Dr. Eddy Graham's Hebridean Weather Blog

by Dr. Eddy Graham

Edward Graham's Journal (Details)

Beware of the Black Frost!

Posted by Dr. Eddy Graham on 13 February 2016, 9:53 PM

There has been a very welcome switch to 'easterly' weather over the past few days across the Hebrides - with low relative humidities permitting an excellent clarity to the atmosphere.

However, one of the risks of such low humidity means the wet-bulb depression is enhanced (evaporation is enhanced), and in such conditions an ice-bulb effect can be observed (see chart).

Scotland's Greatest Bard - Robbie Burns

The result is an invisible 'black' frost - this occurs when the ground and objects freeze, but there is no trace of a visible 'hoar' frost (normally caused by humidities reaching 100%, which isn't the case at present across the Isles). With low relative humidities, this can happen even with air temperatures well above freezing (e.g. +2, +3degC)!!

So you have be warned - beware of the black frost!

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Nacreous clouds: A beautiful spectacle or a terrible beauty?

Posted by Dr. Eddy Graham on 05 February 2016, 12:58 PM

One of the most widespread displays of nacreous clouds ever witnessed in the British Isles took place recently over 1-2 February 2016. In some places (such as Dublin, Ireland), there is no recorded evidence of any previous occurrence, right back to the 19th century, at least (Dixon 1953).

Most of central and southern Scotland, northern England (including Manchester and Leeds) and eastern Ireland witnessed the clouds over an unprecedented length of time. In Dublin, the clouds apparently remained in the sky for nearly 48hrs (again a very unusual duration). A few example photographs are shown below (courtesy Garry Quinn photography and Kieran Commins, Met Eireann).

nacreous clouds

By gquinnphotography.com

nacreous clouds

By gquinnphotography.com

The clouds were coincident with an moderately-intense ozone hole of 200-250 DU (Dobson Units) over north-west Europe (normal ozone is about ~360 DU) - lower values have been documented in the past, for example 165 DU in November 1999 (Graham 2002). This is to be expected in this case, for ozone is responsible for heating of the stratosphere - and so a lack of it usually means a colder stratospheric air temperature. If cold enough (below -80 to -85degC), nacreous clouds (also known as 'Mother-of-Pearl' or 'PSC: Polar Stratospheric Clouds') can form.

nacreous clouds

By Kieran Commins (Met Eireann)

The clouds involved in this display were generally considered to be Type 2 PSC, and so not directly involved in ozone depletion. However, it is possible that some Type 1 PSCs may have been present too (they deplete ozone at a rate of about 1% per day). Some photographs of suspect PSC Type 1 clouds were taken early on 3 February (please ask author if interested). 

The ozone layer is, of course, vital for life on Earth. Without it, we would suffer from harmful UV radiation, which causes skin cancer and damages crops. Northern Hemisphere ozone, although nowhere nearly as low as in the Antarctic, has shown some loss in recent decades.

Here's the Northern Hemisphere ozone distribution for 2 February, courtesy of NASA Ozone Arctic Watch (http://):

nacreous clouds

As stated by Hood and Manny (2002), such holes in the Northern Hemisphere are mostly caused by dynamics in the stratosphere, and the contribution from ozone depleting PSCs is minimal.

And here's the 30hPa air temperatures (about 24km, which was the height of the clouds during the November 1999 event, as shown by Graham [2002], courtesy of NOAA CPC (http://):

nacreous clouds

As you can see, there's a clear minimum of stratospheric air temperature below -80degC, located right over the UK/Ireland i.e. highly suitable conditions for PSC formation.

And finally, on Twitter on 2 Feb, I'd thought that I'd spotted the nacreous clouds themselves on NASA Terra Channels 7-2-1. It looks like there was a hydraulic jump generated by the very strong west wind (nearly 200kts at jetstream level) hitting the Wicklow mountain perpendicularly, side-on (see sat image below). Dörnbrack et al. (1999) state that the air temperature can drop significantly in stratospheric mountain wave crests (due to rapid uplift). In the case of 1-2 february, the air was likely cooled rapidly to saturation and a low-enough temperature for PSC formation (i.e. below -85degC).

