October 2016: Near-Record Dry in Stornoway & Sunny

[Edward Graham]

Greetings from the far NW of Scotland, where October has been the 2nd driest on record in Stornoway since 1873. Total precipitation was 36.0mm at the airport (less than one third of normal); only the October of 1946 was drier. So it's almost a 1-in-a-century event (but with some caveats, see below).

It was also a sunny month, with percentages exceeding 150% across large parts of NW Scotland and Hebrides - see the recent Met Office press release on this: http://www.metoffice.gov.uk/news/releas ... 2016-stats. In Stornoway, I estimate it was the 4th sunniest October since 1929 (so a 1-in-a-20-year event, but again not without possible caveats, see below).

All this marks a stark change from the prevailing weather over the past ~2years, during which we have suffered with considerably more than our fair share of very wet, dull and unsettled weather. How refreshing it is now to see high pressure build towards mid-Atlantic and Greenland; I feared it was never going to happen again!

Here are some graphs:

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tn_October2016-SUNSHINE.png (69.64 KiB) Viewed 25683 times

And the caveats are the following:
- I don't believe the Stornoway Met Office precipitation dataset is homogenous, especially prior to ~1915. But even recently, there has been a change of rain gauge (it is contained within a turf wall) and values appear biased now when compared to other local rain gauges over long-term periods.
- Likewise, the sunshine record is hardly homogenous, especially since the replacement of the Campbell stokes recorder ~2000. Stornoway gets a lot of weak sunshine in the autumn/winter months - even today with a low sun, the pyramometer lies within the shade of the fence posts of the Stornoway enclosure for up to 5% of the time (see photo: pyranometer is on the left).

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Eddie Graham, Stornoway.

[Nicholas Gardner]

Edward, a similar story here though not as extreme with sunshine around 130% of the average with 165.4 hours.

October is usually one of the wettest months of year (closely followed by November & December) and a huge contrast to the normally very dry September. It really seems as if October is the start of the rainy season but this October had 'only' 57.9 mm (65%) of rain which occurred in a just a few fairly brief, heavy spells. This still made it the wettest month (by quite a margin) since the normally dry month of June (when thunderstorms were to blame for the high rainfall amount).

It seems as if the whole of the western side of the British Isles had a dry and sunny October due to the 'easterly' flow that dominated the month. And I am glad you got some decent weather at last!

Note that this was my sunniest October since I started recording sunshine in 2006.

[Edward Graham]

Nicolas
Yes a nice easterly month: But interestingly, from a statistically point of view Cork in Ireland is equally as wet in an easterly as in a westerly. And I spotted this: On Oct 3rd, Valentia (nearby Co. Kerry) had 105.5mm daily total on 3rd October - one of the highest 24hr falls on record at this long-term station
See http://www.met.ie/climate/monthly-weather-reports.asp
E.

[Len Wood]

Edward,
it would have been a record dry October here if there had not been a deluge (49 mm) which came on 24/25th, caused by a depression moving up from France.
Total for the month ended up as 78.6 mm, 70% of average since my record began in 1984.

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