Storm Outlook - Sat/Sun Jan 17/18th

[martinastro]

According to some of the guys on the UKWW there looks to be a storm heading for the UK over the weekend. Although it's a little early yet about the specifics it so far looks like N. Ireland is going to get the brunt of it. A very active cold front with heavy rain and the possiblity of convective gusts and tornadoes. Here's some of the discussion. I will add more to this thread as the week goes on...

Looking at the charts +96 - +120 the storm progged to be just to the west of Scotland & North of Northern Ireland has a particularly steep pressure gradient on its South/east quarter, something like 50mb over a few hundred miles.
The low is expected to be sub 950mb whilst pressure over Edinburgh in the region of 1000mb.
But overland it seems northern ireland will have the isobars the closest.
Quite a stormy period for those areas up north?

Looks like 60 knots 925hpa winds are expected to be associated with Saturdays cold front countrywide... likely to be rather a lively affair with possibility for LEWP echoes, strong convective gusts and maybe a tornado or 3!

Looking at GFS for the 19th and 20th, also showing much cooler temps with 510 Dam levels and -5's at 850hpa with models showing significant snowfall possible after this event. A long way off, so I am sure the models will change by then

60kt L6 winds across central England is fairly strong Dave... not unusual maybe, but certainly notable if that can be translated in to gusts at the surface. 70-80kt gusts in the NW more the order of the day if models have a good handle on things... enough to be disruptive...

GFS 12Z increases these to F11 winds now at surface in NW and Irish Sea and 80kt L6 winds in convective set up nr NW Ireland. That IS significant & could give 90mph gusts to surface there.

[martinastro]

Update 08.15 Thurs 15th Jan

The upper pattern over the UK continues to be dominated by a large amplitude trough / ridge pattern over Western Europe and the Eastern Atlantic, which has formed as a result of a deep surge in cold air moving SE out of Eastern Canada. The ridge amplification over Europe has created another high over Scandinavia under very cold conditions.  (very low temps over Scandinavia at present)

To the west a sharp upper trough is grinding slowly against this upper block whilst further west sill another trough is the forerunner of some very cold air sweeping SE out of Canada and creating a huge thermal difference to the SE of Newfoundfland.  Over North America a strong JEt is diving South into the NE US and this will feed into the boundary SE of Canada to create an extremely powerful Jet over the next 48Hrs

The weather over the UK is dominated by the large straddling cold front which lies from West of Scotland south to the Canary Islands with minor ripples/waves along its length. The upper trough mentioned above driving this - becomes even weaker with time and disrupts - the southern end sinking SE and the northern portion relaxing away to the north carrying the main surface inflexion with it.  This becuase the upstream pattern is becoming much more zonal with less trough / ridge amplitude.

Snow has fallen overnight extensively across the Southern UPlands and parts of the Grampians (moderate falls in place) whilst at present the cold front is delivering bursts of rain from SCotland to Cornwall - some of it moderate in nature.   The cold front probably making it into central areas late today before dying a death. It will take its successor (now in Mid Atlantic) to push across the UK tomorrow.

Beyond that the main event over the weekend is the Rapid Cyclogenesis taking place over the Atlantic driven by the deepening of a low coming NE from nr Nova Scotia (currently over NE US) and coming under the Left Exit diflfuence of a very powerful cross Atlantic JEt (around 230knts at peak) The UKMO GM has consistently been forecasting this low to deepen later and turn north nearer to the West of Scotland bringing a much higher risk of 80-90mph gusts into the NW of Scotland and Hebrides.  The 00Z ECM whilst not as deep does now have the centre closer to the mainland so this will now need to watched carefully as some of the other models (NOgaps and GME ) also support a track closer to the mainland.  WInds to 50-60mph and gusts to over 80mph would result. 

Elsewhere the cold front coming east on Sat Night is very potent, driven by a large scale upper trough and a strong thermal divide. The front giving gusts to over 60mph as it sweeps through (risk of 60Knts in the far SW on coasts) aslo delivering a (relatively) short burst of heavy rain and quite a squally affair.  Lots of Showers followoing on Sunday and many of them wintry in nature (Hail, Sleet and Snow)

The developments for Monday continue to be highly doubtful.  The GFS, UKMET and to a certain degree ECM bring a flat wave across Biscay and a slowly developing cold air features across England further north (eventually developing a low over Eastern England or the SOuthern N Sea) However several GFS Members, GME/DWD and Nogaps develop a much deeper feature and bring a storm across England and Wales on Monday with attendant risk of disrtuption. 

Clearly the development is highly sensitive to the intial starting conditions and subsequent development of the trough/Jet pattern over North America and the Western Atlantic.  At this stage i would like to see more support from the (higher resolution) operational Models before increasing the likelyhood (at this point id say a 25%-30% alternative solution) and that the GFS Operational Solution which is not too far from the ECM presents a mid way course, the next 24 hrs should clarify one way or the other.