However, closer analysis of MetOp imagery shows that this particular cloud had a cloud top temperature of only -30C to -40C. So alas, no PSC! (they are probably too thin optically to be seen on standard visible/infra-red satellite imagery, Graham 2002).

nacreous clouds nacreous clouds nacreous clouds 

(with thanks to Bernard Burton of http://www.woksat.info/ for this final image)

Conclusion: Whilst outstandingly beautiful, a more holistic view of these clouds could easily be 'Harbingers of Doom'. I think more research is needed on the exact causes of this outstanding display.

Appendix: Nacreous clouds (such as above) form in the lower stratosphere between 20-25km. Previous sightings near/around the British Isles include the following:

  • 16 Feb 1996: Northern England
  • 30 November 1999: Aberdeen and E Scotland
  • 19 January 2008: Belgium
  • 9 December 2012: Aberdeen and Isle of Harris
  • 1-2 February 2016: This event

i.e. Their incidence appears to be on the increase during recent decades, which is in line with global ozone depletion caused by human pollutants, but it may also be coincidence.

Websites on previous sightings:


Stornoway 5 February 2016


Dixon, F.E. (1953). Weather in old Dublin. Dublin Historical Record13(3/4), pp.94-107.

Dörnbrack, A., Leutbecher, M., Kivi, R. and Kyrö, E. (1999). Mountain‐wave‐induced record low stratospheric temperatures above northern Scandinavia.Tellus A51(5), pp.951-963.

Graham, Eddie. "Nacreous clouds in November 1999 and record low ozone."Weather 57, no. 3 (2002): 107-109.

Hood, L.L. and Manney, G.L. (2002). Nacreous clouds. Weather57(10), pp.393-394.


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No @eddy_weather!

Posted by Dr. Eddy Graham on 31 January 2016, 3:54 PM

Alas, Eddie has come down the the lurgy recently, so I'm not issuing any weather news or updates at the mo, thank you @eddy_weather

Wild weather for Burns' week

Posted by Dr. Eddy Graham on 24 January 2016, 9:10 PM

It's Burns' Day tomorrow (Mon 25 Jan), and after some very pleasant but cold winter weather over the past two weeks, it's looking likely that we'll see a return to more seasonal winds, heavy rain and gales over the coming week - much as happened in the year of Burns' birth.

Scotland's Greatest Bard - Robbie Burns

A severe gale is possible on Tuesday accompanied by heavy rain. More heavy rain and further gales will follow during the week, and it may turn much colder (with brief snow) at times later in the week.

Keep posted with me on Twitter at: @eddy_weather

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Snow extent across Scotland

Posted by Dr. Eddy Graham on 15 January 2016, 11:12 AM

Sneachd (gorm) tro na Crìochan na h-Alba 's an Gàidhealtachd an-de (as seen by the NASA Terra satellite) @eddy_weather

Scotland snow extent

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Never promise snow to children unless you are certain!

Posted by Dr. Eddy Graham on 10 January 2016, 11:07 PM

Recent weather updates on @eddy_weather

Lesson #1 in Forecast Meteorology:

Snow by Henryk Żychowski

Every year, in every country which has a winter, the forecasting pros (and not-so-pro) almost always stumble up at least once with one of the following errors:

Type 1:  You fail to forecast snow and it snows -> bad for you as your local council will be mad, but who cares, as the kids are delighted and it's a surprise snowfall, yippee!

Type 2: You forecast snow and it doesn't come -> worst case scenario as the council is still mad and your kids hate you too for months!

So what's it to be? Snow or no snow this week?

Update Tue 12/1/16: Probability of significant lying snow this week is reducing now; Wed pm is colder, but maybe Thurs milder. Then colder again Fri, let's see!

Original Post Sun 10/1/16: Currently, for Stornoway and the Hebrides, it's looking slightly possible that we may get some lying snow for a day or two between Wednesday and Friday of the coming week - but it won't last, it'll probably be gone by the weekend as mild southwesterlies will soon return. Of course the snow will come earlier on the Clisham - watch out for ice too!

P.S.. I note the astronomical tides are very high tonight and tomorrow. With a low air pressure of 970hPa tonight, the combined tide and surge could be +5.5m, so please watch out if you're near the coast at high tide.



