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October 31, 2014

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Reigate Grammar School, UK. Local weather observation and education. SkyWarnUK storm spotting. RiverSearch monitor River Mole. RMetS education committee. Use professional websites  for decision making purposes. Town VP2 updates website every 10mins, wind every 5secs. CoCoRaHS rain gauge. Data to Met Office + Weather Underground.

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The MetOffice charts above show the formation and life-cycle of a December 2014 “weather bomb”, involving the process more properly called rapid cyclogenesis. There are reasons why meteorologists dislike the term “weather bomb” but perhaps the most obvious is that the sensationalist short-hand use of the term “bomb” detracts from the complex processes and variable scale and location of impacts.  The term “bomb” tends to hype stories in the press that can cause over-reaction and unnecessary concern. On the other hand it gets people reading about the weather, which is a good thing (like this post, ahem!).

Nevertheless, a “weather bomb”, a term borrowed from the US and New Zealand, is short-hand for a potentially extreme event.  Bomb depressions are deep low pressure systems that form by the process of Rapid Cyclogenesis (RaCy for short).  RaCy is the rapid formation of a deep depression when the central pressure falls more than 24mb in 24 hours.  Such RaCy depressions are usually of marine origin. About 12 such RaCy bomb depressions hit the UK in the exceptionally stormy winter last year 2013.  Although by no means the most powerful, the first and most famous RaCy depression of last winter was the St Jude storm that hit Southern England with moderate force in October 2013.  Pictures below are from that event and can be compared to the enormous scale of the more recent Atlantic bomb depression of December 2014.

The “bomb” depression that struck this December 2014 seemed to catch media attention, despite the impressive weather impacts being almost wholly restricted to the less populated NW, especially Scotland, where people are entirely used to coping with such lively weather.

http://www.stornowaygazette.co.uk/news/local-headlines/weather-bomb-cuts-off-power-to-18k-homes-1-3630321

December 2014 rapid cyclogenesis: the weather story

The December 2014 “weather bomb” was a depression (low pressure system) which formed rapidly far out west in the Atlantic between SE Greenland and Iceland.  The formation was associated with a fast moving jetstream and the surface convergence of sub-tropical air from the south west meeting a frigid NW polar airstream from Canada and more local air direct from the Greenland ice cap.  The big temperature differences between these air masses accelerated uplift and the lowering of central pressure.

impressive but not the day after tomorrow

impressive but not the day after tomorrow

Descending dry stratospheric air is another defining feature of RaCy systems.  Cold dry air from aloft turbo-charges the depression as it is injected into the depression.  The cold air aloft increases lapse rates in the surface airmass and causes air to rise more purposefully creating a dramatic fall in central pressure.  Descending cold dry stratospheric air can be spotted on the water vapour satellite images as a dark dry slot ingressing into the depression circulation over time and following hard on the heels of the cold front as it is blasted across the Atlantic.  The water vapour images below show the rapid development of the system during Tuesday 8 December.  In later images it is possible to see the speckly cumulonimbus clouds emerging in the unstable cold sector following the cold front. Such instability was caused by the descending dry air.

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Rather than going through the rather measured development stages of a Norwegian Model cyclone, a RaCy depression usually follows a life cycle more like the Shapiro-Keyser model below (though at the time of writing I am not certain as to whether the December 2014 RaCy depression formally fitted all aspects of this model).  Several key characteristics of the December 8 cyclone fit the S-K model fit and this is the usual model associated with RaCy depressions.

2014-12-08_22-28-06

The Shapiro-Keyser depression life-cycle model often features a cold front that is blasted rapidly ahead.   so rapidly that it “fractures” from the wrapping warm front further north. This is known as a T-bone fracture and experts can identify the moment of fracture using satellite photos. Additionally, cf course, upper air moves faster than the surface wind that suffers frictional drag even across relatively smooth ocean.

satellite features of emerging RaCY depression

satellite features of emerging RaCY depression

This meant that the cold front moved so rapidly that it split vertically into a fast moving upper front and a slower moving surface cold front. The cold front literally had its head ripped off!  The frigid upper cold air travelled over a shallow moist zone of warmer sub-tropical air and it is this that increased lapse rates and caused immense instability in the polar air stream that eventually arrived in Scotland.  Instability can be seen on the visible satellite pics as speckly masses of cumulonimbus clouds shown best in the satpic above.  In the charts and sat pics below note the wind speed associated with this polar air and the tropical air preceding it in the warm sector.

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In the S-K model the cold front is sometimes weakened during the formation process while the warm front remains active, wrapping itself in knots around the central “eye” of the storm.  The 850mb chart below shows temperatures of this cold upper air at 1500m above Scotland. The bomb depression this December seems to have matched this because, while the cold front was relatively weak (narrow squall line) the exceptionally unstable polar air behind it was arguably the defining characteristic of this system, bringing persistent convective storms and an outstanding 5000 lightning strikes and thunder-snow blizzards across higher ground in Scotland during the advection of this exceptionally cold and unstable air for an Atlantic NW airstream.