Given the uncertainties on Monday - there seems little point in going beyond, except to say there is good support from the GFS, its ensemble and the ECM for the very unsettled and sometimes stormy weather to persist with a very powerful and developmental Atlantic.  There is a good chance over the next 10 days or so to see at least one damaging storm cross the UK...

Paul

[martinastro]

UKww Weather Warning – SEVERE GALES/STORM FORCE WINDS
 
Valid from: 1500z Saturday 17th January - 2100Z Sunday 18th January 2009;
 
Areas affected: Cornwall, W Wales, Cumbria, N Ireland, W Scotland, NE Scotland and N Isles.
 
General evolution: Broad and intense (>200 kt) jet stream will continue to develop across a large swathe of the North Atlantic, close to 50N latitude, with a large upper trough overspreading the UK during Saturday. A fast moving Atlantic depression will deepen explosively as it tracks north-eastwards just to the NW of the UK. Its active occlusion/cold front will swing east across the whole of the UK during the forecast period, clearing E England early on Sunday. A strong pressure gradient/low-level jet just ahead of this front will bring severe gales to much of the forecast area. The central pressure of the low is expected to fall to circa 945 m.b. as it passes to the NW of the Hebrides, bringing a risk of storm force winds to the far N and W of the forecast area. A small cold air low moving east across western Scotland later on Sunday is likely to increase the wind to severe gale force again over N Ireland, NW Wales, SW Scotland and Cumbria.
 
Forecast: South or south-westerly winds will rapidly strengthen to gale and then severe gale force across much of the forecast area during Saturday afternoon and evening, accompanied by periods of heavy and prolonged rainfall. Gusts of 55-65 mph will be widespread and frequent just ahead of the surface front, with occasional gusts of 65-75 mph possible, especially in the most exposed locations. In addition, intense post frontal gradient winds close to the depression’s very deep centre, will move across the far north of N Ireland, the far north and west of Scotland and finally the N Isles between 17Z and 06Z. For 2-3 hrs in any one location gusts of 70-80 mph are expected, with a risk of isolated 80-90 mph gusts in the far NW of Scotland. Tree damage, falling tree limbs and very hazardous travelling conditions are likely in the forecast area, with possible structural damage in the very strongest gusts. While there will be a brief lull in the winds during Sunday morning, westerly winds occasionally exceeding 65 mph in gusts are likely across exposed parts of N Ireland, NW Wales, SW Scotland and Cumbria on Sunday afternoon and evening. The rainfall aspect of this forecast will be monitored closely, but currently the expected amounts just fall short of the Watch criteria.

UKww will monitor this Warning and upgrade or update it if necessary.

 Issued by MCD for UKww, 1045Z  16/01/2008

[martinastro]

Met Office warnings from N. Ireland.

Sat...

A swathe of severe south to south-westerly winds will affect Northern Ireland, south-west Scotland, Wales and many parts of western England during the afternoon and evening of Saturday. Gusts to 70 to 80 mph are expected. Disruption to transport and power supplies is possible and there may be damage to buildings and trees. This warning will be superseded by FLASH warnings. Issued at: 1153 Fri 16 Jan

Sun...

There is a moderate risk of a severe weather event affecting Northern Ireland, central and western Scotland and Cumbria. Frequent snow showers during Sunday has the potential to give moderate accumulations over higher roads and temporary accumulations at low levels.  Issued at: 1136 Fri 16 Jan

[JohnC]

It's overnight though, Martin which is a bit of a bummer for photographs but maybe sunrise  Sunday morning there will be enough punch on the back of it to give you some good seascapes.

[brianb]

It's overnight though, Martin which is a bit of a bummer for photographs

I quite agree, all the "interesting" weather should occur during the daytime, nights should be clear & calm

[martinastro]

The leading sector of the cold front arrives over western Ireland during day time. It will probably hit my area soon after dark. 

There doesn't seem to be much convection associated with the front itself now which is very disappointing but maybe the post frontal air mass could produce something on Sun. RTE forecast gave thunderstorms this evening anywhere across Ireland although no one else is backing this up. If the front fails to deliver I will have my eye on the possible snow showers/possible blizzards. Could be interesting and even produce nice scenes on the mountain tops.

I wouldn't let darkness put me off though  . Time exposures of moving convection can look very dramatic....that's if the tripod doesn't take to the air!  . It does look to be mostly clear after the cold front at night so it could be a crazy opp to see comet Lulin...that's if anyone is brave enough to look in such powerful gales.

[martinastro]

The Unsettled weather is now reaching the UK, the much hyped strong Jet is now emerging from North America and will peak in Speed tomorrow at over 220Knts. The fronts have weakened as they crossed the UK over the  last 48hrs, however a much more cyclonic shape to the upper flow will now begin to dominate. WV Imagery shows a PVA Filament assoc with a decaying short wave driving in across the West and SW at present (responsible for the increase in activity and decrease in cloud top temps over the last few hrs.

