Deep low, 24 December 2013

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Deep low, 24 December 2013

Postby Stephen Burt » 2013 Dec 22, 11:19

I'm posting a new thread here to make the topic clearer.

In the 'Christmas update' thread I posted this yesterday:

The situation for the Christmas Eve low does indeed look interesting. This evening's Met O 72 h forecast chart deepens it to below 936 mbar (i.e. a closed 936 mbar isobar) not far off Lewis at 12z Tuesday. Meanwhile, the ECMWF forecast for the same time has a closed 924 mbar isobar slightly further off NW Scotland, and GFS a closed 928 mbar isobar in a similar position to ECMWF.

All three would imply that the barometer could fall to around 936 mbar in the northern Hebrides and the far north-west of Scotland, and quite possibly a bit below this at Sule Skerry, where there is a currently-operational AWS (IIiii 03010).

The lowest MSL pressure recorded at a land station within the British Isles back to 1886 has been 937.6 mbar recorded at Stornoway at 0020 GMT on 20 December 1982: at Sule Skerry it may have dropped as low as 936 mbar on this occasion. I wrote this event up in Weather (Burt SD. 1983. New UK 20th century low pressure extreme. Weather, 38: 208–213, and Burt SD. 1983. The lowest of the Lows ... Extremes of barometric pressure in the British Isles, Part 1 – the deepest depressions. Weather, 62: pp 4-14). Since 1949 and in the UK and Republic of Ireland, only the extreme north-west of Scotland has experienced barometric pressures below 940 mbar, and then only once, in December 1982.

On the morning of 8 December 1886, the barometer may have fallen as low as 924 mbar over northern Ireland, although the lowest authenticated value was 927.2 mbar at Belfast at 1330h, close to the centre of the depression. The British Isles record stands at 925.6 mbar, recorded at 2145h on 26 January 1884 at Ochtertyre, near Crieff (56° 23’ N, 3°53’W, 101m AMSL). This remains the lowest unchallenged
MSL pressure reading yet recorded in the British Isles. Corroborative evidence is afforded by the (MSL) readings of 927.2 mbar at Aberdeen at 2330h, 927.3 mbar at Dundee at 2230h, 927.4 mbar at Culloden, near Inverness, at 2300h, 927.5 mbar at Oban at 2100h, 928.8 mbar at Glasgow and 929.6 mbar in Edinburgh. Contemporary sources agree that these were the lowest pressures recorded in Scotland for at least the previous 120 years.

The all-time North Atlantic record stands at 912–915 mbar between Iceland and Scotland near 62°N 15°W on 10 January 1993.

Unless the track and depth of the storm are seriously amiss - and these 'bomb' events are difficult to get exactly right 72 h in advance - I think it very unlikely that the all-time British Isles record will be approached, but we could well see the 1982 Stornoway extreme surpassed, giving the lowest MSL pressure in these islands since 1886.


With the updates from the midnight model runs now in, the position and depth of the storm are becoming more closely defined. At present, the depression is in the eastern North Atlantic. At 0600z the central pressure was 1008 mbar within a double frontal system in a very pronounced baroclinic zone off Newfoundland. It is now racing eastwards under the influence of a very strong jet. The Met Office model forecast for midnight tonight is for a central pressure 982 mbar around 51°N, 24°W. At midnight on Christmas Eve the MetO model has a closed 932 mbar isobar around 57°N, 14°W - about one-third of the way between Ireland and Iceland, while the ECMWF forecast for the same time has the centre slightly further west (about 58°N 18°W), with a closed 930 mbar isobar. Both are consistent in very rapid deepening of around 50 mbar in 24 h.

The really interesting possibilities come 12 hours later. Although ECMWF is going for a track some way off north-west Scotland, the MetO model runs the low close to the northern Hebrides. The MetO forecast for 1200z on Tuesday shows a closed 932 mbar isobar just off Lewis. The forecast chart as it stands implies perhaps a minimum of 932-934 mbar at Stornoway. As explained above, if this does happen it would eclipse the 937.6 mbar recorded at Stornoway on 20 December 1982 as the lowest barometric pressure observed anywhere in the British Isles since 1886, when the pressure fell to 927 mbar in Belfast.

It will be interesting to see how the 12z model runs develop the system when they appear this afternoon.

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
 
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Re: Deep low, 24 December 2013

Postby Len Wood » 2013 Dec 22, 16:30

Hi Stephen,
The fax from NOAA for 0000 UTC 24 Dec seems to have the low as 924 mb at 58N 13W

http://weather.noaa.gov/pub/fax/QDTM85.gif

Hurricane force for the Western Isles by the looks of it.

With 976 mb here on the S Devon coast, that is quite a pressure gradient.
I am sure it is going to be at least a severe gale in the English Channel.
Len

Wembury, SW Devon coast
N50.33 W4.13
Altitude 83 m asl
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Re: Deep low, 24 December 2013

Postby Stephen Burt » 2013 Dec 22, 19:43

Len, that chart is from one of the US models - probably GFS. Each model will handle evolution, depth and track slightly differently - interesting that this is deeper than MetO or ECMWF. For North Atlantic evolution, MetO and ECMWF generally have a slight edge over the US models.

The latest MetO guidance T+48 has the same central pressure at 12z Tuesday, 932 mbar, but with the centre a bit further off NW Scotland - more similar to yesterday's ECMWF forecast - and as a result the lowest land pressure looks as if it will be about 940 mbar rather than 932 mbar. This would still be impressively low - only the second occasion of < 940 mbar anywhere in the British Isles since 1886 - but on current forecasts it now looks less likely that Stornoway's 937.6 mbar in December 1982 will be beaten. There's still time for that to change, though!