In the S-K model depression life-cycle the warm sub-tropical air is eventually left “sequestered” as a warm pool trapped in the middle of the mature depression which is called a “warm seclusion”.  The usual process of occlusion is bypassed as the centre of the low fills with warm air.  Meanwhile, the rapidly overshooting upper cold front causes S-K cyclones to often elongate in appearance on surface pressure charts, a feature associated with the rapid forward acceleration of the cold front in relation to the tightly wrapped, almost stationary, wrapped warm front. It is this tightly wrapped warm front (sometimes shown as occluded on weather charts) that shows another defining feature of S-K depressions.

As our initial bomb LOW pressure moved due east and filled and decayed offshore near Norway, a wave depression further south on the Polar Front also “bombed-out” to the SW of the UK and swept across Southern England on Thursday-Friday 11-12 Dec.

This was a separate small scale system but technically another rapid cyclogenesis as central pressure fell more than 24mb in 24 hours, but only just.  This illustrates the varying scale of bomb cyclones: some cover vast areas, some a small.  The 11-12 Dec RaCy depression was much smaller in size and intensity, max wind speeds were much more restricted and the whole system several magnitudes smaller in scale than the “mother” cyclone further north. Charts below show the evolution of this storm.

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Finally, the North Atlantic Oscialltion is a measure used to describe and forecast the mean pressure pattern over the Atlantic. A positive NAO indicates “normal” conditions with low pressure over iceland and high over the Azores. This is associated with a zonal west to east flowing jetstream and fast moving cyclones moving rapidly west to east bringing generally mild conditions to the UK in winter. Note the recent positive pattern matching the westerly flow and active zonal jetstream causing the RaCy depressions.  When the NAO turns negative the jetstream is often more wiggly and flows between latitudes in a more meridional flow potentially bringing cold air from the north when pressure patterns are more slow moving and even “blocked”.  A negative pattern is often associated with cold winter weather for the UK. The NAO is not a driver of weather, merely an indicator of pressure patterns.

2014-12-14_17-18-18

 

For a bit of fun we invented our own local Wight-Wash Oscillation (WWO) which is a measure of pressure across the south of England between The Wash and the Isle of Wight.  This would give an approximately similar local version of the NAO but just for fun!  We noted a WWO difference in pressure of 10mb during St Jude and only 9mb during the recent bomb wave depression.  The WWO particularly suits the passage of wave depressions across the Midlands which tend to yield the highest wind speeds for the SE.  It would also work in negative conditions which would give cold easterly winds in winter. Note this measure is just for fun!

Positive NAO remains likely on the run-up to Christmas 2014 so chances of a White Christmas is much reduced. Remember that a White Christmas for us in SE England is the rare exception to the rule.  On a brighter note, the earliest sunset has just passed and we can at least look forward to later sunsets from now on!

2014-12-11_22-45-11

2014-12-04_22-21-24

November 2014 in Reigate weather summary

Average temp 8.9C

Tmax 17.2C

Tmin  -0.5C

Total precipitation 135mm

Max gust 29mph (av wind speed 16mph)

Sunshine 87.5 hours

November weather in Reigate and the SE was rather dull and uneventful in Reigate but the meteorology going on more widely was fantastically interesting!

November was considerably warmer than average.  In the UK November turned out a whopping 2C warmer than the long term CET record.  In addition some areas in the south recorded 200% more rainfall than average.

Our anomalously warm and wet November was due to our weather being dominated by warm moist southerly winds as a trough sat in the Atlantic and a fairly strong blocking high dominated Russia and occasionally Scandinavia.  The northern hemisphere flow encouraged blocking further east and a trough to the west of the UK.

2014-11-12_19-27-35

The blocking high pushed LOW pressure in the Med that fed warm moist winds up to the UK (warm air advection).  Occasional Atlantic fronts caused heavy rain when cooler air on cold fronts advected in from the west to meet this moist flow.  Heavy November rain in the south was caused by this process.  Nevertheless, the usual scaremongering forecasts in the press failed to materialise.

A split jetstream assisted the warm moist feed across much of Europe and led to torrential rain and flooding along south facing coasts in Italy and S France.  To a lesser extent this also occurred in the UK with highest rainfall anomalies found in the south and SE.

Globally November was one of the warmest on record too.  However, the US and Canada recorded one of the earliest coldest and snowiest Novembers on record. The upper air patterns plunged cold Arctic air into North America and, when this frigid polar air crossed the warm Great Lakes, it produced tremendous falls of Lake Effect snow over northern New York State, especially around Buffalo.

