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Possible severe Atlantic storms over the Christmas period


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I'm not sure about that lol, for there to be 40-50mph the average wind needs to be about 20mph+ at least I wasn't aware a Gale was based on average speed as it's gusts that do the damage to surely a wind of 35-40mph plus gusts deserves to be billed a gale?...If that was the case then they wouldn't bother with the weather warnings for a depression producing 50mph+ gusts.

 

This might help if you haven't seen it before:

 

http://www.metoffice.gov.uk/weather/marine/guide/beaufortscale.html

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2 warnings from sky warn

 

SKYWARN UK SEVERE THUNDERSTORM WARNING #047ISSUED: 1000UTC SATURDAY 21ST DECEMBER 2013

 

SKYWARN UK HAS ISSUED A WARNING FOR SEVERE THUNDERSTORM CONDITIONS AS FOLLOWS:DAMAGING AND POTENTIALLY DANGEROUS WIND GUSTS - WALES, IOM, NORTHERN ENGLAND, MIDLANDS, SOUTHERN SCOTLANDHEAVY RAIN LEADING TO A RISK OF LOCALISED FLOODING - WALES, IOM, NORTHERN ENGLAND, MIDLANDSPOTENTIALLY STRONG AND DAMAGING TORNADOES - WALES, NORTHERN ENGLAND, MIDLANDS

 

IN EFFECT UNTIL 2100UTC SATURDAY 21ST DECEMBER 2013

 

POST-FRONTAL SHORTWAVING AND A FURTHER WAVE/COMMA DEVELOPMENT, WITHIN AN UNSTABLE AND WINDY ENVIRONMENT

 

DISCUSSION:

THERE IS STRONG MODEL AND PARTNER AGENCY CONFIDENCE IN THE LIKELIHOOD OF SEVERE THUNDERSTORM RISKS TODAY. ONGOING ACTIVE CELLS IN THE IRISH SEA INTO NORTHERN ENGLAND ARE TESTAMENT TO ADVECTED WARMTH AND INSTABILITY BEING SUPPORTIVE OF STRONG CONVECTION. A WELL-SHEARED ENVIRONMENT AS THE UPPER JET PASSES IS PROVIDING SUFFICIENT FORCING TO SUSTAIN UPDRAFTS, FOCUSSED AROUND A POST-FRONTAL SHORTWAVE. STRONG GUSTS ENHANCEMENT IS LIKELY, WITH SPEEDS OF UP TO 60MPH EASILY POSSIBLE AND A SLIGHT POSSIBILITY OF BRIEF WEAK TORNADOES. INTENSE RAINFALL MAY ALSO PROVIDE A LOCALISED FLOODING RISK, THOUGH STORM MOTION IS EXPECTED TO BE FAIRLY SWIFT.

 

LATER THIS AFTERNOON, UNDER THE DIVERGENT ENTRANCE REGION OF THE PASSING UPPER JET BUT AHEAD OF A DEEPER DEVELOPING JET MAX, ADEQUATE FORCING WILL EXIST FOR SUSTAINED AND ORGANISED CONVECTION AND POTENTIAL SUPERCELL PHASES TO STRONGER UPDRAFTS GIVEN ENHANCED DIRECTIONAL SHEAR ON THE SOUTHERN SIDE OF A DEVELOPING WAVE. SEVERE AND POTENTIALLY DAMAGING WIND GUSTS ARE POSSIBLE, AS ARE SOMEWHAT STRONGER TORNADOES WHERE TOPOGRAPHY ALLOWS. HEAVY RAIN AND COPIOUS HAIL ARE ALSO POSSIBLE, LEADING TO EXCESS SURFACE WATER AND POSSIBLE FURTHER LOCALISED FLOODING GIVEN RECENT GROUND SATURATION. THIS WARNING MAY BE UPGRADED, PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

 

SPOTTER ACTIVATION IS REQUESTED AND SPOTTERS ARE REQUESTED TO REPORT ALL FACTORS EXCEEDING ACTIVATION CRITERIA

 

**** alerts contd below ****

 

SKYWARN UK SEVERE WEATHER WATCH #046

ISSUED: 1100UTC FRIDAY 20TH DECEMBER 2013

 

SKYWARN UK FORECASTS THE POTENTIAL FOR SEVERE WEATHER AS FOLLOWS:

STRONG, POTENTIALLY DAMAGING WINDS - SCOTLAND, NORTHERN IRELAND & IOM, NORTHERN ENGLAND, WALES, SOUTHWEST & SOUTHERN ENGLANDHEAVY RAIN LEADING TO A RISK OF LOCALISED FLOODING - WESTERN SCOTLAND, WALES, NORTHWEST AND SOUTHWEST ENGLANDBRIEF, WEAK TORNADOES - WESTERN SCOTLAND, NORTHERN IRELAND & IOM, NORTHWEST ENGLAND

 

IN EFFECT FROM 1200UTC FRIDAY 20TH UNTIL 0600UTC SUNDAY 22ND DECEMBER 2013

 

DEEP ICELANDIC LOW GENERATING GALES WITHIN AND BEHIND A BROAD ACTIVE FRONTAL ZONE, WITH FURTHER WAVE DEVELOPMENT THROUGH SATURDAY

DISCUSSION:

THERE IS GOOD MODEL AND PARTNER AGENCY CONFIDENCE IN THE POSSIBILITY OF A SEVERE WEATHER RISK THROUGH THE PERIOD. A BROAD AND DEEP ICELANDIC LOW SYSTEM CASTS A WIDE FRONTAL ZONE ACROSS THE UK, WITH GALE FORCE PRE-FRONTAL WINDS AND POTENTIALLY CONVECTIVELY ACTIVE COLD FRONT. A STRONG ONCOMING BRANCH OF THE JET PUSHES THE TRIPLE POINT OF THIS FRONTAL SYSTEM THROUGH SOUTHERN SCOTLAND AND NORTHERN ENGLAND. SOUTH OF THIS AND UNDER THE DIVERGENT RIGHT EXIT REGION, STRONG FORCING ARISING FROM SHORTWAVES WITHIN THE FLOW MAY ENCOURAGE CONVECTIVE ENHANCEMENT TO THE GUST STRENGTH AND A POSSIBILITY OF LEWP PHASES TO THE SPLIT COLD FRONT. NORTH OF THIS, THROUGH NORTHERN IRELAND AND SCOTLAND, INSTABILITY SHOULD BE DEEPER AND MORE COINCIDENTAL WITH THE COLD FRONT, LEADING TO STRONGER DOWNDRAFT GUST ENHANCEMENT AND THE POSSIBILITY OF TORNADIC ELEMENTS OCCURRING BRIEFLY. OVERALL, THE STRONG WIND ENHANCEMENT TO THE RAINFALL COULD SEE AROUND 40MM OF RAINFALL OVER HIGH GROUND AND COASTAL AREAS OF WESTERN SCOTLAND, WALES, NORTHWEST AND SOUTHWEST ENGLAND, PARTICULARLY SO IN THE SOUTH OWING TO THE LONGER PERIOD OF RAINFALL. HIGHEST GUSTS FROM THE REARWARD COLD FRONT ARE EXPECTED FROM NORTHWEST ENGLAND AND NORTH WALES AND NORTHWARD, THOUGH POSSIBILITIES OF STRONG GUSTS ON THE EASTERN SIDE OF NORTHERN ENGLAND AND SCOTLAND CANNOT BE IGNORED. NORTHWESTERN AND NORTHERN SCOTLAND WILL ALSO SEE PERSISTENT GALES AND STRONG GUSTS THROUGH THE PERIOD REMAINING AFTER THE PASSAGE OF TODAY'S FRONTAL SYSTEM.

 

SATURDAY ALSO SEES A FURTHER WAVE DEVELOPING WITHIN THE STRONG WIND FIELD, WITH CYCLOGENESIS POSSIBLY OCCURRING AS IT EMERGES ON THE LEFT SIDE OF THE JET. IF SO, ENHANCEMENTS TO THE FORCING AND DIRECTIONAL SHEAR WITHIN AN ALREADY UNSTABLE ENVIRONMENT MAY LEAD TO ORGANISED CONVECTION AND THE POSSIBILITY OF SEVERE GUSTS AND POSSIBLE TORNADOES THROUGH NORTHERN IRELAND, ISLE OF MAN, SOUTHERN SCOTLAND AND NORTHERN ENGLAND. THE MODELLING OF THIS FEATURE WILL BE WATCHED CLOSELY AND FURTHER UPDATES MAY BE ISSUED. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

 

SPOTTER ACTIVATION IS REQUESTED AND SPOTTERS ARE REQUESTED TO REPORT ALL FACTORS EXCEEDING ACTIVATION CRITERIA.

