Edward Graham's Journal RSS

The #eddy500 cycle challenge of 2018

During the summer of 2018 I undertook an epic cycle challenge, which I called the "#eddy500" .

My target was to cycle 500 miles across the Highlands and Islands of Scotland, and in the process raise money and awarness of eating disorders, which are serious and life-threatening illnesses.

Altogether I raised some £2,100 for the BEAT charity (Beating Eating Disorders) and I gathered and harnessed a huge groundswell of support for my cause. And although I did complete the 500 miles sucessfully, it seems the journey to raise awareness of and to fight eating disorders has only just begun.

Below, you can find a wee summary of my adventure, including some photographs taken en route (see attachments underneath).

To be continued...

tn_download.jpg

To Whom it Concerns 

Now that the summer of 2018 has drawn to a close, I just wanted to finally thank you all again for your support during my #eddy500 cycle challenge this summer. Altogether I have raised well over ~£2,000 for the BEAT (Beating Eating Disorders) charity. Every single penny raised goes to them.

Of course, the cycling may be over for the moment, but the journey doesn't end here, as I hope my challenge will have gone some way towards supporting families with some-one suffering from an eating disorder. But even more important than the money, is the raising of awareness of these severe and life-threatening illnesses.

A reminder for those of you based in the UK, the BEAT helpline telephone number is: 0808 801 0677; And for more information, including online anonymous chat: https://www.beateatingdisorders.org.uk/

For those interested, a quick summary of my cycle follows (attached also are a few photos taken en route):
I did the 500 miles in 11 different stages, starting (day 1 to day 3) by cycling the full chain of the Outer Hebrides of Scotland from north to south, from the Butt of Lewis to the Isle of Barra. The weather was glorious and dry.

I also made it my challenge to visit every populated Hebridean island, but realising that I had missed Great Bernera, I cycled there on 12 July, in yet more fine weather.

From the 23-27 July, the family joined me as we cycled the Great Glen of Scotland together, from Fort Augustus to Fort William, alongside the beautiful Caledonian canal. Again, the weather was stunningly warm, and we plunged into every loch en route, sometimes twice in a single day!

However, on the night of 27/28 July, the weather finally broke with a violent electrical storm, and we got soaked to the skin in a massive cloudburst while cycling the beautiful, lonely parallel roads of Glenroy.

On 30 July, I had another enjoyable run on the bike from Laggan, Glen Cluney, all the way to Inverness Raigmore, on the cycle track. Then it was back to Ullapool and Stornoway, where the children and family needed me.

The worst and most challenging run was on the final day (4 August), return from Stornoway to Scalpay (my final populated island). I waited impatiently to get going on Sat 4 August, starting at 5:30am at the crack of dawn. However, battling against a strong cold wind and miserable skies, by 8:00am I had journeyed only 25 miles. Like Toad, I hid temporarily under a bridge to escape the worst of the weather, falling asleep for ~30mins, only to awake shivering and wishing for my warm bed! Returning over the Clisham (a high pass), the mountain gods seemed to release all of their otherworldly demons at me - with torrential sheets of soaking rain, and I was nearly blown off my bicycle. But I got back safely to Stornoway that night... with 519 miles complete... and I had a long, long and very hot soak in the bath.

High points: Having a celebratory swim at Vatersay (Barra) after completing the first 170 miles; cycling the lonely Glenroy with the family on 28 July; getting fit again (LOL). Knowing that I am doing something positive.

Regrets: I did not get to visit some places on my original itinerary, but such is the nature of cycling and Scottish weather. Another time, another place, je serai lá.

I also quickly realised that Scotland needs many, many, many more cycle routes, completely separate from vehicular traffic - but this perhaps is another fight for some-one else to take up.

So from the heart, thank you again for all of your superb support.

With kindest wishes
Eddie and Family
Stornoway, Bonnie Scotland.

 

Sunny Stornoway topples Tenerife sunshine record!

It's nearly unbelieveable - the past nine days (to 31 May 2018) have seen 119 hours of bright sunshine in , which is an average of 13.2hrs per day, making it sunniest spell in the town for at least 6 years (since June 2012). Infact, we comfortably beat 's (WMO station: 60025) total of 54.2hrs and 's (WMO station: 60040) total of 77.3hrs for the same period.

tn_download.jpg

And the heat still goes on, with no sign of it letting up yet... #Scorchio #Scotland

¡Adios Tenerife! ¡Hasta Luego La Laguna!

Eddie ha terminado su año sabático. ¡Qué aventura en Tenerife! Aquí hay algunas fotos y películas meteorológicas. Muchas gracias a todos, Eddy.

--------------------------------------------------------------------------------------

After six and a half glorious months on Tenerife, Eddy's period of sabbatical leave is now over, and he has returned to Stornoway. What an adventure! See below for a few memorable meteorological photos and movies. It was certainly the "time of my life". With great thanks for everyone, Eddy.

Time Lapse Cloud Movie Videos (Tenerife playlist) here:https://youtu.be/xcWloQsuT0g?list=PL95LKZN9i_Qf4Wlnws8u0OVZ04msIRbpB&t=1

Tenerife

Teide (3708m) rises majestically above the stratocumulus clouds of the trade-wind inversion.

Tenerife

Eerie and stunning view of the Alisio trade-winds across Anaga to Roque de la Forteleza from La Laguna at dawn.

Tenerife

Stunning view towards Santa Cruz de Tenerife (and Gran Canaria more than 100km beyond in the distance), from San Roque, La Laguna.

Tenerife

El Bronco (725m) and Pico Cancelita, Pico Amarillo and Pico Colorado (775m) , La Laguna.

Tenerife

El Bronco and Vega de Las Mercedes, La Laguna.

Tenerife

The Solar Eclipse of 21 August 2017, captured by Eddy from San Roque, La Laguna.

Tenerife

A bumble bee searches for some nectar on La Gomera.

Tenerife

View from Guímar to Izana mountain.

Tenerife

'Purpi-heaven' at Garajonay, La Gomera.

Tenerife

Eddie's final day at the Institute de Astrophysics, La Laguna.

The Weather of Bloomsday 16th June 1904

For all James Joyce fans around the world - today, 16 June, is 'Bloomsday'!

Bloomsday is named after Leopold Bloom, the central character in Ulysses, the novel by James Joyce, arguably one of the greatest works of literature of all-time . The novel follows the life and thoughts of Leopold Bloom and a host of other characters – real and fictional – from 8am on 16 June 1904 through to the early hours of the following morning, in Dublin, Ireland.

Eden_Quay,_Dublin_1900.jpg

 

Ulysses is riddled with enigmata (plural of enigma), tricks and conundra (plural of conundrum). Joyce even got the weather right on the day in question (it was a warm summer's day in Dublin, with a high temperature of 23-24degC, but there was a thunderstorm in the evening!

