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February 7, 2016

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Reigate Grammar School, UK. Local weather station and forecasts for education. Reporting on local and global weather and climate. RMetS education committee. Town VP2 updates website every 10mins, wind every 5secs. CoCoRaHS manual rain gauge. Data to Met Office + Weather Underground.  Status: Reigate data all good :-)

badge_2015Reigate Grammar School awarded MetOffice and Royal Meteorology Society MetMark Award for excellence in weather teaching and promotion of weather understanding and climate awareness. Read some of our best weather club events that helped win the award: HAB launch; BBC school report; River Mole and Gatwick flood reports and St Jude storm post as reported on Radio4 and published student authors in Weather magazine.

Imogen is the ninth named MetOffice storm this winter.  She formed in the Atlantic in an area of steep temperature gradients under control from an active jetstream.

 

Storm Imogen is deepening rapidly today to 953mb, though on arrival in the UK she will be occluding and filling gradually to above 960mb on her track over N Scotland into the North Sea on Monday. The exact track makes a big difference to where the strongest winds are.  Current trends are for the storm to pull wind fields further north so impacts could be less than expected. Keep an eye on the MetOffice forecast as things are likely to change. Below is an outline of Imogen’s likely activity:

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Unlike the previous eight named storms, Imogen has a more southerly track, guided by a more southerly tracking jetstream, and the field of strongest winds and heavy rain are possibly set to impact the densely populated southern part of the UK, including the SE. High waves are also expected on the Channel coast.

 

Strong winds on Sunday night will be associated with Imogen’s fronts running ahead of the depression.  The cold front is an active kata-front, associated with descending cold dry air from the stratosphere running ahead of the surface front and enhancing lift and potentially generating heavier rain and gusty conditions (image and info courtesy UKweatherworld).

On Monday gusts up to 80mph on the Channel coast are possible, while inland the MetOffice consider 60mph possible in exposed places.  Around Reigate and sheltered parts of Surrey, 40-50mph gusts are more likely.  The North Downs could see gusts approaching 60mph. The strongest winds for the SE are likely to be through midday and in the afternoon.

Yellow warnings apply to inland parts of Surrey and SE England while the entire Channel coast has an Amber MetOffice warning. The first impact will be frontal rain tonight.  Fronts passing through overnight into Monday could drop over 20mm of rain in places particularly linked to the occluding “triple point” forecast to cross the SE overnight.

 

Monday is likely to see showers, some heavy, appearing through the day.  Warm sea surface temps in the Channel are likely to cause more on the coast but the brisk winds could bring them inland as the day progresses.

The cause of the strong winds behind the cold front on Monday is a steep pressure gradient.  On Monday tightening isobars show the steep pressure gradient bringing gusty showery conditions in unstable Polar Maritime air behind the cold front later on Monday.

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The Wight-Wash Oscillation (WWO) measures the pressure difference between The Wash and the Isle of Wight and is designed as a guide to wind speed in the SE corner of the UK. The WWO on Monday shows a significant 16mb gradient between The Wash and the Isle of Wight on the WRF model.  The Euro4 model has a more modest 12mb WWO.  16mb would be the largest WWO pressure gradient recorded and greater than St Jude, which was 12mb.

On Tuesday models show a wave depression bringing more rain to the SE, some even show fleeting wintry precipitation on the back end of this low as colder air ingresses from the north.  This is unlikely to be significant, at least on Tuesday, as upper air temps remain mostly too high for snow in the SE.

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ECM colder flow mid-week

Colder conditions are preferred by the ECM as northerly winds bring cool polar air further into the country through mid-week.  The Arctic Oscillation is again going negative which shows pressure rising over the Poles trying to push Arctic air south into mid-latitudes.  However, the NAO remains positive so Atlantic depressions will continue to bring frontal depressions for this week.

The 8-10 day mean shows a deep trough over the UK meaning low pressure and unsettled conditions remain likely into half term.

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The ECM builds heights over southern Greenland which links with higher pressure over the Atlantic, a more northerly feed of cold polar air is likely in this scenario into half term . The ECM has been outperforming the GFS so the more Atlantic driven GFS chart would be the less favoured option.

The Sudden Stratospheric Warming going on over the Pole is another astonishing feature of weather at the moment.  Today (Sunday) temperatures in the stratosphere over Siberia has got up to an amazing +12C from a more usual -70C.  SSW events often build pressure over the Polar troposphere a few weeks later which can cause cold incursions into mid-latitudes.  This is by no means certain but is perhaps our last chance of any sustained cold this winter… if it were to happen it would be late Feb/March. One to watch!