Autumn for the UK as a whole was the third warmest in the record going back to 1910.  Autumnal rainfall was just a tad below average because September was a very dry month.  October and November were well above average for rainfall.  The SE came out average or just above average for rain for the whole of the Autumn.

http://www.metoffice.gov.uk/climate/uk/summaries/2014/autumn

Globally November’s warmth and climate extremes caused the climate change debate to reignite.  The graphs below speak for themselves.  Our November was dominated by our first HIGH ALTITUDE BALLOON launch. The experience of launching our first exploration into near space brought it home to us how thin our atmosphere is, how quickly it is to escape from and thus how fragile it is.  We live perilously close to utterly hostile environments… the views of Earth brought back from our stratospheric balloon were both sensational but somehow frightening in the context of rapid climate change on the only earth we have.

 

2014-11-28_07-39-39

A dedicated team of students from Reigate Grammar School weather station successfully launched a high altitude balloon (HAB) and retrieved the payload on Tuesday 25 November 2014.   After months of meticulous planning and with close cooperation and assistance from the scientists at the Met Office, Met Research Unit, Cardington Boundary Layer Research Facility and in collaboration with Chris Hillcox Near Space Photography, our students launched the 800g balloon and then used GPS trackers to chase and locate the payload as it fell to earth after an extraordinary 3.5 hour flight collecting some of the best amateur high altitude balloon photos of near space.  The students and staff were delighted by the success of their mission which took careful planning and preparation to reduce the risk of failure, which always remained a possibility.  The balloon took 2 hours to ascend 100,000 feet (30km) into the stratosphere, through temperatures as low as -70C in the tropopause, before the balloon burst at pressures 100x lower than at the surface.  The descent took over an hour.  Videos of the story can be found below.  See below also for “Why did we do this?”

Planning

Students spent weeks prior to the launch designing and building a lightweight box (150g) that would carry the payload safely to an incredible altitude up to 30km into the atmosphere.  The payload consisted of several HD cameras, spot GPS trackers and a GSM locator with meteorology sensors which were weighed to ensure the balloon would be able to lift them to the target burst height at 30km (100,000 feet) with 3.5m cu of helium.  All equipment was thoroughly tested (several times).  GPS trackers were tested to ensure phones would pick up the track reliably.  A laptop was enabled to operate on a mobile connection.  GoPro cameras were tested and checked, as were HTC cameras.  A school logo was laser cut onto a small plastic arm that would sit in front of one of the cameras during the ascent.  CAA approval was applied for and received.  Scientists at the Met Office research unit were also closely consulted regarding gas type (99.5% helium, not party grade!) and the practicalities of the launch location such as trees and masts.  Risk-benefit assessments based on MetOffice launch assessments were completed and approved. Various risks needed to be considered beyond allergies to latex and the dangers of helium inhalation,  particularly regarding student involvement in retrieval that might require travel across land that lacked nearby public access.  We checked and adjusted school insurance to ensure full coverage for the flight.  However, in the end, it was the good will and enthusiasm shown by the individuals involved with the student launch that drew the threads together and allowed us to proceed with this unique educational challenge.  Acknowledgements are listed below.

Predicting the right weather 

To avoid the balloon payload shooting off across the North Sea we had to choose a day when the jetstream and higher altitude winds in the stratosphere were relatively slack.  Winds in different directions with height would also be useful to ensure the balloon did not travel too far for retrieval purposes.   A single date could therefore not be fixed in advance due to changing autumnal weather conditions.  Parents of students were sent an open letter with details regarding the potential for this expedition and ways we would contact them to ensure students were available as any possible launch date approached.  The weather at all altitudes was studied carefully and a potential launch date emerged for Tuesday 25 November as a weak high pressure pushed the jetstream and high altitude winds further north.  A suitably safe landing site was also critical to mission success and the HABHUB website landing predictor was regularly consulted in the run up to the launch.  Conditions improved throughout the period until Tuesday looked the most ideal.  We were GO FOR LAUNCH!

 The launch

The launch day started early as the team had to travel well beyond the flight paths of Gatwick and Heathrow.  Our launch site was in Bedfordshire with a predicted landing site NE of Cambridge.

Amanda Kerr-Munslow, a Met Office Boundary Layer Research Scientist, gave the group a very interesting tour of the site, including lasers that measured cloud height.  Dave Bamber the Met office facilities manager then helped students inflate the balloon.  The payload box had last minute modifications completed and was then prepared and carried to the launch bed.  The balloon was carefully transferred, inflated, to attach to the payload at the launch site.  Cables checked, final preparation and then the countdown!  The pictures below show some screenshots captured by the movie cameras on the ascent to 100,000 feet.