After a little bit of detective work (sorry, only a little), I have uncovered the following weather gems in Joyce's magnum opus:

"Warm sunshine merrying over the sea"

"His frocktails winked in bright sunshine to his fat strut"

"Thunder in the air. Was washing at her ear with her back to the fire too. He felt heavy, full: then a gentle loosening of his bowels"

"The deafening claps of thunder and the dazzling flashes of lightning which lit up the ghastly scene testified that the artillery of heaven had lent its supernatural pomp to the already gruesome spectacle"

"past ten of the clock, one great stroke with a long thunder"

OK, ok, next time I'll use 20th century reanalyses by NOAA-CIRES or ERA20C by ECMWF - sorry time does not allow today.

Happy Bloomsday 2017 to all!

@eddy_weather

 

 

Anaga 'Foehn Waterfall' Captured by Eddy in Tenerife

The sub-tropical trade winds have been blowing more strongly than normal across the Canary Isles in recent weeks. Here is an (otherwise) rare example of a foehn waterfall cloud, captured in time-lapse mode (at 1/50 hertz) by @eddy_weather on 2 June 2017, from Santa Cruz de Tenerife - wow!

If you cannot see the animation here - click here!

Bow Waves in the Trade Wind Cloud Inversion Layer

Today in the #CanaryIslands as seen by the NASA Terra sensor (713km above us): Lovely 'bow waves' appear in the trade wind cloud layer as it approaches the mountainous isles from the N/NE. But Aha! How does the wind know each island is ahead of it? Can the wind itself predict what is ahead of it? (answer below)

Capture.PNG.22

Answer: Much like the way a motorway traffic jam propagates backwards against the flow of traffic, the velocity and air pressure fields change considerably in the airflow ahead of the Isles

@eddy_weather

#NASA MODIS Terra

Ocean Sunglint Trails

There were some spectacular trails of 'sunglint' to the lee of Canary Islands yesterday (18 May 2017), as seen by NASA MODIS Terra satellite sensor. Sunglint is the isotropic reflection of the sun's rays from a still water surface (isotropic means it has a preferred direction). In this case, the wind was blowing strongly from the north/north-east, and in the lee of the mountainous islands, the sea is more sheltered from the wind. Thus it is smoother and hence reflects more sunlight back to the satellite sensor.

Looking more closely, one can see the actual impression of the lee atmospheric gravity waves on the sea surface (these are not regular ocean waves - instead these have wavelengths of several kilometres).

Lee-Sunglint-Canarys-19May2017.png

@eddy_weather, San Cristóbal de La Laguna, 19 mayo 2017

El Tiempo en Tenerife by Eddy!

Eddy is presently on sabbatical leave from the University of the Highlands and Islands and is currently working at El Instituto de Astrofísica de Canarias, San Cristóbal de La Laguna, Tenerife (Canary Islands). Here are a few photographs of his new surroundings:

tn_Santa-Cruz.PNG

The view from el Mirador de San Roque (~725m) in La Laguna, down to the city of Santa Cruz de Tenerife, with the island of Gran Canaria beyond across the sea in the distance.

tn_Guajara-Campus.PNG

View to the Guajara campus of the University of La Laguna.

tn_Vega-de-Las-Mercedes.PNG.1

View across towards La Vega de las Mercedes

tn_P4231604.JPG

San Cristóbal de La Laguna is a UNESCO World Heritage Site, with many beautiful buildings dating back to 17th century and earlier.

17620482_1353090421405641_2093394989436408859_o.jpg

Eddy on his first day of work at the Instituto de Astrofísica de Canarias in La Laguna.

17854898_1353090551405628_1571782812311414740_o.jpg

The view from my workplace to the Anaga mountains in the distance. The large satellite dish sits on top of the roof of the nearby Museo de la Ciencia y el Cosmos.

17855417_1353090534738963_3461806743694836052_o.jpg

tn_Teide2.PNG

Of course, a trip to Tenerife would not be complete without a visit to desert landscape of Mt Teide, the world's 3rd highest volcano at 3,718m in altitude

Lava-Flows.PNG

Inside the huge volcanic crater, many different coloured and solidified lava flows can be seen (the black ones on the mountain slope are thought to date from the late Middle Ages)

@eddy_weather, April/May 2017

Happy World Meteorological Day 23 March 2017!

A very happy #WorldMetDay to you today (23 March 2017) from @eddy_weather in the Hebrides, Scotland!

IMG_0276_eriskay_4.JPG

Stornoway: Exceptionally mild winter so far and driest for 6 years

tn_P1291350.JPG

Based on long-term Met Office records for Stornoway (which digitally stretch back to 1873, one of the longest such series in Scotland), the winter of 2016-2017 so far in Stornoway is the 2nd mildest (out of 144 years), 21st driest (out of 144 years) and 48th sunniest (out of 88 years), according to the latest data from @eddy_weather.

Let's look at the data with the aid of a few charts. Firstly,  air temperature: Up to the end of January 2017, the current winter's mean air temperature of +6.9C has only be exceeded once before, in 1989:

Mild-Winter-Temp-Graph.png

Next, precipitation (rainfall & snowfall): We are having a dry winter, the driest in 6 years (since 2011) and the 21st driest in the whole 144-year record (so about a 1:6 or 1:7 year event):

Mild-Winter-Precip-Graph.png

And finally, days with air frost: There have been only 3 air frosts this December and January, which is the joint 10th lowest total since 1873. Overall, there's been a decrease of about 25% in the number of days of air frost since 1873 for these months (see trend line).

Mild-Winter-Frost-Graph.png

@eddy_weather, Stornoway, 5 February 2017.

 

 

'Fairytale' Highlands: The view from 12,000 feet

Flying from Edinburgh to Stornoway recently, I captured the following stunning views of the Highlands. Fog and low cloud filled into the glens like a rising and invading ocean, but the Munro peaks remained glorious and resplendent in the sunshine, just like Greenland nunataks. Here I have identified some of the mountain summits:

Rannoch-Moor-from-Creag-Meagaidh_LABEL.png

1) Looking south across Rannoch Moor

The-Trossachs-LABELS.png

2) North-west across The Trossachs to Ben Lui and Ben Cruachan (near Oban).

Nevis-Range-LABEL.png

3) The Nevis Range and the Great Glen.