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Jonas to UK this week

The phenomenal winter storm Jonas brought NE USA to a standstill over the weekend as more than 20 inches of snow fell on Washington and New York.   Jonas was a truly massive storm and broke regional snowfall records with up to a metre of snow in places, and brought a record storm surge of 9.27 feet on the Delaware coast with significant coastal flooding (beating Super Storm Sandy surge in places*). Weather Underground reported…

This nor’easter, dubbed Winter Storm Jonas, was one for the ages–among the most powerful and far-reaching in regional history.  Jeff Masters Weather Underground

Jonas threw blizzards, storm surge, heavy snow, icy rain and thundersnow at the US over the weekend.  Here is a brief outline of the storm and a look at where it is headed next.  It is worth noting that potentially another Nor-Easter snow storm is possible for this part of the USA later this week, although less likely to be as powerful.

New York had it’s heaviest daily snowfall total on record on Saturday courtesy of Jonas. Forecasters started warnings several days out and the National Weather Service made people aware of the seriousness of this storm in the lead up.

Jonas was a classic and historic “Nor-Easter” storm albeit with the potential added spark of warmer than usual Gulf Stream temperatures.  The system was well forecasted by the NWP models from several days out.  An insignificant low pressure disturbance entered the NW Pacific coast of the North America earlier last week, traversed the continent and emerged out of the SE dragging cold continental air to interact with warm Gulf moisture.

This explosive mix was exacerbated because both the Gulf of Mexico and Gulf Stream sea surface temperatures were anomalously high adding to the moisture and energy available for this storm.

“Take unusually warm Atlantic ocean surface temperatures (temperatures are in the 70s off the coast of Virginia), add a cold Arctic outbreak (something we’ll continue to get even as global warming proceeds), mix them together and you get huge amounts of energy and moisture, and monster snowfalls, like we’re about to see here” Michael Mann, climate researcher who directs Penn State University’s earth systems science center.

The storm got hooked up by a strong jetstream and traveled rapidly north over Friday 22 Jan, hugging the east coast and intensifying as pressure fell into Saturday 23 Jan and leaving the coast by Sunday 24 Jan.

The chart below shows the jet during the lead up to the storm on Tuesday 19 Jan.  Spot the LOW mid-west, this was Jonas in the making.

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jetstream emerging out of Gulf of Mexico… perfect Nor-Easter set up, spot LOW Jonas over MidWest

Another important element making this one of the top two most intense Nor-Easter winter storms on record was HIGH pressure lodged over NE Canada which intensified the pressure gradient and increasing those north-easterly wind speeds.  These strong winds drove ice and snow across a vast swathe of the NE and dumped 2 feet of snow as far north as New York city.

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In addition to large snowfalls the low pressure and strong on-shore winds also created a storm surge risk on high tides.  The coastal impact was recorded by a series of video cameras placed along the New Jersey coast by Hurricane Track’s Mark Sudduth.

Jonas is now forecast to track across the Atlantic, riding the jetstream and deepening on approach to the UK by Tuesday.

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Jonas GEFS tracks set to cross near NW Scotland

Through Tuesday and Wednesday Jonas will bring some stormy and wet but mild conditions especially to the NW of the UK.  Nevertheless potentially 70mph gusts are forecast for parts NW Britain.  Gusty conditions on associated fronts are likely at times here in the SE as well, but nothing like the intensity or disruption of the US version.

Further ahead, at least this week, the NAO and AO are both trending positive and this is set to bring further unsettled conditions across the Atlantic separated by drier periods of higher pressure, but mostly staying a good deal milder than average.

The pressure over the Poles has weakened and the Icelandic low has deepend, both indicating a lack of sustained cold potential in the near future for the UK.  Nevertheless, action in the stratosphere is hotting up with a forecast sudden stratospheric warming afoot.  Sudden warming events in the stratosphere can build pressure over the Poles and increase the chance of sustained cold weather, sometimes, over Europe.  This occurs several weeks after an SSW and the forecast SSW, if it occurs, is still at the end of model runs so… any chance of sustained cold risk can most likely be reserved for several weeks ahead as things stand. The temperature and pressure anomaly scene in the Post – Jonas world looks like this: a warm NW Europe, warm Pole and cold NE USA.

 

Winter storm Jonas References

http://www.wunderground.com/blog/JeffMasters/colossal-noreaster-dumps-record-snow-from-maryland-to-new-york

http://www.realclimate.org/index.php?p=19070

http://mashable.com/2016/01/22/causes-of-east-coast-blizzard-global-warming/#ZQIP9mQOOmqb

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Hurricane Alex and the UK 14/01/2016

Satellite pictures have emerged showing how truly amazing Hurricane Alex really was. These satellite pictures (courtesy MeteoSat, Dundee sat.dundee.ac.uk and eumetsat/eosdis) show that Alex is one of the most northerly and easterly forming Atlantic Hurricanes (second ever, in any month to form north of 30N) and rare for January at this extreme northerly and easterly location.  In typically understated fashion, the official National Hurricane Center tropical discussion hinted at the astonishing nature of this event as the diminutive storm transitioned to a Category 1 hurricane on 14 January.

“Remarkably, Alex has undergone the transformation into a hurricane. A distinct eye is present… ” (11am 14 jan 2016)

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Hurricane Alex (Cat1), just before downgrading to a Tropical Storm, near the UK 15/01/2015

Alex is very likely to be the closest January hurricane to UK shores but Fran and Hannah were Cat 1 hurricanes that came closer, albeit both in October.