(please refresh the page if video is from another playlist)

Payload retrieval

The chase and retrieval were very exciting!  Despite predictive forecasts showing a broadly good landing area (open farmland, flat, few forests, rural, few pylons etc) it was not certain that it would avoid landing in problem locations like hedges or trees, pylons, main roads, rivers, ditches, inaccessible fields remote from a road or someone’s roof!  It was an exciting moment for the team when the tracks stopped at Wicken Fen in Cambridgeshire and the maps appeared to show a landing site in an open field which appeared to be accessible from the road.  Reflective vests on and trackers in hand we rushed off to search and found the payload with the shredded remains of the burst parachute precisely on target.   A wonderfully memorable moment after an exciting and highly rewarding adventurous day for everyone involved.

Why did we do this?

It has been a long-term aim of the RGS weather station to launch a HAB.  Reasons are myriad but the experience of this has been a high quality challenging learning and teamwork experience for students and staff. Practical skills, meteorology and an understanding of the atmosphere were all critical for students to grasp to increase the chances of a successful launch and, importantly, retrieval.  The students more than rose to the challenge!  At RGS the sky is not the limit!

A driving force behind this enterprise has been to raise climate and weather awareness amongst students and more widely.  The images and story brought back beautifully illustrate the fragile atmosphere in which we all live and upon which the human race depends.  From our balloon view the atmosphere was shown as a thin blue veil of gases held precariously against the surface with the blackness of space directly above and not far away.  It is of course widely accepted that humans are forcing climate change which might potentially threaten our existence because we have altered the workings of the delicate atmospheric envelope.  The site and sound of planes cruising far below our balloon demonstrated how we might dominate a tiny hospitable part of the planet but that we reside perilously close to utterly hostile environments.  In this respect it is no surprise that we have probably damaged this delicate life-protecting atmosphere with our activities.  We would like anyone using our pictures to ensure that climate change is explicitly mentioned and that our balloon launch post is linked to any material used.

What next?

This project has proved that the stratosphere is closer than ever and increasingly accessible. School exploration of the stratosphere is now within the budget of schools or groups of schools that can collaborate (rather timely considering recent political announcements).  Currently it costs around £200 to launch a payload to 30km, to launch a further 30km above that would cost £200 million (Antares rocket cost)!  The exploration and science that schools can do at 30km is breathtaking! Floating balloons are also possible for longer experiments.  The IPCC consider that our climate is on the cusp of irretrievable change that will have great impacts in the next 100 years.  It is therefore of the utmost importance that schools engage their students with weather and climate and that exam syllabuses include meteorology and climate across a variety of disciplines.

costing the earth: different missions

This video of the flight has been edited from 6 hours of footage from 3 cameras pointing in different directions (GoPro Hero3, 2 HTCs) over the course of the 3.5 hour flight.  It also includes screenshots and photos showing the story of how students put their payload into near space.

(please refresh the page if video is from another playlist)

11 video questions for classes: (ask “why” / “how” for extension)

  1. Why is the flight path not straight?
  2. At what height do clouds stop?
  3. It rains ice particles from blue sky at some points in the flight.  Why might this happen?
  4. Does all rain that falls out of a cloud reach the ground?
  5. Are any clouds man-made?
  6. Listen to the wind and noise picked up by on-board camera mics during the flight: how does it change?
  7. How does the colour of the sky change with altitude?
  8. How “near space” actually is 100,000 feet (30km)?
  9. Which was the coldest part of the ascent?
  10. As the balloon burst there was a puff of “smoke”, what was this?
  11. Shreds of burst balloon were seemingly left hanging above the descending payload.  What do you think happened to these?

RGS launch team:

  • Piers Rex-Murray
  • Tom Tatham
  • Jasmine Hull
  • Louis Chambers
  • Edgar Povey
  • George Beglan
  • Harry Persand
  • Chris Meredith
  • Fraser Cadman
  • Matt Taylor

RGS staff:

  • Simon Collins
  • Peter Klein
  • Vanessa Ramsden

Acknowledgements and sincere thanks to the following:

Huge sincere thanks to the following for helping us to get our HAB project off the ground.

  • Near Space Photography : Chris Hillcox Chris was incredibly helpful in giving students ownership of their launch in all stages whilst offering any amount of technical know-how we needed to increase chances of success. Chris gave his time extremely generously throughout the enterprise and his expertise was pivotal in the success of the mission.  Many thanks Chris!
  • Royal Meteorology Society RMetS : especially Sylvia Knight who encouraged us to pursue the project and put us in touch with Amanda. Thank you Sylvia!
  • Met Office, Met Research Unit, Cardington : Boundary Layer Research FacilityDavid Bamber and Amanda Kerr-Munslow were on the launch site at Cardington.  Amanda gave us a thorough tour of the scientific research unit and assisted with all practical aspects of getting it organised at Cardington.  David was a hero for staying up all night on an IOP and then staying on to manage students in inflating the balloon.  Many thanks Amanda and David.
  • RGS DT department: thanks to DT department for their workshop space and the free use of their tools and being so patient when we left polystyrene all over the place.  Thanks to Martin especially for helping us with the lazer logo cutting.