Dalwhinnie-LABEL.png

4) Now looking eastwards (from the other side of the aeroplane): Fog winds its way through the Pass of Drumochter

The-Fara_Dalwhinnie_Waves-Zoom-LABEL.png

5) The Fara and Dalwhinnie (the bow waves indicate the fog is flowing upwards from the south, and perhaps is sloshing in seiche fashion e.g. https://youtu.be/liwEP03SgVw?t=4 and https://youtu.be/bWKiRsHSBFw?t=1)

Speyside-under-stratus-glory_LABEL.png

6) A Broken Spectre 'Glory' from the fog top indicates that the fog droplets were 'old', with a variation in size of more than 20%.

Carn-Eighe-Sgurr-na-Lapich.PNG

7) And finally, out of the clouds: Carn Eighe / Sgurr na Lapich with a rather thin snow cover for the time of year.

A radiosounding taken at Abermarle, Northumberland (which was also lying under the fog layer) at 12z on this day shows a strong temperature and humidity inversion at 700-800m. The air temperature was -1.1degC at 766m with 99% relative humidity, whereas at 1050m it was a shocking +8.2degC but with a relative humidity of only 30%.

2017012012.03238.skewt.parc.gif

@eddy_weather, Stornoway, Scotland, 24 January 2017

 

Drax and Ferrybridge Making Clouds

Flying north from Heathrow to Stornoway (via Edinburgh) on Friday 20 January 2017, I was able to spot a plethora of local cloud features. It's all thanks to (a) the quasi-permanent high pressure and temperature inversion across the British Isles lately, and (b) humans.

Firstly, let's look and see what two of the biggest power stations in the UK are up to (from a viewing height of 32,000 feet):

tn_Drax-Ferrybridge-20Jan2017-Zoom1.PNG

Oh dear, it's looks like some stratocumulus or stratus undulatus pyrocumulugenitus!

Let's look more closely:

tn_Drax-Ferrybridge-20Jan2017-Zoom2.PNG.1

Drax is the bigger plant marked 'A' (with presumably a greater emission of water vapour); Ferrybridge is 'B'. Drax's cumulus thermal (pyrocumulus, as it is caused by an anthropogenic heat source) is so powerful, that when it hits the inversion, the cloud oscillates up-and-down downwind (north) in a wave train - that's the undulatus bit.

Now, let's consider the NASA Terra 721 satellite image of the same time. The Drax plume again is most apparent - I wonder if its total water vapour emissions are proportionate to the cloud liquid water extent across the north of England that day? There is surely a link, whether minor or major, as shown by Graham (2007) for the Energie Wasser Bern (EWB) incinerator in Bern Switzerland.

 Drax-Ferrybridge-20Jan2017-Terra721-Zoom.PNG

Reference: 

Graham, E. (2007). Clouds - Nature's Landscape? Montagsseminar, Institut Fuer Angwandte Physik, Universitaet Bern.

 

NASA Terra satellite spies snow extent over Scotland

NASA's Terra satellite flew over Scotland this morning at a height of 705km and captured the following two images:

Capture.PNG.20 Capture2.PNG.7

There's a near complete snow cover over the country but it's all very ephemeral I'm afraid - it'll disappear as quickly as it came!

(False colours: Left: red=snow; Right: cyan=snow).

@eddy_weather, 14 January 2017

Arctic blueskies and snow: View from Stornoway Ranol today

This was the view from Stornoway Ranol hill today, at the top of the Stornoway Golf course: There was about 3-5cm of crisp, frozen snow lying:

2017-01-13 14.18.00.jpg Capture.PNG.19

Capture2.PNG.6

@eddy_weather, 13 January 2017.

First snow of the winter in Stornoway

After the record mild December, at times it felt like it was never going to come... but finally the first snow of the winter is lying across Stornoway tonight - especially on the town's hilly Golf course, where snow enthusiasts (young and old) were out doing some night-time sledging this evening...

2017-01-12 19.13.19.jpg

A few facts on the current cold snap:

  • #thundersnow was recorded in Stornoway three times in the past 36 hours: 5h30 and 16h30 Wednesday, and 8h50 Thursday
  • About 3-5cm of snow is currently lying on undisturbed ground, with deeper drifts in places (due to the strong wind)
  • The air temperature has been ABOVE zero throughout the event (typically +1.5degC), but due to a lowering dewpoint, the snow began to lie properly from midday Thursday due to the ice-bulb effect (yesterday the high winds meant the latent heat transfer was too large and prevented settling of the snow)
  • Most of the snow is actually graupel - soft rimed hailstones!

@eddy_weather, Stornoway, 12 Jan 2017

 

Eddy on #Thundersnow

#Thundersnow is the new weather buzzword that's recently come across the pond from Amerikay...

lightning-552038_960_720.jpg

Listen to Eddie explaining more on BBC Radio Scotland yesterday here: http://www.bbc.co.uk/programmes/b086lh6q at 1hr 26mins 36 secs (or 10:26a.m.).

@eddy_weather

The Weather of 2016 in Stornoway: At a Glance

tn_P1021338.JPG

I've completed a climatological analyses of the weather in Stornoway during the year of 2016.  Rather than write a tedious monologue, I'be summarised all relevant monthly values in a Table, which is presented below.

Overall the year was mild with the mean temperature about +0.5degC above normal (but not as warm as it was in 2014).  Rainfall was close to average (i.e. much drier than in 2015, which was a record wet year) and there was near average sunshine too. The number of air frosts was below normal.

Station:

Stornoway Town 04004

                       

Status:

Semi-Homogenised

                     

Year

2016

                       

Month

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

 Year

Mean Max

7.1

6.7

9.2

9.6

12.9

15.6

16.1

16.8

15.7

13.3

8.6

9.9

11.79

Mean Min

2.8

0.9

3.8

3.4

6.8

10.2

10.8

10.5

10.2

6.9

2.9

4.9

6.18

Mean (degC)

5.0

3.8

6.5

6.5

9.9

12.9

13.5

13.7

13.0

10.1

5.8

7.4

8.98

Highest Max

12.9

10.7

13.5

12.5

19.7

20.0

22.0

22.2

19.2

17.4

13.3

13.1

22.2

Highest Min

10.8

4.9

8.9

6.9

9.8

13.5

14.9

13.9

13.4

12.8

11.2

9.6

14.9

Lowest Max

2.5

3.6

4.6

5.8

9.7

11.9

14.3

14.2

12.2

9.6

3.9

3.9

2.5

Lowest Min

-1.9

-2.3

-2.1

-2.7

2.8

7.2

6.2

4.2

6.2

0.8

-2.5

-1.7

-2.7

Air frosts

7

8

4

3

0

0

0

0

0

0

6

2

30

Grass Frosts

16

23

19

12

1

0

0

0

0

9

17

10

107

Lowest Grass

-6.4

-5.5

-6.4

-5.4

-1.4

4.0

3.1

3.0

1.9

-4.1

-6.7

-6.7

-6.7

Precip (mm)

