Record Wet December 2013 in Stornoway

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Record Wet December 2013 in Stornoway

Postby Eddy Graham » 2014 Jan 01, 16:16

Hi Everyone

I have just added up the total precipitation as measured in my rain gauge (here in Stornoway town) for December 2013, and it gives an enormous whopping total of 307.0mm (12.09in) for the month. This is the 1st time I have ever measured over 300mm in any month anywhere in my life (Dec 2011 with ~240mm in Stornoway had been the only previous occasion when I had ever measured >200mm in an entire month anywhere in my life... so it's even noteworthy from this simple perspective!).

How does this value compare with long-term records for the area?
Well, there is a difficulty in that the long-term Met Office monthly record back to 1873 for Stornoway (available online at http://www.metoffice.gov.uk/climate/uk/stationdata/stornowaydata.txt) is made from numerous different sources, which the Met Office have previously informed me is non-homogenised. Typically, my station in Stornoway town is about 20-25% wetter than the airport, despite it being only 4km to the west of the airport.

Looking specifically at Stornoway airport for Dec 2013, it recorded 252.0mm (taken from Roger's site at http://www.met.reading.ac.uk/~brugge/PREV.html) today. This is the wettest month (of any month) since Feb 1997 when an remarkable 277.4mm was recorded (all the more remarkable since it fell on only 28 days). January 1993 had 274.7mm. As for specifically December, the only total for this month approaching anywhere near the 2013 total is Dec 1985 with 222.1mm. So it looks like it December 2013 has been the wettest ever December recorded at Stornoway airport (since met obs began there pre-2nd world war).

However, a longer time series of precipitation does exist for other sites in the Stornoway area - but this is where it gets complicated (due to above-mentioned fact that Stornoway town in an undoubtedly wetter location than the airport, or least more rain is collected in the rain gauges in the town- as the airport is a windy, open exposed site). Looking at the long-term record, only the Decembers of 1898 and 1900 can compete with 2013:
1898: 377.5mm
1900: 305.7mm

But the 1898 value appears such a conspicuous outlier (i.e. 70mm greater than 2013, it's nearest neighbour), that I am cautious initially of its acceptance (though I am VERY pleased to read in the earlier thread that the full record of British Rainfall is now available online in digitised format - no doubt the answer lies within this invaluable archive).

So we certainly have just endured the 2nd wettest December on record in the Stornoway region since at least 1873, and possibly the wettest ever. An I haven't even begun to mention any of the severe windstorms during the month as well!

I'd be grateful for any comments on the above!

Kind wishes and a happy new year to all COL members,
Eddie Graham
Stornoway town
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: Record Wet December 2013 in Stornoway

Postby Len Wood » 2014 Jan 02, 16:01

When did the rain start in December Eddy?

I had 170.2 mm in my 5 inch gauge, and 98% of this fell from 13 December.
I think this is true for many stations in the southern UK.
Len

Wembury, SW Devon coast
N50.33 W4.13
Altitude 83 m asl
Len Wood
 
Posts: 349
Joined: 2012 Jan 28, 16:12
Location: Wembury, coastal SW Devon, 83 m asl

Re: Record Wet December 2013 in Stornoway

Postby Eddy Graham » 2014 Jan 02, 20:53

Hi Len

The rain was fairly well distributed throughout the month, though the final 10 days were wettest (like most places in UK I imagine). Remember that we are some 700 miles north of you guys, so no balmy anticyclones in Stornoway during this past December!

1st-10th: 81.9mm
11th-21st: 97.0mm
21st-31st: 128.1mm

Total: 307.0mm

Amazingly, the wettest day had only just over an inch (25.7mm) on the 4th.
3 days > 20mm
15 days > 10mm (tellingly, 8 of these in the final 10 days)
26 days >=0.1mm

My met observation site in the back garden was quite a "sight" (sorry excuse pun) on Christmas Day (see attached image) - there was about 1'' to 2'' of standing water across the lawn for much of the week surrounding Christmas.

with best wishes
Eddie Graham
Attachments
25dec2013_42kyt_standing-water.png
25dec2013_42kyt_standing-water.png (211.96 KiB) Viewed 656 times
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: Record Wet December 2013 in Stornoway

Postby Eddy Graham » 2014 Jan 06, 21:59

Dear Everyone

More on this... I have had a delve into the British Rainfall archives for 1898 and 1900.

The plot: Remember that the only month in Stornoway to better December 2013's precip total of 307.0mm is allegedly December 1898 with 377mm (although I expressed some concerns about this value in a previous post, because it is an extreme statistical outlier).

Well, the plot thickens... and I rooted out the following information:
British rainfall does indeed report 14.87 inches (377.7mm) for December 1898. However, it was recorded at "Stornoway Lighthouse" (not Lews Castle which I had incorrectly supposed), which (if the correct location) is on a rocky promontory at the entrance to the harbour. Very interestingly, Symons & Wallis make the following observation when they present the Stornoway data:
"We have repeatedly expressed our doubts respecting the records of rainfall at Lighthouses..."
(Here I had a "Eureka" moment)
Why? Because, the one thing I have learned over the previous month (December 2013) is that a HUGE amount of spray gets airborne during storms here in the Hebrides. I have seen vast swathes of spray travelling for several hundred metres, in one case recently up to 1-2km (even the day after a storm had cleared overnight, the large waves were still releasing a lot of spray, restricting visibility to ~ 2 miles at most). When huge amounts of spray become airborne, the sky often turns a milky white colour (any blue is lost). During the biggest storms, the land near the sea becomes the recipient of huge doses of sea-water (from waves blowing onshore, combined with finer spray). But you might argue - is this not still precipitation in the right sense of the word? (then again, putting a rain-gauge beside a lighthouse in such conditions is certainly NOT representative of the average precipitation conditions on nearby land).

So, pending more detailed research and further analyses, and notwithstanding the fact that December 1898 was certainly an extremely wet month in N & W of Scotland (31.32 inches/796mm of precipitation was apparently measured at Glen Quoich), significant doubts remain in my mind as to the true amount of precipitation in Stornoway in December 1898. I am henceforth referring to December 2013 as "the wettest December on record since reliable observations are available".

p.s. my rain-gauge in Stornoway town is about 4km from the nearest part of the sea that would generate significant airborne spray in a storm, but it is not upwind (90deg away from the prevailing wind direction).

Eddie Graham, Stornoway, 6/1/2014
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


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