Interested in a HAB launch or weather stations for schools?  Contact RGSweather!

short video version

news:

http://www.surreymirror.co.uk/Reigate-school-sends-weather-balloon-near-space/story-25116859-detail/story.html?ito=email_newsletter_surreymirror

October 2014 rain and temperature

October 2014 rain and temperature

sunshine hours October 2014

sunshine hours October 2014

Reigate weather summary for October 2014

Tmax 22.6C

Tmin 2.4C

Taverage 13.1C

Total rainfall 112.3mm (CoCoRahs)

Despite memories of big storms like St Jude last year, October 2014 has turned out more than twice as wet with 112.3mm.  For the UK as a whole October 2014 was a warm month and broke records with the warmest “Halloween” on record.  At an average of 13.1C it was warm in Reigate as well, but oddly did not exceed the 2013 average of 14C. So 2014 was wetter but not quite as warm in Reigate as last year.  It was a quieter month with lower wind speeds and less widespread stormy conditions and it looks like Autumn 2014 will continue in this mild wet style but without the threat of big trains of countless Atlantic storms like last year.  Blocking HIGHS over Russia / Scandinavia and to the North look set to slow down the train of Atlantic weather and send it south into the Mediterranean where wet and stormy conditions have already been experienced (“Medicane” Mediterranean hurricane November Malta 2014)

In the UK as a whole October 2014 was the equal-tenth warmest October for the UK in a series since 1910 according to Central England temperatures (CET).  Globally, unconfirmed data suggests that October might be the warmest on record.

In Reigate much of the heaviest rain came in the first half of October in big convective downpours that were hit and miss.  Some tornadoes were reported across the UK and these were quite damaging in places further North.  We have yet to record a tornado in Reigate.  Tornados are extremely tricky to forecast but several agencies try it.. usually the MetOffice do not mention tornadoes in their forecasts because they are so hit and miss, even when potential is there.  Estofex, UKWW and SkywarnUK are agencies that have an eye on tornadic and severe weather conditions in the UK that RGSweather follows carefully.

MetOffice winter prediction 2014-15 as follows: It states “For November-December-January above-average UK-mean temperatures are more likely than below-average” and “Latest predictions for UK-mean precipitation favour near- or above-average rainfall for November-December-January”.  In contrast, other weather agencies and some seasonal model predictions are suggesting the possibility of a colder winter as various early indicators seem to suggest the possibility of incursions of cold air at times.  In particular, early October extensive Siberian snow cover, cooler than average temps over Siberia and a negative OPI index leading to an amplified jetstream (which seems to be occuring now) seem to suggest the possibility cold blasts at times this winter.  In addition, an Easterly phase of the Quasi-Biennial Oscillation (QBO) in the stratosphere favours a weaker flow of upper westerly winds that shut out cold air for the UK and W Europe.  An easterly QBO phase favours colder winters for us, but not always.  Whilst a strong El Nino has not transpired, there are indications that sea surface temperatures in the Pacific (especially central Pacific) are rising, albeit modestly: El Nino tends to link with cooler Euro winters.  These immediate measurable indicators correlating more or less with cold UK winters are interesting but not necessarily enough on their own to drive the atmopshere toward cold conditions.  They might, however, couple with other connections in the Stratosphere to cause stratospheric warming which, some weeks after, can cause downwelling of cold air into the troposphere and further disruption of the westerly flowing jetstream.  This is especially the case if warming is sudden (SST).  IF this all happens and IF surface pressure patterns play ball then the UK could see some cold snowy conditions! Charts below show some of these connections:

The end of October has continued to be warmer than average for the season and Friday 31 October could be the warmest Halloween on record (current record around 19C). Hi Res models show the highest temps most likely somewhere inland away from cooler seas and an incoming cold front from the west.  If the sun comes out, which is most likely in the SE or East Anglia and under such a dry southerly air flow, temperatures could rise to over 20C, or even 23C in places.  Whilst this unseasonably freaky warmth cannot really be described as a heatwave (there are technical requirements to classify as a heatwave) the headlines might be correct in suggesting a possible record breaking temperature maximum on Friday.

slide into normal

slide into normal

Thereafter, November temps take a tumble nearer seasonal average through next week and at times even below average. So whilst we can enjoy the treat of near summer like temps tomorrow by next week it will be some 10C cooler as Autumnal temperatures and more rain take a hold, though nothing extraordinary.  Compare this with the first winter storm warning of the year on the East Coast USA where temps are set to freeze and the first substantial snow in the mountains is likely to occur this weekend.