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Hannah and Fran Cat 1 hurricanes tracked close to the UK

It is quite common for ex-hurricanes to track across the UK (e.g. Bertha Aug 2014) each year as extra-tropical storms but usually these happen in late summer and Autumn, at the mature end of the hurricane season.  Nevertheless, a hurricane (Category 1) forming on the European side of the Atlantic so far north and east in January, with snow clearly visible on the UK hills is truly amazing.

Some meteorologists think that a hurricane visiting Britain is possible before 2030.

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Alex becomes a hurricane 14 Jan 2016 (image EUMETSAT)

Alex is the first Atlantic hurricane to form in the month of January since 1938 and is the first Atlantic hurricane to exist during January since Alice in 1955.

Hurricane Alex, located in the sub-tropical Mid-Atlantic south of the Azores at approximately 30N 30W, was named on Wednesday by the National Hurricane Center as a sub-tropical storm lingering in the tropical Mid Atlantic took on more hurricane characteristics.

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Hurricane Alex 14/01/2016

Despite sea surface temperatures of only 20C, wind speeds in excess of 80mph started circulating around a tight hurricane eye.  The notable northerly formation would be remarkable in summer, let alone January.

So Alex is certainly remarkable but not entirely unique because two other hurricanes have occurred in January since records began in 1851.

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Hurricane Alex’s eye 14/01/2016

Hurricanes usually form June 1 to November 30, the official “hurricane season”.  This is towards the end of long hot summers, when Tropical seas are at their warmest. Hurricanes are named starting from “A” as the first one of the season.  It is extremely unusual for hurricanes to form in January, and making landfall over the Azores so far north will almost certainly be a first for any hurricane.

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How freaky is Hurricane Alex?

A key ingredient of hurricane formation is a warm sea surface, usually at least 27C to at least 60 metres.  Warm waters fuel the energy hurricanes feed on and, through evaporation of vast quantities of sea water and release of latent heat into the atmosphere, convection is caused and wind speeds increase to a sustained 74mph into a hurricane eye.

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Hurricane Alex, spot the eye (image EUMETSAT)

Alex has formed over relatively cool SSTs, around 20C, which would usually not give birth to a hurricane.

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usual hurricane formation

Meteorologists suggest that unusually COOL upper air temperatures in an upper trough over have assisted convection and the uplift of air to create thundery conditions around a hurricane eye.

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sea surface temperature anomalies Alex

Like other recent remarkable weather events, Alex’s special early arrival is not quite unprecedented and two hurricanes have occurred in the Atlantic in January.  An unnamed hurricane formed in 1938 in the tropical Atlantic, with winds of 70 knots, but only lasted as a Cat 1 hurricane for one day.

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In addition, Hurricane Alice formed on December 31 1954 and lasted as a Cat 1 for 5 days into Jan 1955 before weakening to a tropical storm.  She had a slightly strange SW track towards Venezuela.  Also, interestingly, 1954-55 was a weak La Nina year, strengthening to a moderate La Nina year.  La Nina years are more conducive to Atlantic hurricanes whereas our current very strong, but gradually declining, El Nino state is associated with fewer Atlantic hurricanes.

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Geographically, both Alice and “the unnamed one” formed much further south (around 20N) in the tropical Atlantic than our Alex (around 30N).  So Alex can certainly claim to be an unusual storm because it is so far North AND so far out of the hurricane season.  This might even qualify him as “freak” status.

Currently, Alex is a small storm with a tight hurricane eye where sustained winds exceed 85mph.  It is not expected to strengthen much or last more than a few days as a hurricane system because the track is northerly and this will take it over ever cooler Atlantic waters.  The Azores is on the track of Alex and is likely to experience a highly unusual January hurricane in the next 12 hours.

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Hurricane Alex intensity Cat1

The storm will lower intensity and dissipate over cooler than average North Atlantic waters before making “landfall” most likely somewhere near the southern tip of Greenland.

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Hurricane Alex track January 2016

Here’s some expert explanation of the development of Alex from the very excellent Mark Sudduth of hurricanetrack.com

Alex started life as a tropical disturbance near the Bahamas over unusually warm sea surface temperatures emanating out of the Gulf.

The sub-tropical disturbance never threatened land, except momentarily to risk a nor-easter for the Atlantic US coast.  His track took him safely into the Atlantic.

However, despite his remote location, Alex did impact our European weather indirectly. Earlier this week a trough disruption took some of his tropical energy into Europe via the Bay of Biscay.

This lowered pressure over Europe sufficient to allow an Arctic plunge to push further south across the UK and into the continent.

Warm air from Alex’s sub-tropical source has also possibly helped build pressure to the north over the Atlantic that assisted a tighter pressure gradient over the UK allowing a more brisk Arctic wind chill to build.  This same high pressure will keep him stuck in the Atlantic until he dissipates near southern Greenland.

