Marble-sized hailstones reported N of Stornoway 18th Dec

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Marble-sized hailstones reported N of Stornoway 18th Dec

Postby Eddy Graham » 2014 Dec 21, 13:34

Hi Everyone

Some of you may have seen some recent reports from Stornoway in the 'daily discussion' forum - well, there has been yet more extraordinary weather here, with a report of marble-sized hailstones falling on the evening of Thurs 18th Dec, in the district of Ness, about 20 miles north of Stornoway (near the Butt of Lewis lighthouse).

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The full news report is here: http://www.hebrides-news.com/hailstones ... 01214.html

In Stornoway at the same time, it was squally with frequent hail showers, mainly pea-sized (0.5-1.0cm), but nothing exceptional. Thunder was heard during the morning of the 19th.

Eddie Graham
Stornoway
Eddie Graham
Stornoway, Na h-Eileanan an Iar (Outer Hebrides), Scotland.

Stornoway town COL station, 20 AMSL, local records back to 1873.
Hebridean Weather Blog: http://bit.ly/1IFAPJa
Twitter Weather Feed: https://twitter.com/eddy_weather
Eddy Graham
 
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Location: Stornoway, Scotland

Re: Marble-sized hailstones reported N of Stornoway 18th Dec

Postby jonathan webb » 2014 Dec 21, 22:41

Hello Eddie

It's very interesting to hear this and other reports of the recent intense convective activity which has affected the north and west of Scotland.

I had a look through the TORRO database and no hailstorms of that severity (H3-4) have been reported in the Hebrides in the period since 1930 (I will check earlier records when I have a chance). There have been a few similarly damaging winter hail events in western Ireland, Devon & Cornwall and west Wales (where sea temps would usually be a bit higher) and a couple in Shetland (one January 2007).

I also checked the notes I had on thunder days for some synoptic stations (which I extracted from the MWR some years ago) and the Stornoway records from 1901-1980 gave a highest monthly total of 5 days in February 1916 - so this month surpasses that. I guess the slightly higher than usual sea temps have tipped the balance to the more vigorous and deeper convection?

Best wishes

Jonathan
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Re: Marble-sized hailstones reported N of Stornoway 18th Dec

Postby Graham Easterling » 2014 Dec 22, 16:46

Late autumn/winter is the time for large hail in Cornwall.

I've just checked and in the last 24 years (1991-2014) I have recorded large hail on 40 occasions.

Breaking this down by season:-

Winter:- 23 occurrences
Spring:- 7
Summer:- 0
Autumn:- 10 (of which 8 occurred in November)

38 of the 40 occurrences saw the wind between SW & N. (i.e. polar maritime or returning polar maritime)

Unlike the Hebrides we've been stuck in tropical maritime, rather than unstable polar maritime, so far this winter.
Graham

Penzance Weather Station
Grid Ref:
SW464231 - Post Code: TR18 4TP
19m AMSL - Aspect SSE
In a SE - NW orientated valley

23 Years of Penzance Weather Records : http://penzanceweather.atspace.com/weather.html
Graham Easterling
 
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Location: Penzance, Cornwall

Re: Marble-sized hailstones reported N of Stornoway 18th Dec

Postby Eddy Graham » 2014 Dec 23, 18:02

Many thanks folks for your replies.

I record hail of a diameter 0.5-1,0cm fairly frequently here in Stornoway (I've not calculated the stats, but I estimate it's about ~5 days per winter, based on the past 6 years that I've stayed here) - more commonly it is <0.5cm, but has never been much beyond 1.0cm, at least what I've seen and recorded. Thus, this event of 2-3cm diameter size hail is likely to be rare.... having said that, only last winter, large hail was reported from Tong district 2-3 miles north of Stornoway (as a kind of 'disc' hail) and another resident of nearby Harris reported large hail to me some years ago (he apparently kept some of the stones in his freezer, but never actually showed them to me) - I guess these events don't figure in the Torro database!

So large hail (i.e. marble size or larger) does occur here in the Hebrides, and it is a misconception that Atlantic thunderstorms can't be as severe as 'continental' ones, as the various cases from both Dec 2013 and Dec 2014 show...

Merry Christmas to all and best wishes from Stornoway!
Eddie Graham
Eddie Graham
Stornoway, Na h-Eileanan an Iar (Outer Hebrides), Scotland.

Stornoway town COL station, 20 AMSL, local records back to 1873.
Hebridean Weather Blog: http://bit.ly/1IFAPJa
Twitter Weather Feed: https://twitter.com/eddy_weather
Eddy Graham
 
Posts: 82
Joined: 2012 Jul 18, 17:09
Location: Stornoway, Scotland

Re: Marble-sized hailstones reported N of Stornoway 18th Dec

Postby jonathan webb » 2014 Dec 23, 19:52

Good to hear from you both and very interesting to hear of your observations

Graham, presumably the occasions of large hail you mention refer to 5mm diameter plus? Have there been any incidences with 20mm dia hail?

Eddie, your reports confirm my feeling that severe winter hailstorms are more common than databases indicate, partly because they are most common in less populated areas and also because there is less to damage in winter (crops, vegetation). I recall Atlantic convective storms spiralling around deep lows look as impressive as any convection on satellite imagery!

