Archives For weather summary

2016-04-23_10-19-23

Reigate weather summary statistics for March 2016:

  • Tmax 14.8C
  • Tmin -2.8C
  • Taverage 6.3C
  • Total rainfall 80mm (66.4 aws)
  • Max gust 51mph
  • Total sunshine 118.6 hours

March in Reigate started and finished unsettled with Storm Jake (no impact locally) on 2 March and Storm Katie (moderate impact, see previous post) on 27-28 March.  High pressure located to the north of the UK mid-month kept things more settled and mostly dry here.

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Here’s a time-lapse video from Reigate of showers and a defined cold front passing through associated with Storm Jake on 2 March.  Note the distinct drop in temperature as the cold front arrives (windows fog up) and then the change (veer) in wind direction as the front passes and skies clear.  Spot the wind shear too during the cold front passage.

March was sunnier than average for Reigate with 118.6 hours of sunshine.

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UK-wise the month was sunnier but wetter in the south, mostly due to heavy rain associated with a deep low on 9 March and Katie later in the month.

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deep LOW brought most of March rain to the South

March was also slightly below average temperature in the south.  The CET came out 0.1C above average for March at 5.8C.

Air pressure was lower across the south of Europe than the north during March, hence the drier conditions to the north.

The Atlantic cool blob sea surface temperature anomaly continued to develop during March and this may have had some influence on moderating temperatures regionally.

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Globally, March was the warmest ever recorded March by a considerable margin at over 1.29C above the long term average for the month.

 

Whilst Europe was about average temperature, there were notably extreme temperatures across the Tropics, in particular Indonesia, parts of India and Australia, as well as tropical North and South America and parts of Africa.

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This continues the trend of warming shown in the graph below. Note the correlation of anomalously warm years with El Nino events.

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The current record breaking 2015-16 El Nino is fading fast and is forecast to be replaced by cooler than average Pacific equatorial sea surface temperatures known as a La Nina by the autumn.  This might have implications for a more active Atlantic hurricane season.

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Met Office March summary

refs

http://www.metoffice.gov.uk/climate/uk/summaries/2016/march

 

2016-02-29_19-54-33

8-10 day mean upper air chart

The most wintry set-up of the “winter” has decided to arrive at the start of Spring! High pressure over the Pole is still keen to push out polar air into mid-latitudes as the meteorological Spring starts tomorrow.  The Arctic Oscillation shows this tendency as it has been dipping negative, showing relatively high pressure over the Pole and lower pressure in mid-latitudes. The belated rise in Polar pressure has been attributed to the stratospheric warming which occurred around a month ago.

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Unfortunately, for most of late winter the jetstream has remained strong enough to push a predominantly Atlantic flow into the UK and breach any blocks attempting to drag in sustained cold air. This is shown by the slight but persistently positive North Atlantic Oscillation below: this set-up spoilt any chance of proper cold this half of the winter.

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However, this week the wind is expected to turn more northerly as pressure lowers first over the North Sea and then the Channel / N France. By the weekend the UK will be in a cold Arctic flow courtesy of the same LOW lingering over Europe and a blocking Atlantic ridge. Between them and the jetstream they will do a good job of pulling down a cold Arctic flow this weekend. Spot the cold anomalies in the chart below. Lots of lying snow is not likely but some wintry precipitation is possible at times here, especially a marginal chance on Friday am.  Things change though, so check weather professionals like the MetOffice to make any weather related decisions.

Here is the story of how we get to some belated cold by this weekend.  Tuesday sees an end to the cool clear HIGH that brought Spring-like sunshine to Reigate and Tmax 9C.  A warm front will sweep in tomorrow morning and bring rain for most of the day for the SE.  It will be breezy, though relatively mild in the warm sector shown below, Tmax 10C.

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warm sector Tuesday

Things cool off into Wednesday as an active blustery cold front ushers in colder polar maritime air through the morning.  Any snow is restricted to the NW of the UK.

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The flow swings increasingly to the north west during the day with the possibility of showers later here, some quite heavy, maybe even with the outside chance of hail and thunder thrown in.  Tmax 6-7C.  Update: The video below shows how that showery trough passed through Reigate during Wednesday:

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Thursday is the crux to building a set-up capable of producing any snowfall at all for the SE.  A LOW is forecast to develop from a system off Greenland and cross the Atlantic smartly from the NW.2016-02-29_19-50-10

This low, with rapidly occluding warm sector, will deepen slightly and meet the cool pool sitting over the UK from Wednesday’s Polar attempt. The LOW is expected to arrive late Thursday and track south east overnight into Friday bringing in a cool NE flow capable of wintry precipitation for a while on Friday morning.