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Hurricane Alex and HIGH pressure to the North

However, the existence of Alex has possibly thrown weather prediction models into a spin because the forecasts from models, even short term, are now in a good deal of disagreement about next week.

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models completely disagree… Alex’s influence?

So perhaps Alex has broken more things than just weather records!

and finally… is global warming to blame for Alex?  Well, typically, the answer is both Yes and No!

Read this interesting article below here to get the idea why..

http://www.cato.org/blog/buzz-alex-global-warming

http://mashable.com/2016/01/14/hurricane-alex-forms-january/?utm_cid=mash-com-Tw-main-link#i2kSmA3cnGq1

https://xmetman.wordpress.com/

http://www.wunderground.com/blog/JeffMasters/alex-becomes-the-atlantics-first-january-hurricane-since-1955

Hurricane Pali has also been setting records in the Pacific http://www.aljazeera.com/news/2016/01/hurricane-pali-sets-pacific-record-160113090131993.html

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Atlantic jetstream has been powerful and mostly westerly

This coming week, Arctic air from Svalbard briefly encounters Tropical air from the Bahamas over Europe.  Remarkably, how cold it gets here in the UK and Europe might depend on the story of a sub-tropical storm over the Atlantic just as much as the Arctic air trying to push south.

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pressure is high over the Pole

Pressure has built over the Arctic, nudging cold air uncertainly south into European mid-latitudes.  The build in Polar pressure and relative fall in mid-latitude pressure is called a negative Arctic Oscillation as mentioned in previous posts.  The pattern is already cool because the jetstream is to our south.  The jetstream axis essentially divides the warm tropical air to the south from the cool polar air to the north.

zonal flow with powerful jetstream

westerly flow with powerful jetstream

However, the flow has been mostly westerly and even SW across Southern Britain as the jetstream is blowing purposefully from west to east across the Atlantic.  While pressure remains relatively high over parts of Europe (e.g. Med and Spain), the coldest air has been unable to penetrate very far south.  The jetstream chart above shows the unstable flow we have had this weekend bringing heavy thundery showers, some with hail, over Reigate. Check this pic of mammatus clouds this afternoon over Surrey, after thundery showers with hail.

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mammatus clouds over Brockham, Surrey

 

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cool LOW over UK, south westerlies in the south

It has been cool because the air has been circulating anticlockwise around a deep low over Scotland with a cold source region over Scandinavia. However, the airmass has been modified with a long track over the Atlantic. With such a strong zonal jetstream the more frigid Arctic air has not been able to penetrate far south into Europe, yet.

An unusual sub-tropical storm developed in the Bahamas last week over a very warm Gulf Stream.  This low pressure will come to hover in the Mid-Atlantic this week and it might just hold the key to unlocking some more Arctic air over Europe.

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300hpa shallow trough enter left

A part of the sub-tropical system is forecast to cross into Europe mid-week courtesy of a trough disruption.  This causes a part of the trough to break away and leave the parent “cut-off” in the mid ocean.

low rides jet coat tails into Europe

low rides jet coat tails into Europe

In this case, a small but vigorous “baby” LOW will ride off on the right entrance of the jetstream, a good location for deepening surface pressure, and enter Europe via the Bay of Biscay sometime on Wednesday.

disrupted trough enters Europe

disrupted trough enters Europe

Whilst this vigorous baby low will not impact the UK directly, it is set to lower pressure over Europe and, in its wake, will drag in Arctic air more purposefully SOUTH across more of the continent right to the Mediterranean.  This wind will be significant and create the first proper wintry feel for about three years with wind chill on occasions down to -7C or lower.

Importantly, the trough disruption will also build pressure in the Atlantic to the north of the sequestered parent LOW.  This is often the case in trough disruptions.

builds Atlantic high and lowers pressure in Europe

builds Atlantic high and lowers pressure in Europe

The increasing the pressure gradient in the Atlantic and lower pressure in Europe will push more Arctic air more purposefully south across the UK and into Europe. So the sub-tropical system has been key to unlocking the full Arctic blast!

Details about snow for Reigate will be updated this week.  At this stage heavy snow settling here looks unlikely but some snow fall and wintry showers are certainly possible, especially later mid-week.  It will get gradually colder through to the end of the week.  Thereafter it is, of course, uncertain! The ECM has been performing better as a model than the GFS so, on that basis, continuing cold is more likely than a sudden return to mild westerlies, which the gfs tends to do too quickly. So assume it’ll stay cold into next weekend.

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GEFS cool dip mid January

A cold snap looks more likely next week from around 13 January. Nothing extreme, just a long-overdue “normal” wintry feel is on the cards.

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12Z gefs and ecm ensembles show more distinct dip in temps

 

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ECMWF upper air goes cold

Temperatures are due to take a dip below the seasonal norm.  It’s still a way off so details will change but here’s the current idea moving ahead.