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1st Anniversary of the Stornoway 'Hurricane''

Posted by Dr. Eddy Graham on 08 January 2016, 5:02 PM

Tonight, 8/9 January 2016 is the first anniversary of the Stornoway 'Hurricane', the most powerful storm to affect the British Isles for over 20 years. At its peak, winds reached hurricane force 12 during the night at Stornoway Airport, with a peak gust of 113mph - the strongest in the UK since the 1990s. It was about as severe as Hurricane Debbie of 16 September 1961.

Here's a remainder of some of the damage / synoptic chart that night:

Tonight is also the 176th anniversary of Ireland's greatest natural disaster, Oíche na Gaoithe Móire ('Night of the Big Wind') when hundreds died in a ferocious hurricane, the severity of which has hardly been equalled over the past 300-400 years. It strongly impacted Scotland too, with air pressure dropping to 931hPa in Shetland.


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Strong easterly winds promote good drying

Posted by Dr. Eddy Graham on 06 January 2016, 9:27 PM

The tale is told in the weather statistics:

  • The first six days of January 2016 have yielded a tiny total of 0.9mm (0.03in) of precipitation (rain) in Stornoway town
  • The final six days of December had... wait for it... 67.3mm (2.65in) of rain! (75 times more)

All because of a change in wind direction i.e. an offshore, easterly!

And although chilly, the lovely dry wind has meant some excellent drying conditions following seeming endless weeks of rain.

@eddy_weather, Stornoway, 6/1/2016

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Stornoway 2015: Third Wettest Year at Airport Since 1930

Posted by Dr. Eddy Graham on 02 January 2016, 1:12 PM

Based on official Met Office data, the year of 2015 was the third wettest year on record in the vicinity of Stornoway Airport since 1930, with a total of 1494mm of rain falling. It ranks behind the two wettest years 1990 and 1999 which had totals of 1543 and 1547mm, respectively.

Incidentally, Stornoway town (a generally wetter location than the Airport) recorded 1680mm (66 inches) of rain during 2015.

The long-term trend in rainfall at Stornoway Airport (shown below) indicates an increase in variability and extreme high annual totals over the past 30-40 years.

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Stornoway December 2015 Weather Statistics

Posted by Dr. Eddy Graham on 31 December 2015, 11:51 PM

It was an exceptional month by any measure, climatological or otherwise, although not quite as extremely wet (in terms of anomalous deviation) as parts of southern Scotland, Ireland and northern England (where there has been unprecedented flooding).

It was also an astonishingly warm month in southern England, where the average temperature was more equivalent to late April/May, and flowers therefore came out in bloom (though it was somewhat less mild in Stornoway). These extreme events appear to have occurred in concertina with other worldwide phenomena, such as El Niño and climate change.

Overall it was the 2nd wettest December on record in Stornoway - but the record was only set two years ago in 2013!  And so it ranks alongside 2013 as one of the most extraordinary months of recent times (although what defines 'extraordinary' now in a new climate world is open to question!).

Provisional Stornoway town December 2015 Stats:

Average daily high: 8.8degC (+1.2 above normal)

Average daily low: 3.6degC (+0.9C above normal)

There were an unusually high number of nights during the 2nd half of the month with near-record air temperature in excess of 12 to 13degC.

Precipitation: 280.7mm (11 inches - some 215% of normal i.e. more than double)

Thunder days: 1

Days with hail: 6

Snow falling: 4

Grass Frosts: 14


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YES there's a 'Hurricane' (Force 12) offshore - but NO it's not (all) coming our way!

Posted by Dr. Eddy Graham on 28 December 2015, 5:35 PM

An extraordinarily deep and explosive depression (name 'Frank') will shoot up the Rockall Trough towards Iceland during the afternoon and evening of Tuesday 29 December. On its southern flank, winds are expected to reach Hurricane Force 12 (Cat 1 Saffir Simpson Hurricane), or astonishingly, perhaps even a Category 2 force on the hurricane scale. A storm of this severity is extremely rare, even in winter in the North Atlantic.

However, the centre of the 'Hurricane' Frank will stay offshore, meaning we will be troubled only by its 'tail-end' (frontal system) during the late afternoon and evening. Even so, winds are still expected to reach storm force 10 around the Hebrides, possibly violent storm 11 off the southwest of Uist and Barra. This means gusts of 75-90mph, so it's still dangerous.

