Severe Atlantic Storms over the Christmas & New Year period

[Thunder Snow]

Wonder if we will see a red warning from the met

[Bobby]

The winds have really picked up behind the front, stuff banging and clattering outside in the gusts.

[Nick L]

Wonder if we will see a red warning from the met

 

I'd be surprised. The primary threat is from flooding, the warnings of which are the responsibility of the Environment Agency.

[Sussex Jules]

Wonder if we will see a red warning from the met

Doubt it flooding is covered by Environment Agency, Met Office covers weather and although bad the actual weather forecast is not as bad as it has been.

 

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

[Thunder Snow]

When will the threat pass

[laserguy]

The winds have really picked up behind the front, stuff banging and clattering outside in the gusts.

 

Stuff's banging and clattering around here,too - but it's just the local vandals again.

[alexisj9]

Wind really roaring here now, didn't expect it to yet down here tbh. met office says 44 in the last hour, but it sounds stronger to me.

Edited January 3, 2014 by alexisj9

[Sainsbo]

Not sure that it's been mentioned yet, but the GFS 18Z shows a pretty heavy band of rain travelling up the country from the south on Saturday that it wasn't previously making much out of.

 

 

 

Another inch of unneeded rain falling on already saturated ground.

Edited January 3, 2014 by Sainsbo

[Costa Del Fal]

STORM SURGE Warning and key tide times for Scilly and Cornwall available here: http://www.cciweather.co.uk/warnings/4573724904

[Bobby]

Looks like the Usk in Newport has burst its banks

 

https://twitter.com/dannyelliott17/status/418891449036709888/photo/1

[alexisj9]

Looks like the Usk in Newport has burst its banks

 

https://twitter.com/dannyelliott17/status/418891449036709888/photo/1

Already this storm hasn't really started yet. Been to much rain recently.

[egret]

The current Environment Agency severe flood warning for Barmouth says:

 

"At Barmouth the tide level is expected to reach 3.92 metres above Ordnance Datum."

 

(http://www.environment-agency.gov.uk/homeandleisure/floods/34681.aspx?area=101FWTWN510&page=1&type=Region&term=Wales)

 

Does this means the max hight of tomorrow's am tide is going to be nearly 4 metres higher than normal?

 

Is that right, or does it mean something else?

 

Thanks...

No, I think there are some confusing figures being mixed here. The short answer is that the normal tide height at Barmouth tomorrow would be about 1.5 metres above Ordnance Datum. The difference being that the Admiralty use a different datum for seafarers and tide tables to the datum used by Ordnance Survey for land mapping. Basically sailors do it differently to the army as one tries not to hit the ground while the other prefers not to get their boots wet!

 

If you are really interested, the following longwinded explanation sets out (a bit crudely) where the differences arise. Eating a bowl of prunes may be time better spent for those otherwise inclined  to explore the detail ;-)  

 

Tide levels are normally described relative to a datum set at Newlyn which relates to the lowest astronomical low tide level at that point. I.e the sea bed below that level would not normally become exposed above water. This datum is really set to help navigators judge whether there is sufficient water above a certain point to stop their boat going aground.

 

High tide will always be significantly higher than that level and the height it will reach at any location  depends upon the effects of the seabed and shoreline relative to the incoming tide, before any allowance made for the effects of air pressure and of wind. In some places the tidal range (low to high tide levels) is considerably greater than others due to the land funnelling the tide as it comes in and out.

 

Barmouth would ordinarily have a low tide height tomorrow of 0.7m above datum and a high tide height of 5.6 m above datum without the added effects of air pressure and wind ( so called astronomical tide heights). In other words a range from low to high tide of 5.6 - 0.7 = 4.9 metres. This is due to it being a high tide (so called 'Spring Tide') anyway as there is a new moon (would also occur with a full moon). At other times  it might be somewhere nearer to 3.7m height (2.1m range) during the less high 'neap tides' associated with 'half moon' phases.

 

Environment Agency are interested in things above sea level and use Ordnance Datum, which is different and is based on mean sea level (mid tide height between high and low water states). So if the normal predicted range of tide height at Barmouth tomorrow based on Admiralty charts is 4.9 metres this would be half of that to each side of Ordnance Datum equating to 2.45m above Ordnance Datum. If Environment Agency are stating 3.92 then i would read this as being 3.92 - 2.45 = 1.47 metres higher than normal for that tide. This 1.47 being due to low air pressure 'sucking' the water up and the further effects of wind 'heaping water' up against the UK shore line. On top of this will be the effects of wave height which can cause water to splash over the top of defences. If the actual wave height is (say) 3 metres (top of crest to bottom of waves trough), again half of that height will be above the 'calm water height' meaning that the crest of waves approaching the shore might be 1.47 plus 1.5 = 2.97 above normal high tide level. Breaking waves can splash higher still but the amount of water in such spray is small compared with that in 'green' waves and carries much less energy so is less destructive.