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The current run of wet Atlantic westerlies (above) that has brought flooding to many parts of the country, is due to weaken as pressure rises over the Atlantic and further north over the Pole.   As the persistent Atlantic LOW pressure gradually moves East this week it will bring more rain across the UK.  As it moves further east over the weekend it is forecast to draw down cooler northerly winds from the Arctic next week, at least for a while. (see below). (update: “Atlantic block” noted on chart below is probably overstating it a bit … as HIGH is likely to give way fairly promptly)

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Arctic Oscillation goes negative january 2016

The cause of this Arctic outbreak is indicated by the Arctic Oscillation (AO) going negative.  The AO is a measure of air pressure over the Pole relative to mid-latitudes.  It has been positive for most of the autumn and winter so far and this usually means a strong jetstream and mild wet westerlies for the UK.

When the AO goes negative it indicates building pressure over the Pole and more likelihood of Arctic air “leaking” into mid-latitudes.  The chart below shows the 500mb mean heights for 8-10 days time.  Spot the anomalously high pressure over the Pole relative to the mid-latitudes.

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8-10 day mean 500mb heights (ecm and gfs models)

The negative AO has been predicted by many expert long range forecasters for a long time partly because of a lack of sea ice in the Kara Sea (part of the Arctic Ocean near Siberia).  This is a long-term indicator for potential pressure rises in this region.

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In addition, the recent enormous pump of warm air, courtesy of the Storm Frank, will have encouraged tropospheric height rises over the Pole.  The result is an inflating balloon of relatively cold air waiting to pop into the populated mid-latitudes!

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surface temperature anomalies Jan 14 2016

As well as a push of cooler Arctic air, pressure is also due to rise over the UK.  With increased pressure we can thankfully expect a drier period.

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wintry pressure rise

A classic winter high might be expected to bring dry, bright clear days with cold nights with views of the stars.  On the other hand, frost, fog and icy conditions might also be expected too.  In the SE huge dumps of snow look most unlikely next week from current model runs but lows can move south in the Arctic flow and cause unexpected events. The duration of the cold snap doesn’t look long** as the Atlantic HIGH is swept away by more westerlies.  However, this is uncertain so stay tuned for more regular updates on twitter.  Of course, seek professional forecasts for decision making purposes.

update 06/01 **looking potentially more prolonged now. cold snap turning into a spell.2016-01-05_20-55-31

January 2016 cold snap

2015-16 winter forecasts have long considered the possibility of cold weather in the latter stages from Jan thru to feb. This was explored in a post here

http://rgsweather.com/2015/12/29/winter-is-nigh/

xmetman

I decided to look at the claim made by Paul Homewood in his recent blog Central England Temperature Pause Now 17 Years Long and see if there is any real truth in it. As soon as I saw it I realised that it has a lot more to do with statistics than any real pause in Central England Temperature [CET]. In fact I wrote about this very subject last year in this post: Lies, damned lies, and linear trends, but unfortunately my blog doesn’t have quite the global reach that Paul’s Blog has, and was read by a total of 14 people, one of them being an elderly Aunt who has no idea what I’m talking about. Despite all this I thought I would tweak my application to look at a 365 day running mean of CET from 1996, along with linear trend just to see what Paul…

View original post 308 more words

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Reigate December 2015 summary statistics:

  • Tmax 15.5C
  • Tmin 1.6C
  • Average temperature 10.1C warmest on record (2014 5.3C)
  • Total rainfall 79mm
  • max gust 37mph
  • sunshine 79.8 hours

Like the rest of England and Wales, Reigate had an exceptionally warm December and the warmest on record by a huge margin.

Central England Temperature December records smashed!

2015 warmest December CET ever recorded: 9.7C
December 1934, 1974: 8.1C

This is warmer than any March CET.
Warmer than any November barring 1994
There have been 171 colder Octobers
There have been 26 warmer Aprils
There have been 34 cooler Mays

The CET mean minimum was higher than any April mean minimum ever recorded.  It was higher than the May’s CET minimum

The gap between September and December’s CET was less than 3.0C, the gap between their respective minima was just 1.1C!

The CET mean maximum was 1.8C higher than the previous record of 1974.

(source CET data from UKWW)

In Reigate the average temperature was 10.1C compared to 5.3C, 5.8C and 6C in 2014, 2013 and 2012 respectively.  Whilst our own Reigate records only go back to 2012 (neighbour stations extend this locally back further to 2009), the Central England Temperature record extends back to 1772 and, at 9.8C monthly average, December 2015 smashed all previous mean monthly temperatures by a long way. The official Central England Temperature anomaly (temperature departure from normal long term average) came out at a whopping  5.2C above average, way above previous warm Decembers of 1934 and 1974.

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The chart above shows the monthly average data in Reigate this year as an anomaly departure from the long term average for SE England – (source MetOffice Hadobs 1910-present).  It starkly shows how much warmer December was from the long term average extending back to 1910, Reigate was a full 5.6C above normal!  How much is this down to El Nino? As discussed in previous posts the El Nino ENSO Pacific warming natural cycle cannot explain all of this extraordinary warmth.  In fact, there is little established link between El Nino and UK winter weather.  This is shown in the charts below for previous mega-El Ninos in 1982 and 1997 which had markedly different impacts on our December winter weather.  So there appears to be no real solid link between El Ninos and any crazy warm winter / December weather here.