The intensity of the winds (sting jet, cold conveyor belt) over Rockall can be seen on the NAVGEM model output for 18h Tues - a jet core of 85mph MEAN SPEED is predicted - this is most rare (gusts possibly in excess of 120mph)! 

We need be very thankful that the storm centre won't make landfall on Ireland or in Scotland. I'll be posting updates on Twitter @eddy_weather



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Severe Gale /Storm Wed 23 night into Christmas Eve - Then colder

Posted by Dr. Eddy Graham on 22 December 2015, 9:38 AM

Just a quick update - it's still looking like being very windy overnight Wed 23 / Thurs 24 Dec (Christmas Eve), with severe gale to storm force southerly winds, veering south-westerly (perhaps westerly) later.

At present, it looks like the region of strongest winds (sting jet, cold conveyor belt) will stay (just) offshore to north-west of the Butt of Lewis, but model agreement has not been good recently, neither on the path nor the intensity of this low. So there's still a chance of more extreme winds than forecast (i.e. 80-90mph) - so watch out and take care if you are out and about doing training for Santa deliveries.

The storm will sporadically usher in much colder air for a while -> so the risk of a few snowflakes (and icy frosts) in the days after Christmas should not be ruled out!




Relentless Rain and Wind to Continue for Christmas Week: Risk Storms too

Posted by Dr. Eddy Graham on 20 December 2015, 5:39 PM

The seemingly relentless wind and rain of 2015 look like continuing for the foreseeable future... and it's worth keeping an eye on the weather forecast (from reliable sources such as the Met Office or Met Eireann) as one or two major storms could spring up with short notice.

Current focus is on a violent low forming west of Ireland early on Christmas Eve (with possible hurricane force winds near its eye; may be named #Eva), but most model predictions have kept the worst offshore yet. Keep posted on Twitter for any updates: @eddy_weather

PV anomaly and 500hPa geopotential of Christmas Eve '#Eva' low (FNMOC NOGAPS):

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I'm dreaming of a Black Christmas....

Posted by Dr. Eddy Graham on 17 December 2015, 10:50 AM

With a combination of extremely mild tropical southerly winds, a globally-warmed world enhanced by an extreme El Niño, this December and Yuletide is shaping up to be anything but white!

So here's @eddy_weather's Black Christmas 2015 forecast for you!

I’m afraid it's going to be anything but a white Christmas this year – instead, it’s much more likely to be dark, windy and grey with frequent heavy rain and gales in the days leading up to, and probably beyond, Christmas Day. There’s also the possibility of a major storm or two next week, though we’ll have to wait closer to the time for any warnings to be issued (take note that 'Eva' and ‘Frank’ are awaiting on the list of coming named storms!). So I expect Santa will need to plan his journey carefully, taking advance note of ferry cancellations, and I would certainly hope that he doesn’t leave his last minute shopping until late on Christmas Eve!

(NASA MODIS inverted snow image) @eddy_weather
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Eilean Beag Donn

Posted by Dr. Eddy Graham on 15 December 2015, 9:04 AM

An Eilean Beag Donn an-de, le sneachd air talamh aird 's na beanntan (courtesy NASA MODIS)


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'Christmas Lights' Downpour Captured on Stornoway Radar

Posted by Dr. Eddy Graham on 14 December 2015, 2:47 PM

Large crowds turned out for the annual switching on of the Christmas lights in Stornoway last Friday evening (11 December 2015). Unfortunately a torrential shower of rain and sleet at 7pm spoiled the proceedings somewhat, leaving many revellers cold and wet, and making an early exit for home.

The Stornoway rain radar captured this downpour nicely (see arrow, below) - it can be seen that snow was falling (cyan colours) down to about 500m in height, but this turned to rain at lower levels (purple colours) - so nearly jingly bells, but not quite!


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Glazed Ice (Freezing Rain) Event in Stornoway Town

Posted by Dr. Eddy Graham on 13 December 2015, 7:03 PM

As predicted on Twitter  by Eddie (@eddy_weather), rain showers falling on frozen surfaces led to very dangerous underfoot conditions across Stornoway this morning Sunday 13 December 2015, as footpaths and road surfaces were turned into literal skating rinks (see photograph).

The conditions were caused by light winds and clear skies yesterday evening and overnight (leading to a cooling of the ground to a subzero temperature). When warmer clouds with rain showers blew in from the west, the rain froze instantly on the surface, leaving the treacherous icy conditions.