 

 

This effect of wave height in relation to tide height was very obvious in the storm tides in East Anglia before Christmas when the North facing shoreline of North Norfolk took a hammering from the North Westerly waves, whereas the East facing coast still got high tides due to the surge but did not have to face the additional problem of waves as those coasts were relatively sheltered from NW winds.

 

 

Rather long winded I am afraid and rather off topic, but I hope helps give an understanding of the different conventions.  I still love the fact that doors are 1.981 metres high (the old 6 foot six) rather than a nice round 2 metres which they could be if we just added an inch to the top, all a question of history and resistance to change!

Edited January 3, 2014 by egret

[benb]

No, I think there are some confusing figures being mixed here. The short answer is that the normal tide height at Barmouth tomorrow would be about 1.5 metres above Ordnance Datum. The difference being that the Admiralty use a different datum for seafarers and tide tables to the datum used by Ordnance Survey for land mapping. Basically sailors do it differently to the army as one tries not to hit the ground while the other prefers not to get their boots wet!

 

If you are really interested, the following longwinded explanation sets out (a bit crudely) where the differences arise. Eating a bowl of prunes may be time better spent for those otherwise inclined  to explore the detail ;-)  

 

Tide levels are normally described relative to a datum set at Newlyn which relates to the lowest astronomical low tide level at that point. I.e the sea bed below that level would not normally become exposed above water. This datum is really set to help navigators judge whether there is sufficient water above a certain point to stop their boat going aground.

 

High tide will always be significantly higher than that level and the height it will reach at any location  depends upon the effects of the seabed and shoreline relative to the incoming tide, before any allowance made for the effects of air pressure and of wind. In some places the tidal range (low to high tide levels) is considerably greater than others due to the land funnelling the tide as it comes in and out.

 

Barmouth would ordinarily have a low tide height tomorrow of 0.7m above datum and a high tide height of 5.6 m above datum without the added effects of air pressure and wind ( so called astronomical tide heights). In other words a range from low to high tide of 5.6 - 0.7 = 4.9 metres. This is due to it being a high tide (so called 'Spring Tide') anyway as there is a new moon (would also occur with a full moon). At other times  it might be somewhere nearer to 3.7m height (2.1m range) during the less high 'neap tides' associated with 'half moon' phases.

 

Environment Agency are interested in things above sea level and use Ordnance Datum, which is different and is based on mean sea level (mid tide height between high and low water states). So if the normal predicted range of tide height at Barmouth tomorrow based on Admiralty charts is 4.9 metres this would be half of that to each side of Ordnance Datum equating to 2.45m above Ordnance Datum. If Environment Agency are stating 3.92 then i would read this as being 3.92 - 2.45 = 1.47 metres higher than normal for that tide. This 1.47 being due to low air pressure 'sucking' the water up and the further effects of wind 'heaping water' up against the UK shore line. On top of this will be the effects of wave height which can cause water to splash over the top of defences. If the actual wave height is (say) 3 metres (top of crest to bottom of waves trough), again half of that height will be above the 'calm water height' meaning that the crest of waves approaching the shore might be 1.47 plus 1.5 = 2.97 above normal high tide level. Breaking waves can splash higher still but the amount of water in such spray is small compared with that in 'green' waves and carries much less energy so is less destructive.

 

 

This effect of wave height in relation to tide height was very obvious in the storm tides in East Anglia before Christmas when the North facing shoreline of North Norfolk took a hammering from the North Westerly waves, whereas the East facing coast still got high tides due to the surge but did not have to face the additional problem of waves as those coasts were relatively sheltered from NW winds.

 

 

Rather long winded I am afraid and rather off topic, but I hope helps give an understanding of the different conventions.  I still love the fact that doors are 1.981 metres high (the old 6 foot six) rather than a nice round 2 metres which they could be if we just added an inch to the top, all a question of history and resistance to change!

 

Cheers mate- well explained!

[The PIT]

Well any action well away from here this weekend. Going to breezy but nothing noteworthy looking at the GFS.. Elsewhere it looks an interesting day so stay safe folks.