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The latest charts suggest the track into N France will result in NE winds which could bring snow for a time in the SE on Friday morning.

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meteoearth Friday ppt

It is all rather marginal for us in the SE and Reigate though. A rain / sleet event with a possible wintry mix at times is more likely and nothing much is expected to settle.

By Saturday and into the weekend a cold northerly / NE flow sets as the “Greenland” LOW settles over Europe. Wintry showers could develop across the SE, especially in any distrubances in the Arctic flow.  However, pressure is likely to be on the rise as the Atlantic ridge creeps in from the west under an increasingly anticyclonic jetstream.

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How long any early Spring cold lasts is not certain, the Atlantic ridge looks like toppling over to bring in warmer conditions later next week.

2015-11-21_14-40-20

Quick October weather summary for Reigate 2015.

Summary stats for October in Reigate, Surrey, England

  • T average 11.6C
  • Tmax 19.33 C
  • Tmin 3.2C
  • Rainfall total 61mm (CoCoRaHs)
  • Sunshine 95.3 hours
  • Max gust 24mph (24 Oct)

October CET temperature came out just above average at +0.4C. Significantly, globally, October 2015 was the warmest October ever on record for this month by a significant margin, probably due in part to a strong El Nino.  In fact every month of 2015 so far has been record-breakingly warm and each month has been the warmest recorded anomaly… since 1880.

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October global temperature anomaly 2015

Due to anomalously high pressure for much of the month, South East England rainfall was lower than average at some 76% of the long term average.  In Reigate this amounted to 61mm of rain.

Despite the high pressure sunshine amounts were average or slightly below in the south east with Reigate totting up 95.3 hours of sunshine in the month.

October is sometimes correlated with winter outcomes. Anomalously high pressure in October has sometimes been correlated with cold winter patterns, though this is highly experimental.  In addition, October Siberian snow cover expanded rapidly and beyond the 2014 cover for the same period.  This got winter forecasters further interested in the possibility of high pressure, northern blocking and the increased potential for a cold late winter in the UK.  However, seasonal forecasts have a habit of going awry, as was illustrated by the ill-fated “October Pattern Index” much heralded in the run-up to winter 2014 when it predicted a cold one. The OPI, as far as I can tell, has now disappeared off the seasonal forecasting scene completely.

http://www.metoffice.gov.uk/climate/uk/summaries/2015/october

2015-10-11_10-34-53

September 2015 Reigate weather summary

Reigate September summary weather statistics

Tmax 22.4C

Tmin 3.9C

Average temperature 13.3C

Total rain 79.8mm (CoCoRaHs)

Max gust 25mph (14 Sept)

Mean SLP 1016mb

Sunshine 132.9 hours

September in Reigate turned out to be cooler than average with rainfall amounting to around average totals mostly falling in showers so that there were relatively long dry sunny spells, especially towards the start of the month, with HIGH pressure in charge or nearby for much of the time.

It was sunnier than usual for September at over 130 hours. This was good news for Run Reigate which turned out to be a beautiful day for the runners.

Much of the September rainfall fell in heavy showers, especially in some storms mid-month.  This meant 2015 September rainfall at nearly 79.8mm turned out wetter than 2014, at a mere 22mm.  Despite this it was still just about equal to the long-term average rainfall according to MetOffice anomaly charts.

At a mean temperature of 13.4C September was slightly cooler than average and the CET came out at 1C below the long term average. Globally, September was 0.31C warmer than the long term average.

2015-09-05_22-11-17

Reigate August 2015

August Reigate Summary Statistics

  • Average temp 16.7C
  • Tmax 29.5C
  • Tmin 7.1C
  • Total rainfall 99mm
  • Sunshine 116.4 hours
  • Average pressure 1014mb
  • Max gust 29mph
  • average wind 16mph
  • dominant wind direction SOUTH

August in Reigate, like the rest of Southern and SE England, came out slightly cooler than average at nearly 17C with about twice as much rainfall than the long term average with a rainfall total of 100mm.  (Possibly* half of this fell in one deluge on 24 August when the town centre flooded quite notably from intense rain falling in a few hours (see post below)).