 

http://www.skywarn.org.uk/current.html

 

 

 

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Yes the Met Office will of course update their warning to amber most likely tomorrow and possibly today. 

 

The current warnings were made yesterday and so they are likely to be playing very close attention to how everything is evolving before upgrading the warning. 

 

I doubt they will put it to a red warning, though. It would take gusts in excess of 90 mph for that. 

 

My eyes are also being drawn to the 27, 28th , if the ingredients ''come together'' that pressure system could really pack an almighty  punch. 

 

 

06z control run..

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Run 4

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run 5 Posted Image Posted Image

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Run 6 Posted Image Posted Image

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Run 7 Posted Image

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Run 13 (unlucky for some)Posted Image

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Run 17 Posted Image

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Run 18 Posted Image

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Pretty much every run has the UK under some very high wind speeds on 27, 28th and the West in particular looks to cop the worst of the winds as things stand. 

TheN of course, there is NYE Posted Image...a story for another day

Edited by EML Network
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A 44 mph gust isn't gale force.  Gale force is judged on the average wind speed. On more bizarre days our average winds was 10 mph but we still had 50 mph gusts.

Average over a 10 minute period counts as an official day of Gale but this is hard to achieve inland I am discovering now I have a roof anemometer as even with gusts of 50mph the top 10 minute averages at below 30mph.

Edited by TonyH
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Just about all of the UK is under a yellow warning for strong winds now

 

Posted Image

 

Issued at: 1228 on Sat 21 Dec 2013

 

Valid from: 0900 on Mon 23 Dec 2013

 

Valid to: 2359 on Tue 24 Dec 2013

 

A rapidly deepening area of low pressure will bring very strong winds, reaching southwestern areas during the first half of Monday, lasting well into Christmas Eve across many parts, easing from the south later. Further heavy rainfall will accompany the initial increase in winds. There is the likelihood of widespread gales, with gusts to around 70 mph for much of Scotland, Northern Ireland, west Wales, northwest England, as well as southern coasts of England. Gusts of 80-90 mph are possible, the greatest likelihood of these values being towards the northwest. Although many central and eastern areas of England should see lesser wind gusts, the combination of these winds with heavy rain and heavy holiday traffic may well increase impacts. The public should be aware of the potential for significant disruption to travel due to the very strong winds, and also the risk of some flooding due to the heavy rain. Please keep in touch with the forecasts and warnings, which are expected to be updated again on Sunday.

 

Chief Forecaster's assessment

 

An area of low pressure will deepen rapidly as it passes just to the west and northwest of the UK later on Monday, ending up as an exceptionally deep feature. This will bring stormy conditions to parts of the UK on Monday and Tuesday with the strongest winds likely along coastlines exposed to the south and west, but later perhaps more generally across parts of the north. There remains some uncertainty around the precise depth and track of this system, and hence the areas most likely to be affected by the strongest winds and heavy rain.

 

http://www.metoffice.gov.uk/public/weather/warnings/#?tab=warnings&map=Warnings&zoom=5&lon=-3.50&lat=55.50&fcTime=1387756800&regionName=uk

Edited by Summer Sun
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I have a long drive to do on Monday. Timing is up to me. Would I be right in thinking that earlier would be better than later?

my guess  is  to get  there  by  Monday Tuesday  looking nasty

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On current projections i would be surprised to see amber warnings issued.Unless we can be confident of between 90mph and 100mph as a strong possibility.We should remember that the fear for the ukmo with the St Jude storm was that we could see 100mph + gusts from it hence amber warnings and blanket news coverage.The worst of that potential was not realised of course and ended up over Scandanavia instead.

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Average over a 10 minute period counts as an official day of Gale hard to achieve inland I am discovering now I have a roof anemometer even with gusts of 50mph the top 10 minute averages below 30mph.

John Holmes posted sometime back some good guidelines of average wind to gust which works fairly well. Hopefully he'll post it again sometime.

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I'll dig it out, briefly the rougher the surface the higher the gust ration, so less over the sea and more over rough ground, be hat vegetation or buildings

 

no idea where the table I postut some of it

 

average values of gust over mean hourly speed

flat open country=1.6

centre of towns/outskirts cities=1.9

centre of large cities=2.1

 

so in VERY simple terms, if mean wind speeds say for London were given as 25mph it is POSSIBLE to gust to 50mph

 

also dropping this in the technical thread is it will be easier to find in 24 hours if anyone wants it

 

before jumping to possibly wrong conclusions PLEASE read the post CAREFULLY

Edited by johnholmes
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I'll dig it out, briefly the rougher the surface the higher the gust ration, so less over the sea and more over rough ground, be hat vegetation or buildings

Thanks John I'll save it this time when I see it.