Happy Christmas and best wishes to you and all

Jonathan
jonathan webb
 
Posts: 11
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Re: Marble-sized hailstones reported N of Stornoway 18th Dec

Postby Eddy Graham » 2014 Dec 24, 15:33

Thank you Jonathan for your further reply... and you'll never guess what?... we've had ANOTHER thunderstorm in the night just past (24th Dec, ~4;15-4:30am), thus making a truly amazing total of 7 days this month. The lightning was quite vivid with perhaps up to a dozen flashes and rolls of thunder (once I'd woken up), but the precip core seemed to pass well away from Stornoway. This makes the 2nd Christmas Eve in a row with thunder!

But only small hail or rain as precip...!

With best wishes again for Christmas and the festive season, sincerely
Eddie
p.s. Jonathan, I meant to ask also is it a specific TORRO thunderstorm database that you have for Stornoway 1901-1980? (Would I be correct in guessing that this no longer continues for Stornoway since it became an automated station ~2005?) - (sorry addendum: Yes, I see you compiled it originally from the MWR). Databases such as these (i.e. thunder heard, or snow-lying days/snow-depth) seem to be very hard to get one's hands on... I'd love to have a copy of the thunder database for Stornoway, if at all possible? Also, yes I would think it is a combination of SSTs above average between Iceland and Scotland, and a higher frequency of deep cold Canadian Arctic air being advected over these waters since Dec 7th or so... it might be worth looking at this more closely?
Eddie Graham
Stornoway, Na h-Eileanan an Iar (Outer Hebrides), Scotland.

Stornoway town COL station, 20 AMSL, local records back to 1873.
Hebridean Weather Blog: http://bit.ly/1IFAPJa
Twitter Weather Feed: https://twitter.com/eddy_weather
Eddy Graham
 
Posts: 82
Joined: 2012 Jul 18, 17:09
Location: Stornoway, Scotland

Re: Marble-sized hailstones reported N of Stornoway 18th Dec

Postby jonathan webb » 2014 Dec 24, 17:17

Hello Eddie

Many thanks for your reply....... and update on the lively period of weather in the region.

I have a summary of the Stornoway thunder data for 1901-2000 which I can send you. I should still also have the individual monthly totals written down somewhere and these should not take long to put on an excel sheet - I will check.

It looks as if manual observations at Stornoway airport ceased around 2000; it is one of the longest consistent records of monthly thunder I have seen for a location where a 24 hour watch was maintained. As you rightly indicate, a downside of the automation of synoptic stations has been to make 'eye' observations (snow, hail, thunder) rather limited in the network of official synoptic stations - however, it makes the observations from private/voluntary weather stations and on weather forums even more valuable!

Best wishes, and seasonal greetings

Jonathan
jonathan webb
 
Posts: 11
Joined: 2011 Dec 22, 22:06

Re: Marble-sized hailstones reported N of Stornoway 18th Dec

Postby Graham Easterling » 2014 Dec 26, 11:10

Graham, presumably the occasions of large hail you mention refer to are 5mm diameter plus? Have there been any incidences with 20mm dia hail?


No incidences of 20mm diameter hail that I'm aware of Jonathan. I suspect most hail of that magnitude is associated with summer thunderstorms (that's an assumption, it may be wrong!) The hail here is mainly associated with highly unstable winter polar maritime air. The showers running in off the sea can be quite viscous, sometimes we get a very localised line of rain/hail in a NNW, a bit of a feature of the Cornish winter climate. More details here. http://www.turnstone-cottage.co.uk/DanglerFinal.PDF
Graham

Penzance Weather Station
Grid Ref:
SW464231 - Post Code: TR18 4TP
19m AMSL - Aspect SSE
In a SE - NW orientated valley

23 Years of Penzance Weather Records : http://penzanceweather.atspace.com/weather.html
Graham Easterling
 
Posts: 316
Joined: 2011 Nov 30, 20:29
Location: Penzance, Cornwall

Re: Marble-sized hailstones reported N of Stornoway 18th Dec

Postby jonathan webb » 2014 Dec 27, 23:08

Thanks Graham. Yes, by far the majority of incidences of severe (20mm+) hail have occurred in the summer half year although there are occasional winter events.

It looks as if you have another quite conspicuous Pembrokeshire dangler episode this evening, looking at the radar and windflow................


Graham Easterling wrote:
Graham, presumably the occasions of large hail you mention refer to are 5mm diameter plus? Have there been any incidences with 20mm dia hail?


No incidences of 20mm diameter hail that I'm aware of Jonathan. I suspect most hail of that magnitude is associated with summer thunderstorms (that's an assumption, it may be wrong!) The hail here is mainly associated with highly unstable winter polar maritime air. The showers running in off the sea can be quite viscous, sometimes we get a very localised line of rain/hail in a NNW, a bit of a feature of the Cornish winter climate. More details here. http://www.turnstone-cottage.co.uk/DanglerFinal.PDF
jonathan webb
 
Posts: 11
Joined: 2011 Dec 22, 22:06


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