Along with temperature, pressure is set to fall through the weekend and into early next week as a depression hovers NW of the UK over Iceland and brings Reigate some breezy SW winds on fronts with rain reaching us in the SE on occasions over the weekend and into the early part of next week.  A cold front later on Sunday looks especially likely to be the one to usher in the distinctly cooler polar air overnight into Monday as a trough pushes out the high pressure which moves east taking any remaining mild air into the continent.

During the first part of next week the LOW moves SE over the UK and brings unsettled cooler and damper conditions to Reigate.  This LOW is due to then move further to the south / SE over the continent and deepen to become a feature called a “cut-off” low.  This is modelled to move over the continent to the Alps and N Italy where especially heavy rain is possible and then to parts of the Mediterranean which could cause unsettled conditions to arrive in the NW Med later in the week.

2014-10-30_14-00-21

There is some uncertainty as to how the end of next week and next weekend plays out for the UK and us in the SE once this cut-off feature moves off.  It seems likely that another depression with fronts could sweep across the N of the UK and bring more unsettled conditions towards the end of next week with fronts and rain for the NW.  But there are also signs of higher pressure building from the south again.  Either way, temperatures are going to be more averagely Autumnal and November-like, unlike the warm temperature tricks October has played.

A quick reminder that, unless November and December are markedly cooler (and the jury is out on this) then 2014 is STILL on target to become one of the warmest years on record for the UK and certainly one of the warmest.  Every month has been well above average temperature (see below, CET means Central England Temperature) except of course August which was the coldest for 21 years!  Despite this hiccup October looks to be warmer by over 1.5C and ending on a corker.  Nevertheless, perhaps celebration of such temperatures should be tempered by remembering that this kind of anomalous heat is exactly the kind climate change expected by IPCC predictions and, although anomalous warmth is pleasant for humans, it is just as stressful to wildlife and the environment as severe conditions such as storms and cold snaps.

2014-10-30_14-47-28

Finally, it’s worth noting recent press headlines regarding a possible COLD winter.  Such scare-mongering headlines in the Express and Star and similar papers are usually based on just one or two seasonal forecasts from a few meteorologists who might be described as on the fringes of mainstream weather forecasting.

Whilst RGSweather does not  write seasonal forecasts, it is worth sharing that some of the wider expert and reputable weather community, including both professionals and amateur, is pretty animated about the possibility of a colder than average 2014-2015 winter (that is of course Dec, Jan and Feb).  This is despite several of the standard weather models indicating a rather warm winter at this stage (including our own UK Met Office).  There is a lot of discussion about it.

Making a winter forecast is a complicated process because it is based on many interacting factors in the atmosphere, the cryosphere and the oceans which are combined together by expert forecasters to assess likely winter conditions.

Winter forecast indicators include factors such as the extent and build up of early Autumn snow cover over Siberia/Russia (encouraging HIGH pressure and cold easterlies), Arctic Ice cover (low ice cover warms Poles, increasing pressure, pushing cold air out to mid latitudes), the North Atlantic Oscillation and Arctic Oscillation (based on development of Azores High and Icelandic LOW) and associated amplification of the jetstream, how strong it is and how wiggly (meridional) or straight (zonal) it is, (a weak jetstream with -ve NAO allows polar air to leak out into mid latitudes), the strength of the polar vortex in the stratosphere as indicated by the an equatorial lower stratospheric wind pattern called the Quasi-biennial oscillation (QBO).  A westerly phased QBO is correlated with possible increase in likelihood of Sudden Stratospheric Warming episodes that have been linked to downwellling of cold air into mid latitudes some weeks after a SSW).  Phew, you can see there are loads of tricky indicators to watch.

This year, the October Pattern Index (OPI) is gaining attention as a possibly reliable predictor of winter outcomes.  Basically, the OPI is a clever measure of upper atmospheric conditions in October and particularly how amplified (or wiggly) the jetstream is looking.  Scientists have found that atmospheric conditions in October correlate well with winter outcomes.  A negative OPI, for example,  correlates amazingly well with a negative NAO (north atlantic oscillation) occurring later in the winter.  A negative NAO indicates a weak jetstream, itself possibly caused by low Arctic Sea Ice and high Siberian snow cover.  A negative NAO can, given the right synoptic pressure patterns (placing of HIGH and LOW pressure), be conducive to incursions of COLD air from the Poles reaching mid latitudes like the UK.  All this is experimental but extremely interesting and rather important given the rapid climate change going on in the Arctic.

Update!

Records were smashed today… warmest end to October on record at 24C

 

Reigate weather for next week to 10 days is overall set to calm down somewhat and, for us in the south, be generally drier and warmer than average for the time of year, most of the time. Temperatures are unseasonably warm over the next few days with night times barely falling below teens and daytime reaching 21C.  This is due to the southerly winds bringing warm air from Spain.