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Local topology has a huge impact on gusts, as does wind direction in that specific area. I live pretty high up and S winds blast the house but gusts are usually not extreme multiples of mean wind speeds. W winds however approach us over steep ground and although more sheltered can result in more severe gusts (higher multiple of the mean). This commonly happens in cities with known gust focus areas on street corners and alleyways depending on wind direction.

Obviously the nature of the storm above can result in high level winds being dragged down to the surface meaning the gusts associated with a given pressure gradient can vary such as in a 'sting jet'

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GFS 06Z take on rainfall totals up until midnight on Tuesday:-

 

post-15177-0-54209500-1387637592_thumb.g

 

They could well be above or below those projections but with my current December running above average already, as well as many other folks, it certainly could pose flooding risks. Rivers are running high here, fields are all waterlogged.

 

Plenty of alerts out:-

 

http://www.environment-agency.gov.uk/homeandleisure/floods/142151.aspx

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Storm & Convective Forecast

post-1052-0-58243100-1387638491_thumb.pn

 

Issued 2013-12-21 15:05:55

Valid: 21/12/13 15z to 22/12/13 00z THERE IS A RISK OF SEVERE WEATHER FORECAST
Synopsis
Large and deep low pressure system to the NW of the UK will drive a strong cyclonic southwesterly flow across the UK. A frontal wave will slowly clear SE England, whilst a shortwave trough moves in from the west this afternoon and evening, bringing a risk of severe weather to parts of England and Wales.

... Sern IRELAND, WALES and ENGLAND ...


Satellite imagery shows a comma-convective cloud feature down the Irish/Celtic Sea containing some strong convective cells which are producing lightning over the sea. This convective squall is associated with pronounced shortwave trough which will continue to move east across England and Wales late afternoon and through the evening. The broken line segment convection within this system, aided by strong deep layer shear in the order of 60-70knts, will be capable of severe weather over a widespread area ... namely wind gusts of 60-70mph, hail to 10-20cm in diameter, CG lightning and torrential rainfall leading to flash flooding. Also, though a much more isolated risk, there is potential for one or two tornadoes - especially where winds back ahead of the approaching convective system. Therefore have issued a SLIGHT risk of severe weather over a widespread area including Sern Ireland, Wales and much of England.
 
Edited by Nick F
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Latest from Met Eirann (http://www.met.ie/forecasts/):

 

"Monday will be another stormy day. Driving heavy rain in the morning will give poor visibility and poor driving conditions. Clearing up somewhat for the afternoon with sunny spells developing but passing heavy showers of rain, hail, sleet and snow will occur. Stormy conditions on Monday and Monday night with possible damaging gusts.

Christmas Eve: S
torm force westerlty winds will just gradually abate.S Cold with passing heavy wintry showers but sunny spells too."

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Storm & Convective Forecast

Posted Imageconvmap_211213.png

 

Issued 2013-12-21 15:05:55

Valid: 21/12/13 15z to 22/12/13 00z THERE IS A RISK OF SEVERE WEATHER FORECAST
Synopsis

Large and deep low pressure system to the NW of the UK will drive a strong cyclonic southwesterly flow across the UK. A frontal wave will slowly clear SE England, whilst a shortwave trough moves in from the west this afternoon and evening, bringing a risk of severe weather to parts of England and Wales.

... Sern IRELAND, WALES and ENGLAND ...

Satellite imagery shows a comma-convective cloud feature down the Irish/Celtic Sea containing some strong convective cells which are producing lightning over the sea. This convective squall is associated with pronounced shortwave trough which will continue to move east across England and Wales late afternoon and through the evening. The broken line segment convection within this system, aided by strong deep layer shear in the order of 60-70knts, will be capable of severe weather over a widespread area ... namely wind gusts of 60-70mph, hail to 10-20cm in diameter and torrential rainfall leading to flash flooding. Also, though a much more isolated risk, there is potential for one or two tornadoes - especially where winds back ahead of the approaching convective system. Therefore have issued a SLIGHT risk of severe weather over a widespread area including Sern Ireland, Wales and much of England.

 

 

Think you need to amend the cannon-ball hail ?

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