Remember that the recent Paris climate change conference has sought to set a target of limiting global temperature rise to no more than 2C temperature increase over pre-industrial levels.  Locally we can expect spikes in temperature of course but this 5C anomaly for December, and the fact that 2015 will certainly be the warmest on record globally, shows the huge challenge that lies ahead in keeping temperatures down to less than 2C globally.

It was so warm for so long that wild flowers and plants around Reigate such as daffodils, camelias, forsythia and rhododendrons came into flower as if it was Spring.  This was a lot to do with minimum temperatures being so high with no frosts recorded at all.

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Many records were broken across the UK for highest minimums overnight, which frequently stayed in double figures. Indeed, this December has had a similar mean temperature to that expected in May. Our own station recorded the highest December Tmax at 15.5C on 19 December and the highest overnight Tmin at 12.4C on 26 Dec.2016-01-01_15-28-59

Despite the record breaking deluge further North which made this the UK’s wettest December of record overall), rainfall in Reigate came out around or even a tad below average at 79mm.

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Whilst 2014 was drier still at only 49.4mm, 2013 saw 110mm.  Regionally, South East England got around the average rainfall normally expected in December.  Like November 2015, December continued the sun-less theme with only 79.8 hours of sunshine.

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Apart from the incredible and perturbing warmth (which extended to the North Pole at the end of the month courtesy of Storm Frank) December 2015 was not remarkable for much else weatherwise locally.   Unfortunately, in Cumbria, Yorkshire and North Wales, there was extensive flooding which caused much misery and disruption especially over the Christmas period.  For more on the flooding and other weather stories please check this Flipboard magazine account.

Have a Happy New Year!  Data for Reigate and 2015 has been updated in the data page. 

http://www.metoffice.gov.uk/news/releases/archive/2015/early-dec-stats?WT.mc_id=Twitter_News_Pressrelease

http://www.getreading.co.uk/news/reading-berkshire-news/december-breaks-warm-weather-records-10673765

http://www.independent.co.uk/environment/uk-weather-why-the-recent-devastating-floods-will-become-the-new-normal-a6793291.html

https://xmetman.wordpress.com/2016/01/01/phenomenal-december-of-2015/

https://wansteadmeteo.wordpress.com/2016/01/01/december-2015-exceptionally-mild/

http://www.carbonbrief.org/analysis-how-december-2015-topped-chart-as-uks-wettest-month-on-record?utm_content=bufferf8440&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

http://www.metoffice.gov.uk/news/releases/archive/2016/december-records

http://blog.metoffice.gov.uk/2015/12/31/whats-been-happening-to-our-weather/

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Storm Frank 30/12/2015

Storm Frank brought gales and heavy rain and more flooding to the NW of Britain and especially for parts of Ireland.  It was perhaps fortunate that the storm did not cross directly over the UK but swept north towards Iceland and the Pole. The northward track was due to a developing blocking high of 1047mb over Scandinavia which directed the jetstream and attendant depression north.

The “cause” of Storm Frank was an increasing temperature gradient over the Atlantic which increased the power of the jetstream.

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Polar and Tropical airmass collision

Polar air pouring into the Atlantic from a cold Arctic Canada and Greenland met Tropical air moving up from the Gulf.  This contrast was increased by a cooler Mid-Atlantic and a warm Gulf Stream creating a large pressure difference.

The ingredients for a perfect storm were created as the mother of a jetstream embraced her baby Frank in the Mid-Atlantic.  Infant Frank lay underneath the left-exit of the jetstream and this caused surface pressure to “bomb” extremely rapidly, more than 24mb in 24 hours, creating an unusually low central pressure of 931mb on 30/12/2015.  This process is known as bomb-cyclogenesis and occurred with St Jude storm.

Storm Frank is not a record breaking storm in terms of low pressure. The lowest pressure recorded for a North Atlantic cyclone was 913mb in the Braer Storm in January 1993.  This storm skirted closer to NW Scotland.

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Sub-930mb storms in the Atlantic are not unprecedented, especially in winter.  Several storms have fallen below 930mb in the last 200 years, although only two have been recorded below 920mb.

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However, Storm Frank is unusual because, with assistance from the high pressure over Scandinavia, it has squeezed unusually warm air far north into the Arctic causing a “heat wave” over the North Pole.

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pressure LOW over Atlantic, blocking over Scandinavia

This process is called warm air advection and it has heated parts of the Pole to between 20 or even 30C above “normal”.

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Airmass temperature anomalies

Svalbard, usually around -14C in December, has risen to +8.1C and people in Longyearbyen are revelling in summer clothes outside in the Polar night.

Even the North Pole, usually about -30C in late December, is expected to “melt” for a time even rising above freezing for a short period.