[philglossop]

http://www.plymouthherald.co.uk/Live-updates-Plymouth-flood-alert-storm-sweeps/story-20395451-detail/story.html

 

In it comes- normal flooding suspects so far- but added reports that it's also getting bad around Millbay and Stonehouse Creek.

[Coast]

It's a biggy from ESTOFEX this morning and sums things up well:

 

 

Storm Forecast

Valid: Fri 03 Jan 2014 06:00 to Sat 04 Jan 2014 06:00 UTC

Issued: Fri 03 Jan 2014 00:02

Forecaster: TUSCHY

A level 1 was issued for Ireland, UK, NW-France, parts of the Netherlands and Denmark mainly for severe to damaging wind gusts and an isolated tornado event.

 

A level 1 was issued for NW-Portugal, NW Spain and SW Spain mainly for severe wind gusts, heavy rain and an isolated tornado event.

 

SYNOPSIS and DISCUSSION

 

Fueled by an outbreak of very cold arctic air from E-Canada, an extensive low pressure area grows into a 970 hPa vortex, which covers most of the N-Atlantic. Embedded in that vortex, numerous smaller-scale vortices or mid-tropospheric waves exist. One of those vortices is placed between Ireland and Scotland with a surface pressure between 955 and 960 hPa. This feature drifts to the north/northeast during the forecast with a gradual weakening trend anticipated. Thereafter, numerous more or less pronounced mid-tropospheric waves cross Ireland and UK. Finally a pocket of very cold air at 500 hPa enters the scene from the W during the night and results in a rapidly amplifying trough west of Ireland. Those features will be discussed below:

 

Ireland and Scotland, ongoing at 06 Z until 18 Z:

 

Despite missing convection, a short hint at that wind event seems reasonable. Phase diagrams and diverse model data show one of the most remarkable warm-core events for quite some while with the sub-960 hPa depression N of Ireland moving to the NE ... even showing a deep warm-core structure. A well structured occlusion, connected to a subtropical air mass, bends into that vortex and to its south. This scenario provokes a compact damaging wind field beneath a 850 hPa jet core with wind speeds of 35 to 45 m/s (peak strength during the start of the forecast). Despite gradual weakening a swath of damaging winds likely affects Ireland and Scotland during the daytime hours from SW to NE. Despite the magnitude of that wind event, missing convection precludes the issuance of any level areas.

 

S-C Ireland, UK all the way to Denmark:

 

Behind an eastward sliding occlusion (the same, which provokes the scenario above), deep CAA will be underway with 500 hPa temperatures falling to -30 °C and less. SSTs west of Ireland exceed 11 °C with a marginal decrease towards Ireland and UK. Sufficient vertical lapse rates are forecast for active and deep post-frontal marine convection. Strong and still predominantly unidirectioanl shear accompanies that convection, so downward mixing of 25 m/s winds at 850 hPa cause severe winds to be the main hazard ... next to sleet. However, at least two embedded mid-layer impulses during that forecast increase concerns about more organized convection:

 

The first wave affects S-UK/NW France (09 to 15Z) with a rapid SW-NE motion. Surface pressure fields confirm a weak stamp at low-levels with a temporal increase of BL mixing ratios. Coupled to cooling mid-levels, 200-500 J/kg SBCAPE seems likely over S-UK and NW France. Faint backing ahead of that wave also increases LL directional shear with latest GFS output confirming SRH-1 in excess of 200 m^/s^2. Modest forcing, favorable placement beneath the left exit of a powerful 500 hPa jet, a weakly capped air mass, a 70kt storm motion vector aligned near parallel to a LL wind shift/convergence zone and aforementioned CAPE increase confidence in numerous fast moving showers/isolated thunderstorms with some bowing (severe wind gust) and tornado potential. A compact line of deeper convection could also cause a swath of severe wind gusts. This wind gust risk extends also offshore (east of SE-UK) and may affect the Netherlands and Denmark between noon and the evening hours. Behind that convection, a temporal decrease of convection is forecast over S-UK. However, GFS/WRF show a tongue of slightly unstable air to reside over the Netherlands into Denmark during the evening and overnight hours. A few thunderstorms are possible and favorable directional and speed shear once again point to severe wind gusts and an isolated tornado threat. Hence the level 1 area was expanded well inland over the Netherlands and Denmark.

 

Around noon, an even more pronounced wave approaches Ireland from the west and affects UK during the late afternoon and evening hours. This one keeps directional shear enhanced although decreasing BL moisture and late timing should insert a weakening trend of onshore CAPE during the late afternoon and evening hours. With 850 hPa background flow increasing to 30 m/s it will be hard to distinguish between gusts from the gradient wind flow and convectively induced gusts. The risk however exists for severe to damaging wind gusts .. especially next to showers/isolated thunderstorms. An isolated funnel/tornado event can't be ruled out as well.