157.5

154.7

92.6

53.4

62.9

80.0

143.5

86.8

139.0

38.9

114.6

133.0

1257

Wettest

18.8

24.0

27.7

5.8

11.0

12.5

26.1

20.2

20.6

10.8

23.2

14.3

27.7

Raindays (>=0.2mm)

24

26

22

24

12

17

30

16

23

12

25

27

258

Wetdays (>=1.0mm)

18

23

14

14

10

14

23

12

21

10

21

23

203

Hail

7

12

4

7

2

0

0

0

0

0

6

6

44

Thunder

3

1

0

0

1

1

0

1

2

0

0

2

11

Snowfall

10

16

6

7

0

0

0

0

0

0

5

5

49

Snow Lying

7

2

1

1

0

0

0

0

0

0

0

0

11

Max snow depth (cm)

2

2

2

2

0

0

0

0

0

0

0

0

2

Cloud percent

0.8188

0.7349

0.6956

0.7318

0.7042

0.8073

0.9346

0.6821

0.7243

0.5559

0.6170

0.7917

0.73

 

@eddy_weather, Stornoway, 2 Jan 2017

Record Warm December in Stornoway

With one day of the month yet remaining, December 2016 looks like being a record-breaking mild month in Stornoway.

Eddy reports that the average air temperature for this December will clock in at approximately +7.7°C, almost a full 3°C above normal – or about half a degree warmer than the long-term average temperature for April!

Such a degree of warmth is ‘highly unusual’, and follows very high global air temperatures during both 2015 and 2016. This December will also rank as the warmest of any winter month (December, January or February) for the full period of the Met Office archives, which stretch back over 150 years in Stornoway (one of the longest such series in Scotland).

The following chart places the warmth within the long-term context of all winter months from 1873-2016:

Dec2016-wrm.png

The weather is set to change over the weekend, however, as a short cold snap ushers in wintry flurries and chilly north wind for the New Year.

@eddy_weather, Stornoway, 30 December 2016

#stormConor was Cat 1 Hurricane over Faroes on Christmas Day

You may have missed him, but #stormConor was a fighting wee monster as he passed through Thorshavn (Faroes) on Christmas Day.

 output_xajflx_cropped.gif

The 4pm SYNOP for Thorshavn WMO station 06011 read as follows:

Air Temp: 4.0C Dewpoint: 1.4C Pressure: 966.6hPa Wind dir: NW Mean speed: 72kts (Hurricane Force 12), gusting 102kts (117mph)

and again at 6pm:

Wind gust: 102kts (117mph)

That's several mph stronger than the Stornoway 03026 Hurricane of January 2015. Thorshavn 06011 also recorded 4 consecutive days from 23rd-26th of wind gusts exceeding 95mph (and 3 consecutive days of over 100mph).

The satellite animation above (courtesy of sat24, images copyright METEOSAT)  shows that Conor was a classic Shapiro-Keyser low, with a probable #stingjet being the reason for the exceptional wind speeds (Shapiro-Keyser 1990). Further evidence for the stratospheric intrusion of very dry air (usually found in the region of a tropopause lowering with a #stingjet) can be seen in the following METEOSAT 6.7µm water vapour channel image for 12h (below).  A prominent dark area (dry intrusion) lies directly east of the cloud head tip, and also west of the main frontal boundary:

meteosat-msg_wv062_overlay-vector-overlay.jpg

This dry air arrived in Stornoway during the evening of Christmas Day. A dewpoint of -6.4C was recorded at 18h with a relative humidity of only 45% (due to the 'ice-bulb' effect, the ground was freezing despite an ambient air temperature of +5.5C). The NAVGEM global met model also indicated that widespread tropopause lowering was taking place near #StormConor (red blotches on following chart):

nvg10.tpause.006.europe2.gif

@eddy_weather, Stornoway, 29/12/2016

Reference:

Shapiro, M.A. and Keyser, D.A., 1990. Fronts, jet streams, and the tropopause. US Department of Commerce, National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Wave Propagation Laboratory.

 

#StormBarbara at T+24

Update by Eddy, Friday 11am: The #stingjet of #stormBarbara now looks like staying offshore. Hence maximum expected wind gusts can be reduced from the extreme values given below. So staying wild, but not crazy (thankfully!). See my latest posts on Twitter at: https://twitter.com/eddy_weather

---BEGIN--- (original post)

Please note this is Eddy's final prognostic on #StormBarbara. I will however, be posting analyses and diagnoses during and post-event on Twitter (should power supplies permit so).

Here's how I view the development of #StormBarbara:

Barbara will be a very powerful storm, with maximum wind gusts within the #stingjet* of probably over 100mph. However, there is disagreement still between the models over the exact track of the jet. The final track of this jet will prove crucial regarding the impact of Barbara.

Currently the Global Forecast System (GFS) mean has the #stingjet remaining out to sea, to the north-west beyond St. Kilda, Butt of Lewis, Flannan Isles and Sulisker (see charts below). In this run, gusts of 70-80kts affect N and W Lewis, with up to 100kts (120mph) within the #stingjet, well offshore:

gustkt_033.jpg

However, the all met model ensemble mean (the best estimate from all met models at the moment) indicates that GFS has slow wind bias for the region 58.0degN, -4.0degW (see next chart):

ens_58.0_-4.0_384_kt_06.png

In contrast the COSMO European model (run at highest possible resolution) has a quite frightening prediction with windspeeds in excess of 115mph (180km/h) blasting into west Harris and westside Lewis at 17-18h (see next chart). If realised, this would make it almost as strong as the 'Stornoway Hurricane' of 8-9 Jan 2015.

COSMO-Fri23Dec2016-17 h.PNG

Conclusion: With such disagreement, analyses of real-time satellite imagery will prove key as to the position and area of the sting jet / cold jet which will cause the most violent winds, as well as indicating the Langrangian (relative) speed of the system itself.

p.s. Late addition: I notice the US NAVGEM model is now pulling Barbara further NW again, in line with GFS.

Likely temporal Sequence of Events (very rough guide ± 2-3hrs):

6am: Frontal trough of storm reaches Barra, torrential rain and wind gusts reach 60-70mph.

8am: Same reaches Stornoway

9am-12 noon: Winds increase to gusts of 75mph

~Lunchtime: As frontal trough clears, a temporary 'lull' back to 60-70mph gusts

2pm-8pm: The main hooley, with the most violent winds moving northwest across the Hebrides from Barra to Lewis. Highest wind speeds are likely to last 2-3 hours in duration (depends on speed of system herself). Max gusts are as indicated above (between 80-115mph). If the #stingjet stays well offshore, this stage will be reduced in severity.