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

Re: Deep low, 24 December 2013

Postby Eddy Graham » 2013 Dec 22, 19:51

Hi again folks (I'm just posting my original reply to Stephen here in this new thread; corrections in italic)...

Postscript to Len: I am fearful of any forecasts of hurricane-force winds for here in the Hebrides during the coming event, but as I'm sure you know there's not necessarily a linear correlation between absolute depth of a low and strength of surface wind. We have been lucky twice in the past week (on Sunday last [15/12/13] the low of 947hPa gave a gust of 112mph at Thorshavn, Faroes, and last Wednesday (18/12/13) a possible "sting jet" just missed us [though South Uist & Mace Head in Ireland both reached 90mph]. So far the highest gust at Stornoway Airport [Met Office] this winter is 85mph on 5/12/13)

Dear Stephen

Thanks very much for your detailed reply... and yes that was my next question! (whether to notch it up 20hPa or so, as the Casella barogram paper that I use only goes down to 950hPa). Actually, I normally keep the barograph in the office (as our Maritime dept at the college owns it), but I think I will bring it home for the festive period from tomorrow onwards and reset it here in Stornoway town, about 1km east of the college (as my office will be closed from Christmas until the New Year). We are at an altitude of about ~25m in the town.

This month has been truly extraordinary in terms of the volatility of the weather, and certainly ranks high on my list of lifetime "memorable weather experiences" (though it has been exhausting to keep up with it at times too!). I know the met situation could change significantly yet for T+48hrs, but I am ready in anticipation of an historic meteorological event as well.

A merry Christmas & best wishes to all
Eddie
p.s. I was of course referring incorrectly to the Ochtertyre 1884 record in my last message. As you say, the value was 925.6 mbar (not ~922hPa, as I guessed in my previous message).
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
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Re: Deep low, 24 December 2013

Postby Stephen Burt » 2013 Dec 23, 09:21

The latest MetO model run (00z Monday) have the centre at 931 mbar at 57°N, 13°W at 00z Tuesday.

At 12z Tuesday there is a closed 932 mbar isobar centre at 59°N 9°W, off NW Scotland, with the 936 mbar isobar running across Lewis. It's now looking more likely that the December 1982 value of 937.6 mbar at Stornoway will be beaten, but there's still uncertainty on the track and depth 36 hours out. More updates this afternoon.

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

Re: Deep low, 24 December 2013

Postby Angus Tyner » 2013 Dec 23, 10:15

Quite large 3 hr pressure falls across Ireland this morning.
13.1mb fall in 3 hrs to 09z here, 3rd greatest in my 14 year record.
Ashford Co. Wicklow
Met Eireann Climatological station number 975
COL station number EI018
My Weather Station
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Re: Deep low, 24 December 2013

Postby Graham Easterling » 2013 Dec 23, 11:36

The depression is already making itself felt in west Cornwall. Recent gusts >60mph at Land's End and Culdrose, >70mph on Scilly where it peaked at F9-F10. http://www.metoffice.gov.uk/weather/uk/ ... ather.html

The sea state is fairly horrendous http://www.minack.com/webcams/webcam.jpg . I noticed the lifeboat going out of Newlyn around 10:00, it was fairly hair-raising watching it pass Penlee point.

UPDATE 19:00 on 23rd. Max gust at Culdrose was 71mph. A value probably fairly representaive of exposed south coast locations. Currently (19:00 report) 2,400 homes in Cornwall without power, mainly Marazion & Helston. The wind gradually decreased this afternoon (no sharp drop) but has picked up again this evening. Recent gust of 66mph at Land's End.
Last edited by Graham Easterling on 2013 Dec 23, 20:38, edited 1 time in total.
Graham

Penzance Weather Station
Grid Ref:
SW464231 - Post Code: TR18 4TP
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23 Years of Penzance Weather Records : http://penzanceweather.atspace.com/weather.html
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Re: Deep low, 24 December 2013

Postby Len Wood » 2013 Dec 23, 12:01

Regular gusts to 70 mph at Plymouth Mt Batten in last hour.
I have a feeling it is peaking.
http://www.weatheronline.co.uk/cgi-bin/ ... 24&x=8&y=9


My barograph shows a drop of 22 mb in last 12 hours.
At present 990 mb.

Low off NW UK coast shows 956 mb at 1100z.
http://meteocentre.com/analyses/map.php ... size=large

Driving rain here, have not been out to measure total in my 5 inch gauge yet.
Len

Wembury, SW Devon coast
N50.33 W4.13
Altitude 83 m asl
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Re: Deep low, 24 December 2013

Postby Stephen Burt » 2013 Dec 23, 18:24

UPDATE - 18z 23 December

The latest MetO 12z forecast, now T+24, has the centre at 926 mbar at 59°N, 9°W - some way off NW Scotland. The 940 mbar isobar on this chart clips the mainland of NW Scotland, and Lewis lies within the 936 mbar isobar. So now there looks to be a good chance of beating Stornoway's 1982 value, in the lowest barometric pressure in the British Isles since December 1886. Looking forward to seeing Eddie's barograph record!

A really foul day in southern England - blowing force 6 with moderate to heavy driving rain all day - almost 18 mm here since 0900z. The rivers will be very high tomorrow.

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

Re: Deep low, 24 December 2013

Postby brugge » 2013 Dec 23, 19:30

Stephen,

Yes, Cent S England has now joined most of Scotland in being wetter than average this month:
See http://www.met.reading.ac.uk/~brugge/percr.jpg

Roger
brugge
 
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