshine the year as a whole is set to be unremarkable, both being around normal. However, overall 2012 is set to be cooler than 2011, but warmer than 2010.

  mean temperature sunshine duration precipitation
1 January to 26 December 2012 Actual Difference from 1981-2010 average Actual Percentage of 1981-2010 average Actual Percentage of 1981-2010 average
  degC degC hours % mm %
UK 8.7 -0.1 1354.1 99 1291.2 112
England 9.5 -0.1 1467.1 98 1095.8 128
Wales 9.1 -0.1 1354.0 97 1649.5 113
Scotland 7.3 -0.1 1186.8 100 1546.3 98
N Ireland 8.9 0.0 1234.0 98 1134.8 100
England & Wales 9.5 -0.1 1451.5 98 1172.2 125
England N 8.7 -0.1 1357.0 99 1253.0 129
England S 9.9 -0.1 1525.4 98 1012.6 128

More about the record breaking year of 2012





Sunny March, wet April – how the jet stream is (partly) to blame

26 04 2012

UPDATE: We’ve written a further post explaining a little more behind the continuing dissapointing weather that we have seen through the summer so far.  You can read this at ‘The UK’s wet summer, the jet stream and climate change*

After an unusually dry, sunny and warm March, April has seen some very wet and unsettled weather with below average temperatures. So what has caused this about-turn in the UK’s weather? There are many factors which can impact the notoriously changeable weather in the UK, so no single one on its own can be said to be fully responsible. However, it is possible to isolate contributing factors and, in this case, one of those is the northern hemisphere jet stream. This is a narrow band of fast flowing westerly winds (ie blowing from west to east) in the high atmosphere. This band moves around and also changes its track, from a fairly straight line to something more closely resembling a meandering river. Its position can, and does impact weather in the UK and other parts of the northern hemisphere. In both March and April we have seen what we term a ‘blocking pattern’ in the jet stream, where it meanders north and south instead of making its more usual eastward progress. Despite this, March was the 3rd warmest and 5th driest March in the all-UK record going back to 1910, while April has so far been relatively cool with rainfall already 30% above the average for the whole month across England and Wales. So what is causing the difference? It comes down to the position of the blocking feature. In March, the meandering of the jet stream caused it to pass to the north of the UK – anchoring high surface pressure over the UK. This suppressed cloud, increased sunshine and temperatures, and prevented the usual rain-bearing Atlantic weather systems coming in from the west from reaching us. Soon after the start of April, however, the whole pattern moved westwards, so the peak of the northerly meander moved over the North Atlantic Ocean. The UK, in contrast, found itself under the adjacent southerly meander, with the jet stream passing to the south of the UK over France and Spain. This atmospheric set-up brings low surface pressure, cloud and rain. Because the pattern is still blocked, without a west-to-east jet stream to blow the weather system through, the low gets stuck over the UK, resulting in high rainfall totals overall. Like the weather, we can predict the path of the jet stream with a good deal of accuracy up to about five days ahead but it is more difficult to give detail on longer timescales. Therefore it’s not possible to say exactly what the jet stream will be doing in a month’s time, for example, or exactly how it will impact our weather. You can find out more about the jet stream in our YouTube video. http://www.youtube.com/watch?v=GpsRQtk6IfM

 








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