 

Finally a third wave with very cold mid-layer air (500 hPa below -35°C) pushes east towards Ireland. Rapid amplification of that wave into a large upper trough induces a slowdown and keeps that trough west of Ireland. Nevertheless, it taps into rather moist marine air west of Portugal, Spain and over the Bay of Biscay. Differential WAA increases mid-level lapse rates atop onshore streaming moist marine air over the Iberian Peninsula and France. Isolated to scattered elevated and non-severe thunderstorms are forecast. The westward facing coasts of N-Portugal and Spain however could see surface based activity with strong shear. Severe wind gusts, an isolated tornado event, heavy rain and marginal hail are possible with that activity. France was excluded due to the late arrival of the trough (probably beyond 06Z). 

 

A similar risk is forecast for SW Spain between 00-06 Z. A tongue of subtropical air / high moisture points towards SW Spain with strong shear and moderate MLCAPE. Heavy rain, severe wind gusts and an isolated tornado event are possible.

 

For the rest of Europe no thunderstorm activity is anticipated (despite isolated storms south of Turkey beneath cooling mid-levels).

 

 

 

[Coast]

Skywarn update:

 

SKYWARN UK SEVERE WEATHER WARNING - PARTICULARLY DANGEROUS SITUATION #002

 

ISSUED: 2345UTC THURSDAY 2ND JANUARY 2014

 

SKYWARN UK HAS ISSUED A WARNING FOR PARTICULARLY DANGEROUS SEVERE WEATHER AS FOLLOWS:

STRONG, POTENTIALLY DAMAGING WINDS - (COASTAL AREAS OF) SOUTHWESTERN, SOUTHERN AND NORTHWESTERN ENGLAND, WALES & IOM

 

IN EFFECT UNTIL 2100UTC FRIDAY 3RD JANUARY 2014

 

DEEP LOW GENERATING SEVERE GALES AND STORM SURGE, COINCIDENT WITH SEASONALLY HIGH TIDES

 

DISCUSSION:

 

THERE IS STRONG MODEL AND PARTNER AGENCY CONFIDENCE IN THE OCCURRENCE OF A DANGEROUS WEATHER RISK DURING THE MORNING AND AFTERNOON OF FRIDAY. A DEEP LOW APPROACHING FROM THE SOUTHWEST WILL GENERATE A LONG WAVE TRAIN AND UP TO 1.5M SURGE WHICH WILL AFFECT MOST AREAS OF THE WEST AND SOUTHWEST. GIVEN HIGH TIDES DURING THE MORNING, AND THE PEAK OF THE EXPECTED WAVE AND SURGE EFFECTS EARLY AFETRNOON, THERE IS SCOPE FOR SIGNIFICANT COASTAL FLOODING ALONG WITH EXCEPTIONAL FLOODING OF LOW-LYING TIDAL ESTUARY REGIONS ALSO. WAVE HEIGHTS IN STRONG WINDS WILL ALSO BE SIGNIFICANT, PERHAPS UP TO 10M IN PLACES AND WITH LONG-PERIOD SWELLS LEADING TO EXCESSIVE VOLUMES OF WATER OVER-TOPPING SEA DEFENCES. THIS WARNING MAY BE UPDATED. DIRECT OBSERVATION AND TRAVEL ARE NOT ADVISED FOR COASTAL REGIONS OF THE WARNING AREAS.

 

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

 

**** alerts contd below ****

 

SKYWARN UK SEVERE WEATHER WARNING #001

ISSUED: 1530UTC THURSDAY 2ND JANUARY 2014

 

SKYWARN UK HAS ISSUED A WARNING FOR SEVERE WEATHER AS FOLLOWS:

STRONG, POTENTIALLY DAMAGING WINDS - WESTERN AND SOUTHWESTERN SCOTLAND, NORTHERN IRELAND & IOM, NORTHERN ENGLAND, WALES, SOUTHWEST ENGLAND

HEAVY RAIN LEADING TO A RISK OF LOCALISED FLOODING - WESTERN SCOTLAND, NORTHWEST & SOUTHWEST ENGLAND, SOUTHEAST ENGLAND

 

IN EFFECT UNTIL 0900UTC SATURDAY 5TH JANUARY 2014

 

DEEP LOW PASSING CLOSE TO THE NORTHWEST, GENERATING SEVERE GALES AND DAMAGING GUSTS

 

DISCUSSION:

 

THERE IS GOOD MODEL AND PARTNER AGENCY CONFIDENCE IN THE LIKELIHOOD OF SEVERE WEATHER RISKS THROUGH THE PERIOD. OVERNIGHT INTO FRIDAY, A SUB-950MB LOW APPROACHES IRELAND BRINGING 40-50MPH MEAN WINDS WITH GUSTS ABOVE 80MPH TO COASTAL NORTHERN IRELAND AND MUCH OF WESTERN AND SOUTHERN SCOTAND, ESPECIALLY THE WESTERN ISLES. DURING FRIDAY DAYTIME, THE UNSTABLE POST-FRONTAL ENVIRONMENT MOVES ACROSS IRELAND AND THE REST OF THE MAINLAND BRINGING MEAN WINDS OF 40MPH AND GUSTS ABOVE 70MPH THOUGH MAINLY AROUND COASTS AND HIGH GROUND. GIVEN THE TIMING OF HIGH TIDES, THERE IS A POSSIBILITY OF COASTAL FLOODING DURING THE WARNING PERIOD FROM OVER-TOPPING WAVES.

 

GENERALLY AROUND 10-25MM OF RAINFALL IS EXPECTED DURING THIS PERIOD, AWAY FROM THE EAST, THOUGH SOME LOCATIONS MAY INCUR HIGHER AMOUNTS OWING TO OROGRAPHIC ENHANCEMENT. MANY AREAS COULD SEE SOME FLASH FLOODING DEPENDENT ON RIVER AND GROUNDWATER LEVELS. DURING THE EARLY HOURS OF SATURDAY, A FURTHER WAVE DEVELOPMENT IN THE WAKE OF THIS LOW MAY DELIVER SOME HEAVY CONVECTIVELY ENHANCED BURSTS OF RAINFALL TO AREAS OF SOUTHERN ENGLAND, WHICH FURTHER ENHANCES THE FLOOD RISK. THIS WARNING MAY BE UPDATED. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

 

 

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

[stevofunnelcl]

Just come back from Westwood Ho seafront

 

Damage to sections of the sea wall. Sections just picked up by the waves and displaced

Sections of the wall, that normally are not overtopped with waves

Large pebbles thrown up onto the walkways

 

Quite a crowd down there watching it, and i missed the peak of the high tide

 

Been a while since i've seen the ocean that high... huge waves rolling in

[stevofunnelcl]

Just took a quick video (still in processing)

Flooding in the Burrows

Waves over topping the sea wall

This was one hour after high tide

 

[SteveCoops]

Well I'm on the ferry. It's packed as others are cancelled... Let's see what the Irish sea has in store for us!

[johnholmes]

Well I'm on the ferry. It's packed as others are cancelled... Let's see what the Irish sea has in store for us!

glad its' you and not me mate

I did that crossing just once in a Force 9 S-SW, took over 6 hours and spent nearly 2 hours out of the Holyhead harbour watching my street lights! yuk

[SteveCoops]

glad its' you and not me mateI did that crossing just once in a Force 9 S-SW, took over 6 hours and spent nearly 2 hours out of the Holyhead harbour watching my street lights! yuk

Where is the dislike button?The staff are giving out 3 sick bags each... Edited January 3, 2014 by SteveCoops

[weatherobsuk]

At least the seabirds will be getting fed today

[alexisj9]

Where is the dislike button?The staff are giving out 3 sick bags each...

You could have delayed your journey I would have.

[NL]

Looking like ESTOFEX's forecast is coming into fruition with a line of deep convection already affecting SW UK heading through Cornwall presently.

 

The first wave affects S-UK/NW France (09 to 15Z) with a rapid SW-NE motion. Surface pressure fields confirm a weak stamp at low-levels with a temporal increase of BL mixing ratios. Coupled to cooling mid-levels, 200-500 J/kg SBCAPE seems likely over S-UK and NW France. Faint backing ahead of that wave also increases LL directional shear with latest GFS output confirming SRH-1 in excess of 200 m^/s^2. Modest forcing, favorable placement beneath the left exit of a powerful 500 hPa jet, a weakly capped air mass, a 70kt storm motion vector aligned near parallel to a LL wind shift/convergence zone and aforementioned CAPE increase confidence in numerous fast moving showers/isolated thunderstorms with some bowing (severe wind gust) and tornado potential. A compact line of deeper convection could also cause a swath of severe wind gusts.

http://www.estofex.org/

 

Netweather 5min radar.

 

http://www.sat24.com/en/gb

Edited January 3, 2014 by NL