Deep low, 24 December 2013

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Re: Deep low, 24 December 2013

Postby Martin Rowley » 2013 Dec 24, 13:32

Stephen Burt wrote:At 03023, South Uist Range, lowest hourly synop ob 938.1 at 10h, still falling 016 then, 938.2 now rising at 11h, so the minimum probably just under 938 mbar.

Stornoway 11h 938.1 falling 020, so it might yet reach 937.5 before picking up.

Plotted meteocentre 10z chart: http://meteocentre.com/analyse/map.php? ... n&area=eur

SB


... Just to clarify, the values quoted above for South Uist Range (03023) are the STATION LEVEL pressure (3gp), not the MEAN SEA LEVEL pressure (4gp).
Re-stating:
1000Z station level pressure = 938.1 mbar, mean sea level pressure = 938.5 mbar
1100Z station level pressure = 938.2 mbar, mean sea level pressure = 938.7 mbar.

On a general note, care needs to be used with METAR values: they are rounded /down/ to the nearest whole millibar [an aviation safety requirement] ... such that 938.9 mbar becomes 938, and on the meteocentre charts, this will be plotted as "380", implying a lower value that is actually the case - in this case nearly a mbar lower.

Martin.
Martin Rowley
West Moors, East Dorset [ altitude: 17 m/56' ]
NGR SU 082 023: postcode BH22 0GB
50deg49min15secN, 01deg53min03secW
Martin Rowley
 
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Re: Deep low, 24 December 2013

Postby Stephen Burt » 2013 Dec 24, 13:35

The 1982 record has definitely been surpassed - Stornoway (03026) reporting 936.8 mbar at 13z synop, now rising, so the min there was probably close to 936.5 mbar - about a millibar below the 1982 lowest.

We may yet get a few tenths lower if there are observations from elsewhere in Hebrides, of course, and I'm looking forward to seeing Eddie's barograph trace!

SB
-----
Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
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Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading

Re: Deep low, 24 December 2013

Postby Eddy Graham » 2013 Dec 24, 17:18

Dear Stephen

What a day!
(I have just returned from BBC studios in Stornoway; was live on air reporting the air pressure record, and am also on Scottish TV tonight - would not have been possible without your confirmation of the previous records over past few days! etc..)

Well - the roof stayed on the house (no joking), But overall, the wind wasn't really that bad (compared to some Hebridean storms). I estimate gusts around 11am-12 noon approaching 75mph, a full storm force 10 average speed. I see SYY (03026) recorded gusts of around ~71-72mph at the same time.

I have taken a photograph of my barograph trace - I will try to attach it to this message. Unfortunately, I fear the record/barogram is not completely worthy, however, as the lowest pressure recorded (circa. 13h) was 940hPa (i.e. 970hPa on the trace, based on my +30hPa adjustment yesterday). However, when I made the adjustment yesterday, pressure was falling rapidly, and so I may well have adjusted in error by +33/+34hPa (as pressure was falling rapidly at the time; I used SYY 12h00 report), in which case the lowest today was ~936hPa. However, the barograph is old, and my fear is that the aneroid capsule is under-expanding (in low pressure), though I have not tested this theory to date. Also our loft (where I placed the barograph) is not heated in winter; the air temperature was ~11/12degC, so this might also have impacted upon the trace.

We had (yet another) thunderstorm this morning at 7am - there appears to be a slight pressure pulse from this on the barograph record. There was also one at 1am too (though I was asleep!).

I also made two videos of the storm at Stornoway Harbour - thankfully, the town was spared from the rise in sea-level, though it was a close call. Much spray & many waves broke over the sea-wall threatening the town hall & Stornoway town centre, but flooding was limited to large pools of water on the road, etc.. Many people had a scary experience retrieving their cars from the car park beside Stornoway Harbour, getting soaked by waves & spray within a few seconds.

http://www.youtube.com/watch?v=KP3qV3btmgg&feature=youtu.be
and
http://www.youtube.com/watch?v=kuWnq53KHfA&feature=youtu.be

The worst seems like it is over now, the wind veered and eased considerably this afternoon once the "extended eye" passed over around 13h00.

Merry Christmas everyone!
Eddie
Stornoway, 24/12/2013, 17h20
Attachments
baro-trace-sty-24dec2013.png
Stornoway town pressure trace 24/12/2013
baro-trace-sty-24dec2013.png (103.95 KiB) Viewed 511 times
Last edited by Eddy Graham on 2013 Dec 24, 17:31, edited 1 time in total.
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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Re: Deep low, 24 December 2013

Postby Stephen Burt » 2013 Dec 24, 17:30

Glad you're safe, Eddie. Thanks for sharing those videos. It was windy here last night, but I can't imagine what it must have been like in the Hebrides today ...

I will ask MetO for the sub-hourly detail from the Stornoway AWS to establish the lowest point. If you come across any reliable pressure observations from elsewhere on the island, perhaps you'd let me know. Weather Underground have 936.2 mbar just after 1300z from a Davis AWS at Butt of Lewis, which appears sound. Somewhere on the western coast might have been 1-2 mbar lower though.

Meanwhile, still falling at Sule Skerry, which might also get down to 937 mbar, although as a remote offshore island it can't be included in the 'land' record. (Yes, I know Lewis is an island too ... )

SB
-----
Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
Stephen Burt
 
Posts: 247
Joined: 2011 Dec 02, 19:36
Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading

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