Snow and sleet did not fall because the air above ground was actually warmer than that at the surface. The Stornoway rain radar (image below) clearly shows this on Friday night: Snowflakes melted at about 200-300m in altitude, turning into rain drops - which later froze on the subzero ground surface.

Eddie, @eddy_weather, Stornoway, 13 Dec 2015

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Icelandic 'hurricane' reaches 163mph

Posted by Dr. Eddy Graham on 10 December 2015, 5:54 PM

In a stunning action-reply of last winter's Stornoway 'Hurricane', southern Iceland experienced an exceptional wind storm last Monday night (7-8 December 2015). Wind speed gusts reached 163mph (263 km/h) at one station in the south of the country - you can read more here: https://www.facebook.com/severeweatherEU/photos/a.1423656947857402.1073741825.1377757209114043/1749187795304314/?type=3&theater and here: http://en.vedur.is/about-imo/news/nr/3247

Meanwhile, our extraordinarily wet start to winter continues - over 150mm of rain has been recorded in Stornoway town over the past 10 days (one of the wettest short-term periods on record for winter in the town) - however, there are strong signs of quieter spell of weather on the way, with hints that a high pressure 'block' with easterly winds may establish itself for a few days, at least, mid-to-late next week (Edit: Later models show the high pressure receding by early-to-mid week).

Photos (below) are of majestic thunderhead cumulonimbus clouds over Stornoway today, Thursday 10 December. Cloud top temperatures dropped below -50degC in some instances, leading to lightning, thunder and large hailstones (see http://www.woksat.info/etcxl10/xl10-1456-d-apt-w.html) as well as storm force squalls. Sferic maps (Icelandic Met Office) showed many lightning strikes off the Butt of Lewis. 

Eddy, Stornoway, 10 Dec 2015

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Another Big Atlantic Storm Friday 4 December

Posted by Dr. Eddy Graham on 02 December 2015, 2:26 PM
Update (Thurs 9:45am): Expect winds to pick up from the S/SW around midday tomorrow (Friday), max gusts are expect to be over 70mph across the Hebrides & NW Scotland, which are strong enough to cause disruption and the risk of injury from dislodged items.
Winds will then die down around 6-7pm for a while as the heavy rain clears, before picking up again overnight Fri/Sat.

Original Post:
It looks like there's gonna be another very deep Atlantic low pressure system of 936-938mb this coming Friday 4 December 2015.

However, it looks like we'll miss the worst of the storm this time, as centre of the storm (and therefore region of most violent winds) is currently forecast to pass well to the north of Scotland, in direction of the Faroes and Iceland.
Having said that, another period of very wet and very windy weather (max gusts 70--75mph, poss 80mph) is likely, but there's unlikely to be as much snow or ice as recently.
Storms with intensity below 940hPa used to be rare in the North Atlantic, but they seem to be occurring with a greater frequency over recent winters.
@eddy_weather, Wed 2 Dec 2015


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Snow cover over Scottish Highlands on St. Andrew's Day

Posted by Dr. Eddy Graham on 01 December 2015, 2:24 PM

The NASA satellite sensor MODIS Terra took these two x great shots of the snow cover over the Scottish Highlands yesterday, St. Andrew's Day (30 November) 2015. All dreich and melt today though... (left-true colour; middle - orange; right - cyan)


Eddy, Stornoway, 1 December 2015

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Nan Seachd Siantan - Sunday 29 Nov 2015

Posted by Dr. Eddy Graham on 29 November 2015, 10:54 PM

Nan 'Seachd Siantan'  (or the full seven elements of the heavens) made an appearance on Lewis, Sunday 29 November. They are namely : Snow, Hail, Rain, Sun, Lightning, Thunder, and a Gale. A rainbow was even spotted too!

Two massive squalls passed across the island during the afternoon, the first around 3pm which affected North Harris, bringing blinding snow down to sea-level and ferocious squalls of up to 75mph (see photo below after its passage).

The second affected North Lewis and Stornoway town around 4pm, resulting in heavy hail and snowfall accumulations around the town. There was a literal "day-darkness" as the storm spread over the town - and there was lightning too.

The Gaelic omen of Nan Seachd Siantan = sorry it's not good at all!

