29th November - 6th December 2011 Atlantic Storms

[Robbie Garrett]

I thought I'd create a thread for discussing the events that may unfold next weekend, as it looks to be quite a significant event now if the models play correctly.

Mondays - Secondary low??

I love snow guys, and cold weather but my god is this looking interesting. (I wont say great, as I live in the firing line (London)

What's your thoughts?

I'm hoping the MetOffice are keeping a close eye on the secondary low (If that's what is is) and even if it's on there model forecasts etc, as any further north and that surely is 60mph sustained winds across some of the most densely popular parts of Europe, let alone the UK.

Also when would the MetO issue severe weather warnings?

Edited November 27, 2011 by Robbie Garrett

[weatherobsuk]

It's a welcome sight to see such interesting weather, with even discussions about the METO sending up one of the recon aircraft to take measurements within Tuesdays frontal passing. That said these kinds of events don't happen often, and unfortunately as we've seen this weekend 7 people in the UK already have been killed by such RACY systems. All we can really do is continually keep letting those know around us what's going on, check on the neighbours and to keep loose-objects safely stored away.

Looking at the model runs itself though the METO has a trough following on behind Tues/Weds Cold Front which will aid in loweing upper atmospheric heights for a very brief time. I'm looking out for any convective passing as the feature moves over as these cells will be what brings the SLW speeds closer to ground level. However being at 210m asl already I think even topography might be in my favor also.

[kold weather]

Models are strongly developing the main driver low on Saturday and the gradient is fairly tight so gales, probably severe gales for Scotland looking quite probable at the moment. Still time for this event to be downgraded but there is plenty of active weather to come in the next week that is for sure!

[matt_in_dudley]

NOOOOOOO!!!!! I'm moving house this coming weekend!!!

[ZONE 51]

Thought i would start this to focus on the potential gales or severe gales for Tuesday this week.

0900hrs Tuesday-NAE 00z

Edited November 28, 2011 by ElectricSnowStorm

[ZONE 51]

Rainfall 0600-1200hrs-NAE 00z

alot of rainfall for some places, flooding i would expect.

The gales becoming widespread, some regions at risk of severe and possibly damaging gusts,

GFS 00z wind gusts in Knots at the surface, the deep oranges and reds indicating the most strongest gusts, some gusts might get higher then these shown here. chart is for midday.

(note - GFS 00z seems an upgrade in wind strength from the 18z, especially across the central Northern areas, looking at the surface pressure charts from 1500hrs it does show this as tighter pressure/isobars.

The gales/severe gale sweeping from West to East though Tuesday, from early morning/early hours even.

The Gales likely to hit the South coast through the period to, so a widespread risk.

Edited November 28, 2011 by ElectricSnowStorm

[NO LONGER POSTING]

Looking at some other charts...

[Coast]

Seems to be some significant wind and gusts through Ireland and the upper parts of Wales and the Midlands tomorrow:

MetO not having it quite so windy:

[kold weather]

Models really blow up the low on the 3rd, looking very impressive now. Still time for it to head further north and leave us in a slacker flow but the GFS/ECM both suggest potenial for a big event over Scotland and Shetland in particular.

[johnholmes]

The positive thing about storms is that at least 24 and often 48 hours from their onset its relatively easy to get the path predicted more or less to within a 50 mile band and thus give ample warning for safety meaures, be it due to wind or high tides.

Not that its much consolation for those who will be affected. It does lessen the risk to life though by a large amount. This also apples to shipping remembering what happened off Anglesey in the last one.

The 24-48 prediction can really be done without computer models so I hope the Met O do allow their forecasters to use their basic training!

[Liam J]

Very intersting times ahead this week with many wind events about to kick off! Tuesday, Wednesday, then overnight Wedsnesday into Thursday are looking very active with gales or severe gales in places, becoming widespread.....

Then we get to Saturday!!! Hmmm... still a lot of time for change with this event but the model outputs are in agreement for an intenese depression close to the UK, obviously a strong signal being picked up on for this wind storm to develop.

I wouldn't be surprised to see hurricane force 12 mentioned in shipping forecasts if this event comes off as currently being progged.

Edited November 28, 2011 by Liam J

[chionomaniac]

With a very active jet stream and increased polar vortex strength, the pattern ahead looks to be very zonal. Where the jet stream is strongest between the boundaries of cold polar air and milder mid latitude air the possibilities exist for some strong cyclogenesis to occur, with the UK well set to be in the firing line for any severe depressions that result.

One such depession is forecast to hit Northern areas this Saturday.

The first clues to the possible formation of a vogorous depression can be found looking at the jet stream chart for this Wednesday. A area of strong jet stream winds of up to 200mph can be seen leaving Canada heading towards the tip of Greenland.

These winds are generated by the contrast in temperatures seen in the boundary between the air masses. The difference in temperature leads to a difference in pressures.

Rolling on to Friday and even though there is little in the way of evidence of what is about to occur, the large gradient in 850's temperature over a relatively small area coinciding with the jet streak is enough to trigger cyclogenesis.

Whilst the strong jet streak remains and the thermal gradient exists cyclogenesis will continue. The path taken depends upon the direction of the jet stream.

The strongest winds in the jet stream are known as the jet streak and it is where the upper winds leave the jet streak on the polar side ( known as the left exit ) where the centre of the depression is located marked with an arrow below:

The upper winds at this point are rapidly diverging creating the low pressure and are replaced by an inrush of lower winds that are trying to equal out the pressure difference. It is the inrush that is felt at the surface.