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South East England rainfall August 2015: 177% of long term average

Across SE England the MetOffice official records showed the rainfall total of 103mm was 177% of the August 1961-1990 long term average, so nearly double the usual total in some locations, especially near the south coast (100% being the average monthly total for August in this case). Don’t forget that August is often a wet month and that August 2014 had 84mm.  Nevertheless, if you think our Summers are getting cooler and wetter then, yes, you could well be right!  Read on to find out more.

The mean 500mb pressure pattern for August above shows a deep trough in the Atlantic, dug unusually far to the south for the time of year, and a continuation of the dominant high pressure over Europe from July, nudged further east maintaining the heat wave in Europe, especially Central Eastern Europe.  This looks like it should have promised a hot August for SE England with an average upper flow from the south and a surface mean flow from the SE. Unfortunately this pattern did not deliver any heat of note, but it did deliver occasional heavy showers and some thunderstorms, with notably torrential rain showers delivering big precipitation totals in a matter of hours.

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August 2015 heat stayed in Europe and away from UK

Despite the average southerly and SE flow bringing occasional thundery Spanish Plumes, the real heat stayed stubbornly on the continent and only fleetingly wafted temperatures exceeding 25C across the SE.  While France regularly baked in 30C+ daytime heat, Reigate and the SE could only struggle to Tmax temperatures of 25C and only once nudged 30C. Notably, the mean temperature was a tad below the 1981-2010 average but above the 1961-1990 average, showing how recent decades have been warmer.  So August was either above or below the long term average, depending on what LTA you choose. This is a small example of how weather statistics can be presented by the media to suit any argument regarding climate change.

The August monthly Central England Temperature (CET) came out at 0.1C above the long term average but this hides the cooler than average Tmax attained in a disappointing month.  This again illustrates how headline figures hide many subtle interpretations of weather statistics.  Overall, August was nearly average from the perspective of long term Central England Temperatures, with the East coming out slightly above average compared with a cooler West.  Maximum temperatures were widely lower than usual for August.

At 116.4 hours, sunshine was also only average or a tad below the 1961-1990 average.

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sunshine duration August 2015

The dominant wind direction this August was from the SOUTH (i.e. a southerly wind).  The highest rainfall totals experienced in Reigate are brought, on our 4 year “long term average”, by southerly winds.  This makes sense because mean southerly winds are from warm source regions, travelling across Biscay and the Channel, and are frequently associated with humid warm sectors that precede fronts where heavy thundery showers can occur.

Our more frequent prevailing Westerly / SW winds bring our familiar frontal rain but this often peters out before reaching the South East as most rain is dumped over the western hills of the UK.  In contrast, warm southerly winds containing more water vapour arrive laden with precipitable water (PWAT) ripe for torrential convective downpours across Southern and SE England. The Downs (both the North and especially the South Downs) can also have a marked orographic effect enhancing this southerly rainfall pattern, whereas they have little impact on frontal rain from the west.  This warm humid southerly set-up was responsible for the Reigate deluge on 24 August, also known as a Spanish Plume.

Finally, research shows that UK Summers have got cooler and considerably wetter since 2000.  Cooler by just 0.4C (this despite some warm years) but total summer precipitation has increased by some 50mm over the last 15 years and the 10 year moving rainfall average is on the rise, most likely due to torrential rainfall events. This change to rainfall being delivered in torrential but sporadic events is in-line with climate change predictions.

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Reigate summers have got cooler and wetter since 2000

Rainfall challenge! *Our local rainfall totals are proving mighty tricky to verify at the moment.  We use three sites for measuring rainfall locally: an automatic tipping bucket rain gauge at RGS, a manual CoCoRaHs rain gauge at the same site and a local sister site in town. Unfortunately they rarely agree and sometimes vary quite considerably. Also, the manual rain gauge is used to measure monthly totals because emptying it everyday (during the holidays for example) is not always possible. Calibration of the AWS and regular rain gauge measurements is therefore an immediate target. Meanwhile, all rainfall figures are available on request and posted in these summaries along with official MetOffice rainfall figures for the South East.

Refs

https://xmetman.wordpress.com/2015/09/04/summers/

http://www.metoffice.gov.uk/climate/uk/summaries

http://www.metoffice.gov.uk/climate/uk/summaries/2015/august

2015-07-09_11-50-48

June 2015 Reigate summary

June in Reigate, Surrey continued the Summer 2015 theme of mostly cool, dry and sunny but with an unsettled start and THREE attempts at continental heat from Spanish Plumes in one month. (please note that the chart above hugely exaggerates the rainfall.. check the rain scale in mm.  I have yet to fix down the scales month on month!). 