This is probably only the second time this has happened on record.  It is especially remarkable considering, of course, that there is 24 hour darkness and the sun is not set to rise until March 21!  Any warmth is therefore entirely due to warm air advecting north on the back of Storm Frank.

With the HIGH over Scandinavia pushing cold easterlies into SE Europe Athens and Istanbul are expected to be colder than Longyearbyen in Svalbard. Infact it is snowing in Athens and Istanbul while it is now raining in Longyearbyen on Spitsbergen in the High Arctic.

Unfortunately the weather is set to continue stormy with more depressions arriving through New Year.  This time they might even impact the South of UK more with gales and heavy rain expected here too.  The temperature is set to cool to average so the anticipated cold lurking out east is not expected to arrive soon. Northern blocking is expected but this does not seem to be leading to any cold break-outs imminently. Nevertheless, the weather is telling some extraordinary stories at the moment.

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http://www.telegraph.co.uk/news/weather/12075282/North-Pole-temperatures-spike-above-freezing-as-Storm-Frank-sends-warm-air-north.html

http://mashable.com/2015/12/28/freak-atlantic-storm-uk-frank/#ZA9mGgejhaqi

https://www.washingtonpost.com/news/capital-weather-gang/wp/2015/12/30/freak-storm-has-pushed-north-pole-to-freezing-point-50-degrees-above-normal/

Winter is nigh?

December 29, 2015 — 6 Comments

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The synoptic situation above shows the remarkable contrast building up around Europe this week.  While much of the UK still sits in a mild SW flow brought in by a powerful SW jetstream, a HIGH pressure building over Scandinavia is set to drag in Siberian easterly winds to Eastern and SE Europe which is due to get much colder.

Whilst the jetstream is forecast to sink a little south of the UK by early January, which is the colder side, it is not certain whether any proper cold will reach the UK just yet. The UK looks increasingly sandwiched between bitterly cold easterly air and cool Atlantic NW air.  A stormy and wet set-up is likely with temperature contrasts like these, but will it snow?

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The ECMWF is certainly keen on something cold as pressure falls across the UK and Europe and allows the chance of LOWS ingesting nearby cold continental air.  This could mean snowy weather for the North, especially on hills, in early January, for example.

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However, for the SE Tmins stay above freezing on the chart below for nearby Gatwick, Surrey, and note the absence of snowfall, at least for now.

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While the ECM shows the potential for cold UK conditions by early January, the GFS maintains a more broadly westerly Atlantic flow with temperatures falling to average.

Both show a cooler regime and more persistent rainfall for us in the SE. A fall in pressure means LOWS will also make more direct passage across the UK during early January.

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The jetstream is shown to move south of the UK over the next few weeks. This will bring colder air across the country and lower pressure.

The terrible flooding in the North and West of England and Wales contrasts with the drier than normal December down here in the SE, running at about 70% of normal rainfall so far this month.  Unfortunately, a significant Atlantic storm, named Frank, is bombing-out right now in the Atlantic and is set to bring gales and more heavy rain to the NW, albeit not due to track directly across the UK.

Storm Frank will stay mostly in the Atlantic and arrive in Iceland on Wednesday night. It is unlikely to impact us much here in the south east other than some blustery and wet weather especially through Wednesday pm/evening as the cold front passes over.

Polar Maritime air behind this front will bring a cooler average feel by Thursday. Further wet and windy weather is likely later in the week and into New Year.  The arrival of this NW/westerly air probably spells an end to the extraordinarily warm long-fetch south westerlies that have made December 2015 by far the warmest on record. Whilst there will be warm sectors passing through the persistent warmth is less likely through January.

The wider atmospheric conditions hold more interesting clues than models as to which way the weather could proceed through January.  A more powerful than usual stratospheric vortex has built around the Pole this December. The extra-powerful vortex has possibly been caused by the excessive heat injected into the global atmosphere by the mega-El Nino: increasing the temperature gradient between mid-latitudes and the Pole and thereby increasing the strength of polar vortex as temperatures in the Polar stratosphere have fallen in the polar night.  Much catastrophic weather has been blamed on the El Nino “bar fire” burning across the Pacific.  Whilst Texas tornadoes and Pacific hurricanes are more likely to be directly linked to ENSO, UK flooding and weather has only tenuous links.  El Nino has now reached a peak but will continue to output through Spring until likely turning neutral and even reaching an opposite cool La Nina state by next winter. (more on El Nino impact on UK weather here )

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Mega El Nino December 2015

The powerful stratospheric vortex has “sealed in” cold air into the Pole throughout December (Globe a below).  However, the vortex has been taking a hammering from perturbations from the troposphere known as vertical waves (Globe b). If sufficiently powerful, these waves can lead to sudden warming in the stratosphere which can distort, split or even destroy the vortex, allowing cold Polar air to “escape” into mid-latitudes (Globe c).

Stratospheric experts differ somewhat in their forecasts but, overall, the feeling is that something is afoot high up which could erupt into a full break up of the vortex by Mid-January, something called a sudden stratospheric warming.  This what a SSW looks like in 3D.