The strength of the jet streak and contrast of the temperature of the air masses are all important in determining the strength of the ground speed of surface winds later on.

So far it look like the depression will bottom out at around 952mb so it will be interesting to see what fluctuations will affect this in the following days and runs.

c

Edited November 28, 2011 by Coast

[Coast]

Going to join this one up with the other thread running here:

http://forum.netweat...73

[chionomaniac]

Going to join this one up with the other thread running here:

http://forum.netweat...73

cheers

[chionomaniac]

Can you rescue the images please coast?

[Coast]

Can you rescue the images please coast?

Think that's right!

[chionomaniac]

Think that's right!

Thanks. They must have got lost in the netweather broom cupboard for a bit!

[Zenarcher]

GFS 12z has moved the low for Saturday/Sunday further north to where the ECM has placed it. But at the same time it's been changed from 955mb to 950mb despite this the winds have been slightly downgraded due to it being pushed further north. Still looking like severe gales over Northern England and most of Scotland meanwhile the far North of Scotland including Shetland and Orkney will see storm force.

Edited November 28, 2011 by weathermaster

[Cookie]

long way off yet, focusing all my attention on the current wild weather here.

[AWD]

Models really blow up the low on the 3rd, looking very impressive now. Still time for it to head further north and leave us in a slacker flow but the GFS/ECM both suggest potenial for a big event over Scotland and Shetland in particular.

and that's exactly what the 12z has done, moved it a tad further north, so although still a severe storm for Scotland, not quite as severe as what previous runs had it!

Still, the exact track will probably change again in the coming days, although I expect only slightly!

[Jane Louise]

No mention of thunderstorms, mind!

-------------------------------------------------------------

SKYWARN UK SEVERE WEATHER WATCH #063

ISSUED: 1730UTC MONDAY 28TH NOVEMBER 2011 (GJ/SM)

SKYWARN UK HAS ISSUED A SEVERE WEATHER WATCH FOR THE FOLLOWING REGIONS:

ALL AREAS UK

IN EFFECT FROM 0300UTC UNTIL 2359UTC TUESDAY 29TH NOVEMBER 2011

ACTIVE COLD FRONT WITHIN AN UNSTABLE ENVIRONMENT

THERE IS A POSSIBILITY OF SEVERE WEATHER AFFECTING THE INDICATED REGIONS IN THE TIME PERIOD SPECIFIED. THREATS WITHIN THIS WATCH INCLUDE, BUT ARE NOT LIMITED TO:

HEAVY RAIN...STRONG GUSTS...FRONTAL VORTICES...T1/2 TORNADOES...FLASH FLOODING

DISCUSSION:

THERE IS MODERATE MODEL CONFIDENCE IN THE POTENTIAL FOR A SEVERE WEATHER EVENT DURING TUESDAY. A COLD FRONT CROSSES THE ENTIRE UK EASTWARD FROM EARLY MORNING, AFFECTING MOST PARTS DURING THE AFTERNOON. UNDER THE LEADING EDGE OF A STRONG JETSTREAM WITH A SLACK WIND FLOW BEHIND, THE PRE-FRONTAL ENVIRONMENT IS EXPECTED TO GUST TO 50KTS WITH POTENTIAL FOR CONVECTIVE ELEMENTS WITHIN. THE FRONT APPEARS TO BE SPLIT, WITH THE UPPER SECTION COOLING THE MID LEVELS OVER THE SURFACE FRONT, GIVING RISE TO POTENTIAL INSTABILITY BOTH AHEAD AND BEHIND. A STRONG SHEAR PROFILE IS SUPPORTIVE OF VORTICES WITHIN THE FRONT, AS WELL AS POSSIBLE TORNADOES. OVERALL PRECIPITATION ACCUMULATIONS ACROSS SCOTLAND AND NORTHERN ENGLAND COULD WELL EXCEED 60MM FOR THE PERIOD, PARTICULARLY STEEP SLOPES AND SHARP CATCHMENT AREAS. THIS WATCH MAY BE UPDATED OR UPGRADED.

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

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

[Liam J]

Some lively conditions tomorrow as the cold front pushes east, gusts in excess of 60mph for Northern and Western parts of England and Wales with a risk of tornado's.

The winds will veer from southerly to westerly as the cold front passes and continue very strong with some very squally gusts in the process, perhaps up to 70mph. Although not likely to be as severe this event is similar to October the 17th when ahead of the cold front the winds gusted to 75mph for short time which resulted in local structural damage and uprooted trees around West Cumbria.

Edited November 28, 2011 by Liam J

[Liam J]

UKWeatherworld issued a severe weather warning - squall line development, 60-70mm of rainfall and wind gusts of to 65-75mph to the west of the UK with disruption possible.

http://www.ukweatherworld.co.uk/Pages/Weather-Warnings.aspx

[knocker]

Max temp here today was 13C. It appears that the only tea plantation in the UK on the Tregothnan Estate is extending it's season into Dec. for the first time. I love this cold spell.

The 1800z charts.

[weatherobsuk]

Another possibility of coastal flooding going off GFS wind direction & strength from midnight Saturday up until the morning hours. The main low area looks to be crossing NEwards in a similar fashion to 'Berit' only this has a break-away front associated with it (possible squall line) that moves Southeast into the North Sea and towards Denmark.