The main developing low is now in the Atlantic, extremely cold air has spread into the Atlantic from Canada - cloud movements and temps suggest Sub 490DAM thickness values have come east from Labrador. The low now just starting its cross onto the cold side of the Jet and that Rapid Cyclogenesis is about to begin. 

The key features are highlighted above. The developing cloud head, dry wedge and warm conveyer are all characteristics of ensuing rapid development. The UKMEt Models have always been towards the easternmost solutions presented, however other models have come on board. There is reasonable agreement on track - though Ensemble Guidance suggests there is still an area open to doubt. The question is how much development will there be. The UKGM generally does a fair job with the intensification of Atlantic Lows under RACY, the GFS sometimes a bit high and the NAE overdevelops due to too focus on the PVA component.

Mesoscale Models will get the low enter their domain over the next 24hrs, however the higher resolution NAE and FRench Arpege suggest a possibility of a very deep centre developing close enough to the UK to bring the risk of some very stormy weather tomorrow night. Areas at risk are the FAR N and NW of Ireland and Western Isles and Western and NW Mainland Scotland. Risk of sub 950mb low, and coinciding with maximum deepening brings risk of Sting Jet in this kind of scenario. If this was to develop then gusts above 90mph or greater are a possibility in the above mentioned areas. Damage to property and disruption is a possibility if this develops as the low moves NNE. A very tight centre is indicated therefore the positioning is critical. Outside this "bulls eye" the winds strong but not as intense. Strong SQually Cold front crossing east over the UK tomorrow evening and night bringing Severe Gales to Coastal SW England and in the Channel, and gusts above 60mph in exposed places.  Showers turning readily to Sleet /SNow in the north on Sunday as WBFL lower with the modified canadian air moving across. 

Continued problems in the Monday Tuesday period. Risk of small scale developments (beyond the resolution of some of the globals picking up in the flow and deepening rapidly. Some GFS solutions and to some extend the French Arpege model hinting at such developments. Regardless cold, wet and showery with increased risk of snow in showers on Monday across most places except the far south where WBFL will continue to be higher than further north...From Paul Blight UKww Manager - Education & Warnings, Associate Fellow Royal Meteorological Society

[martinastro]

Cold front now well inland over W Ireland and producing lightning at the S tip of the country and over the Atlantic.

[martinastro]

Update 11.30Z

Rapid cyclogenesis is now beginning to occur with large falls reported from Buoys west of Ireland.  WV Imagery indicates the Jet Core with the low now on the developmental cold left exit side and an upper trough with PVA to enhance the development. Rapid Scan imagery indicates the developing cloud wrap-around from which any "StingJet " type feature will descend later this evening.  Upper Jet was analysed at over 220Knts at 00Z by aireps.

Cold front is dynamically weak at present but will develop strongly as the day progresses and the upper trough driving it sharpens and pushes the occluding system across the UK. 

All seems to be on course with Sat Imagery and obs showing no significant deviations from Model Guidance so far.

The 00and 06Z Model Suites from the various centres, converged on a track just to the west of Lewis (which is amazingly what the UKGM was forecasting 3-4 days ago, showing its excellence in this field) The GFS /ECM are probably a little shallow with their depth (950mbs) and the NAE a little deep (it overcompensates for convective deepening in the process) and therefore around 945mbs is probably a good middle ground.

Winds

Ahead of the cold front - gusts to 60-70mph likely in coastal Irish Sea and along the South Coast this evening and overnight. 50mph inland possible.

Possible Sting Jet

Satellite imagery as said (and as illustrated below) is showing some classic early stages of a possible Sting JEt feature as low reaches maximum depth around Midnight into the Early Hrs of Sunday.  The strong Jet winds above the B/L are dragged down in simple terms and 925mb winds of 100mph are possible.  This develops to the NW of Ireland later today and moves across the Inner and Outer Hebrides.  Gusts of 80-90mph likely with an increasing and significant risk of gusts of 100mph occuring for a time as the wrap around clears north.

2nd Squally features crossing northern and southern england overnight, bring gusts to 60mph, Hail and Thunder and given coastal friction in Southern England slim risk of a Tornado.

Paul

[martinastro]

[martinastro]

[Roman White]

What a wonderful animation today - major cyclone heading straight to Ireland, an interesting low-cloudness layer slowly moving across N Russia - Finland. Though nothing visible above Ukraine - only strong SE wind.

Thanks for posting it here

[brianb]

The current forecasts (BBC & Met Office) are showing the depression veering north east, with the strongest winds gusting 90mph+ over the Outer Hebrides, but still severe gales over Northern Ireland. Hope they're right ....

[martinastro]

N. Ireland is going to get hit bad. Scotland might experience the worst storm for years. The Met Office have issued a red alert for that region which I have never seen before since they produced the new traffic light colour warnings. Look at the main cold front on the vis sat animation, it's incredibly linear and tall....that's going to cause some action. Wind and rain are already going at it here now. I was amazed how fast it arrived..gettting stronger all the time. I was going to take some video from home but don't know if my camera could take the soaking...

Keep safe out there.