2014-10-17_22-57-53

A slack static cold front divides the really warm air over the SE from the cooler air to the NW. This cold front will bring cloud and rain at times across the SE, especially to the south coast, as it drifts SE over the weekend.  Winds on the coast will also be more noticeable over the weekend with 20mph+ possible, but staying mild over the weekend. The temps are likely to slip very slightly as the weak cold front edges SE on Sunday bringing some rain through the SE and more wind to the south coast.

Unfortunately, there is a hiccup to this generally benign warm weather. A gradual rise in pressure is set to be sharply upset temporarily by the remains of Hurricane Gonzalo, now battering Bermuda as a Cat 3 storm and due to arrive UK early next week late Mon /Tues.

Gonzalo hiccup

Gonzalo hiccup

Gonzalo is modelled to arrive early/mid next week.  Forecasts suggest Gonzalo will merge with the persistent Atlantic low near iceland and ride the jetstream across the Atlantic arriving late Monday as a 980mb low (not especially low) , bringing gales initially to the west and NW coasts and then gales to through the North Sea later the same day.  Some heavy rain is likely but the SE and Reigate looks currently likely to miss the worst.

After its passage across the north of the UK, the centre of Gonzalo appears to move SE down into the North Sea and behind a potentially vigorous cold front usher in significantly cooler NW winds of some potency, albeit briefly.  These appear to peg down temps a while, especially on NE coasts. Thereafter, indications are for a gradual improvement in the south as high pressure builds over the continent, albeit with some fronts reaching across to the south at times before a HIGH pressure seems to be suggested for the last week in October.

2014-10-17_22-26-02

If this comes off a dry and settled spell can be expected for half term.  The location of the HIGH starts in the south where mild conditions can be expected but the anticyclone could slip north and topple east.  if this happens then temps will fall as a cool easterly flow are brought in from a cooler continent creating a more foggy autumnal feel.  The charts below show the possible scenario for the last week in October and very start of November with things cooling off.

So in summary the weather for half term is generally settled, warmer and drier than average for the time of year but with a significant hiccup as Gonzalo arrive early next week bringing a plunge of cool polar maritime air down across the UK and the north sea behind this sharp active system.  Thereafter, a gradual improvement to the last week of October when an anticyclone is set to build across the UK bringing autumnal foggy end to October as temperatures drop to November.  Note that extra-tropical storms upset models so keep an eye on any changes to this forecast.

forecasters: SAC and Chris M

 

 

 

Update: confirmed tornadoes today (see foot!)

Potentially interesting, albeit tricky, weather tomorrow for UK, Wednesday. A deep surface LOW sits to the SW of Ireland and is dragging through complex series of fronts associated with various airmasses.  Occluded fronts are tightly wrapped around the LOW, which is due to migrate NE away from the UK during the weekend and pressure to rise.  For the SE tomorrow it’s not so much the fronts but an unstable mass of warm southerly surface air that will be the main cause of any heavy showers tomorrow and some potentially thundery weather, especially when this warm air is forced up by anything… coast, hills or fronts.

Here’s likely scenario for us in Reigate, Surrey SE: Rain is likely, possibly exceeding 10mm, which is fairly wet for SE: higher is possible.  Most of this is likely to be convective rainfall due to unstable and moist air moving in from the south overnight.  Showers, possibly heavy and thundery, are most likely in the morning as the warm surface air moves into our area, causing lapse rates to increase moderately and this encourages lift and cumuliform clouds.  If the sun comes out then surface heating could spark heavy showers and thunderstorms as warm air rises freely through the atmosphere, encouraged by the jetstream overhead that effectively drags air off the ground.  One of the ingredients for thunderstorms, LIFT, is therefore partly in place tomorrow, although it will depend on sunshine for greatest effect.  If it stays overcast, which is possible, then little exciting weather action beyond just rain is likely.

The above charts also show that the southerly / SW airstream is humid because, as it converges on the coast, the model shows rainfall increasing significantly. This increased rainfall on coasts is often caused by convergence which is due to air arriving onto the coast quicker than it is leaving (check the lower wind speeds inland) so the wind effectively PILES UP on the coast and is forced to rise as it has nowhere else to go except UP!  This is called convergence. It is clear from the charts above that any HILLS also encourage lift as South Wales and even the South and North Downs appear to be pushing rainfall totals up locally: this is orographic or relief rainfall.  The charts below shows another feature of the weather tomorrow: the winds are shown to be VEERING with height (left diag) which allows WARM air to advect (move into) into our region (right diag).  Read on for more about how veering winds and WARM AIR ADVECTION can encourage stormy weather.