10pm-midnight: Worst hopefully over.

The Christmas Day Storm (perhaps #StormConor): It looks like it will also be a strong storm, but current model runs suggest a track further still to the NW. Let's deal with him only after ##StormBarbara!

22 Dec 2016, @eddy_weather, Stornoway

  * Please note that I am using the term 'sting jet' for both sting jets and cold jets (or cold conveyor belts). This is not strictly correct meteorologically speaking - but since the public are more familiar with the term sting jet, I am using this term alone to avoid confusion.

---END---

 

Thundersnow in Stornoway on the Winter Solstice

There was snow with thunder and lightning in Stornoway today (21 December 2016). It was captured by the Stornoway Lews Castle College radar (see below):

C0N2CfLXEAA-dMu.jpg

The occurred just after 16h: See the bright red colour (top right image) & pink (bottom left), as well as large vertical velocity Doppler shifts (shades, bottom right). These are indicative of large hail, large snowflakes and considerable turbulence respectively, leading to the exchange of electrical charge. You can learn more about what the colours mean here: https://uhi-mahara.co.uk/view/view.php?id=24843

Known as 'thundersnow', it is a common misconception that thunderstorms require heat and warm weather for their development. This is a false premise: What thunderstorms really need is atmospheric instability, which is a frequent occurrence in deep cold polar airflows over warm ocean surfaces, such as happens fairly often in NW Scotland during wintertime.

@eddy_weather, Stornoway, 21 Dec 2016

 

Storm #Barbara to be first major storm of winter

#StormBarbara - here she comes Friday (23 December) at 90mph+. Another storm is possible late Christmas Day. The devil will be in the detail, so please keep alert to Met Office warnings, as the exact track of each storm (yet to be pinned precisely) will determine their severity on land. Don't be fooled by any temporary lulls - it may be just the eye of the storm passing over (though I think both eyes will stay out to sea on these x 2 occasions). I shall be tweeting updates on Twitter (as long as the power holds): https://twitter.com/eddy_weather

C0HED8ZWEAAD7QH.jpg

Official Met Office Warning:
http://www.metoffice.gov.uk/public/weather/warnings/#?regionName=he&from=rss&sn=07EA8E4A-143C-8CC5-83B2-1B54CA34F60A_3_HE&utm_source=dlvr.it&utm_medium=twitter&tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1482451200

@eddy_weather, Stornoway, 20 Dec 2016

Big Change in Weather For Xmas

Well you've heard it all already - I'm pretty confident that the big change in Atlantic weather that I mentioned last week is now imminent (caused initially by the collapse of an intense cold air dome over Canada last week).

Expect severe gales in the run-up to Christmas, with (brief) snow Wednesday night/Thursday; otherwise torrential rain, violent hail squalls, storm force gusts, thunder and lightning too. Keep alert too to closer short-term warnings (from reputable providers of course e.g. The Met Office) - some of the individual storms could be very potent, and blow up (and out) within less than 24hrs.

'Tis the season...

Podcast from the Met Office today:

@eddy_weather, Stornoway, 19 Dec 2016

Warmest December Fortnight on Record in Stornoway

The past fortnight (5th-18th December 2016) has been the warmest fortnight on record in December in Stornoway, confirms @eddy_weather. Digitised meteorological records in the town go back to 1873, one of the longest such series in Scotland. The mean daily high temperature has been +11.9C, and mean daily average has been +8.9C.

This statistic will be easier to understand when presented in the following graph. The last time it was nearly so mild in December was in 1971 (with a mean daily high of +10.9C and mean daily average of +8.4C in the two weeks up to 20th December), but it has never been as mild as present at any time in recorded history.

December warmth

This news exposes the absurd "post-truth" forecasts of last month (e.g. "Four months of Snow Ahead") in the true light and fact of day.

@eddy_weather, Stornoway, 18 Dec 2016

Eddy's Outlook for Christmas week: Very stormy with frequent severe gales, torrential rain and hail squalls - with snow likely over the winter solstice (Wed night 21st/ Thurs 22nd Dec) - but it will be the most unpleasant type of snow (dull, raw and wet rather than deep, crisp and even!). Possibly even stormier for Christmas Eve and Day, watch out! 

October mildness in December: But major weather changes in Atlantic this week!

The past week has been astonishingly mild in Stornoway: The average daily high has been +11.8C, with a daily low of +7.1C; these values are more akin with early-to-mid October than December!

However, major changes are afoot in Northern Hemispheric atmosphere over the next few days. In stark contrast with the winter so far, a dome of extremely cold air (with a 1000-500hPa thickness of less than 480dam) will collapse over eastern Canada, surging out over Labrador and Newfoundland during mid-week. This will create an intense thermal (baroclinic) gradient, likely leading to super-powerful storms in the western North Atlantic (933hPa is forecast near Newfy on Thurs). It's not certain yet whether such energy will transfer east to Scotland - but it's worth keeping on eye on my blog and Twitter in the coming days just in case (NAVGEM met model T+84 and T+126 charts below).

11dec2016_nvg10.thk.084.atlantic.gif

11dec2016_nvg10.thk.126.atlantic.gif

@eddy_weather, Stornoway, 11 Dec 2016

Am faic sinn sneachda aig àm na Nollaig?

Saoil am faic sin sneachda aig àm na Nollaig am bliadhna?

Bha mi a 'bruidhinn ri an fìor-àlainn Cathy Bhàn seachdainn seo chaidh! Seo an clàradh:

Cathy.PNG

Faodaidh tu èisteachd ris a 'clàradh anseo: http://www.bbc.co.uk/programmes/b08305s3#play 

@eddy_weather, Steornabhagh, 7mh dhen Dùbhlachd 2016

Post-Truth Meteorology

Met Office Predicts White Christmas for All Scottish Cities

Four Months of Snow and Bitter Winter Ahead

Do either of the headlines above seem familiar? Did you read them in any of the Scottish newspapers recently? 

Both statements actually come from leading Scottish daily newspapers printed during the last fortnight. The unfortunate reality is that both are lies - such predictions are no more accurate than the average horoscope or crystal ball gaze. But surely these are 'White Lies'  (lies told without any intentional harm)?

Alas, this is not the case either. They are cases of 'Post-Truth Meteorology' - a term I recently coined on the television programme Sunday Politics Scotland, based on the new word of the year 2016: Post-Truth. The meteorological aspect works like this:

Deliberately false media reports about the weather (such as above) are becoming increasingly commonplace.  These 'forecasts' are not made by scientists, but are instead created by journalists with a political agenda and other attention-seekers. However, the publishing newspapers falsely attribute them to scientists and meteorologists (e.g. The Met Office), so as to increase public doubt and confusion over weather and climate change. This can have serious political ramifications, as the public are then less likely to support mitigation measures against climate change (such as renewable energy), or take precautions in the advent of severe weather.