However, all was peaceful this morning, with blue skies and a fresh icy snowcover on Stornoway Golf course, giving excellent winter sledging conditions.


Eddie, Stornoway, St. Andrew's Day (30 November) 2015


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More wild weather on the way 26-30 Nov

Posted by Dr. Eddy Graham on 25 November 2015, 9:38 PM

More wind, gales, heavy rain, squally showers, sleet, snow, hail, thunder - everything indeed meteorologically - is likely over the coming few days, especially across western Scotland and the Isles.

No major or serious storm seems likely or imminent yet, but it's worth keeping a close eye on the forecasts each day, as the weather pattern will be changing quickly and rapidly.

As each fresh rainband and gale pass, air temperatures are set to oscillate by up to 10degC within 24hrs, up and back down again.

Eddy, Stornoway, 25 Nov 2015

For fast-moving tweets during fast moving weather, follow Eddy at: https://twitter.com/eddy_weather

Fri 27 Nov: Air temp in Stornoway today dropped from +11.2C (1am) to 1.2C (6pm) - expect similar stuff over the next few days...

(Brief) Snow Likely later Friday and Saturday; Thaw Sunday

Posted by Dr. Eddy Graham on 18 November 2015, 2:51 PM

With 850hPa temperatures likely to dip to -9degC (minus nine) early on Saturday 21 November (and with a 1000 to 500hPa thickness of 520dam), snow is likely to fall and lie (inland, away from onshore coasts) during the latter part of Friday (20 Nov) and early Saturday (21 Nov). The snow will accompanied by a strong, bitter, northerly wind,

I don't expect it to last long, however -  a thaw will arrive quickly by Sunday (22 Nov). It is also unlikely to lie for long near the windward coasts (as sea temperatures will be nearly 10degC warmer than the air).

There will be a risk of "thunder snow" too (hail and snow with lightning).

Eddie, Stornoway, 18/11/2015

New Daytime Storm Risk Monday 16 November

Posted by Dr. Eddy Graham on 15 November 2015, 5:31 PM

Highest gusts to 5pm Monday: Stornoway 69mph, South Uist 71mph - so yes a fairly wild evening but not crazy as feared - so spot on reaction by all in the end (on what was a tricky forecast).

Regular updates on Twitter: https://twitter.com/eddy_weather

Oh boy, it's a tricky one.. (especially after largely escaping the wrath of #Abigail and I have no wish to 'cry wolf'), but...

It's looking possible that there will be a short but potentially violent spell of winds, lasting perhaps 3-4hours at their worst, tomorrow Monday 16 November, especially across the northern Hebrides i.e. Lewis, Harris.

However, no met model is perfect - and it's of interest that the models have not been performing well at T+24 hours recently.

Nevertheless, the GFS met model has violent storm force 11 winds (65mph+ mean) off St. Kilda at midday, spreading east across Lewis during the early afternoon, but weakening slightly to 50-55mph mean (severe gale 9 or storm force 10) around 3pm on the eastside of Lewis- see charts below:


Abigail came at night - and the warning was later downgraded from amber to yellow. The difficulty tomorrow (Monday) is that it will come during daytime.

If winds do reach in excess of 70-75mph+ (there's still some uncertainty), I recommend everyone staying indoors (school-children too, should they be at school) until the winds abate - the worst thing one can do is to evacuate a building during the height of a storm!

Eddie, Stornoway, 15 Nov, 5:30pm

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#Abigail Statistics

Posted by Dr. Eddy Graham on 13 November 2015, 4:33 PM

Although a potentially potent storm, the Western and Northern Isles together with NW Scotland were spared the worst from storm #Abigail.

Maximum windspeeds as measured across the region were as follows:

Stornoway Airport: 73mph
South Uist: 84mph
Sule Skerry 79mph
Bealach na Ba (above Applecross): 98mph
Lerwick 81mph

The storm did bring very heavy rain for several hours on Thursday, resulting in spot-flooding around Stornoway town. Abigail has also ushered in much colder air today (Friday) with squally showers of hail and sleet likely to continue, with the first winter snows likely to lie on the hills.

The weather outlook remains mostly unsettled and cool for the coming week, though it won't be quite as stormy.

Above, the picture shows the Abigail moving in across Stornoway on Thursday, as seen by the Stornoway rain radar.

Eddy, Stornoway, 13 Nov 2015

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