 

Another ingredient for potentially unstable weather is that winds are VEERING tomorrow, albeit not dramatically, which means they are rotating clockwise directionally with height thus allowing warmer air from the south to move into a location: it is like opening the door to warm air: winds move through a southerly direction and therefore allow warm air to “advect” into our area.  A moderate wind veer is taking place overnight and into tomorrow morning.  Warmer air at the surface is overrun by cooler westerlies aloft that increases lapse rates: steepens the temperature difference between surface and air at altitude.  The air at altitude tends to stay the same temperature and is associated more with direction and origin of airmass than it is with surface heating or advection of warmer air at the surface. An increase in lapse rates adds to instability which encourages air parcels to LIFT off the ground, should surface heating occur if the sun comes out.  The chart above right shows how WARM air is ADVECTED into the South of the UK and migrates NORTH during the day.  This has nothing to do with solar heating… it is an 850hPa chart (1500m) and shows the airmass temperature which is largely independent of surface influences.  It’s a good example of WARM AIR ADVECTION with a moist air stream increasing instability causing showers and possible thunderstorms.

Finally, the warm relatively unstable airmass is being overridden by a NE turning jetstream that will encourages lift and wind shear.  Wind shear is the vertical change of direction and/or speed with height: rotation.  Shear is moderate tomorrow which might also add a twist to rising air that could even produce the odd tornado.  Nice :-)  After writing this Estofex issued a tornado warning Level 1.

Update 8 Oct: confirmed tornados from today 8 October 2014

http://www.bbc.co.uk/news/uk-england-derbyshire-29542740

 

2014-10-02_20-39-59

September was a warm and unusually dry month.  Central England temperature (CET) came out officially as 15.1C which is 1.5C above the 30 year average (Hadcet) and made September the 4th warmest since 1910. In Reigate our average September temp was 16.5C, not unexpected as we are in the warmer SE of the country.  In 2013 the average for September was 14.4C but the range of temperature was greater: 2013 Tmax 30.9C and Tmin 4.6C were both more “extreme” than the respective Tmax 26.7C and Tmin 5.2C of 2014.  Whilst the remainder of Autumn looks to be cooling down markedly now, 2014 remains on target to be an exceptionally warm year overall.  Despite a cool August all the other months have been above average.

The UK average rainfall for September 2014 was 19.4mm for the month, the driest since 1910.  In Reigate we had 22mm of rain recorded (CoCoRahs) compared to over 47mm in 2013.  The rainfall we got in Reigate this September was restricted to a few heavy thundery showers: many of these moved over London and missed us completely.  However, a notable thunderstorm overnight on 19 Sept delivered some cracking thunder and lightning at about 1am and brought 10mm of rain in less than 20 minutes, and woke quite a few people up!

Overall, however, the month was dry: 16 consecutive days of no rainfall at all came early in the month and mostly dry days with just odd showers characterised the rest of the month.  Sunshine hours totalled 120 hours. Pictures below are a medley of photos from an “extreme” month due to the exceptionally dry conditions, the driest in 100 years in some places.  September in Reigate.

 

September has retained some high daytime temperatures which are set to make it 1.4C or so above Central England Temperature (CET) long term average. New York city also experienced some warm Autumn days with 29C Tmax recently, followed closely by London with near 25C Tmax temps over the last weekend of September.  This month has also been exceptionally dry with Reigate recording just 20mm (tbc). The inevitable happens this coming weekend as Autumn arrives, albeit fashionably late.  The chart below shows upper air temps dipping as cooler polar air arrives from 5 October (note upper air temps are 1500m, so don’t panic about the scale!).

fall in air mass temp this weekend

fall in air mass temp this weekend

The charts below also show a defined change for Reigate and the SE over the first weekend in October and into Monday as high pressure and largely rain-free warm settled conditions this week give way to LOW pressure, frontal rain bands and cooler breezy-er conditions delivered by a lively jetstream from the Atlantic. The Icelandic LOW mentioned in previous posts will, at last, nibble through the anticylcone sat over the UK for so long.  It may not be quite curtains for HIGH pressure and warmth for the SE yet and some recovery is hinted at later, but it looks like the persistent dry and settled conditions will push off this weekend and be replaced by more mobile Atlantic action.

For Reigate, the change afoot starts gradually, with the odd light shower possible Wednesday, Thursday seeing a rise in pressure again and a continuation of warm and dry calm conditions to end the week.  However, a glance to the north west will show an active cold front descending SE during Friday and arriving over SE and Reigate during Saturday morning.  It is likely to push through by afternoon and leave brighter fresher conditions through Sunday, which looks not a bad day at all for Reigate, albeit cooler.

 

The jetstream chart for Thursday and next Monday shows a significant shift south directly over the UK. This is forecast to enhance the trough over Scotland and dig it deeper into the south of the UK during early next week.  Breezy conditions are likely into early next week with Monday having possible country-wide rainfall, especially heavy in the south as the warm air lingers CLOSE by to the south and interacts unfavourably with the colder air mass that could produce a lot of rain. The upper air charts below show how close the warm air lingers to the south of the UK.