You can view Eddie talking on the BBC here:

@eddy_weather, Stornoway, Scotland (December 2016)

Climate Stats for Stornoway: November 2016

Following the glorious October, November 2016 proved to another sunny and dry month, relative to normal. The clear skies meant nights were cold, however, with an unusual sequence of 7 frosty (and icy) nights-in-a-row from the 18th to 24th.

Capture4.PNG.1

Statistics from Stornoway town weather station:

https://www.wunderground.com/personal-weather-station/dashboard?ID=ISTORNOW2

Mean Max: 8.6degC (Highest: 13.3degC on 14th, Lowest: 3.9degC on 17th)

Mean Min: 2.9degC (Highest: 11.2degC on 14th, Lowest: -2.5degC on 18th)

Lowest grass: -6.7degC on 18th

Precip: 114.6mm (Wettest day: 23.2mm on 8th)

Thunder: 0; Hail: 6; Snow Falling: 5; Snow Lying: 0; Grass Frosts: 17; Air Frosts: 6; Raindays: 25; Wetdays: 21; Cloud Cover: 61.7%.

Long-Term Trends (based on Met Office records from the town and airport, since 1873):

It was the sunniest November in nearly 20 years, with a total of 57.0hrs. Overall this made it the 11th sunniest in 87 years (see chart below). In terms of rainfall it was the 31st driest out of 144 years, so equivalent to a 1-in-4 or 1-in-5 event. Temperature-wise, it was slightly cooler than normal due to the clear skies, and the number of air frosts was well above average. 5 air frosts were recorded at the Airport with 6 in the town (the long-term average is only 1.8).

 Nov-Sunshine.png

@eddy_weather, Stornoway, 4 December 2016

 

 

 

Maritime Arctic Airmass Views from Stornoway

Spectacular maritime arctic skies during the recent cold snap in Stornoway (by Eddy):

weather image

Varied hues of Cumulus mediocris radiatus, with congestus.

Translation: Small heaped clouds, wider than taller, in a line; with a few taller than wider versions.

weather image

The remains of a cumulonimbus anvil, but the cumulonimbus tower is no more! Cirrus spissatus virga cumulonimbogenitus.

Translation: Horse's hair (ice) cloud, thick with falling snowflake streaks (virga), formed earlier by a cumulonimbus shower cloud.

weather image

Arcus, ahead of an approaching cumulonimbus squall.

Translation: A threatening arched line of cloud racing out from a thunderstorm.

weather image

Cumulonimbus incus capillatus (white cloud in background).

Translation: A raining large heap of a cloud, possibly with thunder, with a flat-top shaped like an anvil, producing ice-cloud like horse's hair.

weather image

A powerful single cumulus congestus thermal (white) rises under the shadow of an enormous cumulonimbus incus anvil (dark left).

Translation: A heap of cloud, taller than wider.

weather image

And a severe hoar frost (air temperature -4.6degC) at 08h00 on 18 November, Stornoway Golf course. The grass min temperature was -6.7degC in Stornoway town.

@eddy_weather, Stornoway, November 2016.

November chill? A diagnosis and prognosis by Dr. Eddy

There's been some speculation that the coming winter will be a cold and snowy one. Certainly the past fortnight (up to 20 November) has been rather chilly across Scotland, with early severe frosts and heavy snow falling on the mountains. So what's the prognosis for the rest of the winter? 

Every winter brings snow, especially in Scotland! And humans have enjoyed speculating (not just on the weather) since time immemorial. And after two or three mild and stormy winters on the trot, it's not that difficult to predict a change in our weather fortunes!

At the same time, however, recent advances in atmospheric science mean that there are some guides to the general state of the hemispheric* weather pattern for perhaps a few to several weeks' ahead in time.

Let's start by looking at today's global weather pattern (courtesy of the University of Maine - see map below). This shows the current air temperature anomaly. There's an intense pink swath across Siberia and central Asia where it is record cold at the moment - but it is equally hot over most of the Arctic Ocean (where there has been unprecedented reduction in Arctic sea ice). A wee smidgen of blue over Scotland and Ireland confirms our current cold snap, but overall the British Isles occupy only a tiny part of the global picture. 

weather image

Today's air temperature pattern arises due to aforementioned 'Arctic amplification' due to sea-ice loss (Serreze et al. 2006), and very unusual stratospheric dynamics. Let's now consider the latter i.e. the stratosphere, which is the region of the atmosphere between 15 and 40km in altitude above our heads.

Stratospheric conditions are sometimes known to 'teleconnect' down to the surface, over the course of several weeks following an event such as a Sudden Stratospheric Warming (Mitchell et al. 2013). Today, NOAA's 50 millbar (~20km) air temperature plot shows clear signs of a polar vortex breakdown (see plot below). In 'normal' circumstances, there should be a circumpolar 'low' surrounded by a 'high'; instead we have a shift of the 'low' south to mid-Atlantic with a 'high' in the Bering strait - current forecasts indicate that this pattern is unlikely to change for at least the next 2 weeks.

weather image

Finally, winter storms in the North Atlantic region take their energy from the contrast in sea surface temperature between the Poles and the Tropics. They also gain energy from the condensation of water vapour evaporated from over the oceans. Here's the current sea surface temperature anomaly from NOAA Earth System Research Laboratory. There remains a cold pool ('the big blue blob'; Josey et al. 2016) in the middle of the North Atlantic, surrounded by warmer water on all sides, much the same as it was in 2015 (when a very stormy and record wet winter ensued). 

weather image

So all-in-all, a dodgy stratosphere, a very dodgy Arctic, and a stubborn big blue blob!

Conclusion: I'd say that we'll continue the cool and variable start to the winter (remainder of November, early December), but there always the chance of severe storms and gales returning, especially during the second half of winter (if the Arctic and stratosphere return to more 'normal' conditions).

@eddy_weather, Stornoway, 20 November 2016

* The Rossby waves, usually at wavenumber 6 or 7

References:

Josey, S., Grist, J., Duchez, A., Frajka-Williams, E., Hirschi, J., Marsh, R. and Sinha, B., 2016, April. Causes and Consequences of Exceptional North Atlantic Heat Loss in Recent Winters. In EGU General Assembly Conference Abstracts (Vol. 18, p. 4562).

Mitchell, D.M., Gray, L.J., Anstey, J., Baldwin, M.P. and Charlton-Perez, A.J., 2013. The influence of stratospheric vortex displacements and splits on surface climate. Journal of Climate, 26(8), pp.2668-2682.

Serreze, M.C. and Francis, J.A., 2006. The Arctic amplification debate. Climatic Change, 76(3-4), pp.241-264.

 

Big Minch 'Danglers' and Sunny Uist and Barra 'on the Lea'

Meso (and micro) scale meteorological effects gradually more become enhanced (i.e. less dominated by the synoptic airflow) when skies clear (allowing greater radiation fluxes) and winds slacken (reducing convective and advective heat transfer).

Today (Sunday 6 Nov 2016), we can see this in action across the British Isles: A strong northerly airflow has led to mesoscale convergence (meeting of air) over the Irish Sea, and a long narrow line of powerful convection (known as 'Pembrokeshire Dangler') has developed, extending more than 200km downstream into coastal Pembrokeshire and Cornwall. This is a common feature of the weather during northerly outbreaks (Mayes et al. 2013; Norris et al. 2013).

sat pic

Meanwhile, closer to home in NW Scotland, we can see a (reduced) similar effect in the Big Minch between NW Scotland and the Outer Hebrides. Showers have been funnelling down between the Harris and Skye hills all day, whilst inland Lewis has stayed dry. Further south, the Uists and Barra have been bathed in glorious sunshine, maintaining a 'clear slot' of sunny skies all the way to Donegal in Ireland ('Sunny Uist and Barra on the Lea').

sat pic

@eddy_weather, Stornoway, 6 Nov 2016

Images courtesy #NASA MODIS channels 367.

References: 

Mayes, J., 2013. Regional weather and climates of the British Isles–Part 5: Wales. Weather, 68(9), pp.227-232.

Norris, J., Vaughan, G. and Schultz, D.M., 2013. Snowbands over the English Channel and Irish Sea during cold‐air outbreaks. Quarterly Journal of the Royal Meteorological Society, 139(676), pp.1747-1761.

 

Best October in decades!

It's been the best October across NW Scotland and the Isles for decades.  Based on the long-term records for Stornoway, with a precipitation total of only 36.0mm (1.42in) it was the 2nd driest in 144 years of record keeping for the Isles (1873-2016) and the 4th sunniest since 1929 (87 years). See the graphs below by @eddy_weather.

graph

graph

Further information can be seen in a recent Met Office press release: http://www.metoffice.gov.uk/news/releases/2016/end-of-october-2016-stats

graph

Various views of NW Highlands and Islands during October fine spell

Below please find a few spectacular NASA Terra satellite images of NW Highlands and Islands, Scotland, during the recent fine spell of weather:

photo

NASA Terra channels 3, 6 and 7: Ice clouds show up as orange or pink, water as black and land as emerald green (11 October)

photo

NASA Terra channels 7, 2 and 1: Ice clouds show up as cyan blue, water clouds as white, open water as black and land as lush green (10 October).

photo

NASA Terra Visible and Infra-Red channels: As close to as we see them with our own eyes (if we were in space) - 5 October.

@eddy_weather, Stornoway, October 2016

Eddy goes East with Etihad

The United Arab Emirates (UAE) of the Middle East present one of the strangest of juxtapositions of climate, land and people on Earth today. Despite having one of the hottest, driest and most inhospitable climates on Earth (air temperatures regularly surpass +50degC during the summer season), the region today boasts two of the most extraordinarily wealthy, ultra-modern and glittering cities found on Earth: Dubai and Abu Dhabi.

Eddy-Weather recently had the good fortune to visit the latter of these two cities (Abu Dhabi). He also spent some time observing the unique weather systems of the region.

The primary reason why the weather is so hot in the UAE is because it lies on the eastern fringe of the world's greatest sandy desert, the Rub' Al Khali of the Arabian Peninsula. At a latitude of only 24degN, the Sun remains very strong all year-round (and is directly overhead in the zenith during the summer season). The UAE also lies exactlly under the influence of the global descending arm of the Hadley Cell circulation, the Earth's most powerful air circulation system. Furthermore, lying beside one of warmest seas on the planet (the Persian Gulf), the weather can get extremely humid as ocean temperatures frequently reach well above +30degC. Here are some photos:

photo

View across Abu Dhabi to the southwest. Note the hazy blue skies - the restriction in visibility is due to a combination of fine desert dust and anthropogenic aerosols, some of which are likely to be hygroscopic at high relative humidity.

photo

The Abu Dhabi National Oil Company (ADNOC) headquarters and Etihad towers (location of the Fast and Furious Tom Cruise Hollywood movie), in downtown Abu Dhabi.

photo

Eddie on the Marina seafront.

photo

2nd wonder of the modern world: The Sheikh Zayed Grand Mosque

photo

The Dusit Thani hotel (515ft high): "A little town in heaven"

photo

The thermodynamic upper air plot (tephigram) shows conditions typically of the region, with two separate inversions at 920mb and 600mb above Abu Dhabi, with a surface air temperature of +33degC. Very dry air lies above both inversions.

@eddy_weather, October 2016

 

Intense Narrow Rain Band passes through Stornoway 27/9/2016

Intense bursts of rain caused by a 'Narrow Rain Band' (NRB) were captured by the Lews Castle Micro-Rain Radar in Stornoway this morning, Tues 27 Sep 2016. Having only been recognised as unique and distinct meteorological features in their own right in the past decade or so, these bands of rain comprise of heavy downpours only a few kilometres wide, but can stretch for tens to hundreds of kilometres in length. They may cause considerable disruption, as they are sudden, squally events, and are often accompanied by severe wind gusts and torrential bursts of rain, lasting all for a few minutes.

radar

As this morning's Stornoway radar images show (above), NRBs are shallow features, originating from turbulence in warm low-level clouds. Note that there are at least 2 x separate NRBs in the plot above - the final one at 0745UTC (08h45 local time) was hardly more than 1,000m deep.

@eddy_weather, Stornoway, 27 Sep 2016

 

Here come #Karl and #Lisa!

The remains of two separate tropical storms (#Karl #Lisa), currently just short of hurricane status, are heading towards our Scottish & Hebridean shores. But please don't panic; although they do add a bit of "oomph" or "turbo-boost" to our regular low pressure systems, hurricane force winds are generally *rare by the time such systems reach us. Instead, expect a regular spell of 'fiadhaich' (wild and wet) weather.

radar  radar

* Occasionally these storms reach full hurricane force status in Autumn e.g. Debbie on 16/9/1961. But on average, it is during December, January and February that we suffer the most severe gales.

@eddy_weather Stornoway 23 Sep 2016

New Storm Names for Winter Ahead Issued: And Beware of Bogus Weather Sites!

Following the overwhelming success of the inaugural pilot project last year (2015-16), #NameOurStorms is being rolled out again for the coming winter by the UK Met Office and Met Eireann (the Irish National Met Service). Naming storms saves lives  - because people (including who control the infrastructures that protect us) are made more aware of the danger posed by such storms, allowing preventative and adaptive measures to be put in place against potential damage and loss.

For example, up to the mid-1990s it was common for a winter wind storm with a maximum gust of between 90 and 100mph to cause the loss of 5 to 10 or more lives across the British and Irish Isles. Today, despite the increasing severity and frequency of winter storms over recent years, the number of injuries and deaths has plummeted due to better awareness.

Here are this year's names: Some really popular ones are included this year: #Ewan #Malcolm #Oisin #Conor #Angus, though I'm perhaps less keen on #Doris (storm in a teacup?) and #Wilbert

radar

Final word of warning: There is an unfortunate over-abundance of unqualifed individuals proclaiming meteorological advice and expertise on the web today (e.g. Facebook 'weather' sites, Old Moore's Almanac, Exacta Weather). Many of these are operated by unqualified individuals, with little, if any, training or belief in the science of meteorology.  I strongly recommend that you take these with a pinch of salt. Certainly, do not make any safety decisions based on their forecasts  - use official sites only! 

Tip: Accredited individuals will usually have the initials RMet, CMet or FRMetS (or an equivalent qualification) after their name (in the same way that accredited trades persons have e.g. CEng, FRCS after their name). Reputable organisations are usually easily identified as having a long track record of providing met information to service providers.

20 Sep 2016, Stornoway @eddy_weather, FRMetS!

LE Radar detects strong (and wet) warm front

The Lews Castle College Stornoway precipitation radar captured a textbook example of a warm front passing over the Hebrides today (Sunday 11 Sep 2016). See the following plot (explanation below):

radar

Top left (Fall Velocity): Raindrops fall faster than snowflakes. Hence, the level at which the fall velocity changes rapidly (today 1600m, rising to 2700m after passage of the warm front) indicates the melting height of precipitation particles within the atmosphere. As a warm front brings warmer air, so the melting level rises - as seen towards the right of the image.

Top right (Raw reflectivity): This is raw signal sent back to the radar. It is useful for detecting the type of precipitation (e.g. hailstones, snow or rain). Today it's rain at the surface I'm afraid.

Bottom left (Rainfall rate): This is how much rain is falling on the ground in mm/hr. We have rates typical of the Hebrides this afternoon, about 2mm/hr.

Bottom right( Doppler mode): This is super snazzy information tells us which way the precipitation particles are moving, up, down, left or right, etc..

Tweets from the LE RADAR can be seen every 15 minutes on Twitter at: https://twitter.com/lewscastleradar and on Facebook at: https://www.facebook.com/eddyweather/. The radar is a powerful tool for research into precipitation at the University of the Highlands and Islands.

@eddy_weather Stornoway (11 Sep 2016)

Autumnal gales and rain on way for Hebrides

Hurricane season reaches a peak in September over the Caribbean and western Tropical Atlantic Ocean, as this is the warmest time of the year in this region. When the met conditions are right (which they will be over the next few days), the Coriolis force directs warm, moist plumes of this tropical air north-eastwards across the North Atlantic Ocean towards the British Isles. This usually results in heavy rain, and strong, sometimes damaging gales* for the western Atlantic "Arc" seaboards of Scotland and Ireland.

As of today (Wed), the met models are currently forecasting gales on Thursday 8 Sep, Friday 9 Sep, with possibly a severe gale later Sunday 11 Sep (keep on eye on the forecasts for updates). Winds could reach over 60mph during the worst gales. Heavy rain is also expected. Here are the current GFS forecasts of mean windspeed (gusts up to 50% stronger) for Thurs 09hz Fri 18z and Sun 18z.

Scotland ScotlandScotland

Why so windy? Current sea surface temperatures are 'off the wall' across most of the northern Pacific and Atlantic oceans (see chart from NOAA ESRL) - and since mid-latitude depressions take most of their energy from the contrast in temperatures along the polar front, it's no surprise it's getting stormy.

Scotland

*The strongest winds ever recorded in Ireland occurred on 19 September 1961 during the passage of ex-hurricane Debbie with max gusts of 120mph.

@eddy_weather, Stornoway, 7 Sep 2016

Highland Clouds Revealed as Harmonic Oscillators

We all know well that mountains influence the weather, and in Scotland even more so than elsewhere... However, today (6 Sep 2016), we were treated to a much more benign, indeed beautiful reminder, of how the Highlands hills act in harmony with nature – that is, in concertina with the mountains, the atmosphere resonates just like a musical guitar or violin string – with the evidence portrayed in the clouds.

We can see clear evidence of this resonance today in the forms of stratocumulus lenticularis and undulatus clouds on today’s NASA Terra satellite image, where the clouds take the shape of classic herring-bones (or lee waves), as seen across most of central, southern and western Scotland.

Scotland

Close inspection of the distance between each cloud crest reveals a wavelength of approximately 10km in southern Scotland, and 12km in the far northwest.

And now for the Atmospheric Physics bit:

Using basic met data, the Brunt-Vaisala Frequency (N) equation can also be used to determine the wavelength of the clouds. N is calculated as follows, where g = gravity (9.8ms-1), θ is the average air temperature (Kelvin) and dθ/dz is the rate of drop of temperature with height (Km-1):

Equation

Using data from today’s regular atmospheric radio-soundings at Valentia (Ireland) and Lerwick, Shetland (see http://weather.uwyo.edu/upperair/sounding.html), θ was ~280K and dθ/dz  was approximately 12K in the lowest 3,000m of the atmosphere. Infra-red thermal satellite images also confirmed that cloud top temperatures were relatively warm, between +5 and +8degC, with a strong series of inversions between the surface and 700hPa. Mean windspeeds were about 25ms-1 (50 knots) across the profiles.

Using these values, the Brunt Vaisala frequency (N) works out to 0.01183 s-1.

As the period of oscillation (τ) of the harmonic is = 2π/N, so τ = 2π/0.01183 = 530 seconds (or about 8 minutes). This means it takes 8 minutes for the wind to blow from one wave crest to the next.

This result can be confirmed using the standard formula V = λf  (Velocity = Wavelength x Frequency), using V = 25ms-1 (average windspeed from the soundings) and Wavelength λ = 12km (12,000m) as observed in the satellite images.

V = λf

25/12,000 = f = 0.0020833 s-1 or 1/0.0020833 = 480 seconds (also 8 minutes!)

QED

And this is what was seen from the ground in Dingwall, on the night before (during the same harmonic event) - photo courtesy Andrea Goddard:

Scotland

@eddy_weather, Stornoway, 6 September 2016

309 entries