  • Average Temperature  15.7C
  • Tmax 30.6C (25.6)
  • Tmin 5.5C (6.2)
  • Total rainfall 15mm (30)
  • sunshine 192 hours (175)
  • max gust 28mph

(Figures in brackets are from June 2014)

The month started unsettled with a deep low pressure 976mb crossing Scotland from a very much cooler-than-usual North Atlantic bringing brisk winds for the time of year and comparatively cool temperatures.  Another Atlantic LOW crossed Scotland through the first week 991mb (see satpic).

A weak first attempt at a Spanish Plume 5-6 June developed ahead of an Atlantic cold front and gave some limited thundery activity early morning on 5 June, these cells went on to become more significant further north east over E Anglia.

Pressure rose thereafter as an anticyclone built firmly over the UK.   This HIGH eventually slipped north and a heat LOW from Iberia brought the threat of a second Spanish Plume around 12-13 June.  This misfired and caused little convective activity over Reigate at least.  This turned out to be a significant mis-fire for convective forecasters, despite some limited activity here and there the overall level of activity was low and certainly nothing occured over Reigate except very late in the day when some congestus puffed up.

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Spanish Plume mis-fired 12 June 2015

High pressure built again with weak fronts skirting across the SE bringing some pleasant mid-level and upper level cloud, nice sunrise and sunsets and some good atmospheric optical phenomenon at times.

Towards the end of June a third attempt at a Spanish Plume yielded more heat and more purposeful thundery activity that eventually spilled over into decent thunderstorms into the start of July.  This was a modified Spanish Plume and more details can be found on the post written up here and here.

The end of June 2015 heat spike produced some 30C+ temperatures and in Reigate 30.6C was recorded on 30 June.  Overall the month was sunny but a shade cooler than average according to the CET central england temperature record.

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The UK anomaly charts reflect the overall dry pattern with notably little rainfall for the month.  In Reigate the total rainfall measured was 15mm.

Although this June was not consistently hot tp push up the CET (central england temp), we did nevertheless have episodes of unusual heat, especially at the end of the month with the end of June / early July heat spike.  This heat wave was more severe and prolonged in Europe.  A “cause” of the Euro heat wave, with significant heat in Spain and Portugal, was an OMEGA BLOCK or “shruggie”  that built through June and lasted into early July.  This Omega Block pattern may also be linked to rapid melting of the Greenland icecap that has been recently reported as heat builds there under high surface pressure.

A weather pattern that resembles an atmospheric version of the shruggie — ¯\_(ツ)_/¯ — is directing furnace-like heat toward Spain, France and England on Wednesday, with high temperatures near 40 degrees Celsius, or 104 degrees Fahrenheit, as far north as Paris.

The heat wave is also affecting southern parts of England, with temperatures in the upper 30s Celsius, or mid-to-high 90s Fahrenheit. Those temperatures on Wednesday were the warmest recorded in the UK in at least nine years, according to the UK Met Office.

Andrew Freeman, Mashable 1 July 2015

heat wave / mini!

heat wave / mini! south east England Surrey

http://www.metoffice.gov.uk/climate/uk/summaries

http://www.climatecentral.org/news/maps-greenlands-melt-season-19196

http://mashable.com/2015/07/01/england-france-spain-heat-wave/

2015-05-11_10-22-47

April 2015 Reigate weather chart

April in Reigate was a mostly dry, very sunny, rather calm and relatively warm month.  However, the settled weather came at a price with a significant air pollution event on 10 April. Also, April showers were conspicuous by their almost complete absence so convective weather fans were left disappointed.

Here are some April details for Reigate:

  • Tmax 14.4C
  • Tmin -1.9C
  • Average Temperature 6.8C
  • Total rainfall 23mm
  • Max gust 46mph
  • sunshine total 136 hours (sunniest April on MetOffice records!)

April was 43% drier than average across SE England and this shows up in the diminutive 23mm of rain in Reigate.  Pressure rose early in the month and so April turned out 150% sunnier and about 1C warmer than average too. The central England temperature for April came out at 1.1C above long term average.

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It was the SUNNIEST April on record for the UK according to the MetOffice.  In Reigate we enjoyed 136 hours of sunshine in April.

sunny April 2015

sunny April 2015

The significant downside of this calm weather was high AIR POLLUTION. There was a high pollution warning for a time when easterly / south easterly winds brought high levels of PM2 particles into the SE and across London from Benelux countries.

Here are some photos from Reigate during April showing what a mostly very pleasant month it was.

http://www.metoffice.gov.uk/climate/uk/summaries/2015/april