A Sudden Stratospheric Warming could then mean, depending on how surface pressure patterns pan out, that some sustained proper cold arrives a few weeks later around late January into February.  This is due to pressure rising over the Poles as a result of warming in the Stratosphere. The increased pressure over the Poles further strengthens the negative Arctic Oscillation giving greater risk of cold outbreaks across mid-latitudes and snowy weather.  Even without a major warming, the super-powerful zonal westerly winds in the stratosphere appear to be abating (chart below: top arrows) due to the perturbation from the troposphere which is forecast to continue.  Whilst lower down the tropospheric jetstream nudges south of our latitude (lower black arrow) as anomalous or neutral winds expand out from 60N (red circles).  This means an increased possibility of cold leaks from the Pole reaching our latitude above 50N.

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Unfortunately, at the moment, none of this is catastrophic for the stratospheric vortex because, to date, the waves and warming have been insufficient to knock this King Vortex off his perch.  Nevertheless, El Nino years see a greater chance of SSWs and, as the westerly QBO weakens, it seems odds-on for such a full sudden stratospheric warming event.

Meanwhile, action nearer the surface in the troposphere (up to 10km) has been even more interesting with changes taking place that may render any stratospheric influence less relevant at least in the medium term. Notably, the Arctic and North Atlantic Oscillations are both trending negative.  This means pressure is building in the north relative to the mid-latitudes and could allow more polar air to push out into Europe. A cold outbreak is also possible in the USA.

Until now, December has been dominated by a positive Arctic Oscillation and positive North Atlantic Oscillation, hence the mild conditions.  A change to negative AO and NAO is therefore a significant indicator of cooler weather ahead.

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warming Pole negative AO

The chart above shows mean anomaly 2m temperatures for the 5 days 08-13 Jan 2016.  Note the extraordinary warmth over the Pole which helps to build pressure.  Note also the cold pool in the Atlantic, associated with cooler sea surface temperatures residing there.  This will be significant because NW polar maritime winds will be cooler than usual and could bring more snow to the NW and especially upland UK, even if we fail to get any truly bitter easterlies. Spot the cold lurking in the N/east of Europe and Russia waiting to pounce should we get a LOW sliding east through the Channel, for example!  Finally, the MJO is an important influence on winter outcomes worth exploring.

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The MJO or MOJO or Madden Julien Oscillation is a measure of convective activity which starts in the Indian Ocean and migrates east as a series of thunderstorms across to the Pacific and thence around the planet in a 30-60 day cycle. Here is a video about how the MJO impacts Australia, but it also impacts weather elsewhere.

The intensity and state of the MJO connects with global weather and correlates to known pressure patterns in the northern hemisphere. We have just left MJO Phase 5.  The expected mean pressure pattern associated with MJO Phase 5 (in ENSO positive phase) correlated pretty well with the pattern that turned out.  See charts below.

The MJO is now going through a nicely organised phase. This could mean that the correlation with real weather patterns continues into the weeks ahead.  Here below is the expected 500mb pressure pattern for Phase 6, which we are just entering and then Phase 7 and 8 which are due in early January.  Note the strong westerlies of Phase 6, which certainly equates with the current state of affairs, as does the building Scandinavian HIGH. This is not a cool phase for the UK.

Phase 7 sees a HIGH pressure building out from Scandinavia as a possible northern block.  This equates with the emerging negative NAO and potential easterly / Arctic winds winding round the base of the HIGH.  It is an increasingly cool phase for Europe, so matches expectations as we move into early January.  Phase 8 is a high pressure phase in Europe as the LOW moves further into the Mid-Atlantic.  High pressure can be cool dry frosty at the surface depending on the exact location of the high pressure.  This is expected by 13 Jan.

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Finally, Phase 1 and 2 (above) are both cool phases as they build Atlantic / Greenland blocks to the NW and place a trough over the UK dragging in potentially cold NE or NW. These MJO phases could weaken according to MJO forecasts but the signal is due later Jan/early Feb.  The MJO is just one teleconnection in winter weather forecasting it will be one to watch in the coming weeks and most interesting to see how it verifies with prevailing conditions.  Below are some links to explore the MJO yourself.

This is a round-up of the atmospheric situation and not a forecast. In summary, however:

  • models are struggling with all the action, ecm might be preferred as gfs does not take account of much vertical extent into the stratosphere, while ecm does. ecm is showing colder runs generally.
  • stratospheric vortex is taking a hammering and a SSW is predicted for January (AER)
  • QBO westerly regime is weakening somewhat, allowing more potential for cold.
  • MJO entering cool phases upcoming in January (esp Phase 7,1 and 2)
  • AO and NAO going negative which indicate blocking in North.
  • latest ensembles show high latitude blocking across Scandinavia to Greenland.

All the above give more likelihood of colder weather for the Northern Hemisphere, albeit not necessarily for the south of England!

http://www.americanwx.com/raleighwx/MJO/MJO.html

http://www.meteonetwork.it/models/mjo/

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtm